Proximity to macroalgal beds together with herbivory influence the recruitment of macroalgae on an inshore reef in the central Great Barrier Reef

Recruitment plays a key role in shaping the distribution of benthic organisms on temperate and tropical reefs. Macroalgae are common components of benthic communities on inshore coral reefs, yet little is known of the factors influencing their recruitment. In this study, we quantified the effect of proximity to macroalgal beds (0, 15, 30, 45 m from the bed) and herbivory (caged vs. uncaged) on the recruitment of macroalgae propagules to terracotta tiles deployed for 4.5 mo (December 2023 to April 2024) on Orpheus Island, inshore central Great Barrier Reef. Total macroalgal recruitment to tiles was 14-fold higher within macroalgal beds compared to areas outside the bed and declined with increasing distance from the beds. However, this pattern was largely driven by the high abundance of Sargassum (55% of all propagules) and Padina (8%) propagules on the tiles, the 2 most abundant taxa in the macroalgal beds. Other taxa such as Lobophora and Dictyota mostly recruited to tiles away from the macroalgal beds and were rare or absent on tiles within the beds; propagules of green and red macroalgae were rarely found on the tiles. Herbivory reduced the recruitment of macroalgae outside the beds, although its effect varied among macroalgae genera and bays. Our results highlight that short dispersal distances ( Sargassum ) and herbivory can limit macroalgal recruitment, but their relative importance varies spatially and among taxa. Importantly, these macroalgal beds can facilitate the local persistence of dominant taxa while deterring the settlement of other macroalgal taxa.