Estuaries and Coasts DOI 10.1007/s12237-012-9510-2
NOTE
Habitat Affects Survival of Translocated Bay Scallops, Argopecten irradians concentricus (Say 1822), in Lower Chesapeake Bay Ana L. Hernández Cordero & Rochelle D. Seitz & Romuald N. Lipcius & Caitlin M. Bovery & David M. Schulte
Received: 26 September 2011 / Revised: 3 April 2012 / Accepted: 18 April 2012 # Coastal and Estuarine Research Federation 2012
Abstract Bay scallop (Argopecten irradians) populations existed in Chesapeake Bay until 1933, when they declined dramatically due to a loss of seagrass habitat. Since then, there have been no documented populations within the Bay. However, some anecdotal observations of live bay scallops within the lower Bay suggest that restoration of the bay scallop is feasible. We therefore tested whether translocated adults of the southern bay scallop, Argopecten irradians concentricus, could survive during the reproductive season in vegetated and unvegetated habitats of the Lynnhaven River sub-estuary of lower Chesapeake Bay in the absence of predation. Manipulative field experiments evaluated survival of translocated, caged adult scallops in eelgrass Zostera marina, macroalgae Gracilaria spp., oyster shell, and rubble plots at three locations. After a 3-week experimental period, scallop survival was high in vegetated habitats, ranging from 98% in their preferred habitat, Z. marina, to 90% in Gracilaria spp. Survival in Z. marina was significantly higher than that in rubble (76%) and oyster shell (78%). These findings indicate that reproductive individuals can survive in vegetated habitats of lower Chesapeake Bay when protected from predators and that establishment of bay scallop populations within Chesapeake Bay may be viable. Keywords Chesapeake Bay . Argopecten irradians concentricus . Restoration . Survival . Bay Scallop
A. L. Hernández Cordero : R. D. Seitz (*) : R. N. Lipcius : C. M. Bovery : D. M. Schulte Virginia Institute of Marine Science, College of William and Mary, P.O. Box 1346, Gloucester Point, VA 23062, USA e-mail:
[email protected]
Introduction Beginning in the 1930s, bay scallop (Argopecten irradians) populations declined considerably along the Western Atlantic coastline as a result of habitat loss (i.e., decline of seagrass beds), overfishing, and harmful algal blooms (Fegley et al. 2009). In Chesapeake Bay and its vicinity, bay scallop population demise was primarily a result of habitat loss due to adverse anthropogenic effects, eelgrass wasting disease, and damage from the 1933 “Storm King” hurricane (Castagna and Chanley 1973; Orth and Moore 1984). Since the mid1990s, attempts to establish bay scallop populations have been moderately successful in the seaside lagoons (e.g., South Bay) adjacent to Chesapeake Bay (M. Luckenback, personal communication), where the recovery of eelgrass (Orth et al. 2010) has allowed more intensive scallop introduction efforts. Bay scallop establishment has not been attempted within the lower Bay because of concerns that environmental conditions would preclude the survival of reproducing individuals. Recently, however, anecdotal observations of live bay scallops within the lower Chesapeake Bay (P. Freeman and R. Pemberton, personal communication) suggest that the bay scallop can survive for an unknown period of time in this area. Habitat complexity affects the ecological interactions of species, including the abundance and distribution of structure-dependent invertebrates and fish (Hovel and Lipcius 2002). Eelgrass, Zostera marina L., is viewed as the bay scallop’s preferred habitat (Belding 1910; Gutsell 1930; Thayer and Stuart 1974). Larvae and juveniles require structured nursery habitat (Ingersoll 1886; Fay et al. 1983) and favor eelgrass because it provides a spatial refuge from epibenthic and avian predators (Pohle et al. 1991; Ambrose and Irlandi 1992), as well as from siltation (Thayer and Stuart
Estuaries and Coasts
1974; Castagna 1975) by offering an elevated attachment surface. Adult scallops could also benefit from residing in structured habitats because of reductions in predation, decreased siltation, or increased delivery of food. Bay scallops can also occur at high abundance in natural habitats devoid of eelgrass (Marshall 1947) by attaching to other structures, such as small branching algal species, shells, rocks, or sessile animals (Thayer and Stuart 1974; Smith et al. 1988). Preference for complex habitats is also a function of scallop size. Young bay scallops (25 mm SH) had no preference among cobble, algae, eelgrass, and sand (Chintala et al. 2005). Comparable experiments have not been conducted in the field. This study tested whether translocated adults of the southern bay scallop, Argopecten irradians concentricus, could survive during the reproductive season in vegetated and unvegetated habitats of the Lynnhaven River sub-estuary in lower Chesapeake Bay. Our experiment was designed to assess survival as it related to habitat complexity and not predation; therefore, we assessed survival in the absence of predation. Manipulative field experiments were conducted for 3 weeks, after which we evaluated survival of caged adults in eelgrass Z. marina, branching red macroalgae Gracilaria spp., oyster shell, and rubble at three locations.
