North Inlet Estuary Research Articles

Estimation of chromophoric dissolved organic matter (CDOM) and photosynthetic activity of estuarine phytoplankton using a multiple-fixed-wavelength spectral fluorometer

The utility of a multiple-fixed-wavelength spectral fluorometer, the Algae Online Analyser (AOA), as a means of quantifying chromophoric dissolved organic matter (CDOM) and phytoplankton photosynthetic activity was tested using algal cultures and natural communities from North Inlet estuary, South Carolina. Comparisons of AOA measurements of CDOM to those by spectrophotometry showed a significant linear relationship, but increasing amounts of background CDOM resulted in progressively higher over-estimates of chromophyte contributions to a simulated mixed algal community. Estimates of photosynthetic activity by the AOA at low irradiance (∼80 μmol quanta m−2 s−1) agreed well with analogous values from the literature for the chlorophyte, Dunaliella tertiolecta, but were substantially lower than previous measurements of the maximum quantum efficiency of photosystem II (Fv/Fm) in Thalassiosira weissflogii (a diatom) and Rhodomonas salina (a cryptophyte). When cells were exposed to high irradiance (1500 μmol quanta m−2 s−1), declines in photosynthetic activity with time measured by the AOA mirrored estimates of cellular fluorescence capacity using the herbicide 3′-(3, 4-dichlorophenyl)-1′,1′-dimethyl urea (DCMU). The AOA shows promise as a tool for the continuous monitoring of phytoplankton community composition, CDOM, and the group-specific photosynthetic activity of aquatic ecosystems.

Spectral Irradiance, Phytoplankton Community Composition and Primary Productivity in a Salt Marsh Estuary, North Inlet, South Carolina, USA

We investigated spatial and temporal changes in spectral irradiance, phytoplankton community composition, and primary productivity in North Inlet Estuary, South Carolina, USA. High concentrations of colored dissolved organic matter (CDOM) were responsible for up to 84 % of the attenuation of photosynthetically available radiation (PAR). Green-yellow wavelengths were the predominant col- ors of light available at the two sampling sites: Clam Bank Creek and Oyster Landing. Vertical attenuation coefficients of PAR were 0.7-2.1 m −1 with corresponding euphotic zone depths of 1.5-6.7 m. Phytoplankton biomass (as chlorophyll a(chla))variedseasonallywitha summermaximum of16 μg chl a l −1 and a winter minimum of 1.4 μ gc hla l −1 .T he phytoplankton community consisted mainly of diatoms, prasi- nophytes, cryptophytes and haptophytes, with diatoms and pra- sinophytes accounting for up to 67 % of total chl a. Changes in phytoplankton community composition showed strongest cor- relations with temperature.Light-saturated chla-specific ratesof photosynthesis and daily primary productivity varied with sea- son and ranged from 1.6 to 14 mg C (mg chl a) −1 h −1 (32-803 mg C m −3 day −1 ). Calculated daily rates added up to an annual carbon fixation rate of 84 g C m −3 year −1 .O verall, changes in phytoplankton community composition and primary productivity in North Inlet showed a strong dependence on temperature, with PAR and spectral irradiance playing a rela- tively minor role due to short residence times, strong tidal forcing and vertical mixing.

Sublethal Effects of Crude Oil on the Community Structure of Estuarine Phytoplankton

While the ecological impacts of crude oil exposure have been widely studied, its sublethal effects on phytoplankton community structure in salt marsh estuaries have not been well documented. The purpose of this study was to simulate oil spill conditions using a microcosm design to examine short-term (2 day) changes in phytoplankton community composition and total biomass following exposure to crude oil obtained from the Deepwater Horizon oil spill and a mixture of Texas crude oils. Microcosm experiments were performed in situ in North Inlet Estuary near Georgetown, SC. A control and six replicated experimental treatments of crude oil additions at final concentrations of 10, 50, or 100 μl l−1 of either Deepwater Horizon spill oil or the Texas crude mixture were incubated under in situ conditions. Photopigments were analyzed using high-performance liquid chromatography and community composition was determined using ChemTax. Total phytoplankton biomass (as chl a) declined with increasing crude oil concentrations. Prasinophytes, the most abundant microalga in both experiments, showed no response to oil exposure in one experiment and a significant negative response in the other. Diatoms euglenophytes and chlorophytes appeared relatively resistant to oil contamination at the exposure levels used in this study, maintaining or increasing their relative abundance with increasing oil concentrations. Chlorophytes and cyanobacteria increased in relative abundance while cryptophyte abundance decreased with increasing oil concentrations. The results of these experiments suggest that low levels of crude oil exposure may reduce total biomass and alter phytoplankton community composition with possible cascade effects at higher trophic levels in salt marsh estuaries.

