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Planning & Environment Committee Agenda 12 April 2022 Attachment 3 to Report 6
Ecological Service Professionals
Sustainable Science Solutions
Current and Historical Distribution of
Seagrass in the Noosa Estuary
Prepared for: The Nature Conservancy
Prepared by Ecological Service Professionals Pty Ltd
September 2021
A| PO Box 5815 Manly QLD 4179 T| +61 428 118 496 E| [email protected] W| ecosp.com.au ABN| 84 169 274 391
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Section 2
Ecological Service Professionals
Sustainable Science Solutions
Document Control
Report Title: Current and Historical Distribution of Seagrass in the Noosa Estuary
Project Reference: 2020
Client: The Nature Conservancy
Client Contact: Craig Bohm
Report Version Date Authored Reviewed Issued Comment
Status Number Submitted By By By
Draft 2020.001V1 30/09/2021 S Walker L Thorburn S
M Hayes Walker
E Watson
S Goodwin
Final 2020.001V2 22/12/2021 S Walker S Update with
Walker comments from
TNC
Cover: Dense Zostera bed growing on the edge of Weyba Creek
Citation:
Walker SJ, Hayes M, Watson E, Goodwin S & Thorburn L. 2021. Current and historical
distribution of seagrass in the Noosa Estuary. Report prepared for The Nature Conservancy,
September 2021. 37pp.
© Ecological Service Professionals Pty Ltd
The contents of this report is protected by copyright. All contents shall remain the intellectual property of
Ecological Service Professionals Pty Ltd, unless prior arrangement has been made.
File Name: 2020.001V2_NoosaSeagrass2020.docx
Section 3
Ecological Service Professionals
Sustainable Science Solutions
© Ecological Service Professionals Pty Ltd
The contents of this report is protected by copyright. All contents shall remain the intellectual property of
Ecological Service Professionals Pty Ltd, unless prior arrangement has been made.
File Name: 2020.001V2_NoosaSeagrass2020.docx
Section 4
Ecological Service Professionals
Sustainable Science Solutions
Table of Contents
EXECUTIVE SUMMARY I
1 INTRODUCTION 1
1.1 Background 1
2 METHODS 3
2.1 Study Area 3
2.2 Desktop Review and Initial Mapping 3
2.3 Field Surveys 3
2.3.1 Assessment of Seagrass Habitats 5
2.3.2 Seagrass Condition and Fisheries Value 5
2.3.3 GIS Mapping 6
2.4 Historical Distribution of Seagrass 6
3 CURRENT SEAGRASS DISTRIBUTION AND CHARACTERISTICS 7
3.1 Composition and Distribution 7
3.2 Seagrass Condition 10
4 HISTORICAL CHANGE IN SEAGRASS DISTRIBUTION 14
4.1 Lake Cooroibah 15
4.2 Noosa River – Tewantin 15
4.3 Noosa River – Goat Island 15
4.4 Lake Doonella 16
4.5 Weyba Creek 16
4.6 Lake Weyba 16
4.7 Influential Environmental Factors A-21
4.7.1 Rainfall A-22
4.7.2 Riverine Flow A-22
5 DISCUSSION A-24
6 CONCLUSIONS A-27
7 REFERENCES A-28
Assessing Distribution of Seagrass in the Noosa Estuary
Section 5
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List of Figures
Figure 2.1 Location of study area and reaches assessed along the Noosa River in November
2020 4
Figure 3.1 Dense Zostera muelleri at the mouth of Lake Weyba 8
Figure 3.2 Dense Zostera muelleri patches along the main river channel at Tewantin 9
Figure 3.3 Dense Halophila ovalis growing in Lake Doonella in November 2020 9
Figure 3.4 Small patch of Zostera muelleri growing along the Goat Island in the main Noosa
River Channel in November 2020 10
Figure 3.5 Z. muelleri with dense epiphytic algae in Weyba Creek in November 2020 11
Figure 3.6 Sparse Z. muelleri with moderate (40%) epiphytic algae growing along channel in
Weyba Creek in November 2020 12
Figure 3.7 Small dense patches of Z. muelleri becoming smothered by mobile sand bars in
Weyba Creek 13
Figure 4.1 Extensive seagrass beds (shown as darker patches) at the mouth of Lake Weyba
and entrance to Weyba Creek in August 1986 (Source: QLD Government 2021b) 17
Figure 4.2 Historical distribution of seagrass in the Lake Cooroibah reach in 1989, 2006, 2009
and 2020 18
Figure 4.3 Historical distribution of seagrass in the Tewantin, Lake Doonella and Goat Island
reaches in 1989, 2006, 2009 and 2020 19
Figure 4.4 Historical distribution of seagrass in the Weyba Creek reach in 1989, 2006, 2009
and 2020 20
Figure 4.5 Aerial image of the mouth of Noosa River on 24 February 1992 showing the
majority of the flood plume bypassing Weyba Creek and Noosa Sound, and
extending out into Laguna Bay (Source QLD Government 2021a) A-21
Figure 4.6 Monthly total rainfall (mm) measured at Kiamba BOM station from 1952 to 2014 A-22
Figure 4.7 Total volume of water discharged at Teewah Creek gauging station between 1972
and 2021 A-23
Figure 5.1 Aerial imagery from (a) June 1972 and (b) November 1974, showing the change in
estuarine habitat due to urban development at the mouth of the Noosa Estuary
(Source QLD Government 2021a) A-26
List of Tables
Table 2.1 Criteria used to determine the fisheries habitat value of seagrass based on review
of available literature A-32
2
Table 3.1 Area (m ) of seagrass mapped in Noosa Estuary November 2020 7
Table 4.1 Historical comparison of seagrass area within Noosa Estuary 14
Assessing Distribution of Seagrass in the Noosa Estuary
Section 6
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Executive Summary
This report has been prepared by Ecological Service Professionals (ESP) for The Nature
Conservancy (TNC) and summarises the results of a seagrass survey in the Noosa River
Estuary and lakes in November 2020. Seagrass provides nursery, forage and reproductive
habitat for a broad range of species including species important to recreational and
commercial fisheries.
The current distribution of seagrass was assessed throughout the estuary and lakes in
November 2020 using a combination of direct visual assessment, underwater georeferenced
photo transects and underwater spot checks using a surface view camera, and a grapple
hook for targeted confirmation of seagrass species present where necessary. Intertidal
habitats were assessed on foot where possible. The coverage of seagrass was assessed
visually and in photo-quadrats along several transects in areas where the composition of the
seagrass bed changed. The current distribution was compared with the historical distribution
of seagrass, including likely triggers for change and recommendations for future work.
In 2020, Noosa estuary was dominated by soft sedimentary habitats including extensive
intertidal sand and mud flats, with several large seagrass meadows occurring throughout the
lower estuary. The seagrass beds were dominated by long eel grass (Zostera muelleri sub
sp. capricorni) with occasional sparse patches of Halophila ovalis. The seagrass beds
consisted primarily of Z. muelleri growing in long dense, but patchy beds along the main
channels and around several small islands.
Historically, there are several reports of seagrass (Z. muelleri and H. ovalis) occurring
throughout the Noosa estuary, with the most comprehensive mapping of seagrass in the
estuary occurring in 1987 (Hyland et al. 1989). Notable based on these previous
assessments an updated mapping, there have been declines in the area of seagrass beds
within the Noosa Estuary, particularly in Lake Weyba and Lake Cooroibah, with
approximately 83% of the total area of seagrass lost between 1987 and 2020.
Due to the nature of the Noosa River Catchment, different sub-catchments present a good
comparative opportunity to assess the cause of declines in seagrass extent and likely impact
of management actions. For example, impacts in along the main river channel are likely due
to broader scale impacts from the upper catchment, including runoff from catchment clearing
as well as boating activity. In contrast, seagrass in the smaller sub-catchments in Lake
Doonella and Lake Weyba are likely responding to changes in the hydrodynamic regime,
with seagrass in Weyba Creek being particularly susceptible to shifting sand banks.
Further assessment of the potential resilience of seagrass meadows to resist environmental
changes in the Noosa Estuary are considered necessary to understand where to invest in
future management actions for maximum gains. Consideration should also be given to the
potential for natural recovery or assisted restoration of seagrass meadows once key triggers
for past change are known and potential negative inputs have been managed.
Assessing Distribution of Seagrass in the Noosa Estuary i
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1 Introduction
This report has been prepared by Ecological Service Professionals Pty Ltd (ESP) for The
Nature Conservancy (TNC), and summarises the distribution and condition of seagrass
meadows within the Noosa Estuary and Lakes in November 2020. Specifically, the aim of the
assessment was to identify and map the distribution, coverage and condition of seagrass
within the Noosa River Estuary downstream of Lake Cooroibah and in the Weyba Creek
catchment. The current distribution was compared with the historical distribution of seagrass,
mapped from historical aerial and satellite imagery. An assessment of the likely triggers for
change and recommendations for future work have been included.
