Stephen P. Geiger

Increase in Bay Scallop (Argopecten irradians) Populations Following Releases of Competent Larvae in Two West Florida Estuaries

ABSTRACT We propose the release of ready-to-set pediveliger larvae as a restoration strategy for bivalve shellfish. In this study, bay scallop (Argopecten irradians) larvae were released within two West Florida estuaries (Pine Island Sound and Boca Cicga Bay) currently closed to scallop harvest and where local scallop populations arc severely depleted relative to historical abundances. Populations in both estuaries appear to have limited larval supply and show no tendency toward natural recovery after decades of decline. Larvae were either released into enclosures or free released on four separate dates in each estuary. On a given day we used 1, 2, 3, or 4 enclosures per site; multiple release sites; and multiple releases within a year. Assessments were made via several methods, including larval recruitment to collectors, juvenile quadrat surveys, adult timed surveys, and adult transect surveys. In Pine Island Sound, following the initial larval releases in 2003, an isolated recovery in adult scallops was observed at the release site in 2004 followed by a massive resurgence in the local population in 2005. This population declined dramatically in 2006, however, and had completely collapsed by 2007. In Boca Ciega Bay, the series of larval releases did not immediately produce any detectable scallop patches, but the combined releases did immediately precede a population resurgence to levels greater than had been observed in the past three decades. Scallop abundance increased 10-fold at 10 stations in Boca Ciega Bay from 2007 to 2008. In both Pine Island Sound and Boca Ciega Bay, the increases in scallop populations were probably the result of successful survival, growth, and reproduction of the released larvae, followed by successful recruitment and growth of the subsequent generation.

Biological Assessment of Eastern Oysters (Crassostrea virginica) Inhabiting Reef, Mangrove, Seawall, and Restoration Substrates

The eastern oyster, Crassostrea virginica, plays an essential functional role in many estuarine ecosystems on the east and Gulf coasts of the USA. Oysters form biogenic reefs but also live on alternative intertidal substrates such as artificial surfaces and mangrove prop roots. The hypothesis tested in this study was that non-reef-dwelling oysters (i.e., those inhabiting mangrove, seawall, or restoration substrates) were similar to their reef-dwelling counterparts based upon a suite of biological parameters. The study was carried out at six sites in three zones in Tampa Bay on the west coast of Florida using monthly samples collected from October 2008–September 2009. The timing of gametogenesis and spawning, fecundity, and juvenile recruitment were the same for oysters in all four habitats. Oyster size (measured as shell height), density, and Perkinsus marinus infection intensity and prevalence varied among habitats. This study indicates that oysters on mangroves, seawalls, and oyster restoration substrates contribute larvae, habitats for other species, and likely other ecosystem benefits similar to those of intertidal oyster reefs in Tampa Bay. Oysters from alternative intertidal substrates should be included in any system wide studies of oyster abundance, clearance rates, and the provision of alternate habitats, especially in highly developed estuaries.

Isotope sclerochronology of Mercenaria mercenaria, M. Campechiensis, And their natural hybrid form: Does genotype matter?

Abstract Isotopic variation in northern and southern hard clam (quahog) shells is used in studies including paleoecology, paleoclimatology, and archaeology. It is unknown, however, whether species-specific isotopic differences exist. Three genotypes—Mercenaria mercenaria, M. campechiensis, and their natural hybrid form—are found in coastal Florida waters and differentiation of genotypes can be difficult to determine morphologically. This issue may be problematic when using archaeological shells as paleoclimate archives, because genetic analysis cannot be done on such specimens. Their co-occurrence in coastal Florida waters provides a unique opportunity to study whether all three genotypes of modern individuals record the same environmental information preserved as variation in oxygen and stable carbon isotope ratios. A random sample of 49 individuals collected alive at the same time and from the same locality in Pine Island Sound were classified to genotype using allozyme electrophoresis. Three juveniles from each genotype were selected for isotopic analysis to control for ontogenetic effects. Timing of growth increment formation inferred from oxygen isotope ratios reveals similar overall patterns wherein dark (slow growth) increments formed in mid- to late spring and light (fast growth) increments formed in late fall. Results of the mixed model ANOVA (analysis of variance) indicate that no significant species-related differences exist in the variation of oxygen and carbon isotope ratios, although the Kolmogorov-Smirnov goodness-of-fit test detected a systematic difference among δ13C values of M. mercenaria and M. campechiensis comparison and M. mercenaria and the hybrid shell comparison. Any genotype or combination thereof is, thus, suitable for environmental and climate reconstruction using oxygen isotope ratios. The utility of carbon isotope ratios as an environmental proxy, however, remains questionable.

