Southern Chesapeake Bay Research Articles

On the links between sea level and temperature variations in the Chesapeake Bay and the Atlantic Meridional Overturning Circulation (AMOC)

AbstractRecent studies found that on long time scales there are often unexplained opposite trends in sea level variability between the upper and lower Chesapeake Bay (CB). Therefore, daily sea level and temperature records were analyzed in two locations, Norfolk in the southern CB and Baltimore in the northern CB; surface currents from Coastal Ocean Dynamics Application Radar (CODAR) near the mouth of CB were also analyzed to examine connections between the CB and the Atlantic Ocean. The observations in the bay were compared with daily Atlantic Meridional Overturning Circulation (AMOC) observations during 2005–2021. Empirical Mode Decomposition (EMD) analysis was used to show that variations of sea level and temperature in the upper and lower CB are positively correlated with each other for short time scales of months to few years, but anticorrelated on low frequency modes representing decadal variability and long-term nonlinear trends. The long-term CB modes seem to be linked with AMOC variability through variations in the Gulf Stream and the wind-driven Ekman transports over the North Atlantic Ocean. AMOC variability correlates more strongly with variability in the southern CB near the mouth of the bay, where surface currents indicate potential links with AMOC variability. For example, when AMOC and the Gulf Stream were especially weak during 2009–2010, sea level in the southern bay was abnormally high, temperatures were colder than normal and outflow through the mouth of CB was especially high. Sea level in the upper bay responded to this change only 1–2 years later, which partly explains phase differences within the bay. A persistent trend of 0.22 cm/s per year of increased outflow from the CB, may be a sign of a climate-related trend associated with combination of weakening AMOC and increased precipitation and river discharge into the CB.

Nursery habitat use by juvenile blue crabs in created and natural fringing marshes

Climate change and coastal development pressures have intensified the need for shoreline protection. Nature-first approaches that use natural habitats, particularly marshes, are being promoted globally as ecologically-beneficial alternatives to grey infrastructure. The ability of these novel shorelines to provide nursery habitat to blue crab (Callinectes sapidus), an ecologically and economically important species along the Atlantic and Gulf coasts of the United States, has not been fully evaluated. We quantified the abundance and size distribution of juvenile blue crabs from a chronosequence of living shorelines (created fringing marshes) spanning 2 to 16 years in age since construction compared with paired natural fringing marshes in the southern Chesapeake Bay. Both created and natural fringing marshes are used by blue crabs as primary nursery habitats. Despite interannual differences in abundance, young blue crabs (≤ 2.5 cm carapace width) were observed in similar densities and sizes at living shoreline and natural marshes. The age of the living shoreline was not related to blue crab density, indicating that even the youngest living shorelines (2 years) provided nursery habitat. The potential for living shorelines to serve as nursery habitat for an economically important species may provide additional incentive to implement these nature-based approaches for climate change adaptation.

Minimal effects of oyster aquaculture on local water quality: Examples from southern Chesapeake Bay.

As the oyster aquaculture industry grows and becomes incorporated into management practices, it is important to understand its effects on local environments. This study investigated how water quality and hydrodynamics varied among farms as well as inside versus outside the extent of caged grow-out areas located in southern Chesapeake Bay. Current speed and water quality variables (chlorophyll-a fluorescence, turbidity, and dissolved oxygen) were measured along multiple transects within and adjacent to four oyster farms during two seasons. At the scale of individual aquaculture sites, we were able to detect statistically significant differences in current speed and water quality variables between the areas inside and outside the farms. However, the magnitudes of the water quality differences were minor. Differences between sites and between seasons for water quality variables were typically an order of magnitude greater than those observed within each site (i.e. inside and outside the farm footprint). The relatively small effect of the presence of oysters on water quality is likely attributable to a combination of high background variability, relatively high flushing rates, relatively low oyster density, and small farm footprints. Minimal impacts overall suggest that low-density oyster farms located in adequately-flushed areas are unlikely to negatively impact local water quality.

