Abstract
The brooding gastropod Crepipatella dilatata can feed by scraping the substrate with the radula and by suspension-feeding, which also requires use of the radula. There is a “division of labour” for the radula among three discrete tasks associated with feeding: (1) removing mucous balls from the food pouch; (2) transferring the mucous cord from the neck channel to the mouth (both components of suspension-feeding); (3) scraping the substrate. We hypothesised that the proportion of time used for each feeding activity varies according to environmental conditions. Total radular activity in females was greatest at high tide and in summer. The rate of radular extrusion for ingesting the mucous cord varied seasonally and between brooding and non-brooding females. Non-brooding females exhibited higher rates of radular extrusion for ingesting the mucous cord and for scraping the substrate than did brooders. In females, radular activity in removing the mucous ball from the food pouch was strongly influenced by the tidal cycle during winter, reaching minimum values at low tide. Differences were recorded in substrate scraping among seasons and within tidal cycles, and among males, brooding females and non-brooding females. Brooding females displayed less rasping than non-brooders, since the area available for grazing was restricted by the egg mass. Throughout the year, including low salinity periods, males allocated a greater proportion of total radular activity to rasping than to removing the mucous ball or ingesting the mucous cord. The feeding behaviour of both males and females is modulated by salinity, but the principal determinants of radular activity are the mode of reproduction (brooding in females) and, in males, motility.
Highlights
Many marine organisms are constantly exposed to fluctuations in environmental factors such as temperature, salinity, hydrostatic pressure, light intensity and food availability over various time scales [1,2,3]
A third feeding function of the calyptraeid radula is the removal of the mucous balls formed in the food pouch, a depression located in the frontal region of the mantle [28,29,30], either to the mouth for ingestion or to the mantle rim for rejection as pseudofaeces [23, 27, 30]
Environmental variables Highly significant differences were observed in water salinity among seasons and within individual tidal cycles (p < 0.0001, Table 1A), but there were no significant differences in total particulate matter (TPM) (Table 1B) or particulate organic matter (POM) (Table 1C)
Summary
Many marine organisms are constantly exposed to fluctuations in environmental factors such as temperature, salinity, hydrostatic pressure, light intensity and food availability over various time scales [1,2,3]. A third feeding function of the calyptraeid radula is the removal of the mucous balls formed in the food pouch, a depression located in the frontal region of the mantle [28,29,30], either to the mouth for ingestion or to the mantle rim for rejection as pseudofaeces [23, 27, 30] The material in these mucous balls is acquired by suspension-feeding and originates either on the branchial filaments closest to the head of the animal or from the lateral canal of the mantle, which moves particulate material from the inhalent area of the mantle cavity [23, 24, 27]
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