Impacts of Freshwater Management Activities on Eastern Oyster (Crassostrea virginica) Density and Recruitment: Recovery and Long-Term Stability in Seven Florida Estuaries

ABSTRACT Eastern oysters, Crassostrea virginica (Gmelin 1791), were sampled from seven Florida estuaries from January 2005 through December 2007 as part of the prerestoration monitoring and assessment component of the Comprehensive Everglades Restoration Plan. Study locations included Tampa Bay, Mosquito Lagoon, Sebastian River, St. Lucie estuary (3 study sites), Loxahatchee River (2 study sites), Lake Worth Lagoon, and Biscayne Bay. Settled oyster density was monitored twice per year at stations within each study site. Oyster recruitment, water temperature, and salinity were monitored on a monthly basis. Salinity varied greatly among the estuaries, and each study site fell into 1 of 2 primary salinity regimes: one relatively stable and with higher salinities (mean range, 24–35), and the other more variable and with lower salinities (mean range, 12–17). All 7 estuaries were impacted, to varying degrees, by the relatively active 2005 tropical storm season as well as local water management practices during the study. Two of the estuaries, St. Lucie and the Sebastian River, were severely impacted by controlled introductions of freshwater, which decreased salinities below the range that oysters can tolerate. As a result, live oysters were virtually absent from the study sites in both estuaries in 2005, when the freshwater introductions were most pronounced. At the opposite extreme, long-term reduction of freshwater flow into Biscayne Bay has exacerbated already increasing salinities and has resulted in the absence of reef-building oysters at that study site. Oysters were present at all other study sites, but densities were lower in 2005 than in subsequent years because of substantial salinity decreases after tropical storms in 2004 and 2005. The greatest and most stable oyster densities were found in Tampa Bay, where mean oyster density reached 400/m2 by fall 2007. Recruitment was observed at each site on recruitment arrays retrieved from April through December, although the timing, duration, and intensity of the recruitment season varied annually and among study sites. The Tampa Bay, Mosquito Lagoon, Loxahatchee River, and Lake Worth Lagoon sites exhibited a bimodal recruitment pattern with peaks in the spring and fall. At the remaining sites, which were the most strongly affected by water management practices, recruitment patterns were sporadic and inconsistent throughout the study. The lowest recruitment rates occurred in 2005, when the density of settled oysters was also low, presumably because of reduced salinities resulting from a combination of active tropical storm seasons and controlled freshwater introductions.

VARIATIONS IN GROWTH AND REPRODUCTION OF BAY SCALLOPS (ARGOPECTEN IRRADIANS) (LAMARK, 1819) FROM SIX SUBPOPULATIONS IN THE NORTHEASTERN GULF OF MEXICO

Abstract Bay scallops, Argopecten irradians, sustained a valuable commercial and recreational fishery in Florida during the middle part of the last century. In 1994, after decades of declining stocks, state managers closed this fishery to commercial harvest and severely limited the recreational harvest. In Florida, most bay scallops reproduce only once, generally during the fall at an age of roughly 12. The current 10-week recreational harvest season, July 1 through September 10, occurs at a time when somatic and reproductive tissues are changing rapidly in preparation for the fall spawning season. This study describes changes in tissue weights (reproductive, somatic, visceral) during the 2002 harvest season in scallops collected from six subpopulations along Floridas Gulf of Mexico coast. We observed tissue-specific patterns of weight change during the 7-month study and also noted regional differences. In three Panhandle sites (St. Joseph Bay, Lanark Village, and St. Marks), a shift from somatic growth to reproductive growth occurred later in the year and was more intense than in peninsular sites (Steinhatchee, Homosassa and Anclote). We also monitored recruitment of juvenile scallops at three of the sites from July of 2001 through June of 2003. There were protracted fall and winter peaks within a background of constant, low-level recruitment. The harvest limits allow each person to collect two gallons (7.55 L) of whole scallops or one pint (0.47 L) of adductor muscle meat each day. In June, just prior to the harvest season, the number of whole scallops that would be collected varied significantly between sites (range 55–203), as did the equivalent yield of adductor muscles (range 143–342). Muscle size peaked in August or September, depending on location. The allowable number of scallops collected within the volume-based limits had decreased (41–112 whole scallops or 84–116 shucked scallops) and between-site variability in the numerical harvest was lower.

