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Measurements of coral recruitment can improve understanding of coral population dynamics, but in short duration studies high variance impedes interpretation of this vital rate. Here, coral recruitment in Moorea, French Polynesia, was measured over 13 yr and tested for associations with environmental conditions. Recruitment of spawning pocilloporid corals was recorded using settlement tiles immersed for ~ 6 months at 10 m and 17 m depth, biannually, and the environment was quantified through seawater clarity (Kd490), surface and bottom flow speeds, coral cover, and temperature. Using GAMs, most of the variation (63–74%) in recruitment was explained using depth and three predictors. Recruitment was high in January/February following a year of low seawater clarity (high Kd490), and in August/September following a year of high clarity. Recruitment in January/February was elevated by high coral cover, and by high surface flow during larval dispersal; recruitment was low in August/September following high temperature during gametogenesis. These effects reveal the extent to which early life stages of corals are exposed to annually variable environmental conditions that have differential consequences depending on the phenology of reproduction and recruitment. The temporal mosaic defining interactions between reproduction, recruitment, and environmental conditions create opportunities for acclimatization to affect where and when coral recruitment is successful. [ABSTRACT FROM AUTHOR]

Invertebrate ectosymbionts within the coralla of scleractinians enhance host fitness through protection from corallivores and nutrient addition. Here, we explore the ectosymbiotic relationship between the coral Pocillopora verrucosa and the crab Trapezia serenei and the shrimp Alpheus spp., to test for effects on coral calcification under contrasts of seawater temperature (27.7 °C and 29.9 °C) and pH (ambient, 8.0 and reduced, 7.7). Regardless of temperature, ectosymbionts depressed calcification by 55% (vs without ectosymbionts) at ambient pH; however, ectosymbionts only depressed calcification under ambient pH but not at reduced pH. These results suggest that P. verrucosa grows fastest at ambient pH without ectosymbionts, but when ectosymbionts are present, colonies are protected from further declines in calcification at reduced pH. This implies that there may be a change from a currently parasitic ectosymbiont-coral relationship to a commensal relationship that could increase fitness advantages for corals hosting crustacean ectosymbionts under ocean acidification conditions. [ABSTRACT FROM AUTHOR]