AME 28:55-68 (2002)  -  doi:10.3354/ame028055

ABSTRACT: This study developed a field-based system to examine the influence of cyclical disturbances on populations and metapopulations. We have examined the population dynamics of a tide-pool ciliate that possesses several cycles, endogenously and exogenously induced, ranging in scale from hours to years. Strombidium oculatum Gruber exhibits an endogenous circatidal behaviour: for ~6 h, at low tide, S. oculatum is free-swimming in pools, and ~20 to 60 min before flushing of the pools it encysts on a substrate. Encystment lasts for ~19 h: 2 high tides and 1 intervening low tide. Excystment then occurs the next day ~30 to 40 min after the pools are isolated. This behaviour allows S. oculatum to remain in pools and creates isolated populations; a matrix of such pools on the shore then comprises a metapopulation. Over a 5 yr period, we conducted a study to examine (1) the timing of division and the cell cycle; (2) the endogenous, 25 h encystment-excystment cycle; (3) the tidally induced fortnightly behaviour; (4) the seasonally induced long-term variation in population abundance; and (5) the seasonal change in distribution on the shore. We found that ciliates on the Isle of Man exhibit an excystment-encystment pattern similar to that previously described for populations of S. oculatum in France: cells divide almost immediately after excysting, allowing the ciliate population to rapidly exploit potential food resources; 2 populations exist in each pool, each isolated to a single low tide; the ciliate exhibits seasonal trends in population dynamics, appearing in the spring and disappearing in the autumn; and ciliates appear to survive seasonal changes by remaining at low densities in upper-shore pools during the winter. We have used these data and other measurements of the population dynamics to discern how populations are maintained on the shore, and we discuss these mechanisms in the context of population-metapopulation survival.

KEY WORDS: Ciliate · Circadian rhythm · Circatidal behaviour · Metapopulation · Oligotrich