Specificity of Salt Marsh Diazotrophs for Vegetation Zones and Plant Hosts: Results from a North American marsh

Salt marshes located on the east coast of temperate North America are highly productive, typically nitrogen-limited, and support diverse assemblages of free-living nitrogen fixing (diazotrophic) bacteria. This article reviews and analyzes data from North Inlet estuary (SC, USA), addressing diazotroph assemblage structure and the influence of plant host and environmental conditions on the assemblage. The North Inlet estuary is a salt marsh ecosystem in which anthropogenic influences are minimal and the distributions of diazotrophs are governed by the natural biota and dynamics of the system. Denaturing gradient gel electrophoresis fingerprinting and phylogenetic analyses of recovered sequences demonstrated that the distributions of some diazotrophs reflect plant host specificity and that diazotroph assemblages distributed across marsh gradients are also heavily influenced by edaphic conditions. Broadly distributed diazotrophs that are capable of maintaining populations under all environmental conditions spanning such gradients are also present in these assemblages. Statistical analyses indicate that the structures of diazotroph assemblages in different vegetation zones are significantly (p < 0.01) different. New data presented here demonstrate the heterogeneity of salt marsh rhizosphere microenvironments, and corroborate previous findings from different plant hosts growing at several locations within this estuary. The data from these collected works support the hypothesis that the biogeography of microorganisms is non-random and these biogeographic patterns are predictable.

Infaunal Burrows Are Enrichment Zones for Vibrio parahaemolyticus

Vibrio parahaemolyticus, a species that includes strains known to be pathogenic in humans, and other Vibrionaceae are common, naturally occurring bacteria in coastal environments. Understanding the ecology and transport of these organisms within estuarine systems is fundamental to predicting outbreaks of pathogenic strains. Infaunal burrows serve as conduits for increased transport of tidal waters and V. parahaemolyticus cells by providing large open channels from the sediment to salt marsh tidal creeks. An extensive seasonal study was conducted at the North Inlet Estuary in Georgetown, SC, to quantify Vibrionaceae and specifically V. parahaemolyticus bacteria in tidal water, fiddler crab (Uca pugilator, Uca pugnax) burrow water, and interstitial pore water. Numbers of V. parahaemolyticus bacteria were significantly higher within burrow waters (4,875 CFU ml(-1)) than in creek water (193 CFU ml(-1)) and interstitial pore water (128 CFU ml(-1)), demonstrating that infaunal burrows are sites of V. parahaemolyticus enrichment. A strong seasonal trend of increased abundances of Vibrionaceae and V. parahaemolyticus organisms during the warmer months of May through September was observed. Multilocus sequence typing (MLST) analysis of isolates presumed to be V. parahaemolyticus from creek water, pore water, and burrow water identified substantial strain-level genetic variability among V. parahaemolyticus bacteria. Analysis of carbon substrate utilization capabilities of organisms presumed to be V. parahaemolyticus also indicated physiological diversity within this clade, which helps to explain the broad distribution of these strains within the estuary. These burrows are "hot spots" of Vibrionaceae and V. parahaemolyticus cell numbers and strain diversity and represent an important microhabitat.

