Benthic baselines of the Groote Archipelago's key reefs in the wake of mass coral bleaching and Tropical Cyclone Megan.

Abstract

Coral reefs around the world are experiencing increasingly frequent and intense stress events, leading to benthic phase shifts. The ecological consequences of this are often profound and lasting, necessitating the development of both effective and regionally specific conservation strategies. Actualising positive conservational outcomes require managers to first gain insight into the present ecosystem diversity and structure; yet, in Groote Eylandt, a remote reef and largest island in the Gulf of Carpentaria off the northern end of Australia, this has not occurred. The Traditional Owners of Groote Eylandt (the Anindilyakwa people) have a long history of connection to the sea, but despite this rich history, they have not formally documented changes to their reef systems, which can create challenges for modern collaborative management efforts. Consequently, this study aims to document the benthic composition of key reef sites within the Groote Archipelago. Considering recent consecutive stress events, in the form of coral bleaching and Tropical Cyclone Megan, assessments of individual site health were also performed through frame compositional analysis of video surveys captured using a remotely operated vehicle. Benthic composition of five reefs within the Groote Archipelago were successfully documented. Scleractinian coral cover was documented at all sites, ranging from 5.2-47.1%, although dominant morphology and levels of mortality were site-specific. Branching morphologies were exceedingly rare, with coral composition dominated by massive morphology corals at the sites surveyed. Other major benthic taxa included soft corals, macroalgae, and sponges. Sea surface temperature data from satellites revealed that temperatures were elevated prior to bleaching observations but did not exceed a Degree Heating Week of 2.1, placing these reefs into the "Bleaching Warning" category. Our findings establish a foundational understanding of benthic composition at Groote Eylandt, necessary for further marine conservation within the region. This work also highlights the importance of acquiring data at remote reefs where data deficiencies can complicate local management efforts.