Reef fish carbonate production assessments highlight regional variation in sedimentary significance

Abstract

Recent studies show that all marine bony fish produce mud-sized (<63 µm) carbonate at rates relevant to carbonate sediment budgets, thus adding to the debate about the often enigmatic origins of finegrained marine carbonates. However, existing production data are geographically and taxonomically limited, and because different fish families are now known to produce different carbonate polymorphsan issue relevant to predicting their preservation potential-these limitations represent an important knowledge gap. Here we present new data from sites in the Western Pacific Ocean, based on an analysis of 45 fish species. Our data show that previously reported production outputs (in terms of rates and family-specific mineralogies) are applicable across different biogeographic regions. On this basis, we model carbonate production for nine coral reef systems around Australia, with production rates averaging 2.1-9.6 g m -2 yr -1 , and up to 105 g m -2 yr -1 at discrete sites with high fish biomass. With projected production rates on lower-latitude reefs up to two-fold higher, these outputs indicate that carbonate production rates by fish can be comparable with other fine-grained carbonate-producing taxa such as codiacean algae. However, carbonates produced by Australian reef fish assemblages are dominated by a highly unstable amorphous polymorph; a marked contrast to Caribbean assemblages in which Mg calcite dominates. These findings highlight important regional differences in the sedimentary relevance and preservation potential of fish carbonates as a function of historical biogeographic processes that have shaped the world's marine fish faunas.

Calcium carbonate production by fish in temperate marine environments

“…Particle types were consistently similar among individuals of each species, and also among both species of the Labridae (the only family for which multiple species were sampled). Overall these particles were generally similar in appearance to fish carbonates documented elsewhere from subtropical settings (Perry et al ; Salter et al , , , ), with the exception of a striking dissimilarity in the occurrence pattern of rhombohedral particles. In subtropical settings rhombohedra typically occur as subsidiary particles, often in association with dominant nanospheres and/or material lacking definable form (i.e., ACMC; Salter et al ), and this pattern was observed here for three species sampled at 18°C: Atherinomorus ogilbyi (Atherinidae; Fig.…”

“…Conversely, carbonates produced by a gobiid species sampled at 18°C were similar to those produced by a confamilial sampled at 24°C (Table ; Salter et al ). Because gobiid carbonates are similar to labrid carbonates produced in the subtropics, this result suggests that any temperature effect on these types of carbonate is likely to be family‐specific, or it only operates at temperatures below 18°C.…”

“…In contrast to these findings, carbonates collected from members of the Labridae in temperate settings were somewhat different to those produced by their warm‐water confamilials. Specifically, labrids sampled at subtropical locations (25–27°C; n = 5 species; Salter et al , ) produced carbonates dominated by ACMC with subsidiary LMC spheres and rhombohedra, whereas for those sampled at cool temperate locations (10°C; n = 2 species) the inverse was observed, with LMC rhombohedra and spheres dominating and ACMC being uncommon or absent (Figs. and ).…”

“…Evidence from subtropical settings indicates that fish carbonate products are highly consistent at both the species‐ and family‐level within a temperature range of 23–27°C (Salter et al , , ). Our findings similarly indicate species‐level consistency where tested in temperate settings ( see Table —e.g., H. percoides , A. mate , and N. celidotus , among others), and that this consistency is maintained over thermal gradients—at least for HMC‐producing species (e.g., L. russellii , L. calcarifer , and A. australis ).…”

“…In either case, food was withheld throughout the carbonate sampling period and for at least 48 h prior, or until the gut was completely voided of ingested items and excreta comprised only mucus‐bound carbonate pellets of white, greenish‐yellow, or greenish‐blue appearance. This routinely employed approach precludes sampling of carbonates from dietary sources (Wilson et al ; Perry et al ; Foran et al ; Salter et al ). Although digestive processes during feeding are likely to influence gut chemistry—an issue that merits further investigation—available evidence indicates that intestinal carbonates produced by fed fish are similar to those produced by the same fish when fasted (Salter et al , ).…”