Methods Scallop Collection and Transplantation On 18 June 2008, scallops ranging from 27.7 to 54.6 mm SH (i.e., the size range of the local population) were collected from Middle Marsh in Back Sound near Beaufort, North Carolina, USA (34˚41.940 N, 76˚35.741 W). On 19 June 2008, the scallops were transported in coolers with moist burlap sacks and ice packs to the Virginia Institute of Marine Science (VIMS), ∼4.5 h away, in Gloucester Point, Virginia, USA. This method of transport greatly reduces handling mortality (Peterson et al. 1996). Salinity at the collection site was 32 psu. Once in VIMS tanks, scallops were gradually lowered to 20 psu at a rate of 2 psu per day and then translocated to enclosures at the three study sites in the Lynnhaven River system. Site Selection The Lynnhaven River system is the southern-most subestuary in Chesapeake Bay (Fig. 1a). This study was conducted at three locations: Broad Bay, northern Linkhorn Bay, and Pleasure House Creek within Lynnhaven Bay (Fig. 1b). These locations were chosen based on the following criteria: (1) seagrass beds existed there historically, and
(2) environmental conditions were suitable for bay scallop survival. In selecting the sites, we also considered the potential for restoring bay scallop populations as part of a larger project and chose sites where hydrodynamic conditions were predicted to be retentive of larvae, as indicated by a hydrodynamic model of the Lynnhaven River system (Lipcius et al. 2008). In the model, a large fraction of oyster larvae spawned in the system, particularly those in Broad Bay, Linkhorn Bay, and Pleasure House Creek, were likely to remain in the system and provide larval replenishment. Experimental Design and Technical Approach The manipulative field experiment was conducted at each location using predator-exclusion enclosures, which were 121-L, cylindrical, plastic containers with mesh windows to allow water flow but prevent predator entry. In addition, a 30-cm-diameter circular mesh roof maximized light penetration into the enclosures. Each enclosure was randomly assigned to one of four habitat treatments: Z. marina (“Zostera” treatment), Gracilaria spp. (“Gracilaria” treatment), oyster shell, or rubble (small granite rocks). Rubble habitat is common in the system and has been used as an alternative substrate for oyster restoration (Craig 2005; Nestlerode et al. 2007). At the time of deployment, there was little seagrass within the Lynnhaven River system. Therefore, eelgrass was collected at Allen’s Island in the York River and transplanted into enclosures. Gracilaria, oyster shell, and rubble were collected on site and placed in the enclosures. Zostera was planted at natural field densities (1,000–1,500 shoots m−2; Orth and Moore 1986), and an equivalent volume of Gracilaria, oyster shell, or rubble (∼10 L) was placed in each treatment as an even layer across the bottom of the enclosure. At each location, there were three replicate blocks of four enclosures (one enclosure with each of the four habitats), for a total of 36 enclosures across the three sites. Enclosures were deployed within the shallow sub-tidal zone (water depth, 1– 1.5 m at MLW). The blocks were placed 80 m apart; within each block, enclosures were spaced 3 m apart. In addition, three replicates of two sets of controls were established in Middle Marsh, North Carolina, to address potential environmental and handling effects on scallop survival associated with transportation and translocation. Enclosures had a sand substrate and were scrubbed occasionally to remove fouling organisms. Scallops were held in coolers for 4.5 h prior to transplantation in the handling controls to expose them to similar handling conditions as those used for the scallops translocated to the Lynnhaven River system. Adult scallops were placed in enclosures at a density of 40 m−2, resulting in 10 adult scallops per 0.25 m−2 enclosure: five scallops 0.05, Student–Neuman–Keuls test; Fig. 3). There was significantly higher survival in the Zostera treatment as compared with the rubble and oyster shell treatments (p100 mm in carapace length, four large oyster toadfish Opsanus tau, and scallop shell fragments; these two enclosures had nearly 100% scallop mortality. Otherwise, in other control enclosures, scallops survived and grew well.
Discussion
Table 2 Analysis of variance for scallop survival (arc-sine square-root transformed) of small size class (
