Unravelling the influence of light on inshore coral and sponge recruits and their substrate communities

Recruitment of progeny to coral reef populations involves complex ecological interactions, influenced by environmental factors such as altered underwater light conditions associated with poor water quality. Here, we exposed newly settled corals (Acropora millepora and Acropora cf. tenuis), the sponge (Phyllospongia foliascens), and their substrate communities to various light intensities and spectral profiles relevant to turbid inshore reefs. Coral and sponge recruit survivorship and growth generally exhibited an inverted U-shaped response to light intensity, suggesting environmental optima at lower light levels, while the influence of light spectra remained less clear within environmentally realistic treatment combinations. Crustose coralline algae cover similarly peaked at lower light levels, whereas turf algae increased with higher light conditions. Competitive interactions between the substrate communities and the recruits, along with photophysiological responses, were also assessed. Our results suggest that altered light characteristics associated with turbidity for periods up to six weeks may not be as detrimental to early coral and sponge recruits as other sediment-related stressors.