Early life stages of a Mediterranean coral are vulnerable to ocean warming and acidification

Abstract

Abstract. The ability of coral populations to recover from disturbance depends on larval dispersion and recruitment. While ocean warming and acidification effects on adult corals are well documented, information on early life stages is comparatively scarce. Here, we investigate whether ocean warming and acidification can affect the larval and recruit development of the Mediterranean azooxanthellate coral Astroides calycularis. Larvae and recruits were raised for 9 months at ambient (23 ∘C) and warm (26 ∘C) temperatures and ambient (8.0) and low pH (7.7, on the total scale). The timing of the larval metamorphosis, growth of the recruit polyp by linear extension and budding, and skeletal characteristics of the 9-month-old polyps were monitored. Settlement and metamorphosis were more successful and hastened under a warm temperature. In contrast, low pH delayed the metamorphosis and affected the growth of the recruits by reducing the calcified area of attachment to the substrate as well as by diminishing the skeleton volume and the number of septa. However, skeleton density was higher under low pH and ambient temperature. The warm temperature and low-pH treatment had a negative impact on the survival, settlement, and growth of recruits. This study provides evidence of the threat represented by ocean warming and acidification for the larval recruitment and the growth of recruits of A. calycularis.

Response of two temperate scleractinian corals to projected ocean warming and marine heatwaves

“…Feeding the corals in this study could have mitigated the impact of heat stress compared with real in situ conditions [ 30 ]. Moreover, the combined effect of ocean warming and acidification decreases recruitment and post-settlement growth of early life stages of A. calycularis [ 69 ]. However, warming seems to be the main factor leading to the decrease in calcification and increase in respiration of adult colonies of C. caespitosa and A. calycularis [ 23 , 31 ].…”

Elevated heterotrophic capacity as a strategy for Mediterranean corals to cope with low pH at CO2 vents

“…Overall, our study suggests selection for high baseline heterotrophic capacity on coral recruits that settle at CO 2 vents. Low pH at vent sites could be a selective pressure that would contribute to recruit settlement [ 76 , 77 ] and post-settlement success [ 78 , 79 ]. Our data suggest low pH, vent sites may have selected for individuals that are able to maintain feeding at low pH, which in turn would support the maintenance of energy reserves and net positive calcification.…”