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Characterishcs of the surf diatom Anaulus blrostratus have been recorded over two 28 h studies in an effort to understand the factors responsible for the formation and decay of cell patches In the surfzone. A sequence of anatomical and rnorpholog~cal changes characterising the process of asexual reproduction were observed in field samples. Division frequency, cell dimensions and cell cond~hon all exhibited diel periodicities which were synchronized with observed variations in cell concentrahon within the inner surfzone. Cell division was restricted largely to early morning. Initiated just before dawn, it reached a maximum frequency of 53 % at 0830 h and ceased by 1900 h. The first appearance of recently divided cells lagged behind cell division by approximately 3 h and coincided with the exponential increase in cell numbers in the inner surfzone. Changes have been observed in the outer appearance of cell frustules, which were smooth-walled during the period of maximum d~vislon. During the late afternoon when division frequency was less than 5 %, more than 30 % of all cell margins appeared irregular. There was a strong diel periodicity in the dimension of the pervalvar axis which increased by 52 "/o between 0300 and 0800 h ; t h~s increase was in phase with cell division. The formation of cell patches does not constitute a blooming phenomenon, but is, rather; the result of an advection process which appears to be controlled by or linked to the process of asexual reproduction.

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A winter (June 1981) and summer (December 1981) survey of the seagrass Zostera capensis were carried out in the well developed warm-temperate Swartkops estuary, South Africa. The area covered by Z, capensis increased from 13.7ha (3% of the estuary) in winter to 16.1 ha in December. With few exceptions, this increase was due to the extension of existing beds rather than the appearance of new beds. Over 90% of the beds were found within 6 km of the mouth, and more than half in one of the arms of the estuary (Tipper's Creek). Epiphytes contributed 28% of the total biomass in summer. Subsequent surveys of the estuary in 1984 and 1986, together with historical aerial photographs, have implicted a complex pattern of population dynamics. Variations in population size included flood-or season-related fluctuations and complete, but temporary disappearance of the population in response to catastrophic events. A similar disappearance is recorded for the small population of Z. capensis in the adjacent Sundays estuary.