Relationships betweenSpartina alterniflora andLittoraria irrorata in a South Carolina salt marsh

Bottom-up factors such as nutrient availability have long been thought to be the primary regulators of plant growth in salt marshes. However, that paradigm has been challenged by investigations showing that grazing by the periwinkle snailLittoraria irrorata regulatesSpartina alterniflora growth through top-down forces. Our investigation was conducted between November 2003 and March 2007 within the North Inlet Estuary (NIE) salt marsh to examine relationships betweenS. alterniflora andL. irrorata. The primary goal was to determine if observed in situ densities ofL. irrorata significantly decreasedS. alterniflora productivity at the study sites. The results indicate thatS. alterniflora productivity positively correlated withL. irrorata snail density during winter. However, no correlation was observed during summer. Hence, there was no inverse relationship between snail density and primary productivity and no support for the hypothesis of ‘top-down’ control of marsh plant production. A significant relationship betweenS. alterniflora stem density andL. irrorata density was observed during summer and winter, suggesting that stem density may play a key role in determining the distribution of periwinkle snails in NIE. These results challenge the applicability of theL. irrorata-S. alterniflora top-down control model as a generalized phenomenon in southeastern salt marshes.

Coastal marsh response to historical and future sea-level acceleration

We consider the response of marshland to accelerations in the rate of sea-level rise by utilizing two previously described numerical models of marsh elevation. In a model designed for the Scheldt Estuary (Belgium–SW Netherlands), a feedback between inundation depth and suspended sediment concentrations allows marshes to quickly adjust their elevation to a change in sea-level rise rate. In a model designed for the North Inlet Estuary (South Carolina), a feedback between inundation and vegetation growth allows similar adjustment. Although the models differ in their approach, we find that they predict surprisingly similar responses to sea-level change. Marsh elevations adjust to a step change in the rate of sea-level rise in about 100 years. In the case of a continuous acceleration in the rate of sea-level rise, modeled accretion rates lag behind sea-level rise rates by about 20 years, and never obtain equilibrium. Regardless of the style of acceleration, the models predict approximately 6–14 cm of marsh submergence in response to historical sea-level acceleration, and 3–4 cm of marsh submergence in response to a projected scenario of sea-level rise over the next century. While marshes already low in the tidal frame would be susceptible to these depth changes, our modeling results suggest that factors other than historical sea-level acceleration are more important for observations of degradation in most marshes today.

Mesozooplankton Responses to Climate Change and Variability in a Southeastern U.S. Estuary (1981–2003)

Abstract Long-term trends and relationships between large mesozooplankton (1.5–20 mm) and the physical environment were used to investigate impacts of climate change and variability in the North Inlet estuary, South Carolina. Biweekly collections (365 μm) from 1981 to 2003 demonstrated distinct seasonal patterns and large interannual fluctuations in abundances. Significant long-term decreases in abundances were observed for total zooplankton and 12 taxa (e.g., Gobiosoma larvae, chaetognaths, and adult shrimps), whereas 14 others, including some of the most abundant constituents, did not change (e.g., mysids, amphipods, crab megalopae, and Palaemonetes larvae). The composition of the fauna was similar at the beginning and end of the 23-year period. A significant long-term increase in winter water temperature (2.6°C) and a decrease in summer salinity (3.2) were determined. Relationships between physical conditions and taxa varied in strength and direction, and most did not agree with their long-term trends....

Respiration rates of dominant hydromedusae in the North Inlet tidal estuary during winter and summer

The objective of this study was to quantify the respiratory requirements and oxygen consumption rates for seasonal hydromedusae populations in the North Inlet estuary, Georgetown, SC, USA. Respiration rates were determined for hydromedusae collected in January 2006, 2007 and July 2006 using microrespirometry. The numerically dominant gelatinous predators were Nemopsis bachei (January 2006 and 2007) and Bougainvillia muscus (July 2006). Seasonal oxygen consumption rates were low (0.80–1.27 μmol O2 g−1 h−1). Q10 values were high during January 2006 and July 2006 (4.7), but low during January 2007 (0.5), suggesting hydromedusae were sensitive to the exposure temperatures (7–34°C) in this study and well adapted to the temperature range encountered in this estuary. Moreover, the oxygen consumption rates during July 2006 showed significant differences between the two species. The allometric relationship between respiration rate and hydromedusae weight differed seasonally. Our findings suggest hydromedusae can persist in hypoxic conditions and may partially explain the frequently observed increase in these cnidarians under conditions of low dissolved oxygen concentrations.

