Fish as major carbonate mud producers and missing components of the tropical carbonate factory

Common morphologies of tropical fish-produced carbonate precipitates. (A) Type 1—Ellipsoidal crystallites (size range: < 0.25 to 3 μm long); (B) Type 2—Straw-bundle crystallites (size range: 1–3 μm long); (C) Type 3—Polycrystalline dumbbell-shaped aggregates (size range: typically 1–3 μm long, but large examples to ∼10–15 μm also occur); (D) Type 4—Polycrystalline spheroidal aggregates (size range: < 10 to 30 μm diameter). Occur both as discrete spheres and as multilobate aggregations of spheres; (E) Large polycrystalline aggregates with a semisphere morphology (size range: ∼5 to ∼30 μm diameter); (F) Elongate rod-like crystallites which often occur as intergrown bundles of crystallites (size range: 2–3 μm long); (G) Splayed ellipsoidal crystallites (size range ∼2 μm long and narrow towards their terminal points).

Comparison of mole% MgCO₃ of fish-derived carbonates and skeletal Mg-calcite producing benthic organisms. Latitudinal data for skeletal benthic organisms (white circles) from Chave (25). Fish-derived data from Eleuthera at 25° N plotted as average MgCO₃ contents (+/-1 s.d.) (black circles) based on EDX analysis (n = 50 analyses per fish) of dominant crystallite morphologies observed in each species. Samples are grouped based on the dominant crystal morphology associated with each fish species.

Estimates of fish carbonate production across the Bahamian archipelago. Summary diagram showing estimated volumes of carbonate (millions kg CaCO₃/yr) produced in different habitats across the Bahamas. Production volume estimates are based on measured fish body mass and carbonate excretion data, combined with known habitat-specific fish biomass data for the region (see SI Appendix: Methods).