Species‐specific responses to climate change and community composition determine future calcification rates of Florida Keys reefs

Abstract

Anthropogenic climate change compromises reef growth as a result of increasing temperatures and ocean acidification. Scleractinian corals vary in their sensitivity to these variables, suggesting species composition will influence how reef communities respond to future climate change. Because data are lacking for many species, most studies that model future reef growth rely on uniform scleractinian calcification sensitivities to temperature and ocean acidification. To address this knowledge gap, calcification of twelve common and understudied Caribbean coral species was measured for two months under crossed temperatures (27, 30.3 °C) and CO partial pressures (pCO ) (400, 900, 1300 μatm). Mixed-effects models of calcification for each species were then used to project community-level scleractinian calcification using Florida Keys reef composition data and IPCC AR5 ensemble climate model data. Three of the four most abundant species, Orbicella faveolata, Montastraea cavernosa, and Porites astreoides, had negative calcification responses to both elevated temperature and pCO . In the business-as-usual CO emissions scenario, reefs with high abundances of these species had projected end-of-century declines in scleractinian calcification of >50% relative to present-day rates. Siderastrea siderea, the other most common species, was insensitive to both temperature and pCO within the levels tested here. Reefs dominated by this species had the most stable end-of-century growth. Under more optimistic scenarios of reduced CO emissions, calcification rates throughout the Florida Keys declined <20% by 2100. Under the most extreme emissions scenario, projected declines were highly variable among reefs, ranging 10-100%. Without considering bleaching, reef growth will likely decline on most reefs, especially where resistant species like S. siderea are not already dominant. This study demonstrates how species composition influences reef community responses to climate change and how reduced CO emissions can limit future declines in reef calcification.

Daily variation in net primary production and net calcification in coral reef communities exposed to elevated &lt;i&gt;p&lt;/i&gt;CO&lt;sub&gt;2&lt;/sub&gt;

“…To date, studies addressing the effects of OA on coral reefs have been performed mostly at the scale of individual organisms, and have focused on calcification as a response variable (Schoepf et al, 2013;Comeau et al, 2013;Okazaki et al, 2016), while studies focusing on larger spatial scales (i.e., whole communities) have remained rare, mostly because of technical constraints (e.g., Dove et al, 2013;Comeau et al, 2015Comeau et al, , 2016b. The few experiments addressing the effects of OA on intact coral reef communities have confirmed the threat to calcification rates previously reported for individual organisms, notably by showing a decreased capacity of communities to maintain positive net calcification under conditions mimicking a future ocean in which seawater pH will be depressed 0.15-0.30 units relative to presentday conditions (e.g., Dove et al, 2013;Comeau et al, 2015Comeau et al, , 2016b.…”

Meta-Analysis Reveals Reduced Coral Calcification Under Projected Ocean Warming but Not Under Acidification Across the Caribbean Sea

“…The Intergovernmental Panel on Climate Change (IPCC) has projected that sea surface temperatures in the Caribbean region could rise between 0.6 and 3.0 • C by the end of the twenty-first century (ocean warming), and atmospheric pCO 2 will surpass 600 µatm, causing surface ocean pH to decrease by 0.1-0.3 pH units (ocean acidification) (IPCC, 2014). These projections pose significant threats to reef-building corals throughout the Caribbean, causing mass mortality events, reducing recruitment, deteriorating key physiological processes, and lowering coral calcification rates (Jokiel and Coles, 1977;Grottoli et al, 2006;Davies et al, 2016;Okazaki et al, 2017). Despite the consensus that global change will negatively affect Caribbean reef-building corals, the extent of these impacts vary widely by species, region, or measured physiological response parameter (Harvey et al, 2013).…”

“…Despite the consensus that global change will negatively affect Caribbean reef-building corals, the extent of these impacts vary widely by species, region, or measured physiological response parameter (Harvey et al, 2013). A great example of such variation in coral responses to ocean acidification and warming is seen in Okazaki et al (2017) where some species exhibited no response to ocean acidification or warming while other corals in the same experiment exhibited reduced calcification under one or both stressors. Furthermore, a study conducted by Kenkel et al (2015) demonstrated a variety of physiological responses (i.e., calcification and Symbiodiniaceae physiology) of corals under ocean warming even within a single species.…”

Generality in multispecies responses to ocean acidification revealed through multiple hypothesis testing

“…Ocean acidification (OA) has been identified as a key but understudied stressor for marine organisms, leading to rapid growth in efforts to test its effects on a wide range of potentially susceptible species (Kroeker, Kordas, Crim, & Singh, ; Kroeker et al., ). Although experiments have revealed that many species are negatively impacted by OA, some organisms exhibit mixed responses and we know less about the variation in OA response among closely related taxa or among taxa with similar physiological traits (e.g., Calosi et al., ; Dupont, Ortega‐Martínez, & Thorndyke, ; Gooding, Harley, & Tang, ; Noisette, Egilsdottir, Davoult, & Martin, ; Okazaki et al., ; Ries, Cohen, & McCorkle, ). As a consequence, it is unclear if variation in the response of species to OA is a result of inherent physiological differences among species or a result of infrequent efforts to test for generalities across taxa (Gaylord et al., ; O'Connor, Selig, Pinsky, & Altermatt, ; O'Connor et al., ; Wernberg, Smale, & Thomsen, ).…”

“…Although experiments have revealed that many species are negatively impacted by OA, some organisms exhibit mixed responses and we know less about the variation in OA response among closely related taxa or among taxa with similar physiological traits (e.g., Calosi et al, 2013;Dupont, Ortega-Martínez, & Thorndyke, 2010;Gooding, Harley, & Tang, 2009;Noisette, Egilsdottir, Davoult, & Martin, 2013;Okazaki et al, 2017;Ries, Cohen, & McCorkle, 2009).…”