. In this case fertilization with NH4+ and PO43- is more effective than feeding with algae. However, the concentration of zooxanthellae is only moderately increasing with increasing nutrient concentration. Moreover photosynthesis, respiration rates and calcification seem to be linked to light conditions but not to increasing nutrient concentrations. It is concluded that juvenile clams depend more on autotrophy to satisfy nutritional requirements. The uptake of nutrients is limited and needs to be tested with larger clams and a variety of nutrient combinations.