Planktonic stages of the ecologically important sea urchin, Diadema africanum: Larval performance under near future ocean conditions

Abstract

Diadema africanum is a recently described sea urchin from the Eastern Atlantic archipelagos, and adults play a major ecological role mediating the transition between two alternative ecosystem states: macroalgal beds and urchin barrens. The aim of this study was to describe for the first time the egg characteristics, fertilization and larval development. To determine basic life-history characteristics for this species, we reared larvae through to metamorphic competence under an energy shortage experiment and temperature-pH experiments to characterize the morphological plasticity of larval responses to actual and future oceanic conditions. D. africanum produces eggs that are larger both in diameter (82.7 μm) and volume (0.30 nl) than the eggs of both Diadema antillarum (70.0 μm, 0.18 nl) and Diadema mexicanum (68.0 μm, 0.16 nl). Larval development is similar to other species within the Family Diadematidae, with a Echinopluteus transversus larval type morphology. The combined effects of the climate change-related environmental factors resulted in a reduction in fitness of D. africanum at the warmer limit of its thermal range when combined with low pH. Results suggest that the egg and larval life-history characteristics of D. africanum may have evolved to facilitate long-distance oceanic transport; however, near-future oceanic conditions may compromise larval survival.