TROPHIC CHARACTERISTICS OF THE MANILA CLAM (TAPES-PHILIPPINARUM ADAMSAND REEVE)

Parameters of feeding and food balance in the Manila clam Tapes philip pinarum and in the carpet shell Tapes decussatus were estimated using C-14-labelled algae and bacteria as food. The Manila clam has a wide f eeding spectrum, consuming and digesting various kinds of algae, bacte ria, and rotifers. The optimal concentrations of algae (Nitzschia, Chl orella) were found to be around 8-9 mg l(-1) (wet weight) and those of bacteria, 4.5-5mg l(-1). The threshold concentration of food (where a ssimilation rate=respiration rate) was 1.6-1.7 mg l(-1) of algae and 1 .5 mg l(-1) of bacteria. The filtration rate fell to between 3 and 61 h(-1) g(-1) flesh carbon, or 0.1-0.91 h(-1) per specimen. The food rat ion per day was 3-5% of body weight, or 30-50 mg C g(-1) of flesh carb on with optimal food concentrations. The assimilation of green algae a nd diatoms consumed as food was 50-60%, and the efficiency of the use of assimilated food for growth (k(2)) was 0.36-0.49, depending on the kind of food (algae). The data obtained were used to evaluate trophic conditions for farming clams in the Lagoon of Venice, by comparing foo d requirements with the real food concentrations found in the lagoon. (C) 1995 International Council for the Exploration of the Sea