Effects of dredging and open-water disposal on benthic macroinvertebrates in a South Carolina estuary

Approximately 28,475 m³ of muddy sediments were dredged from a shoal in a South Carolina estuarine system and released near the surface at a nearby site having high tidal current velocities. Effects at the dredged sites included decreased macrofaunal abundance and changes in species composition. These effects appeared to be short term, with substantial recovery occurring within 3 months. Rapid recovery was primarily attributed to immigration through slumping of channel wall sediments similar to those dredged. Detrimental effects on benthic macrofauna in the area of open water disposal were minimal. Most differences noted in community structure between collection dates were attributed to sampling and seasonal variability. The absence of a major longterm disruption to the benthos in the disposal area was probably due to (1) strong tidal currents, which rapidly dispersed the moderate amount of mud sediments released; (2) surface disposal, permitting wider dispersal; and (3) disposal during late autumn, a period of low faunal recruitment.     

Seasonal abundance of atlantic croaker (Micropogonias undulatus) in relation to bottom salinity and temperature in South Carolina estuaries

During 1973 and 1974 seasonal abundance and mean total length of Atlantic croaker,Micropogonias undulatus, were investigated by otter trawl at 33 stations in South Carolina estuaries in relation to bottom salinity and temperature. Relative abundance of Atlantic croaker was measured by catch per unit effort at 3°C temperature intervals and 3‰ salinity intervals. Croaker occurred over a bottom temperature range of 9.0–31.4°C while occurring most abundantly in waters above 24.0°C. No significant correlation between size and temperature was found. Croaker were collected in salinities from 0.4 to 34.4‰. High correlations of size and salinity were evident in 1973 during winter (r=0.79), summer (r=0.82), and fall (r=0.94). In 1974, correlations were significant only during fall (r=0.76).     

The impact of a severe drought on the vegetation of a subtropical estuary

In order to document the effect of the recent drought and the resulting marine intrusion event on plant-community shifts in a Louisiana estuary, we analyzed two vegetation data sets collected in Barataria estuary in 1997 and 2000 and compared community shifts to surface salinity changes at four points along the estuarine gradient within the study area. We used the major vegetation types identified in our previous research of larger data sets and tested the use of a simple vegetation classification technique. This vegetation classification technique is based primarily on the dominant and co-dominant species, and secondarily on the number of taxa observed. To distinguish vegetation types with similar dominant species but different associated species, the vegetation classification technique used a salinity score derived from the species composition. Surface water salinity increases were reflected by a change in species composition in the mesohaline to fresh marshes. The largest species composition shift observed was the shift from oligohaline wiregrass (species rich vegetation type dominated bySpartina patens) to mesohaline wiregrass (vegetation type dominated byS. patens with few other species). Shifts in vegetation composition may have been enhanced by the presence of the major dominant species at a low abundance in other vegetation types. The vegetation classification technique used could classify over 95% of the stations. This vegetation classification technique provides a simple method to classify Louisiana's coastal vegetation based on plant species composition.     

The soft-bottom macrobenthos of North Carolina estuaries

The structure of macro infaunal (>0.5 mm sieve size) assemblages was examined in samples of unconsolidated substrates collected during the summers of 1994–1997 at 208 stations throughout North Carolina estuaries. Numerical classification (cluster analysis) of stations resulted in 14 distinct site groups that reflected discernible habitatrelated patterns in species distributions. Multiple discriminant analysis, performed on synoptic abiotic variables (depth, salinity, dissolved oxygen, pH, percent silt-clay), showed that the separation of site groups was related primarily to salinity. Percent silt-clay had a secondary influence on the separation of sites within similar salinity zones. Species diversity among site groups generally decreased with decreasing salinity and increasing mud content of sediment. Nodal analysis showed a wide range in constancy and fidelity of species assemblages within site groups. Some assemblages dominated by euryhaline species had no particular affinity with any one site group. The strongest affinities, as evidenced by high values of both constancy and fidelity, were displayed by an assemblage of oligochaetes, insect larvae, gammaridean amphipods, and the clamCorbicula fluminea in tidal freshwater muds; and an assemblage of haustoriid amphipods, the bivalveDonax variabilis, the polychaeteParaonis fulgens, and unidentified echinoids at high-salinity sites in outer Pamlico Sound near ocean inlets. A series of stations with impaired benthic assemblages in polluted habitats emerged from the cluster analysis and was distinguishable from other site groups that reflected a greater influence of natural controlling factors (such as salinity and sediment type) on species distributions. These results suggest that the interaction of both anthropogenic and natural environmental controlling factors is important in defining the structure of these infaunal assemblages.     