Salinity affects growth but not thermal preference of adult mummichogs Fundulus heteroclitus.

The effects of an ecologically relevant range of salinities (2, 12, 22, 32) on thermal preferences and growth of adult mummichogs Fundulus heteroclitus were determined for fish from a southern Chesapeake Bay population. Salinity did not affect the mean temperature selected by F. heteroclitus in a thermal gradient, which was identified as 26.6°C based on observations of 240 individuals. Salinity and temperature had significant and interacting effects on growth rates of F. heteroclitus measured over 12 weeks. Growth rates were highest overall and remained high over a broader range of temperatures at moderate salinities (12 and 22), while high growth rates were shifted toward lower temperatures for fish grown at a salinity of 2 and higher temperatures at a salinity of 32. Significant reductions in growth relative to the optimal conditions (28.6°C, salinity of 22) were observed at the coolest (19.6°C) and warmest (33.6°C) temperature tested at all salinities, as well as temperatures ≥ 26.6°C at a salinity of 2, ≥ 28.6°C at a salinity of 12 and ≤ 26.6°C at a salinity of 32. Growth rates provide a long-term, organismal measure of performance and results of this study indicate that performance may be reduced under conditions that the highly euryhaline F. heteroclitus can otherwise easily tolerate. The combination of reduced salinity and increased temperature that is predicted for temperate estuaries as a result of climate change may have negative effects on growth of this ecologically important species.

Canopy Functions of R. maritima and Z. marina in the Chesapeake Bay

Shoots in seagrass beds form canopies: structurally complex habitats that provide refuge for fauna and trap sediment particles by dampening water movement. Unfortunately, seagrasses are faced with continuing negative impacts to survival, including climate change and poor water quality. In areas where several seagrass species coexist, changing conditions may influence composition of beds so one species is favored over another. Two species found worldwide, Zostera marina and Ruppia maritima, are undergoing this shift: as Z. marina dies back, in some locations it is replaced by R. maritima, a smaller-form seagrass with shorter, thinner shoots. This process is occurring in Virginia, USA in the southern Chesapeake Bay, at intermediate depths where the species co-occur. Although changes in seagrass species abundance have previously been documented, few studies have measured the resulting effects on ecosystem functioning. We evaluated three sites to determine whether canopies of the two species displayed similar small epifaunal invertebrate animal assemblages and sediment properties, and found that Z. marina beds exhibited a greater amount of fine surface sediment than those of R. maritima, but found no effect of seagrass species on invertebrate assemblages. Epifaunal invertebrates were however more numerous and speciose with greater biomass, and more abundant with greater shoot density. This study provides baseline information from one summer for areas where the two seagrass species coexist. Although more research is needed, this study suggests in mixed beds, decline of Z. marina could result in coarsening of sediment, but dense R. maritima canopies could harbor similar small invertebrate assemblages.

Policy Targeting to Reduce Economic Damages From Land Subsidence

AbstractGroundwater pumping contributes significantly to land subsidence, which generates economic costs as changes in the frequency of flooding affect property values. We evaluate these costs by estimating the marginal damages from pumping, which define the corrective policy incentive to address land subsidence externalities. In an application to the southern Chesapeake Bay region of Virginia, we find that land subsidence due to groundwater pumping is greatest in inland rural areas, but that the damages from pumping are greatest in coastal urban areas. Our results suggest that cost‐minimizing groundwater policy is spatially heterogeneous and targets the damages from land subsidence due to pumping in different locations, not simply physical land subsidence itself. These results are driven by differences in the spatial patterns of aquifer characteristics, which determine subsidence, and housing density, which determines the damages from subsidence.

