Natural heavy metal concentrations in seawater as a possible cause of low survival of larval mussels

Abstract

BackgroundA period of seismic activity starting in 2010 coincided with a decline in commercial catches of wild seed mussels in a major aquaculture production region of New Zealand. Analyses of over 40 years of mussel seed catch data from in the Pelorus and Kenepuru Sounds, confirmed a marked decline since 2010 in catches of the preferred, green-lipped mussel (Perna canaliculus), the larvae of which is known to have low tolerance of heavy metals in seawater. MethodsHeavy metal mean concentrations were measured throughout the Pelorus and Kenepuru Sounds. The concentrations ranged from < 0.60–3.24, < 16.94–74.35, < 1.47–4.00, 2.23–19.02, 1.86–3.29 and 0.12–0.52 µg L−1 for Cr, Fe, Cu, Zn, As, and Cd, respectively. Seawater from six locations in the Sounds, historically associated with high commercial catches of settling mussel larvae, was used for experimental rearing of green-lipped mussel larvae. ResultsNo mussel embryos survived when incubated in these seawater samples. The mean concentrations of Cr, Fe, As, and Cd were significantly higher in the seawater from the Sounds than in the hatchery seawater. A higher concentration of one or a combination of these heavy metals could be the cause of the poor larval survival. These findings could be crucial for the sustainability of mussel farming in the area.