Eggs and early larvae of the bay anchovy,Anchoa mitchilli,and the weakfish,Cynoscion regalis,in lower Chesapeake Bay with notes on associated ichthyoplankton

The seasonal abundance and spatial distribution of eggs and early larvae of the bay anchovy,Anchoa mitchilli, and the weakfish,Cynoscion regalis, were determined from plankton collections taken during 1971–1976 in the lower Chesapeake Bay. Eggs and larvae of the bay anchovy,Anchoa mitchilli, dominated the ichthyoplankton, making up 96% of the total eggs and 88% of all larvae taken. A comparison of egg and larval densities from the lower Chesapeake Bay to existing data from other East Coast estuaries suggested that Chesapeake Bay is a major center of spawning activity for this species.Anchoa mitchilli spawning commenced in May when mean water column temperatures approached 17°C and abruptly ceased after August. Eggs and early larvae presented a continuous distribution throughout the study area during these months. Eggs and larvae of several sciaenid species, especiallyC. regalis, ranked second in numerical abundance. Larval weakfish were consistently taken in late summer of each sampling year but peak abundance and distribution was observed in August 1971. Sciaenid eggs exhibited a distinct polyhaline distribution with greatest concentrations observed at the Chesapeake Bay entrance or along the Bay eastern margin. Analysis of sciaenid egg morphometry and larval occurrence suggested spawning activity of at least four species. Additional important species represented by eggs and/or larvae in the lower Chesapeake Bay wereHypsoblennius hentzi, Gobiosoma ginsburgi, Trinectes maculatus, Symphurus plagiusa andParalichthys dentatus with the remaining species occurring infrequently.     

Early life history of the red drum,Sciaenops ocellatus (Pisces: Sciaenidae), in Tampa Bay,Florida

The distribution, hatching dates, growth, and food habits of larval and juvenile red drum (Sciaenops ocellatus) in Tampa Bay, Florida, are described. From September 1981 through November 1983, 800 larvae and 7,536 juveniles (98%<100 mm SL) were collected, primarily with plankton nets and bag seines. Analysis of otoliths and length-frequency distributions indicate that spawning took place from mid-August through late November with a major peak during October in 1981 and 1982. Larvae became less abundant, but increased in size, from the mouth to the upper bay, indicating that spawning took place in the bay mouth or nearshore waters. At about 8 mm SL (17 days old) larvae settled out along the bay shore before migrating toward low salinity backwater areas. Juveniles grew to about 55 mm SL by the end of December and 303 mm SL by the end of their first year. Young red drum gradually moved back into the bay with increased size and age. Eighty-five percent of larval stomachs, examined were empty; those with food contained copepods almost exclusively. Fewer than 7% of juvenile stomachs were empty. Small juveniles fed primarily on mysids, amphipods, and shrimp, whereas larger juveniles fed more on crabs and fish. Changes in diet were noted with growth, but few differences were seen among areas or habitat types.     

Recruitment failure of the bay scallop,Argopecten irradians concentricus,during the first red tide,Ptychodiscus brevis,outbreak recorded in North Carolina

In the presence of the first recorded red tide (Ptychodiscus brevis) outbreak in North Carolina, autumn 1987 recruitment of bay scallops (Argopecten irradians concentricus) in the state’s most productive scallop beds was a virtual failure. Recruitment averaged across all of Bogue and Back sounds was only 2% of the mean of three previous red tide-free (control) years. Only from central Core Sound northward, where the red tide occurred later and not as intensively, was bay scallop recruitment normal (93% of control years). Mortality of adult scallops from early December 1987 to late January 1988, while red tide was at bloom concentrations but fishing was prohibited, was 21%. No comparable natural mortality data exist for control years because intense fishing mortality in this period is confounded with natural mortality. Data on abundance of articulated pairs of empty shells strongly suggest that the red tide caused mortality of both adult and newly recruited bay scallops. Bay scallop recruitment in autumn 1988 again failed to restock the traditionally productive scallop beds in western Bogue Sound and in Back Sound, perhaps because the only concentrations of spawners surviving the red tide in central Core Sound and further north were too far distant for successful transport of bay scallop larvae in sufficient abundance to these traditional beds. This potential explanation implies continuing impact of the red tide on North Carolina’s bay scallop fishery until spawning populations increase in Back Sound and western Bogue Sound.     