1.1 Background
Coastal wetlands including seagrass, mangroves and saltmarsh, have a broadly important
ecological function as fisheries habitat, through provision of nursery habitat, protection from
predators, contributing to food webs, controlling sediment runoff and processing nutrients
among other functions (Nagelkerken et al. 2008; McKenzie et al. 2021). Intertidal habitats
are also important for a range of species other than fish such as migratory shorebirds,
waterbirds and crustaceans (Manson et al. 2005; Skilleter et al 2005; Zharikov et al. 2005).
The spatial arrangement of habitats in coastal seascapes are known to affect the
composition of fisheries species at a variety of different spatial scales (Sheaves 2009;
Bostrom et al 2006; Bostrom et al. 2011; Nagelkerken et al. 2015), and the abundance and
diversity of fishes is typically associated with the most diverse and heterogeneous seascape
types (Pittman et al. 2004). For example, species richness is higher in nekton communities
(i.e. fish, crabs and prawns) when mangroves are proximal to continuous seagrass, when
compared with mangroves adjacent to patchy seagrass or bare/unvegetated substrate
(Pittman et al. 2004; Skilleter et al. 2005). Seagrass habitats have high ecological value, and
provide connectivity between inshore (e.g. estuaries) and offshore (e.g. reef) ecosystems,
which is vital for the maintenance and regeneration of numerous fish and invertebrate
populations (Waycott et al. 2009; Waycott et al. 2011).
Seagrass habitats provide food and shelter for a diverse range of marine fauna; they also
support benthic macroinvertebrate communities, which in turn provide a food resource for
many larger, commercially important species of crustacean, mollusc and finfish (Coles et al.
1993; Carruthers et al. 2002). Epibenthic and infaunal invertebrate communities associated
with seagrass meadows are diverse, and are typically dominated by high abundances of
polychaetes (and other worms, such as sipunculids), molluscs (including bivalves and
gastropods), and crustaceans (particularly amphipods and decapods) (Blomfield and
Gillanders 2005). These communities provide a food source for larger crustaceans, molluscs
and finfish, many of which are commercially important (e.g. flathead) (Coles et al. 1993;
Carruthers et al. 2002; McKenzie et al. 2014), including in the Noosa Estuary.
While marine plant communities provide particularly high ecological value habitat for marine
fauna, areas of non-vegetated soft-substrates (including sandy beaches, mudflats and
subtidal soft sediments) are also important (Pittman et al. 2004). Soft sediment habitats in
shallow areas (where suspended sediment loads are low enough to allow sufficient sunlight
penetration through the water column for photosynthesis) also contain benthic microalgae
(BMA) assemblages, which can be an important driver in coastal food chains and macroalgal
Assessing Distribution of Seagrass in the Noosa Estuary 1
Section 8
Ecological Service Professionals
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communities (Ferguson & Eyre 2013). These types of soft sediment (sand and mud) habitats
are the dominant habitat type within the Noosa Estuary.
Seagrasses are highly sensitive to changes in environmental conditions and declines in
water quality (particularly high turbidity) and are therefore considered indicators of
environmental degradation and natural stressors (Heck et al. 2008). As a result, their spatial
distribution can be highly dynamic, and large interannual changes in the extent of seagrass
habitats and community structure resulting from natural disturbances (e.g. flood events,
changes in rainfall) have been documented for example in the Moreton Bay region (Lyons et
al. 2015) and Great Sandy Strait particularly following extensive floods (Preen et al. 1995;
Campbell & McKenzie 2004).
In the Noosa Estuary, the most comprehensive and detailed historical mapping of seagrass
was completed in 1987, recording a total of 47 Ha of dense seagrass primarily in the Noosa
River to Lake Cooroibah and in Weyba Creek (Hyland et al. 1989). A further 923 Ha of
sparse and patchy seagrass was recorded, primarily (94%) in Lake Weyba (Hyland et al.
1989); however, the area of sparse and patchy seagrass is considered to be an overestimate
due to the sparse nature of and difficulty mapping from photographs at the time. There have
also been several small-scale surveys and monitoring programs completed at several sites
throughout the estuary using the established seagrass watch monitoring protocols through
Noosa Integrated Catchment Authority (NICA) (Seagrass Watch 2006; McKenzie & Yoshida
2013; NICA 2014; NICA 2016). These monitoring events were designed to assess long-term
changes in the coverage and species composition of seagrass along permanent transects
(McKenzie & Yoshida 2013). We are unaware of any broadscale assessment of the
distribution of seagrass in the estuary completed since 1987. The most recent monitoring of
seagrass was completed by NICA and USC researcher Dr Javier Lyon, which was used to
develop a method of monitoring the distribution of seagrass using aerial drone surveys and
photogrammetry (Lyon 2018).
Assessing Distribution of Seagrass in the Noosa Estuary 2
Section 9
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2 Methods
2.1 Study Area
The Noosa River catchment has its headwaters in the Cooloola section of the Great Sandy
National Park. There are several main tributaries, and the main river flows through several
shallow lakes, and along a main river channel to the ocean.
The study area for this assessment covered a substantial section of the estuarine habitat in
the Noosa Estuary and lakes, including both intertidal and subtidal zones with the most
upstream extent in Lake Cooroibah (designated as the upper extend of seagrass distribution)
to the mouth of the estuary; and upstream in Weyba Creek to Lake Weyba (Figure 2.1). The
estuary was separated into seven reaches including:
1) Lake Cooroibah (and the main Noosa River channel upstream of the vehicle ferry);
2) Noosa River from Tewantin to the vehicle ferry;
3) Noosa River around Goat Island and downstream;
4) Noosa River mouth and Noosa Sound;
5) Lake Doonella;
6)Weyba Creek; and,
7) Lake Weyba (Figure 2.1).
2.2 Desktop Review and Initial Mapping
An initial desktop review and gap analysis of existing information available on the distribution
and condition of seagrass in the Noosa River Estuary, including spatial data sets, was
completed. Prior surveys and aerial imagery were used to complete an initial broadscale
seagrass and marine habitat map of the study area, based on experienced visual
interpretation of available aerial and satellite imagery and publicly available GIS spatial
layers. This map was used to prioritise specific focal areas for more detailed field validation
and seagrass characterisation (Section 2.3 below).
2.3 Field Surveys
The survey was completed over four days (3 to 5 November 2020 and 8 December 2020)
using a combination of remote techniques from a vessel (including ROV, tow camera and
drop cameras), and visual assessments on foot at low tide (where possible) to identify the
condition and presence of seagrass. Where visibility was low (due to turbidity of waters), spot
snorkel surveys and a small grapple hook were used to confirm the presence of seagrass,
where it was safe to do so and following a strict risk assessment protocol. Detailed methods
are described in Sections 2.3.1 to 2.3.3 below.
The work was completed under a QLD General Fisheries Permit (208641) issued to ESP and
an accepted development application (received 07/09/2020), for the collection and limited
disturbance of marine plants in a fish habitat area where voucher samples were required for
field verification and identification.
Assessing Distribution of Seagrass in the Noosa Estuary 3
Section 10
°
Survey extent and
seagrass lost in 2020
Project: 2020
Author: SW
Coordinate System: GDA2020 MGA Zone 56
Lake Cooroibah Projection: Transverse Mercator
Datum: GDA2020
Legend
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Weyba Creek
Lake Weyba Noosa
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Plan to illustrate location of marine habitats
Data Sources:
© State of Queensland
© Ecological Service Professionals Pty Ltd. (ESP).
Source: Esri, Maxar, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS,
All care has been taken to ensure the accuracy of
AeroGRID, IGN, and the GIS User Community
data.