Protracted Recruitment in the Bay Scallop Argopecten irradians in a West Florida Estuary

ABSTRACT Many studies have indicated that annual spawning of bay scallops (Argopecten irradians) peaks during discrete and limited periods each year. Spawning in most Florida bay scallop subpopulations has been shown to occur in fall, whereas more northerly U.S. populations typically spawn in late spring or summer. In this article we describe our efforts to expand our understanding of the seasonality of bay scallop recruitment dynamics in Florida. Visual surveys were conducted by divers each spring from 1994 to 2009 to estimate adult scallop abundance. Adult abundance was low (6.1 scallops/600 m2) during the first 3 y of the study (1994 to 1996), prompting a 7-y restoration effort intended to enhance the number of spawning adults and thereby enhance the local production of larval scallops. Adult abundances increased to an average of 21.9 scallops/600 m2 in 1997 to 2006, and then rose dramatically to an average density of 154.8 scallops/600 m2 in the most recent years (2007 to 2009). Artificial recruit collectors (n = 12) were deployed monthly near the Anclote River estuary beginning in 1997 and were allowed to soak for 2 mo at a time. Each collectors deployment period overlapped with the preceding and following traps deployment period by 1 mo. The project is ongoing, but only data collected through December 2009 is included here (bay scallops recruited to the collectors during 163 of the 185 deployment periods). For the entire study period, the average recruitment rate was 0.3 scallops/collector/day, the maximum average for a single deployment period was 5.5 scallops/collector/day during November 2001 to January 2002, and the highest rate for a single collector was 19.6 scallops/collector/day during November 2001 to January 2002. In most years, the collectors retrieved in late fall and early winter had the highest settlement rate; a secondary recruitment peak was observed in the spring. A period of protracted recruitment (December 2005 to December 2009) occurred, during which scallops recruited to at least 1 of the 12 deployed collectors deployed during 53 consecutive deployment periods. The average recruitment rate for this protracted period was 0.4 scallops/collector/day; the maximum recruitment rate for a single deployment period (3.5 scallops/collector/day) and individual collector (17.7 scallops/day) occurred during December 2008 to February 2009. Early in our study, scallops were detected in a majority of our recruit collectors, and a protracted period of recruitment (October 2001 to February 2004) coincided with the multiyear restoration effort. However, the recent high adult densities and protracted period of recruitment occurred in the absence of any active restoration in this subpopulation, suggesting that, at least within the Anclote River estuary, the population has stabilized for the short term.

Abundance and Distribution of Large Marine Gastropods in Nearshore Seagrass Beds Along the Gulf Coast of Florida

ABSTRACT Local abundance was estimated and distribution determined for selected large gastropod species based on observations made during underwater visual surveys at 10 sites along the Gulf coast of Florida each summer from 2009 through 2012. The total number of tulip snails (Fasciolaria spp., including the true tulip, Fasciolaria tulipa, and banded tulip, Fasciolaria lilium), lightning whelk (Busycon sinistrum), and horse conch (Triplofusus giganteus) were counted at 190 stations (each 600 m2) each year in shallow-water seagrass beds. Tulip snails were observed most frequently, with a mean density of 1.93 ± 3.56 snails/ 600 m2, with substantially fewer lightning whelks (0.29 ± 1.04/600 m2) and horse conchs (0.10 ± 0.37/600 m2) observed. Horse conchs were distributed more evenly across the 4 Gulf coast regions studied: Panhandle, Big Bend, Nature Coast, and South. Tulip snails were most abundant in the Panhandle and the South, whereas lightning whelks were found predominantly in the South. Snail counts peaked in 2010 and were greatest at the Pine Island Sound site, although mean density was greatest in Sarasota Bay (2.2 snails/600 m2). Snails were observed most frequently at the St. Joseph Bay site, where they were present at 74 of the 80 stations surveyed. Statewide commercial fisheries landings data were examined for years 1994 through 2011 and totaled 130,710 true tulip snails (banded tulip snails were not included), 72,230 lightning whelks, and 33,087 horse conchs. The total number landed of both lightning whelks and horse conchs was greater on the west coast of Florida, whereas the total number of true tulip snails landed was greater on the east coast.