Distribution and abundance of the cownose ray,Rhinoptera bonasus,in lower Chesapeake Bay

Aerial surveys were conducted in the lower Chesapeake Bay during 1986–1989 to estimate abundance and examine the distribution of the cownose ray,Rhinoptera bonasus, during its seasonal residence, May–October. Most of the survey effort was concentrated in the lower and mid-bay regions. Cownose rays appeared uniformly distributed across the bay during mid-summer, but were more abundant in the eastern portion of the bay during migration. North-south distribution varied and reflected the general seasonal migration pattern. Mean abundance increased stepwise monthly from June through September and declined dramatically in October with their emigration from the bay. Abundance estimates from individual surveys varied. The greatest range of individual survey abundance estimates occurred in September (0–3.7×10⁷ cownose rays0 due to high variation in school size and abundance between surveys. Monthly mean cownose ray abundance ranged from 0 in May and November to an estimated maximum of 9.3×10⁶ individuals in September. The magnitude of the population suggests that the cownose ray plays an important role in the trophic dynamics of the Chesapeake Bay ecosystem. The historical data were insufficient to determine whether the population has increased, but these surveys provided the baseline data which would allow future investigation of cownose ray population dynamics in lower Chesapeake Bay.     

Life cycle and population structure of the polychaeteFicopomatus enigmaticus (Serpulidae) in Mar Chiquita coastal lagoon,Argentina

Ficopomatus enigmaticus, a polychaete inhabiting the subtidal zone in the Mar Chiquita coastal lagoon, builds reef-like aggregates that facilitate silt accumulation. To describe the life cycle, samples were take monthly from September 1984 to September 1985. In contrast with other polychaetes, it has two oocyte generations per year; maturation of the oocytes takes approximately 4 mo. Temperature level and day length regime do not appear as environmental signals to the onset of oogenesis, although they possibly affect oogenesis growth. Two periods of spawning and recruitment were observed in November–December and April–May, when water temperature is above 18°C. Hermaphroditic individuals were not found. Sex ratio was male-biased in all months, significantly in November, February, and August (p<0.001). Monthly size-frequency distributions show distinct year-classes with early (November–December) and late (April–May) recruitment. Early recruited cohorts have two spawning periods during a 24-mo lifespan. Late cohorts have one spawning period during their 20-mo lifespan. The life cycle of this species can be summarized as follows: annual iteroparous—1 to 2 batches of small eggs per female during each lifespan, free spawning, planktotrophic larvae, sedentary suspension-feeder worms.     

Early life history of spotted seatrout,Cynoscion nebulosus (Pisces: Sciaenidae), in Tampa Bay,Florida

During two years of sampling, 747 larval and 1,379 juvenile spotted seatrout,Cynoscion nebulosus, were collected in Tampa Bay, Florida; 93% were less than 75 mm SL. Length-frequency distributions and otolith analysis showed that spawning took place from early April until late October. Two seasonal spawning peaks (spring and summer) were made up of many smaller peaks, apparently timed with moon phases. Plankton samples contained larvae that measured up to about 7 mm SL (17 d old). Larvae collected from an upper bay station were less numerous and larger than those collected at other stations. The presence of small larvae from middle and lower bay stations indicated that spawning probably took place from the middle bay to nearshore Gulf waters. Juveniles used seagrass beds as their major habitat, but they were also found in unvegetated backwaters. Spotted seatrout grew to about 35 mm SL in 2 months, 84 mm SL in 4 months, and 140 mm SL in 6 months. Eighty-five percent of the alimentary tracts in larvae were empty; those with food contained primarily copepods. Eleven percent of the stomachs of juveniles were empty. Fish and shrimp were the most important food groups in the diets of fish >15 mm SL. Intraspecific comparisons of diets showed high dietary overlap between larval fish and those measuring 8–15 mm SL and among size classes >15 mm SL.     

