Temperature, species identity and morphological traits predict carbonate excretion and mineralogy in tropical reef fishes

Anthropogenic pressures are restructuring coral reefs globally. Sound predictions of the expected changes in key reef functions require adequate knowledge of their drivers. Here we investigate the determinants of a poorly-studied yet relevant biogeochemical function sustained by marine bony fishes: the excretion of intestinal carbonates. Compiling carbonate excretion rates and mineralogical composition from 382 individual coral reef fishes (85 species and 35 families), we identify the environmental factors and fish traits that predict them. We find that body mass and relative intestinal length (RIL) are the strongest predictors of carbonate excretion. Larger fishes and those with longer intestines excrete disproportionately less carbonate per unit mass than smaller fishes and those with shorter intestines. The mineralogical composition of excreted carbonates is highly conserved within families, but also controlled by RIL and temperature. These results fundamentally advance our understanding of the role of fishes in inorganic carbon cycling and how this contribution will change as community composition shifts under increasing anthropogenic pressures. Marine fishes can substantially contribute to the inorganic carbon cycle through the excretion of intestinally precipitated carbonates, but the underlying drivers remain largely unknown. This study identifies the environmental factors and fish traits that predict carbonate excretion rate and mineralogical composition in tropical reef fishes.

Automated summary

Anthropogenic pressures are restructuring coral reefs globally, and the excretion of intestinal carbonates by marine fishes plays a relevant role in inorganic carbon cycling. This study identifies body mass and relative intestinal length as the strongest predictors of carbonate excretion in reef fishes. The mineralogical composition of the excreted carbonates is highly conserved within families but also influenced by temperature and intestine length. These findings improve our understanding of the drivers and contributions of fishes to inorganic carbon cycling in coral reefs.