tion of the water column). It can be measured at 

 all depths in the system, and provides another 

 parameter for comparison in space and time. 



Transparency. Water transparency is easily mea- 

 sured by Secchi disc. It indicates both sediment 

 loading and biological contributions to turbidity. 



Blue crabs. Because blue crabs require different 

 habitats during various parts of their life cycle, from 

 the water at the Bay mouth to the tributaries, they 

 can integrate information for the whole Bay sys- 

 tem. Abundance may be affected by climate and 

 fishing pressure, as well as water quality, and there 

 may be wide natural variations in abundance. Con- 

 sideration of additional system information will be 

 necessary to interpret changes in abundance. 



Larval forms. Larval forms are potentially good 

 indicators of pollution levels because larvae are 

 much more sensitive to pollutants than adults. 

 Forms that eventually settle on the bottom, such 

 as oyster spat, are the easiest to measure. 



Pollutant concentrations in tissues. Concentra- 

 tions of pollutants in the tissues of commercial 

 fishes and shellfishes can provide indications of bio- 

 accumulation in the benthic and pelagic environ- 

 ments. Concentrations in forage fishes and plank- 

 ton, while a little more difficult to analyze, would 

 provide earlier indications of dangerous accumula- 

 tions that could eventually be passed to commercial 

 species. 



RESEARCH NEEDS 



One problem in assessing the impact of man's 

 activities on the Bay as a system is lack of adequate 

 information on how the Bay system operates, on 

 both short-term and long-term time scales. Short- 

 term information requirements involve such mat- 

 ters as feeding habits, spawning habits, relation- 

 ships of species to toxic substances, migration 

 patterns, fishing patterns, and so forth. The long- 

 term natural variation in population sizes is more 

 difficult to handle, but the information is impor- 

 tant. Since the Bay is a very dynamic system, it is 

 difficult to distinguish between the biological 

 responses to human activities and the undisturbed 

 or "normal" changes which are long-term cyclic or 

 successional phenomena due to the nature of the 

 Bay as an estuary. Spatial scales are also important. 

 Most studies are quite localized, and extrapolation 

 of their results over the whole Bay, a very large 

 system, presents serious problems in interpretation 



and impact assessment. 



Thus one important aspect of research in the 

 Bay is large-scale, long-term work. Parameters 

 which will provide effective monitoring of water 

 quality and ecosystem conditions need to be identi- 

 fied. Some possible indicators have been discussed. 



There is also a need for ecosystem-level studies 

 in the Bay. While a great deal of information is 

 available on Bay ecology, it is still difficult to 

 answer definitively such questions as (1) the rela- 

 tive impact of marsh detritus, upland detritus, sea- 

 grass production, and phytoplankton production in 

 driving the system; (2) the relative importance of 

 physical processes such as climate, temperature, ice 

 regime, or sediment loading; (3) the importance of 

 biological processes such as reproduction and pre- 

 dation; or of human impact such as the effects of 

 toxic substances on commercially important spe- 

 cies in the Bay, or on populations which are impor- 

 tant in their food chains; or (4) the relative impor- 

 tance of water column and benthic processes in re- 

 generation of nutrients, which are crucial to the 

 overall productivity of the system. These questions 

 are pertinent to management decisions as to habi- 

 tat that must be protected, processes to be moni- 

 tored, and the important aspects of water quality 

 and their long-term economic effects. Answering 

 these questions may be an ambitious undertaking, 

 but coordination among investigators would con- 

 tribute toward providing answers. 



In the conceptual model for the Chesapeake 

 Bay ecosystem, (figs. 1 through 8), about 40 key 

 system components are identified by the compart- 

 ments or boxes of the diagrams. Their interactions 

 (arrows) and interrelationships are indicated. Phy- 

 sical and chemical processes that affect the biology 

 of the system are identified. The relationships of 

 several system processes to water quality have been 

 discussed. This conceptualization of the system can 

 be debated, compartments redefined, and new in- 

 teractions included. As understanding of Bay ecol- 

 ogy increases, the diagrams will be modified. The 

 conceptualization reflects current hypotheses 

 about Bay ecology. 



Even at this simple level of resolution, the rela- 

 tive magnitudes (or importance) of the various 

 flows on a Bay-wide, annual basis are not known. 

 Compartment sizes or biomass measured in carbon 

 units can be estimated easily for only a few of the 

 compartments. One approach to research about 



15 



