One-off swim surveys recording total macroalgal cover in the Great Barrier Reef, and their spatial and environmental predictors

Macroalgae are an important component of coral reef ecosystems. We identified the spatial patterns, environmental drivers and long-term trends of total cover of upright fleshy and calcareous coral reef inhabiting macroalgae in the Great Barrier Reef. The spatial study comprised of one-off surveys of 1257 transects at 324 sites on 163 reefs between latitude 11.0° to 23.6°S, coastal to offshore, at 0-18 m depth. The surveys were conducted between 1997 and 2008. Although not recent, the data are ecologically valuable due to their large spatial coverage along complex environmental gradients.Environmental predictors were obtained for each transect from in situ data, and from eReefs, a coupled hydrodynamic-biochemical model.The study found that macroalgae dominated the benthos (≥50% cover) on at least one sites onf 40.4% of surveyed inshore reefs. Spatially, macroalgal cover increased steeply towards the coast, with latitude away from the equator, and towards shallow (≤3 m) depth. Environmental conditions associated with macroalgal dominance were: high tidal range, wave exposure and irradiance, and low aragonite saturation state, Secchi depth, total alkalinity and temperature. Evidence of space competition between macroalgal cover and hard coral cover was restricted to shallow inshore sites. Our extensive empirical data and relationships may serve to parameterize ecosystem models, and to optimize refine reef condition indices based on macroalgal data for Pacific coral reefs.This dataset underpins the study: Fabricius KE, Crossman K, Jonker M, Mongin M, Thompson A . (2023) Macroalgal cover on coral reefs: spatial and environmental predictors, and decadal trends in the Great Barrier Reef. PLOS One.We acknowledge the Traditional Owners of the Sea Country of the Great Barrier Reef, and pay our respects to their Elders past, present and emerging. We acknowledge their continuing spiritual connection to their Sea Country.