Effects of thermal stress on early developmental stages of a gorgonian coral

Abstract

Ongoing sea temperature increase threatens reefs worldwide. In this study we experimentally examined for the first time the response of the early life stages of a long-lived structural gorgonian, the Mediterranean species Paramuricea clavata (Risso 1826), to the highest summer temperature recorded so far in the study area (25°C; the Medes Islands, Northwestern Mediterranean). This temperature also simulates the end-of-century predicted warming (+3°C) over the temperature maxima recorded during the species' reproductive period. The results showed a severe negative impact of constant thermal stress on the viability of P. clavata embryos and larvae, resulting in reduced survivorship, completely abnormal embryonic development and impaired metamorphosis. The deteriorating effect was rapid for embryos (after 7 h), whereas the impact on larvae became evident after 10 d of stress. Larval modifications started 7 d earlier under elevated temperature conditions, but the appearance of spherical, aberrant shapes prevented an assessment of whether metamorphosis was initiated but abnormal, or deterred altogether. The apparent higher sensitivity of embryos suggests that thermal stress during embryonic develop- ment may be the most critical factor for the viability of P. clavata larvae. In the context of an ongo- ing warming trend, the reduced viability of early life stages would jeopardize the persistence of P. clavata, which relies on successful recruitment for replenishment of its populations. Further research into the effects of thermal stress on the reproduction of structural invertebrate species and the viability of their early life stages will improve our understanding of the long-term conse- quences of environmental global change in marine benthic communities.