Chaetognaths in lower Narragansett Bay

A field study of the chaetognaths of lower Narragansett Bay was conducted from March 1975 through May 1976.Sagitta elegans Verrill 1873 was the predominant species, present in all months except August.S. elegans was most abundant in April and May in both 1975 and 1976. Maximum densities exceeded 100 m^?3 in May 1976. It appeared thatS. elegans was replenished in Narragansett Bay by influxes of chaetognaths from Rhode Island Sound. This species was restricted to the sound when bay temperatures exceeded 15 °C. In the bay, maturing chaetognaths were found deeper in the water column than juveniles. This phenomenon may have limited the frequency of older animals in bay plankton samples by concentrating them extremely close to the bottom, out of the reach of conventional plankton nets. The presence of chaetognath eggs in samples taken in Rhode Island Sound, and their absence from bay samples, indicated that breeding took place primarily offshore. Size-frequency analysis showed that peak breeding activity occurred in January, April, and July.     

Effects of thermal discharges on the microstructural growth ofMercenaria mercenaria

The effects of thermal discharges from the Oyster Creek Nuclear Generating Station at Barnegat Bay, New Jersey, are recorded in the microstructural growth ofMercenaria mercenaria, a common coastal marine pelecypod. The analysis of the shell microstructure shows that this bivalve acts as an effective monitor of the environmental conditions existing in the marine waters adjacent to the power station. Many physiological and environmental events such as spawning, winter (freeze) shocks, summer (heat) shocks, thermal shocks, tidal cycles, and major storms are clearly recorded in the shell microstructure. The exact time of occurrence of these events can be determined by counting daily growth increments backwards from the outer shell margins of freshly killed individuals. Microstructural growth patterns reflected in Barnegat Bay specimens indicate that these pelecypods were affected mainly by temperature extremes, temperature variations, tides, type of substratum, and age. Growth patterns in specimens from areas surrounding Oyster Creek (affected by thermal effluent) are significantly different from those from other bay localities (unaffected by thermal effluent).Mercenaria mercenaria within approximately a 1.6km radius of Oyster Creek show a lower summer growth rate (10 percent to 25 percent lower) and a greater number of growth breaks (2 to 6 more per clam) than those away from the creek. The lower summer growth rates occur in bivalves subjected to the effluent because the added heat during the summer months causes water temperatures to exceed a critical threshold for optimum growth in the species. The greater number of growth breaks takes place, in turn, because many of the breaks (thermal shock breaks) are generated by rapidly fluctuating temperatures associated with abrupt shutdowns, massive load reductions and rapid renewal of operations following shutdowns or load reduction periods at the nuclear power station. In addition, the effluent may be upsetting natural spawning events in the clams when abrupt changes in power station operations overlap with spawning periods. In this respect, spawning may be precluded by sharp temperature changes which result in physiological shocks to the animal.     

Life history characteristics of the northern pipefish,Syngnathus fuscus, in Southern New Jersey

The northern pipefish,Syngnathus fuscus, is an abundant component of estuarine faunas along the east coast of the United States, yet little is known of its life history. Northern pipefish were collected from several areas in southern New Jersey, particularly the Great Bay-Little Egg Harbor estuarine system, to determine aspects of its reproduction and to estimate its age and growth. A monthly gonadosomatic index for both males and females indicated a spring through summer spawning period, with a peak in reproductive activity during June. A male brood pouch-somatic index indicated a prolonged male brooding period over spring through summer, with a peak in June. The size of males with broods ranged from 119–222 mm total length (TL), and the number of eggs within a brood varied from 45 to 1380. Individual embryos within a brood were identical in development stage, suggesting each brood resulted from a single mating. Young-of-the-year occurred in samples from May through November, with peak abundance in June. Individuals in this year class were extremely variable in size by the end of the first growing season, varying from 5 mm TL to 200 mm TL in November. At approximately 1 yr of age, individuals were 70–220 mm TL and many were of sufficient size to reproduce, indicating that the events of the first year of life for this species are of central importance to an understanding of its population dynamics.     