Variation in groundwater salinity in a tidal salt marsh basin, North Inlet Estuary, South Carolina

Groundwater flow of freshwater from upland forests into salt marshes is influenced by hydrologic forces that operate over a wide range of temporal scales, including storm events, tidal fluctuations, seasonal variations in rainfall and evapotranspiration (ET). Groundwater salinity can be a useful first order indicator of the balance between these flow processes. A dipole-dipole electrical resistivity survey was conducted approximately monthly during 2005 to measure groundwater salinity across a portion of Crabhaul Creek, a tidal salt marsh basin at the boundary of the upland forest and the North Inlet marsh in South Carolina. The monthly electrical resistivity surveys were designed to provide a detailed, spatially continuous measurement of subsurface conductivity to a depth of 4 m in order to further investigate the seasonal variation in groundwater salinity. Resistivity models were corroborated by simultaneous measurements of salinity in nearby piezometers. The freshwater-brackish water interface was clearly imaged by the resistivity. Movement of this interface occurs on a timescale of months rather than a regular seasonal variation. The average salinity in the marsh basin is highest in late Summer (July–August) when ET is highest, and lowest during the Winter (November–December). The position of the brackish-freshwater interface changes, but is not well correlated to local rainfall or tidal cycles except under specific circumstances. A steady-state hydrological model correctly predicts the average position of the freshwater-brackish interface and suggests a linear relationship between the height of the water table and the location of the interface. These results suggest a complex relationship between precipitation events and groundwater flow from the forest into the marsh.

Effect of summer storms on early life stages of Uca minax, U. pugnax and U. pugilator in North Inlet Estuary, South Carolina, USA

Estuarine fiddler crabs have a complex life cycle that spans vastly different salinity regimes. Larvae are spawned in estuaries and travel to the coastal ocean where development takes place; after metamorphosing to the megalopal stage, fiddler crabs reinvade estuaries where they set- tle and metamorphose. In the coastal ocean, larvae experience relatively stable physical conditions; however, upon reinvading estuaries, they are exposed to great fluxes in salinity and temperature. In this study, we measured shifts in the salinity regime caused by storm events, and determined the impact of these changes on species frequencies of megalopae from 3 Uca species in the water column and of their recently settled juvenile crabs on the benthos along a salt marsh creek in South Carolina. Adults of the 3 species examined are found in different salinity regimes: adult Uca pugnax generally occupy areas with relatively high salinity and plant cover, while U. minax are found in low salinity or freshwater areas; U. pugilator are found in open sandy areas over a broad range of salinities, but gen- erally occupy higher salinity environments than U. minax. For megalopal stages in the water column, we found that the relative proportions of the 3 species changed significantly along salinity gradients and in response to storm events. When the salinity regime normalized, species frequencies for mega- lopae returned to pre-storm proportions. Only U. minax megalopae were present in the water column during a storm event in July, whereas U. pugnax had been the most abundant species in the water column prior to the storm. Although all 3 species were able to survive storm events as juveniles, U. pugnax juveniles survived low salinity conditions significantly better than the other 2 species during the July storm. During a less severe storm in August, which lasted 5 d and altered the existing profile for a week, the benthic juvenile stages did not exhibit significant changes in species frequencies. Our results show that the duration and severity of salinity change are important variables that impact on the presence of these Uca species in the water column, and suggest that the physiology and behav- ior of the megalopal stage strongly influence where populations occur within estuaries.

Geomorphological determinants of nekton use of intertidal salt marsh creeks

Spatial variations in nekton use are often attributed to differences in the configuration and composition of habitat. We predicted that differences in nekton use among intertidal creeks were related to certain geomorphological characteristics. We measured or derived 28 features at 8 inter- tidal creeks in the high salinity North Inlet Estuary, South Carolina, USA. Nekton were collected simultaneously from all creeks once each season for 2 yr. Spatial variations in total abundance and biomass were greater than seasonal variations. Differences of 3- to 30-fold in resident and transient taxa densities occurred among creeks on the same date. Relative use (ranks) was similar among sea- sons and years. In canonical correlation analyses, depth, steepness, flow, and location were primary factors for total nekton and many taxa. Creeks that were shallow, broad, and filled and emptied slowly supported the greatest use. Total nekton use was not related to creek size, amount of edge, or oyster bottom. Grass shrimp Palaemonetes spp., numerically dominant in 83% of the collections, responded most to creek shape. Mummichog Fundulus heteroclitus favored shallow creeks with low flow and low proportions of submerged bottom at low tide. Juvenile spot Leiostomus xanthurus and pinfish Lagodon rhomboides were associated with the same features throughout their seasonal per- iods of occurrence. Persistent differences in nekton use of adjacent intertidal creeks might be explained by behavioral selection for preferred conditions and reoccupation of selected creeks. Geo- morphological variations are significant among sites and must be considered when assessing factors affecting nekton use along salinity and other environmental gradients.

