Morphological and compositional changes in the skeletons of new coral recruits reared in acidified seawater: Insights into the biomineralization response to ocean acidification

Abstract

[1] We reared primary polyps (new recruits) of the common Atlantic golf ball coral Favia fragum for 8 days at 25°C in seawater with aragonite saturation states ranging from ambient (W = 3.71) to strongly undersaturated (W = 0.22). Aragonite was accreted by all corals, even those reared in strongly undersaturated seawater. However, significant delays, in both the initiation of calcification and subsequent growth of the primary corallite, occurred in corals reared in treatment tanks relative to those grown at ambient conditions. In addition, we observed progressive changes in the size, shape, orientation, and composition of the aragonite crystals used to build the skeleton. With increasing acidification, densely packed bundles of fine aragonite needles gave way to a disordered aggregate of highly faceted rhombs. The Sr/Ca ratios of the crystals, measured by SIMS ion microprobe, increased by 13%, and Mg/Ca ratios decreased by 45%. By comparing these variations in elemental ratios with results from Rayleigh fractionation calculations, we show that the observed changes in crystal morphology and composition are consistent with a >80% decrease in the amount of aragonite precipitated by the corals from each ''batch'' of calcifying fluid. This suggests that the saturation state of fluid within the isolated calcifying compartment, while maintained by the coral at levels well above that of the external seawater, decreased systematically and significantly as the saturation state of the external seawater decreased. The inability of the corals in acidified treatments to achieve the levels of calcifying fluid supersaturation that drive rapid crystal growth could reflect a limit in the amount of energy available for the proton pumping required for calcification. If so, then the future impact of ocean acidification on tropical coral ecosystems may depend on the ability of individuals or species to overcome this limitation and achieve the levels of calcifying fluid supersaturation required to ensure rapid growth.

A corrosive concoction: The combined effects of ocean warming and acidification on the early growth of a stony coral are multiplicative

“…This suggests that the planulae may be highly susceptible to the effects of seawater acidification during the period of early calcification in metamorphosis. We suggest that the decline in calcification rates found by Cohen et al 2009 andAlbright et al 2008 were greater compared to our experiment because our treatment exposures did not cover the initial calcification period.…”

“…However, net productivity was observed to decrease in adult corals under higher temperatures and elevated pCO 2 by both Crawley et al (2010) and Anthony et al (2008). The cumulative increase in metabolism of primary polyps in the high temperature and low pH could be associated with the additional energy required to drive proton pumps to maintain sufficient pH-levels in the calcifying space (Cohen et al, 2009) or alternatively, an inefficiency of photosynthesis (Buxton et al, 2009) and more severe photorespiration compared to low pH and subsaturated light conditions (Crawley et al, 2010). A speculative conclusion is that combined high temperatures and low pHs reduce biomass because of the reduction of phosphoglycolate phosphatase and resulting increase in the inhibition of carbon fixation via phosphoglycolate in the Calvin cycle (c.f.…”

“…Likewise, Cohen et al (2009) reported reduced skeletal growth of the cross-sectional area in newly-reared primary polyps of Favia fragum under lowered aragonite saturation and calculated a nearly 80% decrease in the precipitated aragonite. These strong reductions of calcification without invoking increasing temperature, in contrast to our findings, can be explained by the exposure of planulae to lowered seawater aragonite saturation states during settlement and secretion of the primary corallite (Cohen et al 2009). This suggests that the planulae may be highly susceptible to the effects of seawater acidification during the period of early calcification in metamorphosis.…”

Long-term effects of nutrient and CO2 enrichment on the temperate coral Astrangia poculata (Ellis and Solander, 1786)

“…However, the saturation state of the surrounding seawater alone does not control coral calcification as corals can continue to calcify in under-saturated conditions (e.g. Marubini and Atkinson, 1999;Cohen et al, 2009) or dissolve in super-saturated conditions (e.g. Herfort et al, 2008).…”

Immunolocalization of skeletal matrix proteins in tissue and mineral of the coralStylophora pistillata

“…During the past two decades, it has been shown that the basic skeletal units, crystal-like fibers, are built by repeated micrometer growth steps that can be visualized by etching polished skeletal surfaces (14)(15)(16). The resulting macroscopic skeletal structures of individual corals are strongly influenced by environmental factors, especially light (17), physical flow (18), and carbonate saturation (19). The aggregate of these individual coral skeletons is the basis for reef formation in tropical and subtropical shallow ocean margins, and is critical for the sustaining the diversity of fauna found in those environments (20).…”