Population dynamics of the foraminiferan Glabratella ornatissima (Cushman) in Northern California

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Abstract
The foraminiferan Glabratella ornatissima (Cushman) dominates the shallow turbulent coastal zone from central California to the Arctic Ocean. The species was sampled weekly for two years near the Bodega Marine Laboratory, 50 mi north of San Francisco, California, at a depth of 3.2 m below mean low water. Samples consisted of the red alga Corallina chilensis and sediment near the base of the algae. The interaction of environmental seasonality (such as productivity and turbulence) with the life cycle of G. ornatissima affects population dynamics and the temporal and spatial patterns of distribution. The timing and mode of reproduction of G. ornatissima assures that large numbers of individuals are continuously recruited into the population when trophic resources are abundant. During fall and winter, the population consists of adult agamonts and plastogamous pairs. In early spring, sexually-produced embryonic agamonts are released and selectively settle in the algal microhabitat. Agamonts of two different years'' chohorts.sbd.newly released embryonic agamonts and adult agamonts of the previous year cohort.sbd.are present in early spring. Adult agamonts undergo schizogamous asexual reproduction from spring through summer, depending on the time of their release from plastogamous pairs. Agamonts released in early spring reproduce that same year and those released in late summer overwinter as adult agamonts and reproduce the next year. Young agamonts grow into robust adults and gamonts associate in plastogamous pairs. Density of the gamont generation increases manyfold in summer, as adult agamonts reproduce. Single gamonts occur only during summer, forming plastogamous pairs when a minimum age-size class is reached. By fall, nearly all gamonts have associated in plastogamy, and their abundance in algal microhabitats decreases. Neither plastogamous pairs nor adult agamonts attach firmly to the algae, and are transported subtidally by waves, surge and currents. Rapid growth, reproduction and a complex alternation of generations are related to abundant food supply due to seasonal upwelling, increased wave action, and sediment transport.