440 



102 OCEANOGRAPHY IN THE NEXT DECADE 



ters, where long-term water quality monitoring programs exist. 

 The precise causes of any bloom event are difficult to ascertain, 

 but there is increasing evidence that unusual phytoplankton blooms 

 are related to changes in nitrogen-silicon ratios caused by eutrophi- 

 cation. The food-web consequences of the global epidemic of 

 noxious phytoplankton blooms could be severe in some areas. 



Fishing activity also changes the structure of marine ecosys- 

 tems, although the effects of overfishing are often difficult to 

 resolve from long-period cycles in organism abundance. Overfish- 

 ing of the Georges Bank off the northeastern United States has 

 changed the composition of fish species. From the mid-1960s 

 until the early 1970s, herring and haddock declined by about a 

 factor of 10 due to severe fishing pressure. At the same time, 

 squid, dogfish, and sand lance increased, probably because they 

 filled the ecological niches of depleted haddock and herring stocks 

 (Sissenwine, 1986). 



Long-term studies of some coastal benthic communities sug- 

 gest that they have changed significantly owing to eutrophica- 

 tion. A 20-year time series of benthic species abundance data at a 

 station in Puget Sound suggests that eutrophication may be caus- 

 ing shifts in the dominant species as well as increasing the mag- 

 nitude of population fluctuations (Nichols, 1985). Yet, even with 

 decadal time series, cause and effect are difficult to ascribe unam- 

 biguously, in part because anthropogenic effects are difficult to 

 distinguish from natural changes. 



Research Strategies 



The complexity of biological systems and their variability in 

 time and space pose practical problems for designing programs 

 and setting research priorities. Research based on the theme that 

 food-web variability controls variability in fluxes of biologically 

 important elements in the global ocean could take many forms,- 

 efforts must then focus on a subset of key questions and approaches. 



One possibility is to take a comparative approach and focus 

 studies on regions or times of the year with clearly distinguish- 

 able food-web structures, and to examine processes in the eu- 

 photic zone and in deeper waters. A second possible strategy is to 

 plan biological studies to resolve seeming inconsistencies or con- 

 tradictions obtained from geochemical measurements and mod- 

 els. For example, recent interest in vertical fluxes in the North 

 Atlantic (Altabet, 1989) were inspired in part by geochemical studies 

 indicating that conventional views of productivity and particle 



