Naturally low seston concentration and the net energy balance of the greenshell mussel (Perna canaliculus) at Island Bay, Cook Strait, New Zealand

Abstract

This paper describes an investigation of the physiological energetics of the New Zealand greenshell mussel, Perna canaliculus (Gmelin, 1791), which is aimed at determining if mussels are absent from many shores of Cook Strait as a consequence of a negative energy balance resulting from ambient low seston quantity and quality. Seston characteristics and mussel physiological functions were measured under ambient summer conditions at Island Bay, a site in Cook Strait. Estimates of total particulate matter (TPM in mg litre⁻¹), particulate organic matter (POM in mg litre⁻¹), and particulate organic carbon (POC in |ig litre⁻¹) were low but of a similar magnitude to values reported for many comparable temperate regions. However, seston % organic matter (% OM) values were consistently low (<25%) and resulted in negative net absorption efficiency (AE) values and concomitant negative scope for growth (SFG = net energy balance) values. We suggest that the ongoing costs of energy loss associated with extra‐and intracellular digestion (termed metabolic faecal loss) are greater than the energy derived from seston of such low organic matter. Our data indicate that ambient levels of seston % OM of ≤25% are insufficient to promote a positive net energy balance in P. canaliculus, and as such probably play a major role in explaining the almost complete absence of mussels from many Cook Strait shores.

Keywords:

• greenshell mussel
• Perna canaliculus
• physiological energetics
• seston
• scope for growth
• net energy balance
• ecological distribution