Figure 2.1 Location of study area and reaches assessed along the Noosa River in November 2020
Assessing Distribution of Seagrass in the Noosa Estuary 4
* ye Survey extent and
; j seagrass lost in 2020
» : Project: 2020
’ be Author: SW
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Figure 2.1 Location of study area and reaches assessed along the Noosa River in November 2020
4Section 11
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2.3.1 Assessment of Seagrass Habitats
Where seagrass was present, the seagrass beds were assessed further for their extent
(using a hand-held GPS to later define and confirm the current perimeter of patches using
GIS by tracking along the perimeter of seagrass along a channel or around a patch in the
lakes). This was done by taking georeferenced images along the edge of seagrass beds or
walking intertidally and taking a series of points along the edge, then matching to recent
aerial imagery in ESRI ArcMap. The species composition, percent coverage and condition of
seagrass was also assessed qualitatively, based on expert assessment of georeferenced
imagery (video and photos) at more than 1700 points across the study area, using methods
adapted from Roelfsema & Phinn (2009) where a gps is either towed along the waters
surface with the type of substrate recorded either on snorkel or using a drop camera from a
boat. Broad seagrass coverage categories were either determined directly from imagery or in
the laboratory using georeferenced imagery. Georeferenced image capture enable mapping
linked to images showing the seagrass (or other benthic habitat) and allowed for rapid geo-
referenced image collection over a large spatial area of the estuary. Where identification of
the presence of seagrass was not possible from surface view imagery, a field sample was
collected using a grapple hook to confirm identification (particularly of seagrass species).
2.3.2 Seagrass Condition and Fisheries Value
The condition of representative seagrass beds in each of the estuarine reaches was
assessed along several transect completed perpendicular to the channel, with georeferenced
observations and photo quadrats made at regular assessment points (approximately every
5 m) along each transect. The value of fisheries habitat in the study area was assessed
using:
• desktop review of the current literature;
• condition and type of habitat present based on field results; and,
• professional judgement based on the dominant habitat category (e.g. seagrass) using
the criteria adapted by ESP from Wetland Assessment Manual (Price et al. 2007) and
a review of the available fisheries literature1 linking habitat features with fisheries
productivity as outlined in Appendix A (Table 7.1 and Table 7.2).
• habitat patches are scored based on the presence of various criteria, with seagrass in
better condition or having higher value to fisheries species given a higher score. The
total is then summed across each criteria to determine whether the seagrass habitat
is poor, fair, good or very good.
1
Bell & Westoby 1986a, b; Edgar & Robertson 1992; Boström & Bonsdorff 1997; Heck et al. 1995;
Webster et al 1998; Skilleter et al. 2005; Vanderklift & Jacoby 2003; Boström et al. 2006; Jelbart et al.
2007; Price et al. 2007; Shoji et al. 2007.
Assessing Distribution of Seagrass in the Noosa Estuary 5
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2.3.3 GIS Mapping
A detailed map based on the field data showing the extent of seagrass present in the area,
was produced using ArcGIS. Imagery was sourced through QLD Globe and rectified in ESRI
ArcGIS to create a complete mosaic of high-resolution imagery for 2020.
2.4 Historical Distribution of Seagrass
The estuary was split into seven reaches, and the change in seagrass distribution was
mapped from rectified historical aerial imagery available in QLD Globe (QLD Government
2020) and QLD Imagery (QLD Government 2021a). An analysis of the historical changes in
seagrass distribution in reaches of the Noosa River estuary was completed to provide a
comparison of the annual relative change in extent (areal coverage) through time from
September 1989 (i.e. approximate time of Hyland et al 1989 survey, with most
comprehensive aerial imagery collected at approximate 1:25000), November 2006 (18cm
SISP satellite imagery), October 2008 – June 2009 (50 cm SISP satellite imagery), and May
2020 (10 cm satellite imagery) combined with survey data from November 2020. Annual
assessments of the change in seagrass at several sites along Weyba Creek were also
completed from 2015 until 2020 using available aerial imagery. This finer-scale assessment
provided key information on the magnitude of change in seagrass extent over recent years
(2015 - 2020).
Assessing Distribution of Seagrass in the Noosa Estuary 6
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3 Current Seagrass Distribution and Characteristics
3.1 Composition and Distribution
A total of 56 Ha of seagrass was recorded throughout the estuary in November 2020, with
the greatest extent of seagrass occurring in Lake Donnella and along Weyba Creek (Table
3.1). Seagrass species recorded in the intertidal and shallow subtidal included Zostera
muelleri subsp. capricorni and Halophila ovalis. Dense stands of Z. muelleri grew along the
edge of channels in Weyba Creek (particularly around the mouth of Lake Weyba (Figure 3.1)
and Keyser Island), and also along the main river channel at Tewantin (Figure 3.2). Several
sparse patches of H. ovalis were also recorded on the edges of and between patches of
dense Z. muelleri (Figure 3.6). Patches of dense H. ovalis were recorded in parts of Lake
Doonella (Figure 3.3).
Table 3.1 Area (m2 and Ha) of seagrass mapped in Noosa Estuary in November 2020
Reach Coverage Type Area (m2) of Seagrass Area (Ha) of Seagrass
Lake Cooroibah Dense 0 0
Sparse 0 0
Total 0 0
Noosa River – Dense 25,037 2.5
Tewantin Moderate 1,505 0.2
Sparse 3,503 0.4
Total 30,045 3.0
Lake Doonella Dense 0 0.0
Sparse 318,129 31.8
Total 318,129 31.8
Noosa River – Goat Dense 737 0.1
Island Sparse 1,259 0.1
Total 9,313 0.9
Noosa River Mouth Dense 0 0
Sparse 0 0
Total 0 0
Weyba Creek Dense 18,365 1.8
Sparse 2,133 0.2
Total 205,510 20.6
Lake Weyba Dense 20 0.0
Sparse 0 0.0
Total 20 0.0
Total Noosa Estuary 563,018 56.2
The condition of seagrass was generally good to very good (>57% of seagrass surveyed) with patches
generally providing good to very good value for fisheries species (>65% of seagrass surveyed) (Table
3.2; Figure 3.1). The remaining patches generally remain well connected to other seagrass patches or
other structural habitat such as mangroves throughout the lower estuary. The least structurally diverse
seagrass beds were recorded in Lake Doonella, however due to good proximity to deeper water
channels and good connectivity to the mangrove fringe, these habitats still provide good potential
value for fisheries species (Table 3.2).
Assessing Distribution of Seagrass in the Noosa Estuary 7
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Table 3.2 Area of seagrass for each condition index category and value of seagrass habitat to
fisheries based on current condition and structural components
Total Area (m2)
Reach Fair Good Very Good
Lake Cooroibah Seagrass – –
–
Condition
Fisheries Value – – –
Noosa River – Seagrass 3,783 26,262
Tewantin Condition
Fisheries Value 3,783 2,049 24,213
Lake Doonella Seagrass 236,821 81,308 –
Condition
Fisheries Value 191,241 126,888 –
Noosa River – Goat Seagrass – 9,313 –
Island Condition
Fisheries Value – 9,313 –
Noosa River Mouth Seagrass – – –
Condition
Fisheries Value – – –
Weyba Creek Seagrass 99 203,660 1,751
Condition
Fisheries Value 446 7,927 197,136
Lake Weyba Seagrass – 20 –
Condition
Fisheries Value – 20 –
Total Noosa Seagrass 237774 320564 1751
Estuary Condition
Fisheries Value 192542 146198 221349
Figure 3.1 Dense Zostera muelleri at the mouth of Lake Weyba providing good fisheries value
Assessing Distribution of Seagrass in the Noosa Estuary 8
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Figure 3.2 Dense Zostera muelleri patches along the main river channel at Tewantin
Figure 3.3 Dense Halophila ovalis growing in Lake Doonella in November 2020
Assessing Distribution of Seagrass in the Noosa Estuary 9
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Figure 3.4 Small patch of Zostera muelleri growing along the Goat Island in the main Noosa
River Channel in November 2020
3.2 Seagrass Condition
The seagrass growing in the Noosa Estuary was showing signs of stress, as a result of
sedimentation in some areas. Further, many of the seagrass beds growing in the relatively
clear and shallow water of the estuary were covered in a high load of epiphytic algae. The
dense Z. muelleri was typically in moderate condition, with long blades up to 50 cm long that
had a high coverage of epiphytic algae (greater than 40% of the blade) (Figure 3.5). In some
areas of Weyba Creek around Keyser Island, and along the main creek channel further
upstream, the coverage of epiphytic algae on the Z. muelleri blades was extremely dense
(> 80%) and in some cases it completely smothered the seagrass (Figure 3.5). The coverage
of epiphytic algae was particularly high in dense beds around freshwater inputs such as
stormwater drains.
Elsewhere, the coverage of epiphytic algae was sparser, particularly in areas where the
coverage of Z. muelleri was also lower (Figure 3.6). The coverage of epiphytic algae on
H. ovalis was typically very low, although this seagrass species was typically observed along
the fringes of Z. muelleri beds and in areas of increased turbidity such as in Lake Doonella.
