Ecological energetics is the study of the flow of energy through populations and the processes leading to these changes in state and location of matter and energy. When an organism consumes a meal it is digested, some of the matter and energy are assimilated into the animal and used for maintenance, growth, or reproduction. Some of the matter and energy are lost through excretion. By understanding these processes in the individual they can be extrapolated up to a whole population and used to construct food-web models for whole communities.
Most experiments to measure metabolism and other energetic processes occur in a laboratory setting. Because deep-sea animals do not typically survive capture and return to the surface, there is very little data on their ecological energetics. Ongoing research in the lab aims to fill this gap in our knowledge to gain a better understanding of energetics in general and to apply this knowledge to deep-sea ecosystems. With this knowledge we will understand ecosystem functioning and potential for recovery from anthropogenic impacts such as fishing, mining, and climate change.
Our research in this area has shown that the metabolic rates of deep-sea demersal fishes declines with their habitat depth. Species that swim in the water column show greater declines than those that rest directly on the seafloor. The declines are evident in both measurements of oxygen consumption in situ and from activities of metabolic enzymes. Temperature cannot explain most of the decline. Our results conform to the Visual Interactions Hypothesis (originally formulated by Jim Childress) that suggests that at deeper depths, visually orienting animals like fishes, react to prey and predators over increasingly shorter distances as light levels drop. Long chases and evasions are thus increasingly less likely to happen at greater depths. Therefore, the need for robust musculature for swimming is reduced and in turn so is the metabolism of the fishes. They don’t need to process as much energy to maintain the active engines that shallower species have.
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Black, J.A., Neuheimer, A.B., Horn, P., Tracey, D., and Drazen, J.C. (in press). Environmental and ecological drivers of slow growth in deep-sea demersal fishes. Marine Ecology Progress Series.
Gerringer ME, Andrews AH, Huss GR, Nagashima K, Popp BN, Gallo ND, Clark MR, Linley TD, Jamieson AJ, Drazen JC (2018) Life history of abyssal and hadal fishes from otolith growth zones and oxygen isotopic compositions. Deep-Sea Res I 132:37-50 pdf
Gerringer, M.E., Drazen, J.C., Yancey, P.H. (2017) Metabolic enzyme activities of abyssal and hadal fishes: pressure effects and a re-evaluation of depth-related changes. Deep Sea Research I 125: 135-146 pdf
Nunnally C, Friedman J, Drazen J (2016) Respiration of hadal invertebrates measured in situ in the Kermadec trench. Deep Sea Research I 188, 30-36 pdf
Fernandez-Arcaya, U., Drazen, J.C., Murua, H., Ramírez-Llodra, E., Bahamon, N., Recasens, L., Rotllant, G., Company, J.B. (2016). Bathymetric gradients of fecundity and egg size in fishes: a Mediterranean case study. Deep Sea Research I 116, 106-117 pdf
Drazen JC, Friedman JR, Condon NE, Aus EJ, Gerringer ME, Keller AA, Clarke ME (2015) Enzyme activities of demersal fishes from the shelf to the abyssal plain. Deep-Sea Research Part I 100:117-126. pdf
Hannides CCS, Drazen JC, Popp BN (2015) Mesopelagic zooplankton metabolic demand in the North Pacific Subtropical Gyre. Limnology and Oceanography, 60: 419–428. pdf
Robison B, Seibel B, Drazen J (2014) Deep-sea octopus (Graneledone boreopacifica) conducts the longest-known egg-brooding period of any animal. PLoS ONE 9(7): e103437. pdf
Drazen JC (2008) Energetics of grenadier fishes. In: Orlov AM, Iwamoto T (eds) Grenadiers of the World Oceans: Biology, Stock assessment, and Fisheries. American Fisheries Society, pp 203-223 pdf
Seibel BA, Drazen JC (2007) The rate of metabolism in marine animals: environmental constraints, ecological demands and energetic opportunities. Philosophical Transactions of the Royal Society of London, B 362: 2061-2078 pdf
Drazen JC, Seibel BA (2007) Depth-related trends in metabolism of benthic and benthopelagic deep- sea fishes. Limnology and Oceanography 52: 2306-2316 pdf
Drazen JC, Reisenbichler KR, Robison BH (2007) A comparison of absorption and assimilation efficiencies between four species of shallow- and deep-living fishes. Marine Biology 151: 1551-1558 pdf
Drazen JC (2007) Depth related trends in proximate composition of demersal fishes in the eastern North Pacific. Deep Sea Research I 54: 203-219 pdf
Drazen JC, Bird LB, Barry JP (2005) Development of a hyperbaric trap-respirometer for the capture and maintenance of live deep-sea organisms. Limnology and Oceanography: Methods 3: 488-498 pdf
Gutowska MA, Drazen JC, Robison BH (2004) Digestive chitinolytic activity in marine fishes of Monterey Bay, California. Comparative Biochemistry and Physiology A 139: 351-358 pdf
Drazen JC (2002) Energy budgets and feeding rates of Coryphaenoides acrolepis and C. armatus. Marine Biology 140: 677-686 pdf
DEEP-SEA FISH ECOLOGY LAB
More recently our research has focused on patterns of growth in deep-sea species. We have found that growth rates decline with depth such that deeper living species grow more slowly (see decline in growth factor K, to the right), mature later, and often reach great ages (grenadiers can live 70 years and the orange roughy can live at least 125 years). But not all deep-sea species are the same. Just as with metabolism, habitat depth is very important. The deeper living the species the greater chance that its growth will be slower. Recently we have combined many deep-sea fish age and growth studies and studied the patterns in more detail. We also standardized the rates for differing temperatures for different species. Low temperatures in the deep do account for some portion of the slower growth rates there but not all! Declines in growth still occur with depth. This variation is explained in part by variations in oxygen concentration and food supply but only to small degrees. Another large fraction of the variation in growth correlated to variation in metabolism. Some would say that lower metabolism limits growth (a performance model of energy allocation) but some studies show that metabolism and growth are uncorrelated (an allocation model). At this stage, all we can say is that for a number of deep-sea fishes the performance model matches our empirical results. Future studies will have to further elucidate the evolutionary drivers that favor slower growth rates in deep-sea species.