Induction of larval settlement and metamorphosis of Mercenaria mercenaria using excess Ca2＋and Mg2+alone or in combination

Abstract

The induction effect of excess Ca²⁺ and Mg²⁺ alone or in combination on settlement ^{and metamorphosis of} Mercenaria mercenaria larvae were studied by initiating ion supplementation at two different developmental stages. ^Pediveligers were supplemented with a range of excess Ca²⁺ (0–18 mM), Mg²⁺ (0–40 mM) and Ca^2＋/ Mg²⁺ (0–7.5/0–37.5 mM), respectively. Results showed excess Ca²⁺ and Mg²⁺ alone or in combination could induce settlement and ^{metamorphosis of M. mercenaria. The o}ptimal concentrations of Ca²⁺, Mg²⁺, and Ca²⁺/Mg²⁺ were 10 mM, 20 mM and 3.125/15.625 mM, respectively. The supplementation of the above optimal concentration of ions from D-shaped larvae stage also significantly induced larval metamorphosis (P < 0.05), and at the same concentration, the induction effect was better than that initiating from pediveliger stage. In addition, compared with the control group, ion supplementation from D-shaped larvae stage significantly increased the survival rate of pediveligers (P < 0.05) and prolonged the planktonic duration. The longer the planktonic duration, the larger the larval size at the end of the planktonic stage and the higher ^{metamorphosis rate of} larvae. In the hatchery seed production of M. mercenaria, it is recommended to supplement 3.125/15.625 mM Ca^2＋/ Mg²⁺ from the D-shaped larvae stage to induce the settlement and metamorphosis.