There were also instances where seagrass patches were being smothered by shifting
sediment. This was particularly the case along sections of the channel in Weyba Creek and
at the entrance to Lake Weyba (Figure 3.6 & Figure 3.7). The non-vegetated intertidal and
subtidal habitat within the study area was generally characterised by coarse, sandy
Assessing Distribution of Seagrass in the Noosa Estuary 10
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substrates. These habitats had low epifaunal activity (no burrowing crabs were observed in
the sand), with a low density of burrows on the surface (average <1 m-2), and no epibenthic
fauna (such as sea cucumber, bivalves or sea pens) were recorded in the georeferenced
videos or along photo transects. The coarse sandy habitat was unconsolidated and highly
mobile due to strong tidal currents, which likely reduced the suitability for fauna that burrow
into the sediment. Results from the field survey are consistent with studies from the wider
region, which generally recorded low abundances of epibenthic fauna from non-vegetated
soft substrates (Skilleter- et al. 2019).
Stingrays and fish were recorded in the non-vegetated soft sediment habitats in and around
the study area, and numerous stingray pits occurred intertidally, particularly in channel
habitat and at the mouth of Lake Weyba. Large drifts of seagrass wrack (i.e. dead seagrass
fragments detached from the original plant) were not evident throughout the estuary.
Seagrass wrack is an important component of coastal ecosystems, providing microhabitats
and food resources for fauna, and contributing to nutrient cycling (Oldham et al. 2014).
Figure 3.5 Z. muelleri with dense epiphytic algae in Weyba Creek in November 2020
Assessing Distribution of Seagrass in the Noosa Estuary 11
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Figure 3.6 Sparse Z. muelleri with moderate (40%) epiphytic algae growing along channel in
Weyba Creek in November 2020
Assessing Distribution of Seagrass in the Noosa Estuary 12
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Figure 3.7 Small dense patches of Z. muelleri becoming smothered by mobile sand bars in
Weyba Creek
Assessing Distribution of Seagrass in the Noosa Estuary 13
Section 20
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4 Historical Change in Seagrass Distribution
A total of 56 Ha of seagrass was recorded throughout the estuary in November 2020, of
which, the majority of area (31.8 Ha) was recorded from within Lake Doonella and 21 Ha
from Weyba Creek (Table 3.1 & Table 4.1). Unlike previous assessments (e.g. Hyland et al
1989), no seagrass was recorded upstream of the ferry crossing to Noosa North Shore in
2020. In 1987, a total of 42 Ha of dense seagrass was recorded in the Main River Channel
from Noosa to Lake Cooroibah, 62 Ha of patchy seagrass in Lake Doonella and 320 Ha of
patchy seagrass in Lake Cooroibah (Hyland et al 1989). The Hyland et al. (1989)
assessment was confirmed by assessing the area of seagrass in available aerial imagery
from 1987 and 1989, which illustrates the substantial extent of seagrass at that time covering
approximately 3,374 Ha (Table 4.1).
Based on the assessment of aerial imagery, there has been a large decline in the coverage
of continuous and dense seagrass beds in several areas in the Noosa Estuary since 1989
(Figure 4.2, Figure 4.3 & Figure 4.4; Table 4.1). Declines have occurred around areas that
are currently used as mooring areas for vessels such as around Goat Island, or focal areas
for vessel movements such as upstream of Tewantin, upstream of the Eenie Creek Bridge in
Weyba Creek and at the mouth of Lake Cooroibah. In particular, there has been a sustained
reduction and fragmentation of seagrass habitat along the main reach of the river upstream
of Tewantin (Council Chambers) to Lake Cooroibah. The reduction in seagrass coverage
relative to what has been previously observed and recorded by Hyland et al. (1989), or what
has been mapped from aerial imagery in this assessment, is considerable; even if you
consider the coarse seagrass bed categories and nature of mapping completed by Hyland et
al. (1989). We estimate that the seagrass coverage lost has been up to 83%, with only a
small amount of recovery in some areas and the complete loss of seagrass in other reaches
during that time (Table 4.1). The majority of seagrass lost occurred at some time between
1989 and 2006; though seagrass was completely lost in Lake Cooroibah between 2009 and
2020 (Table 4.1). An assessment of the historical changes in each reach is provided below
(Section 4).
Table 4.1 Historical comparison of seagrass area within Noosa Estuary
Reach Area (m2) of Seagrass % change
1987 1989 2006 2009 2020 1989 to 2020
Lake Cooroibah NA 229,624 71,323 61,672 0 –100
Noosa River – Tewantin 106,651 134,541 39,360 36,731 28,540 –79
Lake Doonella 495,772 457,164 127,158 363,764 318,129 –30
Noosa River – Goat
93,865 105,247 28,831 23,539 9,313 –91
Island
Weyba Creek NA 647,065 270,366 239,551 205,510 –68
Lake Weyba NA 1,800,445 0 0 20 –100
Total Seagrass Area
NA 3,374,086 537,038 725,258 561,512 –83
(m2) Noosa Estuary
Total Seagrass Area
NA 337.4 53.7 72.5 56.1 –83
(Ha) Noosa Estuary
NA – suitable imagery not available for assessment across the estuary
Assessing Distribution of Seagrass in the Noosa Estuary 14
Section 21
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4.1 Lake Cooroibah
Based on interpretation of aerial imagery, there was a substantial seagrass bed present in
Lake Cooroibah in 1989 (Figure 4.2). A total of 229.6 ha of seagrass was mapped along the
main navigation channel at the mouth of the lake and extending along the south-eastern
shore (Table 4.1). There were substantial declines in the total area of seagrass occurring in
this reach between 1989 to 2009, with the loss of seagrass along the main river channel as
well as sparse patches within the lake (Figure 4.2). In 2020, the dense seagrass beds lining
the navigation channel were no longer present, replaced with fine silt, particularly at the
mouth of the lake (Table 4.1). The seagrass lining the main river channel upstream of the car
ferry was also not recorded in 2020 (Figure 4.2; Table 4.1).
The primary cause of such a substantial decline in seagrass in this area was likely the floods
in 1992, and subsequent floods in later years, reducing light penetration in the shallow lake
and depositing fine sediment at the mouth of the lake and smothering existing seed banks
before the beds had a chance to become re-established. This area should be prioritised for
enhanced management measures, including possible support for re-establishing seagrass to
improve habitat complexity and water quality outcomes in the estuary. The first step would be
to identify whether there is an existing seagrass seed bank, and if there are other extraneous
environmental issues that has prevented the natural reestablishment of seagrass in the area.
Management actions may include the use of go-slow areas to minimise boat wash along the
main channel, particularly at the mouth of the lake, managing and reducing sediment in
runoff and understanding the current sediment dynamics (redistribution and resuspension) in
the estuary.
4.2 Noosa River – Tewantin
Similarly, there has been an 79% decline in the coverage of seagrass between 1989 and
2020 in this reach, with the greatest declines occurring along the main river channel
downstream of the car ferry (Figure 4.3; Table 4.1). Since 2006, the decline in seagrass
extent has been less; although in 2020, seagrass beds were primarily located within the bay
to the north of Noosa Council chambers in Tewantin (Figure 4.3). There has been a
substantial contraction of beds along the river channel further north. Increased tidal
connectivity relative to further upstream, may create conditions that lessen the impact of
floods, with tidal flushing of less turbid waters decreasing the length of time seagrass is
exposed to low light / high turbid conditions. Given the substantial changes further upstream,
this area will be one to watch for further declines in extent.
4.3 Noosa River – Goat Island
The once dense seagrass beds around Goat Island have declined in extent by approximately
91% since 1989, with just under 1 ha remaining along the northern side of Goat Island and a
few small patches of long dense Z. muelleri along the southern shore (Figure 4.3; Table 4.1).
Like the other areas, the major declines in this area occurred between 1989 and 2006;
however, unlike areas such as Lake Doonella (Section 4.4 below), the seagrass beds around
Goat Island have not recovered and continue to decline. A major decline in the coverage of
seagrass in this reach may be due to increased boat anchoring, as there has been an
increase in the number of anchored vessels on aerial imagery since 2002. Damage from
Assessing Distribution of Seagrass in the Noosa Estuary 15
Section 22
Ecological Service Professionals
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repeated anchoring and growler chains on moored vessels can cause significant direct
physical damage to seagrass beds and creating halos many metres across (Walker et al.
1989; Hastings et al. 1995).
4.4 Lake Doonella
The area of seagrass within Lake Doonella has undergone some substantial historical
changes in the extent, with a decline of 72% recorded between 1989 and 2006 (Figure 4.3;
Table 4.1). This area has recovered quickly following major declines. The seagrass beds in
Lake Doonella are dominated by H. ovalis, which is known to respond rapidly to
environmental changes and can quickly recover within a few years, both through vegetative
growth and regeneration from the seedbank. While the exact mechanisms of change remain
unclear, it is possible that due to the configuration of the mouth of the lake, that there was
lower sedimentation following major flooding in 1992 (Figure 4.7), enabling the beds in this
area to recover from the disturbance in a similar timeframe as observed elsewhere, such as
in Hervey Bay (Campbell & McKenzie 2004).
