Influence of Clam Farming on Macroalgal Growth: A Microcosm Experiment

Abstract

In this work we tested whether macroalgal growth can be stimulated by clams filtration activity and nutrient excretion. Thalli of Ulva rigida were grown suspended in semi-opened microcosms containing sand, in presence and absence of the clam Tapes philippinarum. Macroalgal growth and nitrogen pools were measured on subsamples collected during the experiment whilst oxygen and inorganic nitrogen fluxes were measured via short light and dark microcosm incubations. The presence of the clams stimulated significantly primary production of both macroalgae and microphytobenthos; in the light. gross O₂ fluxes up to 52.5 ± 6.9 and 99.2±4.6 mmol m⁻² h⁻¹ were measured respectively in the chambers without and with clams. Daily inorganic nitrogen fluxes were mostly negative with a peak (−49.4 mmol N m⁻² d⁻¹) measured in the clam chambers. U. rigida cultured with clams had a higher growth rate and maintained a higher nitrogen content than U. rigida in bare sediment chambers.

Keywords:

• Tapes philippinarum
• Benthic fluxes
• Ulva rigida growth
• Nutrient budget