Habitat Affects Survival of Translocated Bay Scallops, Argopecten irradians concentricus (Say 1822), in Lower Chesapeake Bay

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.     

Population Structure of Adult Blue Crabs, <Emphasis Type="Italic">Callinectes sapidus</Emphasis>, in Relation to Physical Characteristics in Barnegat Bay,New Jersey

Blue crabs (Callinectes sapidus) are an important species in coastal or lagoonal estuaries where adult population characteristics may differ as compared to drowned-river estuaries. Barnegat Bay, in southern New Jersey, is composed of two large embayments: one without and one with a salinity gradient. We tested the influence of physical characteristics on the abundance, sex ratio, and size of adult blue crabs and examined variation in measures of reproductive potential (e.g., sperm stores) in both sexes in Barnegat Bay from June to September, 2008–2009. Population structure was distinct between the embayments due to sex-specific responses to salinity: male abundance was negatively correlated with salinity whereas adult females were more abundant in high salinity because of proximity to Barnegat Inlet. This produced high sex ratios in low salinity areas and low sex ratios in high salinity areas. Summer was a growing season for adult males while in late summer-early fall, juvenile males recruited to the adult size class. The spawning season lasted from May to August and ovigerous females were concentrated near the inlets. Information on female sperm stores and ovarian development identified two cohorts of adult females: females that will spawn in the current summer and females that will not spawn until the following summer. Thus, not all adult females near the spawning grounds were members of the current spawning stock. This suggests that annual estimates of spawning stock size which overlook the proximity of females to spawning are overestimating the current spawning stock in Barnegat Bay and other estuaries.     

Seasonal growth in the bivalveMacoma balthica near the southern limit of its range

Shell-length growth inMacoma balthica from San Francisco Bay, California, as measured on living animalsin situ, is highly seasonal despite a mild Mediterranean climate: a long period of near non-growth from May to the following February is followed by a short period of rapid growth between March and May. The rapid-growth period follows the spawning period during January/February and ends as water temperature rises above about 15°C. Despite the shortness of the growth period,M. balthica grows larger at a given age in San Francisco Bay than is recorded elsewhere in the world. Application of a model, developed elsewhere from these same field measurements, shows that (1) measurable growth occurs during the summer/autumn/early winter “nongrowth” period, (2) there is an autumn recruitment, and (3) both spring and autumn recruits combine to form a single “one-year-old” size grouping. None of these features is detectable through growth-ring analysis of field samples, apparently because of indistinct climatic seasons, or through size-frequency histogram analysis because of the combined effects of slow growth and intermittent recruitment.     

Distribution patterns of zooplankton in Tomales Bay,California

Spatial patterns of abundance of the zooplankton of Tomales Bay, California, were studied over one year from August 1987 to September 1988. Samples were taken on six transects up the long axis of the bay, and the species composition and abundance of common species were determined. Distribution patterns were similar to those observed in other estuaries and bays, with species from nearby neritic waters occurring in the outer bay and a few resident species in the inner bay. This pattern may be best explained by size-selective predation within the bay. Most alternative explanations can be ruled out for Tomales Bay, except for possible temperature effects on cool-temperate neritic species. The four common species ofAcartia in Tomales Bay were in two subgenera, each of which included a neritic species and a smaller inner-bay species. The occurrence of the smaller of each pair in the inner bay, which has been observed forAcartia and other species in other estuaries and bays, may also be a result of size-selective predation.     

Tracking cohorts: Analysis of migration in the early life stages of an estuarine fish

