Abstract
Abstract. The biomass distributions of marine benthic metazoans (meio- to macro-fauna, 1 μg–32 mg wet weight) across three contrasting sites were investigated to test the hypothesis that allometry can consistently explain observed trends in biomass spectra. Biomass (and abundance) size spectra were determined from observations made at the Faroe–Shetland Channel (FSC) in the Northeast Atlantic (water depth 1600 m), the Fladen Ground (FG) in the North Sea (150 m), and the hypoxic Oman Margin (OM) in the Arabian Sea (500 m). Observed biomass increased with body size as a power law at FG (scaling exponent, b = 0.16) and FSC (b = 0.32), but less convincingly at OM (b = 0.12 but not significantly different from 0). A simple model was constructed to represent the same 16 metazoan size classes used for the observed spectra, all reliant on a common detrital food pool, and allowing the three key processes of ingestion, respiration and mortality to scale with body size. A micro-genetic algorithm was used to fit the model to observations at the sites. The model accurately reproduces the observed scaling without needing to include the effects of local influences such as hypoxia. Our results suggest that the size-scaling of mortality and ingestion are dominant factors determining the distribution of biomass across the meio- to macrofaunal size range in contrasting marine sediment communities. Both the observations and the model results are broadly in agreement with the "metabolic theory of ecology" in predicting a quarter power scaling of biomass across geometric body size classes.
Highlights
Marine sediments are sites of long-term removal, via burial, of organic carbon derived from productivity at the ocean surface and so play a key role in global biogeochemical cycles
Samples were collected from three contrasting locations in 2000 and 2002: (i) a temperate shelf sea site in the Fladen Ground (FG), North Sea, (ii) an “Arctic” deep-water site in the Faroe–Shetland Channel (FSC), and (iii) a tropical midslope oxygen minimum zone site on the Oman Margin (OM), Arabian Sea
At the physical scale of sediment core samples bacteria dominate the consumption of particulate organic carbon (POC) (e.g. Pfannkuche et al, 1999). We model this additional consumption by rescaling the incoming POC flux to that proportion available to the meio- and macro-benthos
Summary
Marine sediments are sites of long-term removal, via burial, of organic carbon derived from productivity at the ocean surface and so play a key role in global biogeochemical cycles. The amount of organic carbon that is buried is determined by the rate of processing by benthic organisms with the majority of the settling carbon (the POC flux) respired back to the water column (Pfannkuche et al, 1999). A major challenge to understanding benthic ecology and carbon flow, especially in the deep sea, is appropriate characterization of both community composition and its underlying dynamics. The relation of body size to biological processes, provides an attractive alternative approach for meeting this challenge. Body size is an attribute of individual organisms that is closely coupled to key biological processes such as metabolism, as well as to community parameters such as biomass and abundance The advent of the metabolic theory of ecology (MTE, Brown et al, 2004) has raised much interest in and debate of the body-size (allometric) approach among ecologists (e.g. Glazier, 2005; Hildrew et al, 2007) while allometric relations have provided many useful ecological insights into terrestrial and aquatic
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