Dinoflagellate Cysts Within Sediment Collections From the Southern Chesapeake Bay, and Tidal Regions of the James, York, and Rappahannock Rivers, Virginia

Dinoflagellate Cysts Within Sediment Collections From the Southern Chesapeake Bay, and Tidal Regions of the James, York, and Rappahannock Rivers, Virginia

Sea Turtles as Potential Dispersal Vectors for Non-Indigenous Species: The Veined Rapa Whelk as an Epibiont of Loggerhead Sea Turtles

Abstract We present the first record of Rapana venosa (Veined Rapa Whelk) as an epibiont of Caretta caretta (Loggerhead Sea Turtle) and the first observation of rapa whelks in the South Atlantic Bight, USA. Veined Rapa Whelks are invasive shellfish predators. The only known North American population of Veined Rapa Whelks is in the southern Chesapeake Bay. Collections of Veined Rapa Whelks as epibionts on Loggerhead Sea Turtles from Norfolk, VA and Wassaw Island, GA present a previously undescribed vector for whelk range expansion to widely separated coastal habitats. In October 2008, a live juvenile Loggerhead stranded near Norfolk, VA with a Veined Rapa Whelk attached to its carapace. Since May 2005, a total of eight Loggerheads with Veined Rapa Whelks as epibionts have been observed nesting on Wassaw Island, GA. The shell lengths of the two smallest Wassaw Island whelks (1.9 and 2.6 mm) indicate that the whelks settled from the plankton 24–48 hr immediately prior to collection in Georgia. This time fram...

Introduction to the Chesapeake Bay National Estuarine Research Reserve in Virginia

Abstract Designated in 1991, CBNERRVA established a multi-component system along the salinity gradient of the York River estuary that encompassed the diverse collection of habitats found within the southern Chesapeake Bay subregion. With its two principal tributaries, the Pamunkey and Mattaponi Rivers, the York River is the Bay's fifth largest tributary in terms of flow and watershed area. The York River estuary is classified as a microtidal, partially mixed estuary. Tidal range varies from 0.7 m and at its mouth to over 1 m in the upper freshwater tributary reaches and salinity distribution ranges from tidal freshwater to polyhaline regimes. Land use is predominantly rural in nature with forest (61%) and agricultural lands (21%) being the dominant land cover; wetlands comprise approximately 7% of the basins area. Reserve components include: (1) Goodwin Islands (148 ha), an archipelago of polyhaline salt-marsh islands surrounded by inter-tidal flats, extensive submerged aquatic vegetation beds, and shallo...

CBNERRVA Research and Monitoring Program

The overall goal of the Chesapeake Bay National Estuarine Research Reserve in Virginia (CBNERRVA) research and monitoring program is to promote, coordinate and conduct research and monitoring to enhance the scientific understanding and management of the York River and southern Chesapeake Bay coastal ecosystems. The regions of greatest scientific emphasis are located within four Reserve sites located along the York-Pamunkey River estuarine system. Primary research and environmental monitoring areas include: estuarine and shallow water environments including benthic communities, submerged aquatic vegetation and emergent wetlands habitats, open water regions and adjacent watersheds and air sheds. Both national priority (NOAA) and Chesapeake Bay specific (Chesapeake Bay Program) research focus areas are pursued within the Research Reserve with goals to: enhance scientific understanding of coastal ecosystems, surrounding environments and the natural and human processes influencing such systems; and, promote the effective management and conservation of natural and cultural coastal resources through informed decision-making. A System-wide Monitoring Program (SWMP) initiated by the Estuarine Reserves Division (ERD) of NOAA provides standardized data on national estuarine environmental trends through similar measurements of abiotic and biotic variables as well as watershed and land use classifications and measurements at each of the 27 Reserves. Data are compiled electronically at a central data management location and are available via web interface (www.vecos.org). Ongoing York River monitoring programs at the CBNERRVA reserve sites include; meteorological and streamflow monitoring, water quality monitoring and biological monitoring are available through the Reserve or via web interface. Multi-parameter water quality, in situ monitors at both fixed and buoyed stations, point sampling and continuous underway flow-through monitoring form the basis of the water quality monitoring program. Research opportunities at Reserve sites are available to any qualified scientist, academician or student affiliated with a university, college or school, non-profit organizations, and non-academic research institutions. In addition, the Reserve sponsors competitive graduate research fellowships through the NERRS Graduate Research Fellowship (GRF) Program for student research in the York River system.

