Assessing the influence of macroalgae and micropredation on the early life success of the echinoid Diadema africanum

Abstract

The sea urchin Diadema africanum has a significant influence on subtidal rocky reef communities on the Canary Islands, facilitating transitions between macroalgal beds and barren grounds. Barren grounds in the archipelago are characterized by a dominance of crustose coralline algae and a lack of invertebrates and fishes compared to macroalgal beds, which are mainly dominated by brown algae. To assess the impact of these benthic community states on the early life success of D. africanum a manipulative study was conducted during September 2022 in four sites of the eastern coast of Tenerife Island, 'Añaza' (28.4204060 N–16.2954172 W), 'Boca Cangrejo' (28.4061537 N–16.27429 W), 'Las Caletillas' (28.3814250 N – 16.3552938 W), and 'La Jaca' (28.12087153 N – 26.46111758 W. For this purpose, modified experimental larval collectors were employed to examine sea urchin settlement rates in response to two dominant macroalgal species, Lobophora schneideri, in algal beds and encrusting corallines (CCA) in barren grounds. Statistical analysis revealed significant spatial differences in sea urchin settlement and the interaction between site and treatment response. Specifically, the site with higher sea urchin recruitment exhibited lower numbers of D. africanum settlers in treatments containing L. schneideri than in the Control and CCA treatments. Three decapod species (Alpheus macrocheles, Lophozozimus incisus, and Pachygrapsus marmoratus) negatively correlated with D. africanum settlers. These results suggest that larval supply, L. schneideri beds, and micropredator abundance play a role in the early life success of this species. This may imply a community stability mechanism that helps prevent shifts between alternative stable states.