Larvae and juveniles are often most abundant at some distance from where spawning occurs. Such apparent distribution shifts can be the result of larval migration, seasonal shifts in the distribution of spawners, or spatial heterogeneity in mortality. In the present study, a cohort-based method was adopted to test for larval migration of bay anchovy (Anchoa mitchilli) and to estimate its rate and timing. A spatially and temporally extensive series of ichthyoplankton samples was collected in the lowest 122 km of the Hudson River in summer 1998. Bay anchovy eggs and young-of-year individuals were abundant (mean density=1.6 m^?3 and 0.95 m^?3, respectively). Daily age used to define cohort membership was determined from otoliths. Age and length were strongly related (R²=0.74). The age-length relationship varied over the season such that early-season bay anchovy hatched in June grew more rapidly than later-season anchovy hatched in August. Cohorts were defined as week-long birth-data classes, and net migration patterns of 11 cohorts were analyzed. Mean location shifted upriver as cohorts increased in age to 6 wk, at a net rate of about 0.6 km d^?1. Cohort abundance usually decreased over time in downriver regions, but usually increased in upriver regions. The cohort analysis confirmed that the upriver shift in distribution of early-stage anchovy is not entirely due to changes in adult spawning behavior or to clines in larval mortality, and must be partly the result of larval migration.     

Influence of Environmental Factors on Spawning of the American Horseshoe Crab (<Emphasis Type="Italic">Limulus polyphemus</Emphasis>) in the Great Bay Estuary,New Hampshire,USA

The Great Bay Estuary, New Hampshire, USA is near the northern distribution limit of the American horseshoe crab (Limulus polyphemus). This estuary has few ideal beaches for spawning, yet it supports a modest population of horseshoe crabs. There is no organized monitoring program in the Great Bay Estuary, so it is unclear when and where spawning occurs. In this 2-year study (May through June, 2012 and 2013), >5,000 adult horseshoe crabs were counted at four sites in the estuary. The greatest densities of horseshoe crabs were observed at Great Bay sites in the upper, warmer reaches of the estuary. Peaks of spawning activity were not strongly correlated with the times of the new or full moons, and similar numbers of horseshoe crabs were observed mating during daytime and nighttime high tides. While many environmental factors are likely to influence the temporal and spatial patterns of spawning in this estuary, temperature appears to have the most profound impact.     

Seasonal occurrence of larval and juvenile fishes in a Virginia Atlantic coast estuary with emphasis on drums (Family sciaenidae)

The seasonal occurrence and relative abundance of larval and juvenile fishes, particularly members of the family Sciaenidae, from a Virginia Atlantic coast estuary were determined from ichthyoplankton and otter trawl collections made from March 1979 to March 1980. The larvae of 19 species in 14 families were identified in the ichthyoplankton. Larvae of the engraulid, Anchoa mitchilli (bay anchovy), and the atherinid, Menidia menidia (Atlantic silverside), dominated the samples and made up 13 and 22%, respectively, of the 9,440 larvae collected. Peak occurrence of all larvae was from May to August. The juveniles of 28 species in 19 families were identified from otter trawl collections. Juvenile sciaenids numerically dominated the trawl collecions and made up 68% of the trawl catch. Juvenile density peaked during September through December.     

Contrasting Growth Patterns of Suspension-Feeding Molluscs (Mercenaria mercenaria, Crassostrea virginica, Argopecten irradians, and Crepidula fornicata) Across a Eutrophication Gradient in the Peconic Estuary, NY, USA

While many coastal ecosystems previously supported dense meadows of seagrass and dense stocks of bivalves, the impacts of overfishing, eutrophication, harmful algal blooms, and habitat loss have contributed to the decline of these important resources. Anthropogenic nutrient loading and subsequent eutrophication has been identified by some researchers as a primary driver of these losses, but others have described potential positive effects of eutrophication on some estuarine resources. The Peconic Estuary, Long Island, NY, USA, offers a naturally occurring nutrient-loading gradient from eutrophic tidal creeks in its western reaches to mesotrophic bays in the eastern region. Over 2 years, we conducted an experiment across this gradient to examine the effects of eutrophication on the growth of estuarine species, including juvenile bivalves (northern quahogs (Mercenaria mercenaria), eastern oysters, (Crassostrea virginica), and bay scallops (Argopecten irradians)) and slipper limpet (Crepidula fornicata). Water quality and phytoplankton community biomass and composition were concurrently monitored at each site, and the effects of these variables on the growth of estuarine species were analyzed with multiple regression model. Eutrophication seemed to impact shellfish through changes in the quality of food and not the quantity since the growth rates of shellfish were more often correlated with densities of specific cell types or quality of seston rather than bulk measures of phytoplankton and organic seston. Northern quahogs and eastern oysters grew maximally within eutrophic locales, and their growth was positively correlated with high densities of autotrophic nanoflagellates and centric diatoms in these regions (p?<?0.001). The growth rates of northern quahogs were also positively correlated with relative water motion, suggesting an important role for tidal currents in delivering seston to suspension feeders. Bay scallops and slipper limpets were negatively impacted by eutrophication, growing at the slowest rate at the most eutrophic sites. Furthermore, bay scallop growth was negatively correlated with densities of dinoflagellates, which were more abundant at the most eutrophic site (p?<?0.001). These results suggest that nutrient loading can have significant but complex effects on suspension-feeding molluscs with select species (e.g., oysters and clams) benefiting from eutrophication and other species performing poorly (e.g., scallops and slipper limpets). Future management approaches that seek to restore bivalve populations will need to account for the differential effects of nutrient loading as managers target species and regions to be restored.     