FACTORS INFLUENCING REPRODUCTIVE ATTRIBUTES OF STONE CRABS (MENIPPE) IN TAMPA BAY, FLORIDA

ABSTRACT Understanding aspects of reproduction is important for studies of life history strategy and for resource management. The influences of nine factors (five intrinsic, four extrinsic) on the reproductive attributes egg diameter, egg dry weight, and clutch size (i.e., number of eggs in egg mass) of female stone crabs (genus Menippe (Say)) from Tampa Bay, FL, waters were investigated. Two intrinsic factors influenced reproductive attributes: carapace width was positively correlated with clutch size, and egg stage was positively related to egg size. Three intrinsic factors—genotype class, damaged or missing pleopods, and missing claws or legs—had no influence on any reproductive attribute. The four extrinsic factors each influenced at least two reproductive attributes. Egg diameter and weight were significantly larger and clutch size was significantly smaller (1) in females uninfested by Octolasmis mülleri; (2) during the early part of the spawning season, when water temperature was 27°C or less; and (3) during the first year of the 3-y study. In addition, egg diameter varied significantly among season/year combinations. In all cases, when egg diameter and weight decreased, clutch size increased; suggesting that, in female stone crabs, selection for filling the available abdominal space with eggs is strong. Large eggs are known to produce larvae of high fitness in crabs. Because the largest eggs are produced during the early part of the spawning season, females should be protected from harvest during that time. Shortening the harvest season in spring would eliminate those females from vulnerability to the fishery.

Spat Settlement of the Smooth Scallop Flexopecten glaber (Linnaeus, 1758) and Variegated Scallop Chlamys varia (Linnaeus, 1758) in Amvrakikos Gulf, Ionian Sea (Northwestern Greece)

ABSTRACT The seasonal variation and spat recruitment pattern of the scallops Flexopecten glaber and Chlamys varia in the protected aquatic ecosystem of the northwestern Amvrakikos Gulf (Natura, 2000) were examined by using a combination of plankton sampling and spat collection techniques during the spring and summer of 2007. The presence of the larvae was reported in all samples from the beginning of May to the end of August. Peak numbers were obtained at the beginning of June and in mid-July. The highest settlement density was recorded at a depth of 8 m below the surface, indicating the most suitable placement for the spat collectors despite the hypoxic bottom layer underneath.

Calico Scallop Argopecten gibbus Abundance on the Cape Canaveral Bed and on Florida's Gulf of Mexico Shelf

Abstract Annual landings of the calico scallop Argopecten gibbus fishery in the southeastern United States increased from less than 3,000 kg in 1959 to 19.5 million kg of adductor muscle meat in 1984. The fishery began to collapse in early 1986 in Florida and fell below 1 million kg/year in the mid-1990s. From 2002 through 2011, the only reported landings were 550 kg in 2009, but annual landings of less than 200,000 kg beginning in 2012 indicate the resource rebounded enough in that year to create renewed interest in the fishery. When the fishery was developing, the National Marine Fisheries Service (NMFS) sponsored 59 cruises (1956 through the mid-1970s) to map the distribution of the stock and found the calico scallop stocks on Floridas east coast principally occurred around the 40-m depth contour near the shelf break. By the early 1980s, surveys were no longer routinely conducted. Two surveys in the mid-1990s were dedicated to investigating the collapse of the stock. The present study consisted of eight cruises from 2004 to 2006: four each to the beds off Cape Canaveral on the eastern coast and the poorly documented beds off southwestern Florida. Cruises studying baitfish and cruises in the Gulf of Mexico by the Southeast Area Monitoring and Assessment Program (SEAMAP) yielded data that provided additional calico scallop abundance estimates. Abundant, albeit small, scallops were found on both coasts during three of the four cruises to each coast though none were detected in fall 2004 on either coast. Our results concur with those historic NMFS surveys conducted prior to the period of heaviest exploitation of the resource (1974–1999); the center of distribution for calico scallops on the Cape Canaveral beds still occurs near the 40-m depth contour. The essential habitat for calico scallops, shell base, which was suspected to have declined during the most active fishery periods, was found to have persisted consistently at that depth. There were few scallops with a shell height greater than 40 mm, the minimal size considered acceptable for commercial exploitation.