Septic Tank Impacts on Ground Water Quality and Nearshore Sediment Nutrient Flux

AbstractField studies were conducted at three coastal plain sites to characterize inorganic nutrient and fecal coliform bacteria ground water quality and intertidal sediment nutrient fluxes under the influence of residential septic tank effluent. Mean drainfield DIP (dissolved inorganic phosphorus) and DIN (dissolved inorganic nitrogen) concentrations varied between 294 to 336 and 4494 to 5391 μmol/L, respectively, with mean fecal coliform bacteria densities ranging from 105.04 to 106.29 MPN (most probable number) /100 mL. DIP and fecal coliform bacteria exhibited a high degree of attenuation with shoreline concentrations at or near background levels. In contrast, septic tank nitrogen loadings to shallow ground water were significant and resulted in mean shoreline DIN concentrations ∼50 to 100 times greater than adjacent surface water concentrations. Mean site sediment DIP and DIN flux to surface waters varied from 1.1 to 1.6 and 52 to 135 μmol/m2/hr, respectively. Whereas DIP sediment fluxes were similar to reported values for sites adjacent to forested and agricultural lands, DIN fluxes were elevated compared to forested lands and near the lower end of the range reported for agricultural lands within the southern Chesapeake Bay region. Maximum measured sediment DIN flux was 1514 μmol/m2/hr. Estimated waste water nitrogen loading to shallow ground water (5.7 to 10.7 kg/household/yr) was significant and with 0.5 to 1 acre lot sizes, comparable to water table nitrogen loadings from dominant row‐crop land use in the mid‐Atlantic Coastal Plain. Given the trends in population growth in the Chesapeake Bay watershed and other coastal regions, nitrogen loads from septic tanks to these systems should also be expected to increase.

DISTRIBUTION, ABUNDANCE, AND HABITAT AFFINITIES OF THE COASTAL PLAIN SWAMP SPARROW

We examined the distribution and abundance of the Coastal Plain Swamp Sparrow (Melospiza georgiana nigrescens) at previously occupied sites and points within potential habitat. We found Swamp Sparrows throughout their formerly documented range except in southern Chesapeake Bay. Swamp Sparrows were most common in the Mullica River region of New Jersey where we detected individuals at 78% of systematically chosen points with a mean count of 4.1 birds/point. The percentages of points with positive detections in the regions of Delaware River (39%), eastern Delaware Bay (23%), western Delaware Bay (34%), and Tuckahoe River (31%) were lower. The mean count of birds/point was between 0.4 and 0.6 in these regions. A higher resolution Poisson model of relative abundance suggested that the greatest concentrations of Swamp Sparrows occurred not only in the Mullica River area but also along northwestern Delaware Bay. Regression analysis of Swamp Sparrow counts and habitat features identified shrubs (Iva frutescens and Baccharis halimifolia) as a key habitat component. By applying density estimates generated by DISTANCE (Thomas et al. 1998) to the approximate area of potential shrub habitat along Delaware Bay, we estimated that the core population of Coastal Plain Swamp Sparrows was less than 28,000 pairs. We recommend that the Coastal Plain Swamp Sparrow be listed as a subspecies of concern by state and local governments because of its relatively small population size, restricted distribution in the mid-Atlantic region, and narrow habitat requirements.

Salinity tolerance of larval Rapana venosa: implications for dispersal and establishment of an invading predatory gastropod on the North American Atlantic coast.

