Feeding activities of veligers of Nassarius reticulatus and Crepidula fornicata and the use of artificial foods in maintaining cultures of these larvae

Abstract

1. Veligers of Crepidula fornicata (L.) and Nassarius reticulatus (L.) were fed on the algae Cricosphaera ap. carterae, Dunaliella primolecta and Exuviaella baltica (each at a concentration of 20 × 103 cells/ml) in suspension in columns of seawater (height 115 cm), and their movements observed over a 5 to 8 h period. 2. Nassarius reticulatus larvae were also fed on three artificial foods (cornflour, drinking chocolate and Liquifry - consisting mainly of pulverised diatoms) which settle to form a layer on a substratum and their growth was measured over a 12-14 day period. 3. The time taken from the first mouthful to the first defecation was recorded for larvae feeding on all six foods. 4. There are two patterns of swimming activity associated with feeding on algae in suspension dependent upon the food value of the alga to the particular species of veliger. 5. With a good food (Cricosphaera ap. carterae and Dunaliella primolecta for Nassarius reticulatus, Exuviaella baltica for Crepidula fornicata) all larvae congregate at the surface to feed, dropping intermittently 26 to 34 cm while digestion continues. The first defecation occurs about 30 min after feeding begins. 6. With a poor food (Exuviaella baltica for Nassarius reticulatus) and without food, larvae are distributed more evenly throughout the water column and make random swimming movements. 7. When no food is present in the column two rising rates are evident 20-30 sec/cm and 7-8 sec/cm, and one sinking rate 20-34 sec/cm. This also holds in the presence of bad and good foods except in Cricosphaera ap. carterae in which larvae rose more slowly (40 sec/cm). 8. The treatment of the six foods in the gut differs: when the stomach is full, feeding more or less ceases in case of algal foods and faeces are formed after 30 min; feeding is more continuous with artifical foods only some particles being retained for digestion and faeces are produced after 10-15 min. 9. Some growth of Nassarius reticulatus occurs in artificial foods, although it is less than in Cricosphaera ap. carterae, and ceases after 8-10 days. Growth over the first seven days is most vigorous in cornflour, good in Liquifry but poor in drinking chocolate owing to bacterial contamination. Growth resumed when larvae fed on Liquifry were given Cricosphaera ap. carterae indicating that they remained healthy. 10. The concentration of cornflour and Liquifry is a critical factor. At 2 × 103 particles/ml growth was poor, probably as a result of starvation, and a concentration of 20 × 103 particles/ml or higher is recommended. 11. The food value of an artificial food affects growth. Cornflour and drinking chocolate have a very high carbohydrate content giving an unbalanced diet. Liquifry has a more balanced food content but it contains large amounts of indigestible material which must reduce the food value. 12. Artifical foods can be used to maintain cultures of larvae over a short period, but not for long term growth as they lack essential micronutrients present in natural algal foods. © 1970 Biologischen Anstalt Helgoland.