4.5 Weyba Creek
While the extent of seagrass in Weyba Creek has also declined, there are large areas that
remain relatively intact, including the seagrass around Keyser Island at the mouth of the
creek that increased in coverage between 2006 and 2009, but has since declined again in
2020. The mechanisms for substantial change in this reach based on observations appear to
be shifting sand bars, which smother large areas of seagrass, particularly in areas near the
mouth of Lake Weyba. There has been a substantial change in the mouth of Weyba Creek
due to urbanisation and development of mangrove islands and along the foreshore, which
may have altered the water quality or hydrodynamic regimes in this reach. Further
investigation of the possible triggers for high epiphytic algal loads on the existing seagrass,
assessments of the current water quality (including possible eutrophication from groundwater
sources) and the residence time of water within this reach are needed.
4.6 Lake Weyba
The extent of seagrass in Lake Weyba has changed dramatically over the last 30 years, with
large sparse seagrass beds at the mouth of the lake now just a few small patches. While not
specifically mapped due to a lack of suitable aerial imagery, there were extensive seagrass
beds recorded in Hyland et al 1989, which are visible in available aerial imagery (Figure 4.1).
The greatest loss occurred between 1989 and 2006, where large beds of seagrass
disappeared from the lake and did not recover. The triggers for the loss of seagrass within
the lake remain unknown, but may be related to changes in water quality, interactive or
cumulative impacts from flooding (i.e. freshwater flows allowing algae to bloom and
outcompete seagrass) or changes in the hydrodynamic regime that prevent seagrass from
re-establishing. This initial loss of seagrass in the early 1990s, may have triggered a regime
shift to a soft sediment microalgal dominated system where constant resuspension of fine
sediment particles directly smother or attenuate light sufficiently to prevent seagrass from
restabilising naturally.
Assessing Distribution of Seagrass in the Noosa Estuary 16
Section 23
Ecological Service Professionals
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While the exact cause of the decline in seagrass in this reach remains to be determined, this
area could be prioritised for possible remediation activities given their remnant nature and
endurance and suitability of large areas to support extensive historical seagrass meadows.
The restored function, including fisheries productivity gained from re-establishing these
extensive seagrass beds could be substantial.
Figure 4.1 Extensive seagrass beds (shown as darker patches) at the mouth of Lake Weyba and
entrance to Weyba Creek in August 1986 (Source: QLD Government 2021b)
Assessing Distribution of Seagrass in the Noosa Estuary 17
Section 24
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1989
Assessing Distribution of Seagrass in the Noosa Estuary 18
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4 1 1 1 38 0 1329 1782 1018 40 -1
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4 1 1 1 39 0 1298 1821 1605 51 -1
5 1 1 1 39 1 1298 1853 3 14 80 \
5 1 1 1 39 2 1359 1829 43 37 11 eae
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5 1 1 1 39 4 1582 1864 7 5 1 3
5 1 1 1 39 5 2188 1823 8 49 83 |
5 1 1 1 39 6 2226 1827 33 42 40 os
5 1 1 1 39 7 2362 1826 8 2 0 ‘
5 1 1 1 39 8 2466 1842 43 17 96 Plan
5 1 1 1 39 9 2517 1843 19 16 96 to
5 1 1 1 39 10 2544 1821 169 38 22 meson
5 1 1 1 39 11 2721 1842 19 17 96 of
5 1 1 1 39 12 2748 1842 68 17 96 marine
5 1 1 1 39 13 2824 1842 79 17 94 habitats
4 1 1 1 40 0 854 1845 1842 77 -1
5 1 1 1 40 1 854 1886 2 2 74 “
5 1 1 1 40 2 1300 1867 6 33 89 \
5 1 1 1 40 3 1339 1870 19 25 38 gs
5 1 1 1 40 4 1565 1895 4 1 23 i
5 1 1 1 40 5 1596 1867 13 30 60 >
5 1 1 1 40 6 1697 1885 63 25 36 awe
5 1 1 1 40 7 1768 1868 84 39 32 ease
5 1 1 1 40 8 2164 1845 113 77 18 a
5 1 1 1 40 9 2447 1864 65 52 47 pas
5 1 1 1 40 10 2507 1864 102 53 0 cous
5 1 1 1 40 11 2656 1895 40 17 84 land
4 1 1 1 41 0 695 1893 1989 28 -1
5 1 1 1 41 1 695 1896 14 6 43 =
5 1 1 1 41 2 910 1910 21 6 20 4s
5 1 1 1 41 3 1569 1896 42 18 0 ase
5 1 1 1 41 4 1683 1893 172 27 0 Pees
5 1 1 1 41 5 2195 1901 26 20 49 mn
5 1 1 1 41 6 2504 1896 56 16 74 tate
5 1 1 1 41 7 2546 1889 29 31 93 of
5 1 1 1 41 8 2593 1900 91 12 89 Queenslan
4 1 1 1 42 0 685 1895 2293 77 -1
5 1 1 1 42 1 685 1930 15 4 16 SS
5 1 1 1 42 2 798 1895 170 47 17 Peni’
5 1 1 1 42 3 1305 1901 7 15 88 4
5 1 1 1 42 4 1323 1935 15 12 76 4
5 1 1 1 42 5 1347 1916 60 56 61 a
5 1 1 1 42 6 1615 1916 59 20 0 ~
5 1 1 1 42 7 1679 1900 156 46 0 MEee
5 1 1 1 42 8 2185 1905 53 41 52 (eS
5 1 1 1 42 9 2271 1910 34 29 0 a
5 1 1 1 42 10 2464 1921 18 17 96 ©
5 1 1 1 42 11 2490 1921 101 22 96 Ecological
5 1 1 1 42 12 2600 1921 75 17 96 Service
5 1 1 1 42 13 2684 1921 136 17 96 Professionals
5 1 1 1 42 14 2829 1921 31 22 96 Pty
5 1 1 1 42 15 2868 1921 35 17 96 Ltd.
5 1 1 1 42 16 2913 1921 65 22 96 (ESP).
4 1 1 1 43 0 681 1922 2290 76 -1
5 1 1 1 43 1 681 1922 38 76 32 PF
5 1 1 1 43 2 1303 1950 47 35 0 e
5 1 1 1 43 3 1387 1940 21 29 0 “s
5 1 1 1 43 4 1777 1945 27 27 0 we
5 1 1 1 43 5 1822 1945 11 4 26 »
5 1 1 1 43 6 1968 1948 53 25 17 eel
5 1 1 1 43 7 2180 1944 8 22 41 3
5 1 1 1 43 8 2196 1947 19 26 68 =
5 1 1 1 43 9 2236 1937 57 57 25 aN
5 1 1 1 43 10 2464 1948 25 17 96 All
5 1 1 1 43 11 2497 1953 43 12 96 care
5 1 1 1 43 12 2549 1948 35 17 96 has
5 1 1 1 43 13 2593 1948 48 17 96 been
5 1 1 1 43 14 2649 1948 55 17 96 taken
5 1 1 1 43 15 2712 1949 18 16 96 to
5 1 1 1 43 16 2738 1953 69 12 96 ensure
5 1 1 1 43 17 2814 1948 31 17 96 the
5 1 1 1 43 18 2853 1953 91 17 96 accuracy
5 1 1 1 43 19 2952 1948 19 17 96 of
4 1 1 1 44 0 1294 1953 1220 41 -1
5 1 1 1 44 1 1294 1974 11 18 39 Ie
5 1 1 1 44 2 1327 1953 53 41 38 ON
5 1 1 1 44 3 1800 1972 10 20 0 x
5 1 1 1 44 4 1987 1971 8 23 3 H
5 1 1 1 44 5 2081 1973 29 21 48 igs
5 1 1 1 44 6 2178 1968 78 26 39 ec}
5 1 1 1 44 7 2465 1974 49 17 96 data.