The lack of quantitative data on the environmental tolerances of the early life-history stages of invading species hinders estimation of their dispersal rates and establishment ranges in receptor environments. We present data on salinity tolerance for all stages of the ontogenetic larval development of the invading predatory gastropod Rapana venosa, and we propose that salinity tolerance is the dominant response controlling the potential dispersal (=invasion) range of the species into the estuaries of the Atlantic coast of the United States from the current invading epicenter in the southern Chesapeake Bay. All larval stages exhibit 48-h tolerance to salinities as low as 15 ppt with minimal mortality. Below this salinity, survival grades to lower values. Percentage survival of R. venosa veligers was significantly less at 7 ppt than at any other salinity. There were no differences in percentage survival at salinities greater than 16 ppt. We predict that the counterclockwise, gyre-like circulation within the Chesapeake Bay will initially distribute larvae northward along the western side of the DelMarVa peninsula, and eventually to the lower sections of all major subestuaries of the western shore of the Bay. Given the observed salinity tolerances and the potential for dispersal of planktonic larvae by coastal currents, establishment of this animal over a period of decades from Cape Cod to Cape Hatteras is a high probability.

Population biology and secondary production of the suspension feeding polychaete Chaetopterus cf. variopedatus: Implications for benthic‐pelagic coupling in lower Chesapeake Bay

Benthic suspension feeders are functionally important components of many shallow estuarine and coastal ecosystems. Their relative importance in material and energy cycling depends on physical and biological factors, of which population dynamics of individual species are a key feature. We studied the demographics and secondary production of a population of the tubicolous, suspension feeding polychaete, Chaetopterus cf. variopedatus, of southern Chesapeake Bay, Virginia, to better understand its functional role in an estuarine ecosystem. Average worm densities in the study region ranged from 30 to >1000 individuals m−2 and were greatest after the summer recruitment period. Recruitment success varied threefold between 1994 and 1995. A two‐cohort model (juveniles and adults) with seasonality best described the data. High secondary production (18 g C m−2 yr−1 in 1994, 34 g C m−2 yr−1 in 1995) was mainly due to rapid growth and maturation of new recruits during summer and tube production. An interannual difference in production was associated with the interannual difference in recruitment success. General temporal trends of primary production and worm production were similar, and the worm population required 35%–100% of the estimated annual net water column community production per m2 for this region of the estuary. Chaetopterus cf. variopedatus is an important component of the lower bay ecosystem and should be considered when modeling carbon, nutrient, and energy flow. Our results further demonstrate that temporal variations in population dynamics lead to significant temporal variability in the relative importance of benthic suspension feeder effects for ecosystem function.

Fate of atmospherically deposited polycyclic aromatic hydrocarbons (PAHs) in Chesapeake Bay.

Factors controlling polycyclic aromatic hydrocarbon (PAH) distributions in southern Chesapeake Bay surface sediments were investigated with samples collected seasonally from five sites. Principal components analysis (PCA) suggests unique sources (combustion vs petroleum) and partitioning differences (volatile vs particle reactive) among PAHs, but a common mode of entry for these contaminants to Chesapeake Bay sediments. The fractional concentrations of all PAHs in Bay sediments, with the exception of perylene, were positively correlated with their atmospheric dry deposition fluxes (Fdry) to the Bay indicating that atmospheric deposition of aerosol-bound PAHs to the watershed controls their influx to Bay sediments. Overall, PAH concentrations in Chesapeake Bay sediments were well explained by a multiple-regression model (r2 = 0.88, p = 0.0001) with Fdry and sediment total organic carbon (TOC) content explaining most of the variance (57% and 43%, respectively). However, for many PAHs gas exchange across the air-water interface is of similar or greater magnitude even when Fdry is scaled to the watershed surface area. The fate of PAHs input to the Bay from gas deposition was determined to be uptake and metabolism within the aquatic food web rather than deposition to sediments.

Organochlorine contaminant exposure and reproductive success of black-crowned night-herons (Nycticorax nycticorax) nesting in Baltimore harbor, Maryland.

