Opportunistic life histories and genetic systems in marine benthic polychaetes

The decline in benthic marine fauna foll owing an oil spill in West Falmouth, Massachusetts, permitted us to follow the responses of a number of polychaete and other invertebrate species to an environmental disturbance. Species with the most opportunistic life histories increased and declined at the two stations with the greatest reduction in species diversity. The stations with an intermedi ate reduction in diversity showed increases and declines of somewhat less opportunistic species. Electrophoretic studies of the malate dehydrogenase loci of the most opportunistic species, Capitella capitata, indicated short-term selecti on for a single genotype in the large populations present in Wild Harbor following the oil spill . The life histories of the most opportunistic species are summarized . Initial response to disturbed conditions, ability to increase rapidly, large population size, early maturation, and high mortality are all features of opportunistic species. Using these criteria, the species are ranked in order of decreasing degree of opportunism as: r. Capitella capita/a, 2. Polydora ligni, 3. Syllides 'Verrilli , 4. Microphthalmus aherrans, 5. Streblospio benedicti, 6. M ediomastus ambiseta. We propose using mortality as the best single measure of degree of opportunism. A definition based on mortality emphasizes the portion of the life cycle involved in adaptation through shortterm selection. Two types of marine benthic opportunists are described: r. a mixed strategy variety with obligate planktonic dispersal where selecti on wi thin local subpopulations occurs in a single generation, 2. a response-to-selection type with direct development or settlement shortly after release from brood structures all owing selection within local populations through more than one generation.

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