Spatial and temporal dynamics of epiphytic microalgae on the cordgrassSpartina alterniflora in North Inlet Estuary, South Carolina

Epiphytic microbial biomass (as chlorophylla) was measured monthly in North Inlet Estuary, South Carolina, for 16 months on spatially distinct stem sections (bottom and middle) of dead and livingSpartina alterniflora growth forms (tall, medium, and short) exposed at low tide. The highest biomass was located on the bottom section of tall plants, presumably due to their relatively longer contact with creek water and associated phytoplankton, and their closer proximity to marsh sediments with associated benthic microalgae, both recruitment sources for epiphytes. Dead plants left standing from the previous year’s growth cycle had higher epiphytic biomass than living plants, which occurred mostly in late spring through fall. Epiphytic biomass was highest in the winter (mean of 1.77 mg chla (m2 marsh)−1) and lowest in the summer (mean of 0.34 mg chla (m2 marsh)−1). Because phytoplankton andSpartina production are lowest in the winter, the results emphasize the relative importance of epiphytes to growth of herbivores in this season.

Recruitment to adult habitats following marine planktonic development in the fiddler crabs, Uca pugilator, U. pugnax, and U. minax

Three congeneric species of fiddler crabs, Uca pugilator (Bosc, 1802), U. pugnax (Smith, 1870), and U. minax (LeConte, 1855), co-occur in estuaries along the east coast of North America, from Cape Cod to northern Florida. Although U. minax adults are generally found at lower salinities than the other two species, the distributions of all three species overlap to some degree. The distribution of megalopae and juvenile fiddler crabs (from first crab stage to those with a carapace width of 3.0 mm) was examined at four sites along a salinity gradient (from 35.0±2.0‰ to 3.0±3.0‰; \(\bar x\, \pm \,{\text{SD}} \) ) in the North Inlet Estuary, South Carolina, USA, in August 2002. A PCR-RFLP technique was developed to identify individuals from the genus Uca to species from first zoea through the early crab stages. An examination of the distribution of early life stages showed that U. minax reinvades low-salinity adult habitats at settlement, following planktonic larval development in the coastal ocean. Also, juveniles of U. pugilator were found to occupy Spartina alterniflora stands, where adult conspecifics rarely occur. Species frequencies were different for adults compared to early life stages in low-salinity areas of the marsh, where populations overlap. Settlement and survival dynamics of early life-history stages in wet and dry years likely determine the distribution of adult Uca spp. populations along salinity gradients in estuarine ecosystems.

Genetic Isolation Discovered among Previously Described Sympatric Morphs of a Meiobenthic Copepod

We sampled female Nannopus palustris Brady, 1880, from the North Inlet Estuary, South Carolina, U.S.A., monthly for a year to determine seasonal variation in a female polymorphism previously described. Two fat morphs (one with a notched and one with a straight basal region of the terminal seta of the caudal ramus) and a thin-bodied, previously unknown, morph were present sympatrically in different relative frequencies throughout the year. Total abundances peaked in February and were lowest in the summer. All three morphs differed significantly in width, but only females with notched terminal setae were significantly shorter in body length than thin and fat females. Genetic analyses of mitochondrial (cytochrome b) and nuclear (D3 expansion segment of 28S rDNA) genes demonstrated that the females with notched terminal setae were distinct from the thin and fat females with straight terminal setae, and the latter two shared common alleles. Concordance between mitochondrial and nuclear gene trees supports that notched females are a separate species from the thin and fat forms with straight terminal setae. We have yet to find a male with a notched basal region of its principle terminal setae or any male sharing alleles in common with notched females.

