Phase heterogeneity in carbonate production by marine fish influences their roles in sediment generation and the inorganic carbon cycle

Abstract

Marine teleost fish are important carbonate producers in neritic and oceanic settings. However, the fates of the diverse carbonate phases (i.e., mineral and amorphous forms of CaCO3) they produce, and their roles in sediment production and marine inorganic carbon cycling, remain poorly understood. Here we quantify the carbonate phases produced by 22 Bahamian fish species and integrate these data with regional fish biomass data from The Bahamas to generate a novel platform-scale production model that resolves these phases. Overall carbonate phase proportions, ordered by decreasing phase stability, are: ~20% calcite, ~6% aragonite, ~60% high-Mg calcite, and ~14% amorphous carbonate. We predict that these phases undergo differing fates, with at least ~14% (amorphous carbonate) likely dissolving rapidly. Results further indicate that fisheries exploitation in The Bahamas has potentially reduced fish carbonate production by up to 58% in certain habitats, whilst also driving a deviation from natural phase proportions. These findings have evident implications for understanding sedimentary processes in shallow warm-water carbonate provinces. We further speculate that marked phase heterogeneity may be a hitherto unrecognised feature of fish carbonates across a wide range of neritic and oceanic settings, with potentially major implications for understanding their role in global marine inorganic carbon cycling.

Reef fish carbonate production assessments highlight regional variation in sedimentary significance

“…4); and (3) with respect to warmer reefs, the possibility that fish carbonate polymorphs will differ across thermal gradients. Significantly, our polymorph outputs contrast markedly with data from Bahamian reefs, where ACMC accounted for only 4-13% of fish carbonate production, and HMC (55-75%) dominated (Salter et al, 2017); a disparity explained mainly by differences in fish family assemblages. On the Australian study reefs, 60-87% of the teleost biomass for which products have been assessed comprises significant ACMC producers (primarily Caesionidae, Labridae, Pomacentridae), whereas in The Bahamas, 71-90% comprises HMC producers (primarily Haemulidae [grunts] and Lutjanidae; see Fig.…”

“…The high solubilities of some fish carbonate polymorphs are also likely to influence sedimentary significance (Salter et al, 2012;2017); an especially important consideration here because >50% of production in most Australian test reefs can be attributed to fish families that produce large amounts of highly unstable ACMC (Pomacentridae [damselfishes], Labridae, and Caesionidae [fusiliers]; Fig. 4).…”

“…Our understanding of the sedimentary significance of fish carbonates is, however, limited by the small number of taxa studied to date, and the restricted biogeographic range captured by existing research (limited to the Caribbean; Perry et al, 2011;Salter et al, 2012Salter et al, , 2017. The first issue is problematic because different fish families produce different carbonate polymorphs; the discrete solubilities of each having implications for preservation potential (Salter et al, 2017).…”

“…The first issue is problematic because different fish families produce different carbonate polymorphs; the discrete solubilities of each having implications for preservation potential (Salter et al, 2017). Though progress is being made in elucidating the controls on precipitation processes (Schauer et al, 2018), a means of predicting the polymorphs produced by any given family remains elusive.…”

“…Much shallow mud production has been ascribed to post-mortem breakdown of carbonate-secreting taxa (especially codiacean algae and seagrass epiphytes) along with microbially mediated and abiotic precipitation (see Gischler et al, 2013). In addition, evidence has emerged that all bony marine fishes (teleosts) precipitate mud-sized carbonates in their intestines (Walsh et al, 1991), and that these can be excreted at rates relevant to carbonate sediment budgets-especially in habitats with high fish biomass, such as coral reefs (Perry et al, 2011;Salter et al, 2017).…”