2021 State of the Environment Report Marine Chapter – Expert Assessment – State and Trend – Bryozoan reefs

Updated: 2021-08-29

The Marine chapter of the 2021 State of the Environment (SoE) report incorporates multiple expert templates developed from streams of marine data. This metadata record describes the Expert Assessment "State and Trend of Bryozoan Reefs". ***A PDF of the full Expert Assessment, including figures and tables (where provided) is downloadable in the "On-line Resources" section of this record as "EXPERT ASSESSMENT 2021 - State and Trend – Bryozoan Reefs"*** ---------------------------------------- DESCRIPTION OF SPECIES/HABITAT/COMMUNITY FOR EXPERT ASSESSMENT Bryozoans (lace corals) are a species-rich group of colonial animals composed of soft and hard-bodied forms; almost 1,000 described and known undescribed species were recorded from Australia (Gordon 1999), occurring off both temperate and tropical coasts. Colonies vary in height or diameter from less than one millimetre to over one metre, and occur as flat sheets, plant-like tufts, fleshy lobes or coral-like growths. In association with small sponges, ascidians and hydroids they form low-relief structured matrix habitat variously termed bryozoan ‘reefs’, ‘thickets’ and ‘turf’ (depending on its height and composition). The matrix acts to stabilise sediments, and its bio-fragments are one of the most conspicuous and abundant components of shelf sediments, e.g. up to 75% of the sediment volume in the GAB (James et al. 2001). These sediments support small infauna (e.g. polychaetes, amphipods and molluscs) that are prey for larger species including fishes; the surfaces and interstices of some bryozoan colonies can support extremely high numbers of other taxa (>100 spp.) including polychaetes, molluscs, crustaceans and ascidians (Bradstock and Gordon 1983). Accordingly, it may be inferred that bryozoans play a vital role in the maintenance of benthic biodiversity. Collectively, bryozoan habitats are one of the main habitat types on the deep continental shelf, shelf break and shallow margin of the upper continental slope. They are typically interspersed with plains of sediment characterised by low microfauna in association with detritus and absence of epifauna, and rocky reefs. Bryozoan matrix forms on unconsolidated sediment and may cover low profile reef. Surveys of the Tasmanian ‘shelf-edge’, the region of the seafloor where the flat continental shelf drops away rapidly to form the continental slope, between 150 and 400 m showed that most bryozoan reef occurred between 200 and 350 m where if forms an important habitat for giant crabs. However, in relatively sheltered areas, including parts of the Tasmanian east coast, bryozoan habitats extend into ~60 m depth on the shelf. Similarly, in the eastern GAB, extensive areas of the shelf and break have high cover of bryozoans (Ward et al. 2003). The shelf edge is an important area for bottom contact fisheries including trawl and trap fisheries, and these represent the major pressure on bryozoan habitats. Bottom trawling has the potential to degrade and remove these habitats (Williams et al. 2009) and impact on other fisheries such as giant crab (Leon et al. 2017). On the GBR shelf, branching and busy bryozoans cover extensive areas in the vicinity of Broad Sound and Shoalwater Bay, the Pompey & Swains Reef Complexes, and the Capricorn-Bunker Regions — in high current channels near Hydrographers Passage, encrusting types form extensive areas of nodules with other associated biodiversity (Pitcher et al. 2007). Over 320 bryozoan taxa (mostly at the genus level) were identified by the latter study, and 124 taxa were mapped in detail throughout the GBR. Bryozoan habitats have been sampled using benthic sleds and dredges in many locations across their temperate and tropical Australian distribution, including the SE, GAB, GBR, Torres Strait, Gulf of Carpentaria and Pilbara. Those samples provided details of species identity, morphology and community composition. However, in situ observations (required to assess status) are limited to the shelf in the GBR, Torres Strait, Pilbara, parts of the Twofold bio-region, but in deeper waters only a few areas around Tasmania due to the logistic difficulty of conducting research at these depths. Around Tasmania, latitudinal variation in composition (as observed in camera imagery) appeared to be slight, with differences between samples driven by depth, and whether the samples were from within canyons. DATA STREAM(S) USED IN EXPERT ASSESSMENT Data used is outlined in the reports and publications listed in reference section. ---------------------------------------- 2021 SOE ASSESSMENT SUMMARY [see attached Expert Assessment for full details] • 2021 • Assessment grade: Good overall. Poor in South-east and Temperate East Assessment trend: Predicted stable-to-slightly improving trend Confidence grade: Barely adequate quality evidence, some consensus Confidence trend: Limited or barely adequate evidence, some consensus Comparability: Grade and trend are comparable to the 2016 assessment • 2016 • Assessment grade: Good overall. Poor in South-east and Temperate East Assessment trend: Predicted stable-to-slightly improving trend Confidence grade: Barely adequate quality evidence, some consensus Confidence trend: Limited or barely adequate evidence, some consensus Comparability: Grade and trend are comparable to the 2011 assessment • 2011 • [only assessed in the south-east region] Assessment grade: Poor Assessment trend: Stable Confidence grade: Limited evidence or limited consensus Confidence trend: Limited evidence or limited consensus ---------------------------------------- CHANGES SINCE 2016 SOE ASSESSMENT No change.