Distribution of juvenile Uca pugnax and U. pugilator across habitats in a South Carolina estuary, assessed by molecular techniques

Uca pugnax and U. pugilator are common fiddler crabs in salt marshes on the Atlantic coast of the United States. As adults, U. pugnax frequent muddier, vegetated (typically Spartina alter- niflora) substrate while U. pugilator usually occupy sandier, open habitats. It is unclear where juve- nile U. pugnax and U. pugilator reside because the early crab stages of these species are difficult to identify by simple gross morphology. Using a novel restriction fragment length polymorphism (RFLP) protocol to distinguish postlarval U. pugnax and U. pugilator, we studied their distribution along a horizontal gradient in the North Inlet Estuary, South Carolina. We collected juvenile crabs along tran- sects at 3 different sites that spanned S. alterniflora-covered mud and open sand habitats with adult populations of U. pugnax and U. pugilator, respectively. Over 75% of the juveniles collected were U. pugnax, showing greater recruitment by this species. U. pugnax juveniles of all sizes preferred the same muddy habitat occupied by adults, but habitat preferences of juvenile U. pugilator varied by site. Generally, U. pugilator displayed a shift in distribution from S. alterniflora cover to sandier habi- tat during early juvenile stages. The younger stages may prefer S. alterniflora-covered, muddier habitat because it provides better cover from predators, or so that they can avoid displacement by currents during high tides; alternatively, they may be able to feed better on muddy sediment. U. pugi- lator develops specialized mouthparts to scrape organic matter from larger sand grains, but these are not present in early juveniles nor in U. pugnax juveniles. Although young juvenile U. pugnax strongly favored S. alterniflora cover, older juveniles (those large enough to dig burrows for protec- tion) were occasionally found in sandier habitat with U. pugilator.

Iron limitation of phytoplankton in an urbanized vs. forested southeastern U.S. salt marsh estuary

Over the last two decades, escalating rates of coastal development have altered macro- and micronutrient loading patterns to many southeastern U.S. estuaries. This study addresses a potential consequence of urbanization-associated coastal deforestation that may have important implications for estuarine ecosystem productivity: a reduction in bioavailable Fe. We compared the potential for Fe limitation at representative sites in two neighboring South Carolina salt marsh estuaries, one (“Parsonage Creek” site in Murrells Inlet estuary) impacted by urbanization-associated clear-cutting, and the other (“Oyster Landing” site in North Inlet estuary) undeveloped and surrounded by forests. The urbanized estuarine site was marked by lower dissolved Fe concentrations compared to the forested estuarine site. In bioassay experiments conducted from 1996 to 1999, the addition of chelated Fe to natural phytoplankton populations stimulated chlorophyll a concentrations in water from Parsonage Creek on 6 of 11 sampling dates. Chlorophyll responses in Oyster Landing water also were observed on two of those sampling times, dates that followed periods of relatively low rainfall. In one experiment, the addition of Fe+NO 3 − to Parsonage Creek water led to significantly higher chlorophyll concentrations than when NO 3 − was added alone, but Fe+NH 4 + addition did not result in higher chlorophyll than NH 4 + addition alone. It was hypothesized that the difference in NO 3 − and NH 4 + responses was related to a greater tendency towards Si depletion in Fe-stressed NO 3 −-grown samples, or alternatively, to the higher Fe requirement for NO 3 − assimilation relative to that needed for NH 4 + assimilation. In bioassay experiments using Fe-deplete semi-continuous cultures of Synechococcus WH8101, Fe addition did not affect the net growth rate of cultures transferred to water from either estuary, but increased the chlorophyll a content of cells transferred to Parsonage Creek water. Finally, photosynthesis vs. irradiance parameters ( α, P max) obtained from Oyster Landing samples (<2 μm size fraction) were similar to those measured in Fe-replete Synechococcus continuous cultures, while the same parameters derived from Parsonage Creek samples were much lower and comparable to those from Fe-deplete cultures. The results indicate that phytoplankton population growth from high salinity salt marsh estuaries can be Fe-limited. Also, the potential for Fe limitation was more prevalent in a urbanized deforested estuary than in an undeveloped forested estuary, consistent with the hypothesis that organically bound Fe from coastal forests plays an important role in supplying Fe for the growth of estuarine phytoplankton.

