Calcium carbonate production by fish in temperate marine environments

Abstract

Marine bony fishes are an important source of calcium carbonate with relevance to sediment production and inorganic carbon cycling. However, knowledge of the production and fate of these carbonates is based primarily on data from warm‐water reef fishes, with efforts to assess global‐scale implications constrained by assumptions that this small cross section of the global fish community is widely representative. Here we test the extent to which temperature influences fish carbonate mineralogy and morphology by comparing products from temperate settings (20 species at temperatures spanning 10–18°C) against existing data (23–27°C). Overall, carbonate products were mineralogically, compositionally, and morphologically similar throughout the thermal range, and in most cases, we observed no differences within species (18 vs. 24°C) or families (10 vs. 25°C). Confirmation of within‐family consistency over large thermal gradients is significant because: (1) it facilitates a substantial range expansion over which fish carbonate production models can be constructed, even where family‐level product data are geographically limited; and (2) it implies that the solubility of products from any given fish family varies only due to local carbonate saturation states at excretion (and not crystallographic differences). The only exception was in two members of the Labridae (wrasses), which produced low‐Mg calcite (LMC) and minor amorphous calcium–magnesium carbonate (ACMC) at 10°C; the inverse of products from confamilials at 25°C. This finding could have significant implications for understanding the role of fish carbonates globally because ACMC is a highly unstable carbonate polymorph, whereas LMC is very stable.

Toward a better understanding of fish‐based contribution to ocean carbon flux

“…Most published data are only relevant to shallow tropical, subtropic, or temperate regions, and existing family-level data sets represent less than 10% of the global fish biomass, leaving the vast majority of fish species unaccounted for in attempts to model inorganic carbon fluxes on a global scale. While carbonate mineralogy and morphology has been fairly consistent at the family level in these previous studies (Salter et al 2019), a significant challenge is to identify suitable species and measurement approaches that can examine if these characteristics remain consistent across communities such as mesopelagic fishes.…”

“…The limited information on solubility of fish-derived carbonate minerals suggests that high-Mg calcite has a solubility that is approximately double that of aragonite (Woosley et al 2012). However, given the expanding range of observed carbonate mineralogies of fishes (Salter et al 2012(Salter et al , 2014(Salter et al , 2017(Salter et al , 2018(Salter et al , 2019, more quantitative data on solubility and dissolution rates for these different types of carbonate are needed.…”

“…In addition to the role of fishes in the biological pump, fishes also influence the cycling of inorganic carbon (Wilson et al 2009; Perry et al 2011; Salter et al 2019). Specifically, marine bony fishes continuously produce carbonates in their guts as a by‐product of the osmoregulatory need to continuously drink seawater.…”

“…In addition, when fishes are feeding, the inorganic carbonate mineral will add dense ballast to fecal pellets and thus potentially accelerate the sinking of excreted organic carbon in the feces. Although much of the understanding of gut carbonate mineralogy and morphology has been conducted using shallow tropical (Wilson et al 2009; Perry et al 2011) and subtropical (Salter et al 2012, 2017, 2018) reef fish, Salter et al (2019) compared new data from temperate fish species and these previously studied reef species across a range of temperatures (10–27°C). They observed fairly consistent carbonate mineralogy and morphology at both the species and family levels across this wide thermal range.…”

“…Hence, there is an unexplored, but possibly important and dynamic, interaction between the PIC and POC portions (i.e., POC : PIC) of fecal pellets of fishes and their contribution to carbon fluxes. Data that now cover 82 species from 45 families reveal a diverse range of CaCO 3 mineral types, including low‐Mg calcite, aragonite, and highly soluble amorphous Ca–Mg carbonate, which vary greatly in their solubility (Brečević and Nielsen 1989; Perry et al 2011; Salter et al 2012, 2017, 2018, 2019; Foran et al 2013). Most published data are only relevant to shallow tropical, subtropic, or temperate regions, and existing family‐level data sets represent less than 10% of the global fish biomass, leaving the vast majority of fish species unaccounted for in attempts to model inorganic carbon fluxes on a global scale.…”