4 1 1 1 45 0 427 2080 2787 40 -1
5 1 1 1 45 1 427 2081 114 39 96 Figure
5 1 1 1 45 2 554 2081 56 30 90 4.2
5 1 1 1 45 3 652 2081 166 31 89 Historical
5 1 1 1 45 4 833 2081 198 31 96 distribution
5 1 1 1 45 5 1046 2080 35 32 96 of
5 1 1 1 45 6 1092 2089 166 31 96 seagrass
5 1 1 1 45 7 1275 2081 27 30 96 in
5 1 1 1 45 8 1317 2081 55 31 96 the
5 1 1 1 45 9 1388 2081 86 31 93 Lake
5 1 1 1 45 10 1489 2080 188 32 91 Cooroibah
5 1 1 1 45 11 1694 2081 99 31 96 reach
5 1 1 1 45 12 1810 2081 27 30 90 in
5 1 1 1 45 13 1853 2080 150 40 86 (a)1989,
5 1 1 1 45 14 2020 2080 48 40 92 (b)
5 1 1 1 45 15 2081 2081 100 36 93 2006,
5 1 1 1 45 16 2198 2080 46 40 92 (c)
5 1 1 1 45 17 2257 2081 91 31 96 2009
5 1 1 1 45 18 2361 2081 66 31 93 and
5 1 1 1 45 19 2444 2080 48 40 90 (d)
5 1 1 1 45 20 2505 2081 198 31 96 distribution
5 1 1 1 45 21 2720 2081 27 30 95 in
5 1 1 1 45 22 2762 2081 90 31 95 2020
5 1 1 1 45 23 2866 2081 66 31 96 and
5 1 1 1 45 24 2948 2089 80 23 96 area
5 1 1 1 45 25 3044 2081 62 31 96 lost
5 1 1 1 45 26 3119 2081 95 31 96 since
4 1 1 1 46 0 653 2136 87 31 -1
5 1 1 1 46 1 653 2136 87 31 96 1989
4 1 1 1 47 0 3229 2241 37 28 -1
5 1 1 1 47 1 3229 2241 37 28 96 18Section 25
°
Historical distribution of
D E
seagrass in Tewantin
Doonella & Goat Island
Project: 2020
Author: SW
Coordinate System: GDA2020 MGA Zone 56
Noosa River - Projection: Transverse Mercator
Noosa River - Tewantin Datum: GDA2020
Tewantin
Legend
Reach
Noosa River - Seagrass extent 1989
Noosa River -
Goat Island
Goat Island Seagrass extent 2006
Seagrass extent 2009
/ake
Doonella Seagrass extent 2020
La Seagrass lost since 1989
L
/ake
Doonella
F G
0 0.25 0.5 1 1.5 2
Kilometers
Noosa River - Noosa River -
Tewantin Tewantin
Noosa River - Noosa River - Noosa
Goat Island Goat Island Heads
/DNH
Doonella
/ake
Doonella Plan to illustrate location of marine habitats
L Data Sources:
Lake © State of Queensland
© Ecological Service Professionals Pty Ltd. (ESP).
All care has been taken to ensure the accuracy of
data.
Figure 4.3 Historical distribution of seagrass in the Tewantin, Lake Doonella and Goat Island reaches in (a)1989, (b) 2006, (c) 2009 and (d) distribution in
2020 and area lost since 1989
Assessing Distribution of Seagrass in the Noosa Estuary 19
Section 26
°
E Historical distribution of
D seagrass in Weyba Creek
Project: 2020
.H\VHU
.H\VHU Author: SW
,VODQG Coordinate System: GDA2020 MGA Zone 56
,VODQG
Projection: Transverse Mercator
Datum: GDA2020
Legend
Reach boundary
Seagrass extent 1989
Seagrass extent 2006
Seagrass extent 2009
Seagrass extent 2020
Seagrass lost since 1989
Lake Weyba Lake Weyba
F G
0 0.25 0.5 1 1.5 2
Kilometers
.H\VHU
.H\VHU
,VODQG
,VODQG
Noosa
Heads
Plan to illustrate location of marine habitats
Data Sources:
© State of Queensland
Lake Weyba Lake Weyba © Ecological Service Professionals Pty Ltd. (ESP).
All care has been taken to ensure the accuracy of
data.
Figure 4.4 Historical distribution of seagrass in the Weyba Creek reach in (a)1989, (b) 2006, (c) 2009 and (d) distribution in 2020 and area lost since
1989
Assessing Distribution of Seagrass in the Noosa Estuary 20
a Pa as aa = Pe eae Sea ee Historical distribution of
a) een pe aN ie Sy Pa i ae Pe a Sy ss Ap een ree seagrass in Weyba Creek
Ne Ai erseu ee rs eo.
Pe cs ei 17 Cae Ne R Bae ie - AE Se a PE”
gach arte ieee _ pe aia, ate oointe eve ce mks Wc a Project: 2020
[Pee eh diese has a5 FES Fe hi Beek ae eg ae Ge 4 ie) ia Toject:
eek See’ MC = 3 bey te eee iars ih een ‘i Sabet a2 Author: SW
’ aa Wek ti, Wha arenas a 5 TY ae Sa :
Island /4 ei. Lae Pre renee EF iRee » LE Coordinate System: GDA2020 MGA Zone 56
= — 1 aires Ray eee. ay pie, > i eee { Projection: Transverse Mercator
Bator ry pe oe Oar ay Eee Eo EA | Yael Datum: GDA2020
{>on Pea PY SG ee
ake. PA Ss ! eg ee a Te, Rr ec
} pee als: BA ee eed By: | spiced ew Bary ae os Sy SEC e Legend
ON IS Me So oo i See! eer ee ee
‘a Peat #3! sae eS mk Ng ae ami Ea
fa, / Set ieee. is Reach boundary
om etext ek ex ES ae Se et po se eS :
, ey he aoe A as . ES i By Oo, eg aM
: % eo Ne. SES ha pe ata ED ITE
: ty een aos , ss Hit eta cin | Seagrass extent 1989
“A ig bah Seis) 9 ay RS ; AS = Seagrass extent 2006
te y ea | = NE ee aad
Lt ¥ ae ’ SRE Sh *
7 Ns fn) \ eS s vy Seagrass extent 2009
iS Ne Bie HM seagrass extent 2020
. : a WR ee Roe
, et Oe Ge
is 5 ee . ‘ pea Seagrass lost since 1989
Lake Weyba + ees Seo eC oF
aes i 3
rete Peo ein es cs Rear el Ro PRN Ea
ae — At OO RRS i a - ee ee
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Fei hasan a Fer e EN ale eh} bd PRO 0 0.250.5 1 1.5 2
ee a Rn ee NS Be ee ee a
Ee eas Sed et Wie Via Sr Perietinpee ean ie pee Aaa ae “Cease Kilometers
Pe eek er oe a SB Sa Bars, ey ay Mier ae pe iy, IE aa SS
Feet Rie gee ident YR A Paco Tak Ceca nae D
Fao melae ESS ta Lee oo Ke Rh 2) Pvc WCU Jin ia, me eer ie Rae
Sie cree 2 aN Die ae ee Be NT a Pes tae Sea ae ea
Fe Wi i Pe A Sale wi ms Ler eile hy Pe eR SE EN SJ Oo® SOE Sy
fc a ea eae S (etapa eae ee iy SSeS is UR ite ab irr
ea ee a En reas SR Re s A en eae
Re ni erat ae cee, | Se Pa ee 8 Be rae meee a Gs
Pe cee clot. dae ie rs oR | in re Pare ae
ee id i rem ni aor A. A RP ee Voc ee Be OO ee RR
ee ga a 4 ae ee ee en ee CS) eee Pee Nes oe Saree Sats eae aie by 4
Ll 2 ee Opes ee } lies Pe er es Secret ne I) A aed
He Nga foster ie oR es el OD ee age eee “
Ea SS aa ie eg SEN he be ee) ORE oe 2
AN Sed bee rie ae Nee PS eae OY Amer wae . Be
a fi See ce Te a a ae a rd Be ee Agee Noosa
eaeligg yt Si) meet ocsor ee | i Kes. sani R Sears” _ pS a
ee a eT a Cas DN ga Sy ae z a ~} Heads
prea Ba OR Py sae ee Sh ee DS al Ce
pat Bek yee 4 oe : Ss oR Pe
ENN) WEN Rs ALA i cde Beye
OR, SS ers be dest) Waa abt Some SA, Stree
aa ‘ Bm hase § Court oer / \ ee ot Se
S . 8 a an e . mal ee \
iN ; ee eT Ey We * BM “Py a. 1
. eS eye De) \ a. REI ‘ ote |
~ wae y Ad um | ~~ = Bs a) *, SSae UES i Plan to illustrate location of marine habitats
eo, len tn ty ae > NOAA
“ Le > # a . MN Data Sources:
ae ee — pig © State of Queensland
4 {ef : Y eyba © Ecological Service Professionals Pty Ltd. (ESP).
4 at All care has been taken to ensure the accuracy of
- : fi data.
