Microcosm responses to environmental perturbants

Abstract

A flow-through microcosm facility using unfiltered ocean source water is described. “Stagnation” cleaning has proven to be a simple and effective way of maintaining seawater distribution systems free of fouling organisms and is recommended. A valveless system for regulating water flow is also recommended. The microcosm facility has been used experimentally as an extension of field surveys being conducted in Hawaiian harbors. Examples of two essentially different types of microcosm experiments are presented to illustrate this interactive approach to environmental research. One approach disturbs an established microcosm community with specific environmental perturbants and follows both the community response and recovery over prolonged time periods. Examples of perturbation by elevated nutrients and by elevated copper concentrations are given. The ability of reef flat communities to trap and retain phosphorus even in a flow-through system is demonstrated. Added copper is shown to result in a number of responses not seen in the legislatively-preferred copper toxicity tests. The second approach involves transferring substrates from the field into the microcosm and following response with time. Again, two examples are given—one involving the transfer of fouling panels, the other, of sediments. Profound changes are seen when fouling panels are transferred from a high-nutrient into a low-nutrient environment. Nutrient-rich sediments, however, are shown not to influence water-column nutrient concentrations in the microcosms, but do acquire increased infaunal populations over a 3-month period. Finally, an example of how the findings of the microcosm experiments are applied in the field is provided. The case is made that although this approach necessarily involves multivariate experimental preparations which sometimes lack precision, it is nevertheless a required and fruitful procedure in the search for better understanding of the environmental dynamics of harbor communities.