Exfoliation of epithelial cells in the scallop, Placopecten magellanicus (gmelin)-seasonal variation and the effects of elevated water temperatures

Potter, Tracy Marie (1995) Exfoliation of epithelial cells in the scallop, Placopecten magellanicus (gmelin)-seasonal variation and the effects of elevated water temperatures. Masters thesis, Memorial University of Newfoundland.

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Abstract

It has previously been shown that large numbers of ciliated and non ciliated cells (6-15μm) were released by adult sea scallops, Placopecten magellanicus, during summer months in Newfoundland. Proportions of scallops exfoliating cells was closely correlated with maximum water temperatures and peak gametogenic activity in this area. These results suggested that epithelial sloughing could be a response to stresses associated with elevated water temperatures and/or spawning activity. Scanning electron microscopy (SEM) was used to illustrate the damage to the pallial structures, particularly the disappearance of ciliated cells from the gills, mantle and gonad in specimens known to have sloughed cells. -- In the first component of this study, juvenile and adult sea scallops were monitored during 1992-93 to establish whether or not this species exfoliated epithelial cells throughout the year. An electronic particle counter was used in this seasonal study to distinguish epithelial cells from natural particulate matter and instantly determine which scallops were exfoliating cells, Both juvenile and adult scallops released relatively small amounts of epithelial cells during most months of the year. This observation for juveniles and for adults monitored during months when gametogenic activity was minimal, indicated that exfoliation does not occur as a result of reproductive activity alone. SEM analysis revealed little difference in surface characteristics of the gills, mantle and gonad from scallops observed to have sloughed small numbers of cells when compared to tissues from scallops that had apparently not sloughed any cells at all. These low rates of epithelial exfoliation throughout the entire year and lack of damage to the pallial tissues were considered to be consistent with cellular turnover and normal physiological function. -- In the second component of this study, adult scallops were monitored to determine the effects of elevated water temperatures (14-21.0°C) on the frequency (proportion) of scallops sloughing cells and the rates of cell release. A baseline sloughing rate of approximately 5,300 cells minute⁻¹ was established for scallops held at ambient temperatures of approximately 8.0 to 10.0°C. Sloughing rates greater than this were considered to be a measurable response to stress associated with elevated water temperatures. Only at the highest experimental temperature (21.0°C) were sloughing rates significantly higher than baseline levels. SEM analyses revealed some damage to gills, mantle find gonad tissue when scallops were exposed to relatively high temperatures for short periods of time, less than five days. -- This is the first study to establish that a species of marine bivalve is exfoliating cells throughout most of the year and that an environmental stressor, such as elevated water temperatures, can produce a detectable increase in sloughing rates. The determination of exfoliation rates using this technique may prove to be a useful quantitative of environmental stress, including anthropogenic pollutants, not only for this species but possibly for many others.

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