Short-term population dynamics of Tisbe cucumariae (Copepoda: Harpacticoida)

Population dynamics of a benthic harpacticoid copepod (Tisbe cucumariae) were studied in a seawater-system holding tank during fall-spring, 1979/1980, and January, 1981. These populations were opoortunistic scavengers, especially on the dead bodies of Ciona intestinalis, a solitary tunicate. Copepod population densities, life-history stage structures, sex ratio and percentages of females with egg sacs were determined in the absence or in the presence of dead tunicates (from death through dissolution to final disappearance). Taken together, all the data are consistent with a hypothesis for food-dependent cycling of populations of T. cucumariae through the following 4 density states: (1) a maintenance state of low density, which is the usual condition during the absence of a concentrated food source; (2) a colonization state of moderate density, which results from attraction and immigration to a new food source; (3) a bloom state at the food source, where a high density results from intensive reproduction combined with a tendency of all life stages to remain at the site; (4) a dispersal state of moderate density as the copepods emigrate from the site of the consumed food. Evidence is also presented for a facultative slowing of naupliar development in T. cucumariae in the absence of a concentrated food source such as a dead tunicate. Possible advantages afforded by delayed development are discussed in terms of risk-spreading in a stochastically hostile environment.