Ecological energetics is the study of the flow of energy through populations and the processes leading to these 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 digestion efficiency, 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 so that we can better understand their functioning.
Research in this theme has involved experiments in the laboratory on deep-sea fishes to study assimilation efficiencies and the development of a high pressure retaining fish trap to capture delicate deep-sea fishes on the deep-sea floor and return them to the surface under pressure and at cold temperatures. Biochemical techniques utilizing the activity of metabolic enzymes and assays for the composition of fish tissues have also been utilized. Most recently, through NSF funding, in situ chambers to measure fish metabolism are being built. Below is this project's title and summary.
An investigation of patterns in deep-sea demersal fish metabolis and feeding rates
The deep sea is the largest habitat on earth. Many studies of deep-sea animals have documented feeding habits and regional and depth related patterns in biomass, abundance, and community composition. The void in our studies of deep-sea benthic communities is information on metabolic rates. Metabolic rate sets the pace of many processes such as resource utilization, growth, and reproduction which in turn control many ecological processes. Our lack of rate information has been an obstacle to constructing dynamic food webs. Two hypotheses have been advanced with which to predict deep-sea animal metabolism. The recent "Metabolic Theory of Ecology" claims to explain the majority of variation in metabolism using temperature and body mass alone. However, studies of many deep-sea pelagic animals groups, show order of magnitude metabolic declines with habitat depth in a way that is not explained by these models. The visual interactions hypothesis explains these declines as the result of a relaxed selection pressure for sustained locomotory capability due to declining light levels and reaction distances between predators and prey. Very little data for deep-sea benthic or demersal animals are available with which to evaluate these hypotheses. The benthic habitat and its fauna are obviously different from the pelagic in many ways. A comprehensive dataset for these animals is required to test these hypotheses so that we can reasonably estimate the energetic demands of benthic animal populations.
The proposed work will test these hypotheses by measuring the metabolic rates of demersal fishes from 100-4000m and estimating their energetic demands. Demersal fishes are an ideal group to study. Many of them are top predators which can play a vital role in communities by controlling prey populations, exerting selective pressure, and influencing general community dynamics. Many are rapidly attracted to bait and are considered facultative scavengers. This behavior will facilitate in situ experiments with unique respirometers measuring metabolic rates of many species for the first time. Many additional species will be captured using trawls and used in biochemical assays of metabolic and locomotory capacity to augment and broaden the in situ results. Feeding rates of the demersal fish community from the shelf to abyssal plain will be estimated using the described patterns in metabolism and compared with estimates using the predictions of previous hypotheses.
Intellectual merit - The metabolic rate and locomotory capacity information collected from the proposed work will fill a void of particular relevance to deep-sea benthic ecology. We will be able to assess the generality of the visual interactions hypothesis as well as more general mass/temperature hypotheses. As a result, the proposed research will dramatically enhance our understanding of the patterns of energetic parameters in marine animals. The ability to predict rate processes will enable us to estimate the feeding rates of these top predators which will lead to better food web and biogeochemical models of deep-sea benthic ecosystems. It is also paramount to gather key energetic information on deep-sea species soon because of expanding human activities in their environment. Deep-sea fisheries directly exploit demersal fishes and they continue to move down slope. Metabolic rates are tied to growth rates and together they are integral to estimating productivity of fish stocks. By developing information for food-webs this study could also shed light on how these fisheries will affect the ecosystems by removing top predators. All ocean inhabitants face the threat of ongoing anthropogenic reduction in ocean pH and in the deep sea, animals may also face the consequences of CO2 sequestration. The sensitivity of deep-sea animals is expected to be high and linked to low metabolic rates. The proposed work will generate knowledge to help assess the impacts across taxa and deep-sea habitats.
Broader impacts - This project will support the education and research of two graduate and two undergraduate students. Results will be made widely available to the oceanographic community through scientific publications and conference presentations. The project also includes an opportunity for a teacher-at-sea (RET) whose experiences will be transferred back to the classroom to enrich the education of many young students. The teacher will participate in the cruise, in the lab, and work with the PI and his graduate students to develop materials and lesson plans. She will construct a web site for this experience and her developed curriculum, to expand its use throughout the K-12 community. The goal of this RET is to create enthusiasm and instill curiosity for the marine environment in the students of the Hawaii Public School system, many of whom come from groups typically underrepresented in science and engineering.
Publications relating to this topic include:
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Energetics of grenadier fishes. In Grenadiers of the World Oceans: Biology, Stock assessment, and Fisheries (pdf coming soon)
This material is based upon work supported by the National Science Foundation under Grant No. 0727135. Any opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation (NSF).