NUTRITIONAL, PHYSIOLOGY OF METRIDIA LUCENS AND M. LONGA FROM THE GULF OF MAINE1

Open Access
Publisher Website
Google Scholar
Abstract
Respiration, feeding, and assimilation were studied in two species of Metridia from the Gulf of Maine. The smaller M. lucens respired at a higher rate per unit dry weight than the large form, M. longa. M. lucens demonstrated a normal physiological response to increasing temperature up to 18C and M. longa up to 14C. Maximum respiration occurred during spring for both species and tended to decline in fall and winter. Both species were similar in their feeding behavior. Filtration rate was inversely related to food concentration, but the slope of the curve varied with different foods. With small‐sized food (5 µ), the filtration rate was generally lower than with the large‐sized food (300 µ). Food ingestion increased with increasing food concentration up to a certain level, beyond which it declined. Maximum ingestion of organic matter was less with small than with large‐sized food. Both species exhibited strong preference for animal food (Artemia nauplii) over phytoplankton when offered together. Filtration rates were insufficient to meet respiratory losses at concentrations of particulate carbon found in the Gulf of Maine, whereas studies with Artemia nauplii suggest that the animals were able to acquire food in excess of their respiratory requirements. Dietary requirements were met more easily from a mixed diet than from a single food. M. longa was less attracted to laboratory food, and the amount of food ingested was not consistent with its greater body size. M. lucens was a voracious feeder and must be considered an important predator on small zooplankton. The fat content of M. longa was generally higher than that of M. lucens.

This publication has 1 reference indexed in Scilit: