THE EFFECTS OF ARAGONITE SATURATION STATE ON HATCHERY-REARED LARVAE OF THE GREENSHELL MUSSEL PERNA CANALICULUS

The major cultured mussel species Perna canaliculus is now supported by hatchery production, providing the opportunity to explore and optimize environmental parameters to enhance production. Other cultured bivalve larvae have demonstrated performance that is directly correlated to the aragonite saturation state (Omega(ar)) of their tank water, with low or undersaturated water being detrimental and artificially elevated Omega(ar) enhancing productivity. Trials were, therefore, designed to specifically explore Omega(ar) sensitivity in preveliger (0-2 days old, prodissoconch I - PD1) and veliger (2-21 days old, prodissoconch II = PD2) stages of P. canaliculus separately. For the PD experiment, commercial incubation tanks (control Omega(ar) 1.9) were modified to target Omega(ar) 0.5 or 0.8 by elevating pCO(2), or 2.9, 4.5, and similar to 7 by the addition of sodium carbonate. In the control environment, 72.8% +/- 2.9% of fertilized eggs formed viable D veligers within two days; an increased yield of 82.6% +/- 3.8% in Omega(ar) 4.5 was found to be nonsignificant. In comparison, only 12.7% of the Omega(ar) similar to 7 and <1% of the Omega(ar) 0.5 and 0.8 eggs attained the veliger stage, with the remaining underdeveloped or malformed. By 2 days postfertilization, reactive oxygen species were significantly elevated in the undersaturated treatments, whereas DNA damage, lipid hydroperoxides, and protein carbonyls were significantly higher in the Omega(ar) 0.5 and similar to 7 treatments. Antioxidant enzyme levels were significantly lower in these extreme treatments, whereas Omega(ar) 4.5 larvae showed elevated superoxide dismutase, glutathione reductase, and peroxidase levels. Carry-over effects persisted when veligers were transferred to control conditions, with no net recruitment from undersaturated Omega(ar), 29.4% of eggs surviving to pediveliger under control conditions, compared with 33.2% following Omega(ar) 4.5 exposure or 1.9% from Omega(ar) similar to 7. In the PD2 veliger trial, linear shell growth halved in undersaturated water, but was unaffected by elevation of Omega(ar). Mortality rate was consistent across all treatments, suggesting relative resilience to different Omega(ar). It is recommended that hatcheries trial Omega(ar) 4-4.5 enrichment in preveliger incubation water to improve yield and minimize oxidative stress. Preveliger stages present a potential survival bottleneck, and focused research exploring sensitivity to near-future ocean acidification is, therefore. needed.