Energetics of life on the deep seafloor

Abstract

With frigid temperatures and virtually no in situ productivity, the deep oceans, Earth's largest ecosystem, are especially energy-deprived systems. Our knowledge of the effects of this energy limitation on all levels of biological organization is very incomplete. Here, we use the Metabolic Theory of Ecology to examine the relative roles of carbon flux and temperature in influencing metabolic rate, growth rate, lifespan, body size, abundance, biomass, and biodiversity for life on the deep seafloor. We show that the relative impacts of thermal and chemical energy change across organizational scales. Results suggest that individual metabolic rates, growth, and turnover proceed as quickly as temperatureinfluenced biochemical kinetics allow but that chemical energy limits higher-order community structure and function. Understanding deep-sea energetics is a pressing problem because of accelerating climate change and the general lack of environmental regulatory policy for the deep oceans.L ife requires energy. The flux and transformation of energy influences processes and patterns across levels of biological organization. Three distinct types of energy affect biological systems: solar radiation in the form of photons, thermal kinetic energy as indexed by temperature, and chemical potential energy stored in reduced carbon compounds (1). Genomic, phenotypic, and taxonomic diversity and complexity are correlated with variation in energy availability in space and time (1, 2). For example, the acquisition of mitochondria through endosymbiosis allowed for increases in energy expenditure, which in turn, facilitated increases in coding genome size and complexity (3). Global variation in metabolic rates and life history traits, particularly in ectotherms, in part reflects variation in temperature (4). The tremendous range in body size among metazoans is tied both to patterns of carbon accessibility and temperature (5-7). The rapid proliferation of higher-order taxa during the Mesozoic Marine Revolution is posited to have been driven by increases in energy availability (8, 9).The deep oceans, which encompass depths below 200 m, cover most of Earth and are especially energy-deprived systems. Globally, temperatures of most of the seafloor vary between −1°C and 4°C (10). These cold temperatures limit the biochemical kinetics of metabolism. Photosynthetically active radiation is nonexistent, and consequently, primary production is virtually absent, occurring only through alternative pathways, such as chemosynthesis. However, chemosynthesis represents a small percentage of total ocean production (0.02-0.03%) and a small percentage (3%) of carbon flux to nonchemosynthetic systems (11). The chemical energy that sustains most deep-sea organisms is sequestered from sinking particulate organic carbon (POC) derived from primary production in the euphotic zone hundreds of meters to kilometers above. POC flux decreases with depth in the water column, because material is remineralized, and distance seaward from productive coastal regions. At ...

Biodiversity–ecosystem functioning relationships in long-term time series and palaeoecological records: deep sea as a test bed

“…B 371: 20150282 a significant predictor of deep-sea species diversity in palaeoecological and long-term time series datasets, but less so in modern observational datasets [28,36,[61][62][63][64][65]. Instead, POC flux tends to be a significant predictor of deep-sea biodiversity in modern observational datasets [66,67], and indeed, POC flux can vary more greatly across short (e.g. seasonal) time scales [29,30] than temperature [65].…”

Unravelling the environmental drivers of deep-sea nematode biodiversity and its relation with carbon mineralisation along a longitudinal primary productivity gradient

“…Deep-sea diversity has been documented to vary positively (Glover et al, 2002; Published by Copernicus Publications on behalf of the European Geosciences Union. Lambshead et al, 2000Lambshead et al, , 2002, negatively (Gooday et al, 2012) or unimodally (Leduc et al, 2012a;McClain et al, 2012;Tittensor et al, 2011) with productivity for different taxa and geographic regions. These differences in diversityproductivity trends may be related to the differential productivity ranges considered (Rex and Etter, 2010).…”

Controls on the standing crop of benthic foraminifera at an oceanic scale

“…Increases in standing crop with food supply are expected and supported by ecological theory (e.g. McClain et al 2012). Surprisingly, on the shelf there is a significant negative relationship between POC flux and standing crop (Fig.…”

“…First, the combination of data collected with different size fractions introduces a covariate, which will increase error in estimates. Foraminiferal standing crop was, as would be expected (McClain et al 2012), significantly higher in samples taken with smaller sieves and there were some spatial patterns in the size fraction analysed (Fig. S2 in Supplement 1).…”

“…The body of ecological theory (e.g. the metabolic theory of ecology; Brown et al 2004) and observations for other taxa would support a temperature relationship, relating temperature increases to elevated metabolic rate, biomass and population sizes (McClain et al 2012). However, it should be recognised that the range of temperatures exhibited in the deep sea is relatively small compared with other environments.…”