Mercenaria mercenaria introductions into Florida, USA, waters: duration, not size of introduction, influences genetic outcomes

Abstract

Wild stocks of hard clams from the genus Mercenaria historically supported commercial fisheries, but, as these stocks have been depleted, market demand has been filled by clams produced in aquaculture operations. Along the east coast of the USA, M. mercenaria is indigenous and used for aquaculture. Indigenous Gulf of Mexico (GOM) clam populations consist of M. campechiensis, a species less suited to aquaculture because of its short shelf life. Aquaculture operations have introduced M. mercenaria into GOM waters, resulting in altered Mercenaria species composition to the detriment of M. campechiensis. Where M. mercenaria have been introduced, the population now includes both M. mercenaria and M. campechiensis, and hybrids are common. This is particularly evident where commercial aquaculture is ongoing and introductions are, therefore, continuous. Where shortterm introductions have occurred for research purposes, M. mercenaria is restricted to oyster reefs. At those sites, and at sites where no documented introductions of M. mercenaria have occurred, hybrids are rare and M. campechiensis dominate the more common sand/seagrass habitats. As the 2 species continue to interbreed, pure M. campechiensis will become rarer and hybrids more common, potentially resulting in reduced fitness of M. campechiensis from GOM waters. The trend towards hybrids may be ameliorated by an increased intensity of gonadal neoplasia in the hybrid clams. These results indicate that M. mercenaria introductions into the GOM, even on the relatively small scale of scientific research efforts, have a substantial and long-lasting influence on the genotype composition of hard clam populations in GOM waters.

Ocean Acidification Has Multiple Modes of Action on Bivalve Larvae

“…The Mediterranean mussel broodstock used in previous experiments [ 20 ] were obtained from Carlsbad Aquafarm located on Agua Hedionda Lagoon, CA, where the stock has been farmed for roughly 20 years and shows no indication of hybridization with other mytilids based on morphological characteristics (Mark Smith, manager, pers. comm) or genetic analyses [ 111 ]. The outer lagoon, where the mussel farm is located, is well flushed by the Pacific Ocean and this coastal region does not experience the significant seasonal upwelling found along the central Oregon coast where the M .…”

Size-dependent pH effect on calcification in post-larval hard clam Mercenaria spp.

“…Although this was not an a priori factor in our experimental design, the Source differences provide important insight for future studies. Genetic analyses of northern hard clams Mercenaria mercenaria from the Florida hatchery have shown that nearly 25% of the hard clams in the hatchery are hybrids with the southern hard clam M. campenchiensis (Arnold et al 2009). The southern hard clam is generally believed to have a higher growth rate, and this would support our findings of higher calcification in the clams from the FL hatchery; however, the differences in growth among northern, southern, and hybrid clams are complex and vary with habitat (Arnold et al 1998).…”

“…were obtained from Cherrystone Aqua Farms (Cheriton, Virginia) and Southern Cross Sea Farms (Cedar Key, Florida). Although we intended on using M. mercenaria in our experiments, Arnold et al (2009) documented that M. mercenaria hybridizes with M. campechiensis in the Southern Cross Sea Farms hatchery, with roughly 25% of the hard clams having the hybrid genotype and the remainder being pure M. mercenaria. Differences exist in growth rates among genotypes and vary with environmental factors (Dillon & Manzi 1989, Arnold et al 1996, with hybrids typically growing faster.…”

Biodeposition, respiration, and excretion rates of an introduced clam Mercenaria mercenaria in ponds with implications for potential competition with the native clam Meretrix meretrix in Shuangtaizi estuary, China

“…Several studies have concentrated on the seeding breeding, cultivation, and growth performance of M. mercenaria (Weiss et al, 2002;Zhang et al, 2003;Chung et al, 2007;Weiss et al, 2007;Zarnoch and Schreibman, 2008;Arnold et al, 2009;Wall et al, 2011Wall et al, , 2013, but only a few have investigated its physiological ecology (Sma and Baggaley, 1976;Grizzle et al, 2001;Wen et al, 2004;Parent et al, 2008). In addition, suspension-feeding bivalves are well known for their active biodeposition capacity.…”

“…For example, the Asian clam Corbicula fl uminea modify invaded habitats to the point where indigenous species can no longer survive (Gonzalez et al, 2008;Sousa et al, 2009;Simard et al, 2012). The zebra mussel D reissena polymorpha have caused reductions in native fi lter-feeders (Naddafi et al, 2007;van Appledorn et al, 2007), and the hard clam M. mercenaria have a substantial and long-lasting infl uence on the genotype composition of the hard clam populations in Gulf of Mexico waters (Arnold et al, 2009). Surprisingly, only a few quantitative or experimental studies have examined the impacts of introduced bivalves on the native ecologically and commercially important species.…”