Figure 4.4 Historical distribution of seagrass in the Weyba Creek reach in (a)1989, (b) 2006, (c) 2009 and (d) distribution in 2020 and area lost since
20Section 27
Ecological Service Professionals
Sustainable Science Solutions
4.7 Influential Environmental Factors
Several factors may have contributed to the decline in the extent of seagrass in Noosa
Estuary. In particular, flooding has resulted in substantial declines in seagrass elsewhere in
the region at a similar time as observed here (Preen et al 1995; Campbell & McKenzie 2004).
An assessment of available rainfall and riverine flow data was completed to determine if
similar events contributed to the substantial declines observed in the Noosa Estuary.
The Noosa River flooded in 1992 (approximately 757 mm of rain fell over a two-day period in
February 1992 recorded at Kiamba) (Figure 4.6), which may have been a trigger for
substantial loss in seagrass extent due to mobilisation of sediment. This corresponds to a
period of substantial loss of seagrass in several key areas, particularly in Lake Cooroibah
and along the Main Noosa River channel. The impact of flooding on seagrass distribution is
likely to differ depending on the reach, as the flood plume did not extend substantially up the
Weyba Creek (Figure 4.5) and may have lessened the potential impact on light attenuation
(duration and magnitude) and therefore seagrass survival.
Figure 4.5 Aerial image of the mouth of Noosa River on 24 February 1992 showing the majority
of the flood plume bypassing Weyba Creek and Noosa Sound, and extending out into
Laguna Bay (Source QLD Government 2021a)
Assessing Distribution of Seagrass in the Noosa Estuary A-21
Section 28
Ecological Service Professionals
Sustainable Science Solutions
4.7.1 Rainfall
The highest daily rainfall at the Kiamba Bureau of Meteorology (BOM) Station 0405252 in
February 1999 again exceeded a total monthly rainfall of 1012 mm of rainfall for the month
with high daily rainfall in excess of 100 mm of rainfall occurring on the 1, 2, 8, 9 and 10
February 1999 (Kiamba BOM station 040525) (BOM 2021a) (Figure 4.6). Similarly high
rainfall was recorded at Boreen Point on the banks of Lake Cootharaba of 1012 mm of
rainfall for the month with high daily rainfall in excess of 100 mm of rainfall occurring on the
1, 2, 8, and 9 February 1999 (Boreen Point BOM station 40756) (BOM 2021b).
1400
1200
Monthly Total Rainfall (mm)
1000
800
600
400
200
0
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
Date
Figure 4.6 Monthly total rainfall (mm) measured at Kiamba BOM station from 1952 to 2014
4.7.2 Riverine Flow
Total river discharge measures at Teewah Creek at Coops Corner (QLD Gauging Station
140002A3) (QLD Government 2021b) generally reflects the rainfall in the area, with several
peak monthly flood flows occurring since records began in 1972 following periods of high
rainfall. In particular, the highest recorded monthly flow occurred in February and March
1992 with a total monthly flow of 25813 ML and 15980 ML respectively for each month
(Figure 4.7). In contrast, the long-term average monthly flow is 2858 ML, more than 80%
lower than recorded during those peak flood flows. The total monthly flow recorded in
February 1992 was the highest on record for this gauging station. Other period of prolonged
flows occurred from February to June 1999 and flow exceeding 10000 ML per month in
August and September 2007, January and February 2008, December 2010, January 2011,
March 2012, February 2013 and February 2020 (Figure 4.7). Peak flows in the upper
catchment and subsequent flooding can be cause substantial mobilisation of sediment from
the upper catchment, along creeks and rivers to Laguna Bay.
2
The Kiamba Bureau of Meteorology (BOM) Station 040525 is approximately 26 km to the west of
Tewantin, and is the closest weather station that was operational in 1992 and 1999.
3
Flow has been recorded from May 1972 until present.
Assessing Distribution of Seagrass in the Noosa Estuary A-22
Section 29
Monthly Volume (ML)
10000
15000
20000
25000
30000
0
5000
1/1/72
1/4/73
1/7/74
1/10/75
1/1/77
2021
1/4/78
1/7/79
1/10/80
1/1/82
1/4/83
1/7/84
1/10/85
1/1/87
1/4/88
1/7/89
1/10/90
1/1/92
1/4/93
Assessing Distribution of Seagrass in the Noosa Estuary
1/7/94
1/10/95
1/1/97
Date
1/4/98
1/7/99
1/10/00
1/1/02
1/4/03
1/7/04
1/10/05
1/1/07
1/4/08
1/7/09
1/10/10
1/1/12
1/4/13
1/7/14
1/10/15
1/1/17
1/4/18
1/7/19
1/10/20
Figure 4.7 Total volume of water discharged at Teewah Creek gauging station between 1972 and
Sustainable Science Solutions
Ecological Service Professionals
A-23
Section 30
Ecological Service Professionals
Sustainable Science Solutions
5 Discussion
Seagrasses are highly sensitive to changes in environmental conditions and declines in
water quality (particularly high turbidity), and are therefore considered indicators of
environmental degradation and anthropogenic stressors (Heck et al. 2008; Waycott et al.
2009). Large scale seagrass loss has occurred in the past in Australia and across the globe
(Short & Wyllie-Echeverria 1996), with the most significant and substantial extent of loss in
Southern Queensland usually following a major flood or cyclonic event (Preen et al 1995;
Campbell & McKenzie 2004). Minor or local scale impacts to seagrass occur due to human
disturbances such as physical damage from propeller scaring, anchoring (Millazo et al.
2004), boat mooring (Walker et al. 1989; Hastings et al. 1995), boat wash (Bishop 2008), and
pollution from oil spills, herbicide runoff and inputs from stormwater (Short & Wyllie-
Echeverria 1996; McMahon et al 2005; Waycott et al 2009). The rate of seagrass loss
recorded across the globe between 1879 and 2006 has been estimated at approximately
27 km2 per year (i.e. a total of 3370 km2) (Waycott et al 2009). More recently attention has
focussed on assessing the potential for recovery following catastrophic changes in the face
of climate change (Waycott et al. 2009; Kendrick et al. 2019).
The Noosa River flooded in 1992 (approximately 757 mm of rain fell over a two-day period in
February 1992, recorded at Kiamba BOM station 040525; refer Section 4.7.1), which may
have been a trigger for substantial loss in seagrass extent. At a similar time in Hervey Bay,
more than 1,000 km2 was reported as being lost following two major floods and a cyclone in
a 3-week period (Preen et al. 1995). The loss of seagrass was thought to be due to light
depravation due to turbid waters (Preen et al. 1995), and points to the need to manage
terrestrial runoff and protect water quality (and in particular water clarity) to support a thriving
seagrass community in an estuarine system. Recovery of seagrass meadows in deeper
water (greater than 10 m) of Hervey Bay took more than 2 years post disturbance, due in
part to seed germination from the existing seed bank (Preen et al. 1995). Recovery in
shallow water meadows took even longer, with suspected burial of the seed bank due to
redistribution of sediment thought to be a primary factor for the prolonged recovery in some
areas (Preen et al 1995).
Based on analysis of historical imagery, there was no substantial recovery of seagrass in
some parts of the Noosa Estuary once it was lost, likely due to smothering of the existing
seedbank by fine sediment and destabilisation of the channel sediment, particularly along the
main channel and at the mouth of Lake Cooroibah. The smothering of seagrass seedbanks
can prevent reestablishment of seagrass, particularly in shallow habitat, where sediment is
continually resuspended (Preen et al. 1995).
A further loss of seagrass occurred in Great Sandy Strait following flooding of the Mary River
in February 1999, with more than 90% of intertidal seagrass lost (Campbell & McKenzie
2004). Recovery of seagrass took at least 3 years and was primarily achieved through
natural seed germination.
Urbanisation of the foreshore, increased vessel traffic (boat wash), and increased anchoring
and mooring of vessels in the river, particularly in the lower estuary, may have contributed to
direct physical damage to seagrass or changes in water quality and hydrodynamics,
particularly close to the river mouth, which may alter the way that sediment is transported out
into Laguna Bay during flood flows or is retained in the estuary. Further work is required to
Assessing Distribution of Seagrass in the Noosa Estuary A-24
Section 31
Ecological Service Professionals
Sustainable Science Solutions
understand the impact of this change on the potential suitability of habitats for seagrass,
particularly in Weyba Creek and along the main river channel.