The declining size of the Baltimore Harbor black-crowned night-heron (Nycticorax nycticorax) colony has been hypothesized to be linked to polychlorinated biphenyl (PCB) exposure. In 1998, a "sample egg" was collected from 65 black-crowned night-heron nests (each containing > or = three eggs) for contaminant analysis, and the remaining eggs in these 65 nests, plus four two-egg nests, were monitored for hatching and fledging success. Eggs were also collected from 12 nests at Holland Island, a reference site in southern Chesapeake Bay. Samples were analyzed for 26 organochlorine pesticides and metabolities and 145 PCB congeners. Pesticide and metabolite concentrations, including p,p'-DDE, were well below thresholds associated with adverse reproductive effects at both sites. Average concentration of total PCBs, 12 Ah receptor-active PCB congeners, and toxic equivalents in eggs from Baltimore Harbor were greater (up to 35-fold) than that observed in Holland Island samples. Overall nest success at the Baltimore Harbor heronry was estimated by the Mayfield method to be 0.74, and the mean number of young fledged/hen was 2.05, which is within published productivity estimates for maintaining a stable black-crowned night-heron population. Using logistic regression, no significant relationships were found between organochlorine contaminant concentrations in sample eggs and hatching, fledging, or overall reproductive success. Processes other than poor reproduction (e.g., low postfledging survival, emigration, habitat degradation) may be responsible for the declining size of the Baltimore Harbor colony.

Dissolved organic iodine in marine waters: role in the estuarine geochemistry of iodine.

Non-volatile dissolved organic iodine (DOI) can be a major, or even the dominant, species of dissolved I in coastal, inshore and estuarine waters. It can be converted to IO3- in the presence of an oxidizing agent and to I- by reacting it with a reducing agent. Depending on the exact experimental conditions, the yields of these reactions may not be quantitative. In previous analytical schemes for the determination of IO3-, I- and DOI in marine waters, if oxidation or reduction steps are involved and the concentrations of one or more species are estimated by difference, the presence of DOI can lead to an overestimation of the concentrations of the inorganic species determined by difference and an underestimation of the concentration of DOI. In two cruises covering the James River to the southern Chesapeake Bay and from the southern Chesapeake Bay to the Atlantic, above a salinity (S) of 2, the contribution of DOI to total I increased with decreasing salinity and reached a maximum of 80%. DOI, I- and IO3- were successively the dominant form of dissolved I at 0.1 < S < 15 in the James River estuary, 15 < S < 30 in the Southern Chesapeake Bay and S > 30 in the Atlantic Ocean at the Bay mouth, respectively. Total I behaved conservatively (i.e., no evidence of consumption or production) during estuarine mixing during both cruises. In the southern Chesapeake Bay, total inorganic I was also approximately conservative. The primary process affecting the speciation of dissolved I was the conversion of IO3- to I-. In the James River estuary, there were indications of the conversion of both IO3- and I- to DOI. The concentrations of total I, IO3-, I- and DOI in James River water were 0.121, undetectable, 0.068 and 0.053 microM, respectively. These concentrations of total I and I- are significantly higher while that of IO3- is noticeably lower than those used presently for estimating global riverine input of these I species to the oceans. The riverine flux of DOI to the oceans is presently unknown.

The Trophic Contributions of Rotifers in Tidal Freshwater and Estuarine Habitats

Distribution patterns and trophic contributions of rotifers from freshwater through polyhaline estuarine waters were examined in the southern Chesapeake Bay and its major tributaries for a two-year period. Trichocerca marina and Synchaeta spp. were the major taxa in abundance, followed by Polyarthra vulgaris, Keratella cochlearis and Brachionus spp. There was a significant negative correlation between salinity and rotifer density, biomass, and number of species. Rotifers were a component of the microzooplankton biomass during specific periods and at particular sites, dominating summer assemblages in tidal freshwater and river–estuary transition sites, plus the winter communities in estuarine waters. This observation indicates that rotifers may play an important trophic role by seasonally replacing metazoan nauplii as a biomass source in both tidal freshwater and estuarine ecosystems. The annual contribution of rotifers to the total microzooplankton biomass exclusive of heterotrophic dinoflagellates was brief but intensive, achieving over 50% of annual biomass during a 2–3 month period. Despite the small annual mean contribution of rotifers to the total microzooplankton biomass, rotifers may have a limited, but significant impact on the trophic dynamics of the zooplankton community in Chesapeake Bay and its major tidal tributaries.

