The effect of variation in quality and quantity of periphyton on feeding rate and absorption efficiencies of the snail Neritina reclivata (Say)

Abstract

The rates of feeding (mg food ingested · h −1 · g −1 dry whole snail) and absorption were measured in the grazing snail Neritina reclivata (Say). Feeding studies were conducted in situ on periphyton grown on clean glass plates. Plates were allowed to accumulate periphyton for 1–2, 3–4, and 5–6 wk before feeding studies began. This was done at five intervals over a year. Rate of feeding was determined by a “harvest method”. Biochemical composition of the different ages (accumulations) of periphyton and feces was measured. Periphyton biomass and chemical composition varied seasonally. Periphyton production (g AFDW ·m −2 · day −1) was highest in summer and for certain seasons, showed a slowing of growth after 3–4 wk of accumulation. Production in 1986–1987 was 5 times higher than in 1983–1984. Lipid was the highest (by weight) biochemical component, followed by protein and carbohydrate. Levels of all three biochemical components are greatest in periphyton grown for 1–2 wk, with this difference being significant for carbohydrate. Ash was significantly lower in 1–2 wk periphyton. Snails grazing on 1–2 wk periphyton (as compared with 5–6 wk periphyton) derived 1.5 times (significant) more energy. Snail rates of feeding were significantly higher on periphyton accumulations of 3–4 wk as compared with 1–2- or 5–6-wk accumulations. Rates of feeding were generally highest in spring, summer, and fall. In all years, there was a significant positive relationship ( r 2 = 0.76, n = 96) between periphyton production and rates of feeding. In any one feeding experiment, absorption efficiencies were highest for 1–2 wk accumulations of periphyton, and next highest for 3–4-wk periphyton. In any one feeding experiment, absorption efficiency appeared to be affected by quality of food rather than rate of food ingestion. However, over the entire study, there is no significant correlation between absorption efficiencies and rates of feeding or quality of food. On a yearly basis (1986–1987), more carbohydrate was absorbed (57%) than protein (47%). Lipid was not absorbed. Overall, total energy absorbed by the snail is most affected by rate of feeding, and rate of feeding is a function of periphyton production.