Seagrass meadows around the globe are sentinels for change in the environment. They are
primary producers, capable of engineering the environment by converting sunlight, nutrients
and carbon from the environment to stabilise soft sediments and create structured complex
habitats that support high biodiversity including fish and invertebrates of commercial
importance (Jelbart et al 2007; Nagelkerken et al. 2008; Waycott et al. 2011). The loss of
seagrass in Lake Cooroibah and along the Noosa River at Tewantin and around Goat Island
significantly decreases the potential ecological functions that seagrass can provide, including
filtering water and sequestering carbon in the Noosa Estuary. The loss of biological filtration
habitats such as seagrass, saltmarsh, mangrove and oyster reef habitats is not new in
Noosa, with the substantial loss of habitat occurring at Hays Island in the early 1970s. This
dramatic change to the mouth of Weyba Creek (Figure 5.1) may have altered water
movement and created conditions that favoured the persistence of seagrass in some areas,
and the decline in others. The loss of seagrass, particularly the large extent of loss from
within the lakes may have contributed partly to the reported the declines in availability and
therefore total catch of prawns in the estuary (Thurstan 2015); however, further work is
required to assess the links between loss of seagrass and declines in prawn catches in
Noosa. Elsewhere, seagrass beds are known to have a significant role as a nursery habitat
for prawns in estuaries and embayments (Skilleter et al. 2005).
Assessing Distribution of Seagrass in the Noosa Estuary A-25
Section 32
Ecological Service Professionals
Sustainable Science Solutions
a)
b)
Figure 5.1 Aerial imagery from (a) June 1972 and (b) November 1974, showing the change in
estuarine habitat due to urban development at the mouth of the Noosa Estuary
(Source QLD Government 2021a)
Assessing Distribution of Seagrass in the Noosa Estuary A-26
Section 33
Ecological Service Professionals
Sustainable Science Solutions
6 Conclusions
The Noosa estuary is dominated by bare sand and mud habitats with occasional dense
seagrass beds, rocky reefs and shellfish-dominated reef habitats. In 2020, seagrass covered
a total of 56 Ha throughout the estuary, with the largest continuous remnant patches
occurring at the entrance to Lake Weyba, along Weyba Creek (including around Keyser
Island), in Lake Doonella and along the small bay off the main river channel at Tewantin.
Notable declines in the area of seagrass beds have occurred within the Noosa Estuary,
particularly in Lake Weyba and Lake Cooroibah, with approximately 80% of the total area of
seagrass lost between 1987 and 2020.
Due to the nature of the Noosa River Catchment, different sub-catchments present a good
comparative opportunity to assess the cause of declines in seagrass extent and likely impact
of management actions. For example, impacts in along the main river channel are likely due
to broader scale impacts from the upper catchment, including runoff from catchment clearing
as well as boating activity. In contrast, seagrass in the smaller sub-catchments in Lake
Doonella and Lake Weyba are likely responding to changes in the hydrodynamic regime,
with seagrass in Weyba Creek being particularly susceptible to shifting sand banks.
Further assessment of the potential resilience of seagrass meadows to resist environmental
changes in the Noosa Estuary are considered necessary to understand where to invest in
future management actions for maximum gains. Consideration should also be given to the
potential for natural recovery or assisted restoration of seagrass meadows once key triggers
for past change are known and potential negative inputs have been managed.
Given that the cause of major changes to the extent of seagrass was most likely physical
disturbance during a natural disaster, suitable management of the estuarine habitats in
Noosa should consider an adaptive approach that examines and implements measures that
maximise the resilience of seagrass beds, including the ability to respond to future natural
disasters and human pressures that are predicted to increase in the future.
Assessing Distribution of Seagrass in the Noosa Estuary A-27
Section 34
Ecological Service Professionals
Sustainable Science Solutions
7 References
Bell JD. & Westoby M. 1986a. Abundance of macrofauna in dense seagrass is due to habitat
preference, not predation. Oecologia, 68: 205-209.
Bell JD. & Westoby M. 1986b. Variation in seagrass height and density over a wide spatial scale:
effects on common fish and decapods. Journal of Experimental Marine Biology and Ecology
104: 275-295.
Bishop MJ. 2008. Displacement of epifauna from seagrass blades by boat wake. Journal of
Experimental Marine Biology and Ecology. 354(1), 111-118.
Blomfield AL. & Gillanders BM. 2005. Fish and invertebrate assemblages in seagrass, mangrove,
saltmarsh and non-vegetated habitats. Estuaries, 28:63-77.
BOM 2021a. Climate data for Kiamba BOM station 40525. Accessed at
http://www.bom.gov.au/jsp/ncc/cdio/weatherData/av?p_nccObsCode=136&p_display_type=dail
yDataFile&p_startYear=1999&p_c=-328584583&p_stn_num=040525 in March 2021.
BOM 2021a. Climate data for Boreen Point BOM station 40756, accessed at
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Appendix A Value of seagrass to fisheries
Table 7.1 Criteria used to determine the fisheries habitat value of seagrass based on review of available literature4
Seagrass Patch Criteria Score
Characteristic /
Feature
1 2 3 4
Meadow extent Patchy <5m2 of seagrass bed Patchy bed either intertidal or Continuous bed extending from
surrounded by bare substrate subtidal areas only (patches intertidal to subtidal areas
(no other seagrass bed within separated by more than 5m)
5m of the patch)
Proximity to Poorly connected to other Moderately connected to Well connected to other Well-connected up- and down-
another structural structural fish habitat (Intertidal other structural fish habitat structural fish habitat shore to other known structural fish
habitats (based on seagrass proximal to (Intertidal seagrass proximal (Intertidal seagrass proximal habitats (Intertidal seagrass
wetland proximity mangroves, subtidal seagrass, to mangroves, subtidal to mangroves, subtidal proximal to mangroves, subtidal
score - Price et al macroalgae rocky reef, coral seagrass, macroalgae rocky seagrass, macroalgae rocky seagrass, macroalgae rocky reef,
2007) reef, or another structured reef, coral reef, or another reef, coral reef, or another coral reef, or another structured
habitat) No natural structural structured habitat) Structural structured habitat) Structural habitat). Structural ecosystem
ecosystem merged with ecosystem merged with up to ecosystem merged with 25 merged with >50% of meadow
meadow boundary. (i.e. 25% of meadow boundary or to 50% of meadow boundary boundary or within 100m of other
>1000m to another structural within 1000m of other or Within 100m of other structural habitat within 100m of
habitat and surrounded by structural habitat structural habitat other structural habitat
bare habitat)
Proximity to >1km 200 to 1000m <200m
nearest continuous
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seagrass bed
(>3000m2)
Proximity to deep Deepest edge of seagrass bed Deepest edge of seagrass Deepest edge of seagrass >2m
water channels is < 0.3 m bed is 0.3 – 2m OR Water is depth OR Water is < 2m deep at
> 0.3 m deep at deepest deepest point, with seagrass
point with seagrass growing growing to deepest points of
to deepest point estuary, estuary, lake or lagoon
lake or lagoon
Seagrass Condition Poor (Condition Index <4) Moderate (Condition Index 5 Moderate to Good Good to very good (Condition
Index (as defined to 8) (Condition Index 9 to 13) Index 14 to 16)
by the metrics
below)
Meadow mosaic Small bed area (>930m2) Small bed area (930-2300m2) Moderate bed area (3000 - Large bed area (>5000m2) well
size (patches within available for fish at high tide available for fish at high tide 5000m2) available for fish at connected and available for fish
5m considered the high tide use at high tide
same meadow)
Total Score <8 9 to 12 13 to 18 19 to 24
Fisheries Value Poor Fair Good Very Good
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Table 7.2 Seagrass condition index criteria
Seagrass Condition Criteria Score
Index
Score 1 2 3 4
Structural Complexity Low structural complexity (i.e. Moderate structural complexity High structural complexity High structural complexity (i.e.
max length of seagrass blades (i.e. max length of seagrass (i.e. max length of seagrass max length of seagrass blades
<10cm, depending on blades 10 to 20cm; depending blades 20 to 30cm >40cm depending on dominant
dominant species present) on dominant species present) depending on dominant species present)
species present)
Coverage of epiphytic Low or very high cover of High cover of epiphytic algae Moderate cover of epiphytic Moderate cover of epiphytic
algae epiphytic algae (<20% or >60% of seagrass blades OR algae (20-30%) algae (30-40%)
>80%) low cover of epiphytic (<20%)
Presence of Presence of dense Sparse coverage of Cyanobacterial mats such as
cyanobacterial mats cyanobacterial mats cyanobacterial mats (Lyngbya). Lyngbya absent
(Lyngbya).
Coverage of seagrass Sparse coverage of seagrass Sparse coverage of seagrass Moderately dense coverage Dense coverage of seagrass
(<10%) (10 to 30%) of seagrass (30-60%) (>60%)
Seagrass Condition Poor Fair Good Very Good
Index (as defined by
the metrics below)
Total Condition <4 5 to 8 9 to 13 14 to 16
Index Score
Assessing Distribution of Seagrass in the Noosa Estuary A-34