This study tested the hypothesis that the response of corals to temperature and pCO
2 is consistent between taxa. Juvenile massive Porites spp. and branches of P. rus from the back reef of Moorea were incubated for 1 month under combinations of temperature (29.3 °C and 25.6 °C) and pCO
2 (41.6 Pa and 81.5 Pa) at an irradiance of 599 μmol quanta m−2 s−1. Using microcosms and CO2 gas mixing technology, treatments were created in a partly nested design (tanks) with two between‐plot factors (temperature and pCO
2), and one within‐plot factor (taxon); calcification was used as a dependent variable. pCO
2 and temperature independently affected calcification, but the response differed between taxa. Massive Porites spp. was largely unaffected by the treatments, but P. rus grew 50% faster at 29.3 °C compared with 25.6 °C, and 28% slower at 81.5 Pa vs. 41.6 Pa CO2. A compilation of studies placed the present results in a broader context and tested the hypothesis that calcification for individual coral genera is independent of pH, [HCO3
−], and [CO3
2−]. Unlike recent reviews, this analysis was restricted to studies reporting calcification in units that could be converted to nmol CaCO3 cm−2 h−1. The compilation revealed a high degree of variation in calcification as a function of pH, [HCO3
−], and [CO3
2−], and supported three conclusions: (1) studies of the effects of ocean acidification on corals need to pay closer attention to reducing variance in experimental outcomes to achieve stronger synthetic capacity, (2) coral genera respond in dissimilar ways to pH, [HCO3
−], and [CO3
2−], and (3) calcification of massive Porites spp. is relatively resistant to short exposures of increased pCO
2, similar to that expected within 100 y.
Octocorals represent an important group in reef communities throughout the tropical seas and, like scleractinian corals, they can be found in symbiosis with the dinoflagellate Symbiodinium. However, while there is extensive research on this symbiosis and its benefits in scleractinians, research on octocorals has focused so far mainly on the host without addressing their symbiosis. Here, we characterized and compared the photophysiological features of nine Caribbean octocoral species with different colony morphologies (sea fan, plumes, whips and rods) and related key morphological features with their respective symbiont photobiology. Colony features (branch shape and thickness), as well as micromorphological features (polyp size, density), were found to be significantly correlated with symbiont performance. Sea fans and plumes, with thinner branches and smaller polyps, favor higher metabolic rates, compared to sea rods with thicker branches and larger polyps. Daily integrated photosynthesis to respiration ratios > 1 indicated that the autotrophic contribution to organisms’ energy demands was important in all species, but especially in sea whips. This information represents an important step towards a better understanding of octocoral physiology and its relationship to host morphology, and might also explain to some extent species distribution and susceptibility to environmental stress.
Octocorals are a major component of the sessile benthic fauna worldwide, especially important in tropical regions, such as the Indo-Pacific and Caribbean, where together with hard corals they represent the most common group of macrobenthic animals of coral reefs. Despite their importance, little is known about their physiology, specifically the importance of their symbiotic relationship with the algal endosymbiont from the genus Symbiodinium, and the advantages/ disadvantages associated with this symbiosis. In symbiotic species, the energetic contribution from Symbiodinium to the host might increase their resistance and/or recovery from stressful conditions, but the presence of these algal endosymbionts also limits octocoral distribution to the photic zone, where light is available. During the past few decades, octocorals have gained dominance in some tropical areas where scleractinian corals have declined due to climate change and local perturbations, increasing the need for research related to this understudied group. This chapter summarizes the current knowledge available about the ecology and physiology of octocorals, focusing on differences that are the result of the Electronic supplementary material: The online version of this chapter
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