Reduced heterotrophy in the stony coral Galaxea fascicularis after life-long exposure to elevated carbon dioxide

Abstract

Ocean acidification imposes many physiological, energetic, structural and ecological challenges to stony corals. While some corals may increase autotrophy under ocean acidification, another potential mechanism to alleviate some of the adverse effects on their physiology is to increase heterotrophy. We compared the feeding rates of Galaxea fascicularis colonies that have lived their entire lives under ocean acidification conditions at natural carbon dioxide (CO 2 ) seeps with colonies living under present-day CO 2 conditions. When provided with the same quantity and composition of zooplankton as food, corals acclimatized to high CO 2 showed 2.8 to 4.8 times depressed rates of zooplankton feeding. Results were consistent over four experiments, from two expeditions and both in field and chamber measurements. Unless replenished by other sources, reduced zooplankton uptake in G. fascicularis acclimatized to ocean acidification is likely to entail a shortage of vital nutrients, potentially jeopardizing their health and survival in future oceans.

Temperature and feeding induce tissue level changes in autotrophic and heterotrophic nutrient allocation in the coral symbiosis – A NanoSIMS study

“…A number of studies have shown the significant role that heterotrophy plays in the survival and recovery of corals after severe thermal stress events that left their autotrophic capacity impaired 70 , 72 – 76 . At the same time, as future oceans will be less alkaline, direct negative effects on coral feeding rates 77 , 78 and/or indirect negative effects of ocean acidification on zooplankton abundance in reefs 79 will create specific demands for the autotrophic and heterotrophic mode of nutrition in individual corals. While the preservation of symbiont functioning and initial host energy reserves are the foremost elements of coral resistance to thermal stress 80 , it is the complementing interplay of auto- and heterotrophy that defines the nutritional state and ability of corals to recover after a severe disturbance of their symbiotic state in a warmer ocean 81 .…”

The chemical armament of reef-building corals: inter- and intra-specific variation and the identification of an unusual actinoporin in Stylophora pistilata

“…Stylophora and Pocillopora have relatively high predation rates 85 , and heterotrophy can support a significant part of their metabolism (e.g. 11 , 12 , 42 , 51 ), suggesting a role for the nematocysts and hemolytic activity in feeding. However, the predation rate of Acropora has been shown to be much lower than that of Stylophora and Pocillopora 85 , and while the hemolytic activity of Acropora is also much lower, the nematocyst density in these three corals is similar (Fig.…”

“…With the exception of a phospholipase A2 toxin from the “fire coral” Millepora 37 , 38 (which is a hydrozoan, and thus not a true scleractinian coral) and small cysteine-rich peptide toxins from Acropora millepora recombinantly expressed in bacteria 39 to date no toxins have been isolated or characterized from reef building corals. Nevertheless, early studies described widespread, albeit highly variable, toxicity in corals 40 , 41 , and these organisms catch prey 2 , 12 , 42 , defend themselves from predators 43 , resist microbial infections 5 , 6 , 44 and are involved in fierce chemically-mediated competition for space 20 , 45 , 46 .…”

Heterotrophy of Oceanic Particulate Organic Matter Elevates Net Ecosystem Calcification

“…With the addition of particulate nutrients (e.g., brine shrimp and mixed zooplankton), calcification rates increase and growth rates are maintained under low light (Drenkard et al, 2013;Ferrier-Pagès et al, 2003). The effects of acidification on heterotrophy and calcification are mixed; some studies have found reduced heterotrophy under acidified conditions (Houlbréque et al, 2015;Smith et al, 2016), while others show fed corals sustain calcification rates when exposed to elevated seawater CO 2 (Drenkard et al, 2013;Edmunds, 2011;Towle et al, 2015). While heterotrophy can account for up to 35% of daily metabolic requirements in healthy corals, bleached corals can receive up to 100% of daily metabolic requirements from heterotrophy (Grottoli et al, 2006), though metabolic needs of bleached corals may also be met by catabolism of energy-rich biomass (Wall et al, 2019).…”