Composition of Particulate Organic Matter in the Southern Chesapeake Bay: Sources and Reactivity

The distribution of two classes of lipid biomarker compounds (fatty acids and sterols) was used in conjunction with several bulk parameters (total suspended solids, chlorophyll a, and particulate carbon and nitrogen concentrations) to examine spatial and temporal variability in the sources of particulate organic matter (POM) important to southern Chesapeake Bay. Based on these geochemical parameters, we found that suspended and sedimentary organic matter in the southern Chesapeake Bay is derived from autochthonous sources including a mixture of fresh and detrital phytoplankton, zooplankton, and bacteria. The dominant factor contributing to temporal variability during our study was phytoplankton productivity. Enrichments in particulate organic carbon, chlorophyll a, total fatty acids, total sterols, and a number of biomarkers specific to phytoplankton sources were found in particles collected from surface (1 m) and deep (1 m above the bottom) portions of the water column at several sites during the spring bloom in March 1996 and during a localized bloom in July 1995. Comparison of sites at the mouths of two tributaries (York and Rappahannock rivers) to southern Chesapeake Bay with two sites located in the bay mainsterm indicates spatial variation in the composition of POM was not significant in this region of the bay. The energetic nature of this region of the Chesapeake Bay most likely contributes to the observed homogeneity. Comparison with biomarker studies conducted in other estuaries suggests the high levels of productivity characteristic of the Chesapeake Bay contribute to high background levels of POM.

Vertical migration behavior and larval transport in brachyuran crabs

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 176:103-113 (1999) - doi:10.3354/meps176103 Vertical migration behavior and larval transport in brachyuran crabs Lance P. Garrison* School of Marine Science, Virginia Institute of Marine Science, The College of William and Mary, Gloucester Point, Virginia 23062, USA *Address for correspondence: National Marine Fisheries Service, Northeast Fisheries Science Center, 166 Water Street, Woods Hole, Massachusetts 02543, USA. E-mail: lgarriso@whsun1.wh.whoi.edu ABSTRACT: I documented the patterns of vertical distribution and abundance of zoeae from 3 families of brachyuran crabs in the York River, a sub-estuary in southern Chesapeake Bay (USA). The family groups included species from Ocypodidae, Pinnotheridae, and Panopeidae. I assessed the effects of light and tidal current stage on the abundance and vertical distribution of zoeae using analysis of variance (ANOVA) and logistic regression. Clear behavioral patterns were evident in the logistic regression. Ocypodid larvae exhibited tidally timed behavior with larvae nearest the surface during ebb tides. Pinnotherid larval behaviors were correlated with both light and tidal current phase. Larvae were nearest the surface at night and during ebb tides. Panopeid larvae were near the bottom during early flood tides, near mid-depths during late flood and early ebb tides, and nearest the surface during late ebb tides. These behavioral patterns should result in horizontal distributions that are consistent with those observed in previous studies. The ANOVA reflected similar results; however, high variability between replicates weakened the significance of these patterns. The different analyses reflect processes on different spatial and temporal scales. The samples were replicated on short time scales (5 to 10 min). The logistic regression, a categorical analysis, largely ignores the variation between replicates and reflects average behaviors on the scale of several tidal cycles. In contrast, the ANOVA is highly sensitive to the variation between replicates and reflects patterns on scales of minutes. This high variation reflects turbulent vertical mixing and fine-scale horizontal patchiness in larval distribution. Small-scale physical processes that redistribute larvae both vertically and horizontally may have a strong influence on the variability in dispersal and recruitment success. KEY WORDS: Vertical migration · Zoeae · Larval behavior · Larval transport Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 176. Publication date: January 18, 1999 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1999 Inter-Research.