Population persistence of Capitella sp (Polychaeta; Capitellidae) on a mud flat subject to environmental disturbance by organic enrichment

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Abstract
The exclusive domination of several sibling species of the polychaete complex Capitella capitata in organically enriched areas has been recognized to reflect their opportunistic characteristics, especially production of planktonic larvae with widespread dispersal ability. In the present study it was found that a population of Capitella sp. in an organically enriched mud-flat habitat subject to environmental disturbance was, by contrast, maintained without reliance on recolonization from other habitats throughout 1 yr. Although the population declined markedly after the development of reducing conditions in the sediment in early summer, very small patches with extremely low densities (< 100 ind. m-2) were preserved in restricted areas with moderate organic enrichment within a gradient of organic enrichment. These remnant populations rapidly reconstructed dense patches in the most organically enriched areas during recovery of sediment conditions from late autumn to winter. Although the most enriched areas allowed Capitella sp. to establish dense patches, these areas were accessible only during parts of the year. Nevertheless, the distribution was concentrated in enriched areas, since this deposit-feeder required organically enriched sediment fornormal growth. The population size structure was apparently influenced by the level of sediment organic matter, and individuals large enough for reproduction were rare in less enriched areas. Thus, the association with organically enriched sediment and the population dynamics, as characterized by the dramatic seasonal fluctuations in population size, are attributable to the physiological requirement of this species for organically enriched sediment, the dramatic seasonal fluctuations in the carrying capacity of habitats subject to catastrophic environmental disturbance, and the extraordinarily large potential of Capitella sp. for rapid population growth.

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