Using metabolic theory to assess structure and function in the deep-sea benthos, including microbial and metazoan dominance

Constraining seafloor carbon stocks and flows, and their links to biodiversity, remains a major global challenge, particularly in the deep ocean. We examine the density, biomass, respiration, and species richness size spectra of polychaetes from a time-series study (1991-2011) in the abyssal NE Pacific (Station M, 35°N, 123°W, 4000 m water depth). The spectra met the predictions of the metabolic theory of ecology (MTE) and were consistent with Damuth's rule of energetic equivalence. When combined via MTE, resource supply rate and habitat temperature have valuable predictive power for seafloor standing stocks. Intra-annual comparisons suggested seasonally variable resource acquisition rates and metabolism, consistent with the scope for specific dynamic action in polychaetes. Accepting and applying the assumptions of MTE, Damuth's rule, and 3/4-power mass-scaling of metabolism to the entire benthos, then two thirds of carbon remineralised at the seafloor might be attributable to metazoan invertebrates. This is contrary to the common finding of microbial dominance but may be resolved by considering (1) that only a fraction of microbial biomass may be metabolically active, and (2) that the metabolism of the largest members of the benthos could only be assessed at physical scales very much greater than are usually examined.