Site fidelity, home range, and tidal migrations of juvenile pinfish, Lagodon rhomboides, in salt marsh creeks

We conducted a series of experiments to determine the movements and fidelity of juvenile pinfish, Lagodon rhomboides, in salt marsh creeks within North Inlet Estuary, SC. In Experiment 1, we investigated the fidelity of pinfish (40–100 mm SL) at four subtidal locations (9–617 m apart) along the axis of a major creek. We trapped and marked 2,297 individuals and recaptured 15–22% of the fishes released at each site, almost all of which (99.7%) had been marked at the same location of recapture up to 3 months earlier. In Experiment 2, we investigated pinfish movements between subtidal and intertidal areas. In the 8 weeks prior to sampling 2 intertidal creeks, we marked 950 juveniles in the adjacent subtidal areas. Sampling of the 2 flooded intertidal creeks showed that 9–20% of the pinfish collected bore marks, and all had been previously marked at the subtidal site immediately adjacent to the intertidal creek. Gut analysis of 60 individuals revealed that juveniles collected from the intertidal areas at high tide had consumed about ten times more food than those collected at the subtidal sites at low tide. In Experiment 3, we determined the fidelity of recently settled pinfish (<35 mm SL) and showed that 15% of the 434 marked pinfish remained in the same area; some were at liberty up to 7 weeks. In Experiment 4, we determined home range by tagging and recapturing juvenile pinfish at sites separated by 20 m along a 200 m subtidal transect. We estimated that during periods when the intertidal zone was not accessible, the average home range was 9.4 m with only 10% of tagged fish moving greater than 20 m during the 4 month study. Our results indicate that soon after recruitment to the estuary, pinfish establish strong fidelity for sites within salt marsh creeks and exhibit tidal periodicity in both movements and feeding.

The effect of fiddler crab burrowing on sediment mixing and radionuclide profiles along a topographic gradient in a southeastern salt marsh

Fiddler crabs are one of the principal agents of bioturbation in intertidal salt marshes. The physical, chemical, and biological properties of sediments can be modified by fiddler crab burrowing activity. This study examined the effect of fiddler crab burrowing on sediment reworking and the distributions of 210 Pb and 137 Cs in salt marsh sediments at North Inlet Estuary, South Carolina. Fiddler crab burrow density, turnover, and volume were measured along a transect from the forest to the creek bank. Burrow density ranged between 40 and 300 burrows m -2 with highest densities at the creek bank. Sediment reworking is related to burrow turnover, density and size, Sediment reworking rates ranged between 4.4 X 10 3 and 5.7 X 10 4 cm 3 m -2 y -1 . Excess 210 Pb and 137 Cs profiles indicated that fiddler crab burrowing mixed the top 8 to 15 cm of sediment. Direct field measurements of burrow density, turnover, and size were used as input to a modified version of the regeneration model of Gardner et al. (1987) to assess the effect of fiddler crab bioturbation on 210 Pb profiles. The modification takes into account the filling of abandoned fiddler crab burrows from both the infilling of surface sediment and the collapse of burrow walls. Model results were in good agreement with the observed 210 Pb distributions in the sediments. Overall the results of this study suggest that fiddler crabs directly influence sediment composition and biogeochemical cycles in salt marsh systems.

Grazing of two euplotid ciliates on the heterotrophic dinoflagellates Pfiesteria piscicida and Cryptoperidiniopsis sp.

Pfiesteria piscicida and Cryptoperidiniopsis spp. are common co-occurring heterotrophic dinoflagellates in estuaries along the Atlantic coast of the United States. We isolated P. piscicida, Cryptoperidiniopsis sp., and 2 benthic ciliates (Euplotes vannus and E. woodruffi) from North Inlet estuary, South Carolina, and examined the growth and graz- ing properties of the ciliates on cultures of the dinoflagellates maintained with cryptophyte (Storeatula major) prey. Ciliate growth and grazing parameters on cryptophyte monocultures and mixed diets of cryptophytes and P. piscicida were signifi- cantly higher with E. woodruffi than E. vannus. Also, the net grazing impact of E. woodruffi on P. piscicida prey was higher than the impact on Cryptoperidiniopsis sp., while the E. van- nus grazing effect did not differ with dinoflagellate prey. The results indicate the potential for effective predatory con- trol by euplotid ciliates on nontoxic P. piscicida and Crypto- peridiniopsis sp. under defined laboratory conditions.