Population structure, growth rates, and seasonal abundance of twoSyngnathus pipefish species

Northern pipefish,Syngnathus fuscus, and dusky pipefish,Syngnathus floridae, are among the most abundant ichthyofauna components of the Chesapeake Bay, USA, eelgrass beds,Zostera marina, but population structure and many life history traits remain uncharacterized. We conducted monthly collections from May through September 2003–2005 in Chincoteague Bay, Virginia, to investigate seasonal migration and spawning, sex ratios, size at maturity, sexual dimorphism in length, and growth rates. BothS. fuscus andS. floridae spawned from May through September. Water temperature was significantly correlated withS. fuscus catches, whereasS. floridae abundance peaked after maximum water temperatures. Sex ratio data indicatedS. floridae populations are balanced, whileS. fuscus populations are strongly female-biased. Both species can quickly reach reproductive maturity, potentially within one season, becauseS. fuscus andS. floridae population growth rates average 1.0 mm d⁻¹ and minimum standard length at maturity measures 125 and 103 mm, respectively, for females and 99 and 91 mm, respectively, for males. ForS. fuscus, females were significantly longer than conspecific males during time periods when juveniles were not rapidly maturing. Size sexual dimorphism in this species coincides with reports of extensive paternal care and supports the hypothesis that the strength of sexual selection differs in these species.     

Occurrence and distribution of shortnose sturgeon,Acipenser brevirostrum,in the upper tidal Delaware River

Sampling in the upper tidal Delaware River between Trenton, New Jersey, and Philadelphia, Pennsylvania, from July 1981 through December 1984 demonstrated the existence of a significant population of shortnose sturgeon. The sturgeon aggregate in the river channel during daylight hours, especially in the area between Trenton and Florence, New Jersey (river km 211.8 to 198.8). Occurrence in the river downstream of Florence appears to be restricted by poor water quality during summer months. Sturgeon were present in the study area throughout the year, but largest numbers were collected from May though November. No spawning was observed during this study, but presence of males with milt suggests that spawning possibly occurs in the Trenton area. Preliminary population estimates (Peterson, Schnabel and Seber-Jolly) indicate an adult population of approximately 6,000–14,000 shortnose sturgeon occupying the upper tidal Delaware River.     

Predation by the ctenophoreMnemiopsis leidyi in Narragansett Bay,Rhode Island

The impact ofMnemiopsis leidyi as a predator was studied quantitatively to determine their feeding rates on mixed natural zooplankton. These studies showed that feeding rate was independent of food concentration, but a function of both temperature and size of ctenophore. The feeding rate (liters cleared per mg dry weight per day) ranged from about 0.01 for larger ctenophores at lower temperatures (10–15°C) to about 0.1 for smaller ctenophores at higher temperatures (20–25°C). Combining these results with ctenophore biomass estimates from three years of sampling, numerical estimates were made of zooplankton mortality due to ctenophore predation. The maximum summer cropping byM. leidyi was calculated to be an average of 5–10% per day for the bay as a whole. Although substantial, this predation pressure alone does not account for the observed summer decline of zooplankton.