Physiological Rates Working Group Report

Chairman: Lewis Incze
Rapporteur: Patrick Walsh

9.5.1 Background

The objective of GLOBEC is to understand the influences of physical processes on population dynamics. These influences are mediated directly at the level of the individual by dispersion and by physiological and behavioral responses of the organism to environmental conditions and change. It was the charge of this working group to suggest those rates and responses most central to the achievement of GLOBEC's goals.

9.5.2 Criteria

In selecting physiological and behavioral processes to be emphasized, the following criteria were used.

Identify physiological and behavioral properties which:

Emphasize methods which:

9.5.3 Priorities

Topics which fit the above criteria are listed below. Along with some are examples of potentially useful techniques which might be applied. The examples are tentative and are offered to stimulate thought. Recommendations for further consideration of techniques are given at the end of this section. Development of new techniques are especially needed for topics 1-4.

  1. Measures of Physiological Condition. These include:

    Biochemical or molecular "proxies" for the above are desirable. For example, if an activity of a key metabolic enzyme can be calibrated with an organism's nutritional background or locomotory capability in the laboratory, then assays for the enzyme performed in the field could be used as an index of condition, instead of attempting to perform complex shipboard experiments. Proxies for egg production rates and for assessing "diapause" in copepod stages (e.g., CIV or CV of Calanus finmarchicus) are needed for the same reason and would have the same advantages. Levels of hormones or indicator molecules (e.g., yolk proteins), are possible candidates for these needs. Diapause is placed in quotes because it probably requires clearer definition for the copepods. The final entry is suggested because specific "low performance" indicator(s) should add to the precision of evaluating physiological condition in nature. To wit, a multiple enzyme approach (e.g., contrasting a and d) is thought to be better than one using a single enzyme only. Non-biochemical techniques, e.g., video monitoring in situ, would be useful for a number of applications and certainly would be essential for behavioral applications.

  2. Measures of Growth Rates, Development Rates and Age. RNA/ DNA ratios have been applied with success to larval fish and are being developed for larval lobsters. Increases in sensitivity and ease of use of the assay should be encouraged, with the goal of analyzing single organisms of even smaller size (e.g., the larvae of benthic invertebrates). Assessment of developmental rate is a particular problem for crustaceans; the presence of enzymes associated with molting or other hormonal indices may prove useful in population studies. There are presently effective, though time-consuming, methods for aging larval fishes and bivalves. There is room for improvement, especially further automation, of sample processing and analysis for these organisms. There is virtually no known method that can be used with copepods. Past efforts with lipofuscin in fish have not yielded useful methods (Mullin and Brooks, 1988). Advances in biochemical techniques in recent years may warrant a revisitation of this problem from a different perspective.

  3. Feeding Rates and Diet. Current methods are time-consuming considering the large number of observations needed to meet GLOBEC objectives for field studies. The development of instruments to observe or record feeding activity in situ would be extremely valuable. This would enable independent and undisturbed observations of a variety of organisms over time and with varying conditions. Methods which assess the consequences of feeding (e.g., a short- term grazing chamber or trap that captures fecal pellets) may be one solution. Knowledge of diet is essential to improving our understanding of ecosystem functions and responses. A variety of methods are available to assess dietary components (e.g., immunochemistry, molecular biology, fatty acid composition). These presently could be used to assess simply presence or absence; however, attempts could be made to improve the facility of assays and to extend methods to enable quantification of items. Added benefits of these biochemical/molecular approaches might be in taxonomy, for instance with the complicated Pseudocalanus spp. problem. Another application may be in rapid sample sorting and identification. Expanded use of these techniques will prove invaluable in predation studies at higher trophic levels as well.

  4. Mortality Rates for Populations. Innovations are needed. The traditional method has been to assess changes in abundance of organisms over time after accounting for dispersion and new individuals recruited during the intervening period. Measures of physiological condition (performance/morbidity) and knowledge of predators and predation rates should increase confidence in estimates of population mortality rates. That is, empirical and mechanistic estimates should be coupled.

  5. Bioenergetic/Metabolic Functions. These are essential inputs to mechanistic or deterministic population models. They are undertaken in the study of most marine organisms and are parts of many ongoing studies. Comprehensive measurements and models should be encouraged with the objective of predicting physiological states from physical parameters.

  6. Behavioral Preferences. Certain behaviors of planktonic, settling and post-settlement stages need to be studied to predict organism preferenda and responses to physical conditions and change. Vertical distribution and benthic site selection are among the behaviors of interest. Potential consequences of behavioral responses include growth, feeding and predation. Such things as temperature, turbulence, food, predators, and substrate type are among the environmental variables of concern.

9.5.4 Conclusions

  1. Zooplankton Research This community has for years recognized the need for improved methods for some of the topics outlined above and has recognized the potential value of some of the possible solutions listed. Development of applications in this field has lagged behind the developing technology, however. GLOBEC must address this deficiency, at least for some of the most important rates. This will not only be critical for our own project goals, but will have tremendous benefits to the marine science field in general. We must recognize that some applications are needed immediately and will probably, at least initially, require "quick and dirty" approaches. Regardless, the long-term perspective should not be overlooked as a needed investment in biological oceanography.

  2. Biological Oceanography Most biological oceanographers do not have a good working knowledge of the developing techniques in biochemistry and molecular biology that may benefit them. To address this, GLOBEC should take the following two steps.

These two actions should put biological oceanographers in a much better position to forge collaborations and proposals to work with appropriate biochemical/molecular scientists on certain GLOBEC problems.


Mullin, M. M. and E. R. Brooks. 1988. Extractable lipofuscin in larval marine fish. Fish. Bull. U.S. 86: 407-415.

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