2022-11-08 P&E Agenda - Item 6 - Attachment 1 - Current & Historical Distribution of Seagrass in the Noosa Estuary (40 pages)

                                                           Ecological Service Professionals
                                                                               Sustainable Science Solutions




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