Mussel-ecosystem interactions: review of feedback mechanism in oligotrophic and eutrophic cultivation areas

Suspension feeding bivalves have the potential to influence ecosystem functioning at all trophic levels due to their role in coastal nutrient cycling. The major pathways of bivalve nutrient cycling are: (i) filtration of seston from the water column, (ii) nutrient storage and growth of somatic and reproductive tissue, (iii) respiration and excretion of inorganic metabolic waste products, and (iv) egestion and mineralization of biodeposits. Through these processes bivalves exert a negative feedback on phytoplankton populations (feeding), while simultaneously exert a positive feedback through regeneration of inorganic nutrients thereby stimulating phytoplankton production. The extent and effect of both feedback mechanisms are situation specific and determined by physical and environmental conditions of the area and culture type applied (bottom vs suspended). This study describes mussel-ecosystem interactions as a function of physical, chemical and biological properties of the system. This was done by means of a review for multiple (>10) cultivation areas all around the world and will provide a broad view on the role of mussels in nutrient cycling. The study covered the following aspects: Eco-physiology: the eco-physiology of bivalves has widely been studied for eutrophic conditions, whereas less is known about the specific rates and interactions under oligotrophic conditions. Results will be presented from an extensive study carried out in oligotrophic Norwegian fjords, and physiological differences of mussels under oligotrophic and eutrophic conditions will be discussed. Physical and environmental characteristics: the physical and bio-chemical conditions vary greatly between cultivation areas worldwide, and strongly determine the extent and pathways of bivalve-ecosystem interactions. Nutrient sinks & sources: Budget analysis was performed to define potential nutrient sinks & sources. This provided insight in the relative importance of nutrient pathways between cultivation areas. Feedbacks: The role of mussels in nutrient cycling will be discussed based on positive and negative feedback estimates for the different cultivation areas. Feedback estimates were defined by combining bivalve biomass, eco-physiological rates and system properties specific for each area.