2021 State of the Environment Report Marine Chapter – Expert Assessment – State and Trend – Algal beds

Researchers: Barrett, Neville (Author) ,  Barrett, Neville (Author) ,  Barrett, Neville, Dr (Author) ,  Barrett, Neville, Dr (Author) ,  Emma Flukes (Point of contact)
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Brief description 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 Algal Beds". ***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 – Algal Beds"*** ---------------------------------------- DESCRIPTION OF SPECIES/HABITAT/COMMUNITY FOR EXPERT ASSESSMENT Algal beds are generally thought of as algae associated with hard substratum such as rocky reefs that provides a strong point of attachment for algae to grow and maintain position. The majority of Australia’s algal beds are found in temperate waters and are in many cases replaced as the major habitat-forming benthic organisms by corals in more tropical environments where intense grazing by herbivorous fishes contains algal biomass, particularly in clear offshore waters. The changeover from temperate algal covered reefs to coral dominated reefs is a gradual transition, but, as a broad generalisation, is considered to be in the vicinity of the Abrohlos Islands in Western Australia and Brisbane in Queensland, and is driven by the northern limit of the canopy forming kelp, Ecklonia radiata. Throughout this range, algal beds are found from the intertidal zone down to approximately 30 m depth where light availability limits growth. Despite this, lower limits may be much reduced in turbid or coloured water, or substantially exceed this in clear offshore water. Algal beds are composed of many constituent species with more than 1500 species of red, brown and green algae known from temperate and tropical Australia. Despite this, the overall canopy forming species are dominated by a far smaller subset of species, including Ecklonia radiata (the common kelp) which tends to be the dominant habitat-former and the most conspicuous species on temperate reefs, particularly on moderate to high energy coasts where it can form an extensive monospecific canopy above other algae. Given this ecological dominance which is consistent at continental scales, the overall health and extent of Ecklonia is considered to be a suitable indicator of the state of algal beds in general. Despite this, Ecklonia is typically replaced as a dominant species by Sargassum and Cystophora species in sheltered waters such as the Tasmanian north coast and upper reaches of South Australian gulfs, and may replace other species that are under stress (such as Macrocystis pyrifera - the “giant kelp” in Tasmania, or Scytothalia dorycarpa in Western Australia). Hence understanding the condition of algal beds can often require a region-specific knowledge of trends in key species in addition to Ecklonia. DATA STREAM(S) USED IN EXPERT ASSESSMENT Data used is outlined in reports/papers in the reference section, coupled with quantitative analysis of kelp cover undertaken as part of the SoE Rocky Reef assessment (Stuart-Smith et al.). ---------------------------------------- 2021 SOE ASSESSMENT SUMMARY [see attached Expert Assessment for full details] • 2021 • Assessment grade: Good Assessment trend: Stable to deteriorating Confidence grade: Adequate high-quality evidence and high-quality consensus Confidence trend: Adequate high-quality evidence and high-quality consensus Comparability: Grade and trend are somewhat comparable to the 2016 assessment. • 2016 • Assessment grade: Good Assessment trend: Stable to deteriorating Confidence grade: Adequate high-quality evidence and high-quality consensus Confidence trend: Adequate high-quality evidence and high-quality consensus Comparability: Grade and trend are somewhat comparable to the 2011 assessment. • 2011 • Assessment grade: Very good Assessment trend: Stable Confidence grade: Adequate high quality evidence and high quality consensus Confidence trend: Limited evidence or limited consensus ---------------------------------------- CHANGES SINCE 2016 SOE ASSESSMENT No change in overall categories, but noting ongoing decline in the SE due to interaction between Centrostephanus urchin range expansion due to warming and loss of top predators due to removal of top predators by fishing. Also noting that while there had been some recovery in WA following the 2011 heatwave (detailed in the Rocky reef SOE assessment) these systems are vulnerable to predicted increasing frequencies of heatwaves.

Lineage Statement: QUALITY OF DATA USED IN THE ASSESSMENT Data quality is high, based on multiple studies of cover and trends at local to national scales, as indicated in references and the quantitative analysis for Rocky Reefs.

Lineage

Notes Credit
Peer reviews of this assessment were provided by: Scott Ling (IMAS, UTAS)

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