Coralline algae in a naturally acidified ecosystem persist by maintaining control of skeletal mineralogy and size

106

166

Coralline algae provide important ecosystem services but are susceptible to the impacts of ocean acidification. However, the mechanisms are uncertain, and the magnitude is species specific. Here, we assess whether species-specific responses to ocean acidification of coralline algae are related to differences in pH at the site of calcification within the calcifying fluid/medium (pH ) using δ B as a proxy. Declines in δ B for all three species are consistent with shifts in δ B expected if B(OH) was incorporated during precipitation. In particular, the δ B ratio in Amphiroa anceps was too low to allow for reasonable pH values if B(OH) rather than B(OH) was directly incorporated from the calcifying fluid. This points towards δ B being a reliable proxy for pH for coralline algal calcite and that if B(OH) is present in detectable proportions, it can be attributed to secondary postincorporation transformation of B(OH) . We thus show that pH is elevated during calcification and that the extent is species specific. The net calcification of two species of coralline algae (Sporolithon durum, and Amphiroa anceps) declined under elevated CO , as did their pH . Neogoniolithon sp. had the highest pH , and most constant calcification rates, with the decrease in pH being ¼ that of seawater pH in the treatments, demonstrating a control of coralline algae on carbonate chemistry at their site of calcification. The discovery that coralline algae upregulate pH under ocean acidification is physiologically important and should be included in future models involving calcification.

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Coralline algae elevate pH at the site of calcification under ocean acidification

Cornwall

Comeau

McCulloch

2017

106

166

“…We used the abiogenic aragonite calibration equation of (DeCarlo et al., ) to calculate Ω a for the two coral species from the v 1 full width at half maximum intensity (FWHM). Although v 1 peak width has been applied to investigate CCA responses to ocean acidification in several studies (Kamenos et al., , ), there is no abiogenic high‐Mg calcite Ω calibration. We therefore used v 1 FWHM as a qualitative proxy of CCA calcifying fluid Ω.…”

Section: Methodsmentioning

confidence: 99%

Similar controls on calcification under ocean acidification across unrelated coral reef taxa

Comeau

Cornwall

DeCarlo

et al. 2018

Ocean acidification (OA) is a major threat to marine ecosystems, particularly coral reefs which are heavily reliant on calcareous species. OA decreases seawater pH and calcium carbonate saturation state (Ω), and increases the concentration of dissolved inorganic carbon (DIC). Intense scientific effort has attempted to determine the mechanisms via which ocean acidification (OA) influences calcification, led by early hypotheses that calcium carbonate saturation state (Ω) is the main driver. We grew corals and coralline algae for 8-21 weeks, under treatments where the seawater parameters Ω, pH, and DIC were manipulated to examine their differential effects on calcification rates and calcifying fluid chemistry (Ω , pH , and DIC ). Here, using long duration experiments, we provide geochemical evidence that differing physiological controls on carbonate chemistry at the site of calcification, rather than seawater Ω, are the main determinants of calcification. We found that changes in seawater pH and DIC rather than Ω had the greatest effects on calcification and calcifying fluid chemistry, though the effects of seawater carbonate chemistry were limited. Our results demonstrate the capacity of organisms from taxa with vastly different calcification mechanisms to regulate their internal chemistry under extreme chemical conditions. These findings provide an explanation for the resistance of some species to OA, while also demonstrating how changes in seawater DIC and pH under OA influence calcification of key coral reef taxa.

“…Crustose coralline algae from Mediterranean CO 2 vents ( Lithophyllum, Titanoderma, and Phymatolithon spp.) (Kamenos, Perna, Gambi, Micheli, & Kroeker, ) and temperate laboratory studies (Pauly, Kamenos, Donohue, & LeDrew, ) ( Lithothamnion glaciale ) provide evidence that they are able to buffer against changes in water p CO 2 , preserving their Mg concentrations until extreme (pH <7.4) p CO 2 conditions are encountered demonstrating absence of sublethal skeletal trade‐offs in low pH. This is possible because of coralline algal skeletal mineralogy, a high‐Mg calcite (Kamenos, Cusack, Huthwelker, Lagarde, & Scheibling, ) and their ability to change its polymorph (Kamenos et al, ).…”

Section: Introductionmentioning

confidence: 99%

Coralline algal skeletal mineralogy affects grazer impacts

McCoy

Kamenos

2018

Self Cite

In macroalgal-dominated systems, herbivory is a major driver in controlling ecosystem structure. However, the role of altered plant-herbivore interactions and effects of changes to trophic control under global change are poorly understood. This is because both macroalgae and grazers themselves may be affected by global change, making changes in plant-herbivore interactions hard to predict. Coralline algae lay down a calcium carbonate skeleton, which serves as protection from grazing and is preserved in archival samples. Here, we compare grazing damage and intensity to coralline algae in situ over 4 decades characterized by changing seawater acidity. While grazing intensity, herbivore abundance and identity remained constant over time, grazing wound width increased together with Mg content of the skeleton and variability in its mineral organization. In one species, decreases in skeletal organization were found concurrent with deeper skeletal damage by grazers over time since the 1980s. Thus, in a future characterized by acidification, we suggest coralline algae may be more prone to grazing damage, mediated by effects of variability between individuals and species.