Reproductive ecology and dispersal potential of varnish clam Nuttallia obscurata, a recent invader in the Northeast Pacific Ocean
Dudas, Sarah E.
Dower, John F.
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The fecundity, larval development, and temperature and salinity tolerances were determined for the varnish clam Nuttallia obscurata (Reeve 1857), a recently introduced species in the Northeast Pacific. Adult varnish clams from 2 populations were collected in British Columbia, Canada throughout the spawning season to determine sex, fecundity, and timing of spawning. Adult varnish clams were also spawned in the laboratory and the larvae reared at a range of temperatures and salinities. The highest larval growth rates were observed in the 20°C and 20 psu treatments. Planktonic duration ranged from 3 to potentially 8 wk, with higher temperatures and salinities resulting in a shorter planktonic phase. Larvae reared at 9°C, and at 10 and 15 psu, grew slowly and survived for a minimum of 1 mo but did not reach metamorphosis. These results indicate that varnish clam larvae have a wide range of salinity and temperature tolerances, but grow optimally at warmer temperatures and higher salinities. Varnish clams have comparable larval environmental tolerances and spawning duration to co-occurring bivalves. However, their fecundity appears to be slightly higher and they reach sexual maturity earlier, potentially providing an advantage in establishing new populations. The lengthy planktonic phase, combined with favourable oceanographic circulation patterns, has contributed to the rapid dispersal and geographic range expansion of the varnish clam in the Northeast Pacific.