Physiological Rates Working Group Report
Chairman: Lewis Incze
Rapporteur: Patrick Walsh
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.
In selecting physiological and behavioral processes to be emphasized,
the following criteria were used.
Identify physiological and behavioral properties which:
- are sensitive to physical conditions and/or change;
- are indicative of the state of the individual; and
- will yield good returns for the level of effort invested in methodological developments.
Emphasize methods which:
- can be applied to small sample sizes, ultimately, to the individual;
- can provide for rapid sample processing, enabling quick turn around
and large sample numbers; and can be taken to sea.
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.
- Measures of Physiological Condition. These include:
- General performance capabilities (e.g., locomotion);
- Egg production rates;
- Entrance to "diapause";
- Morbidity/low physiological capability.
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.
- 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.
- 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.
- 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.
- 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
- 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.
- 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 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.
- Convene a workshop of biochemists/molecular biologists/geneticists
with a small group of biological oceanographers to discuss the most
promising techniques for oceanographic applications. The above goals and
both short and long time-frames should be considered. A list of methods
and areas for development should result.
- After the above, consider supporting a classroom short-course of
techniques and ideas. The course would be advertised and open to the
community at large. The format of such a course might be prescribed by
the above workshop participants.
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.