Impacts of Climate-Related Drivers on the Benthic Nutrient Filter in a Shallow Photic Estuary

In shallow photic systems, the benthic filter, including microphytobenthos and denitrifiers, is important in preventing or reducing release of remineralized NH₄ ⁺ to the water column. Its effectiveness can be impacted by climate-related drivers, including temperature and storminess, which by increasing wind and freshwater delivery can resuspend sediment, reduce salinity and deliver nutrients, total suspended solids, and chromophoric dissolved organic matter (CDOM) to coastal systems. Increases in temperature and freshwater delivery may initiate a cascade of responses affecting benthic metabolism with impacts on sediment properties, which in turn regulate nitrogen cycling processes that either sequester (via microphytobenthos), remove (via denitrification), or increase sediment nitrogen (via remineralization, nitrogen fixation, and dissimilatory nitrate reduction to ammonium). We conducted a seasonal study at shallow stations to assess the effects of freshwater inflow, temperature, wind, light, and CDOM on sediment properties, benthic metabolism, nitrogen cycling processes, and the effectiveness of the benthic filter. We also conducted a depth study to constrain seasonally varying parameters such as temperature to better assess the effects of light availability and water depth on benthic processes. Based on relationships observed between climatic drivers and response variables, we predict a reduction in the effectiveness of the benthic filter over the long term with feedbacks that will increase effluxes of N to the water column with the potential to contribute to system eutrophication. This may push shallow systems past a tipping point where trophic status moves from net autotrophy toward net heterotrophy, with new baselines characterized by degraded water quality.     

Small-scale spatial variation of macrobenthic community structure

Examination of small-scale spatial variation in essential to understanding the relationships between environmental factors and benthic community structure in estuaries. A sampling experiment was performed in October 1993 to measure infauna association with sediment composition and salinity gradients in Nueces Bay, Texas, USA. The bay was partitioned into four salinity zones and three sediment types. Higher densities of macrofaua, were found in sediments with greater sand content and in areas with higher salinity. High diversity was also associated with high homogeneous salinity (31–33‰) and greater sand content. Macrofauna biomass and diversity were positively correlated with bottom salinity, porewater salinity, and bottom dissolved inorganic nitrogen (DIN). Furthermore, species dominance shifted along the estuarine gradient.Streblospio benedicti dominated at lower salinity, but,Mediomatsus ambiseta andMulinia lateralis were the dominant species at higher salinity. Statistical analyses revealed significant correlations for sediment characteristics (i.e., increased fine sediments, water content, and total organic carbon) with decreased total abundance and diversity. Increased salinity and DIN were correlated with increased total biomass, diversity, and macrofauma community structure. These physico-chemical variables are regulated by freshwater inflow, so inflow is an important factor influencing macrofauna community structure by indirectly influencing the physico-chemical environment.     

Temporal and spatial patterns in abundance and diversity of fish assemblages in Elkhorn Slough,California

Assemblages of ichthyofauna of shallow inshore habitats along Californía’s central coast are described in terms of species composition, abundance, and life-style categories. A total of 22,334 fishes from 65 species and 27 families was collected with otter trawls at six sites in the main channel and tidal creeks of Elkhorn Slough, a tidal embayment and seasonal estuary, and two nearshore ocean stations in Monterey Bay during 44 months between August 1974 and June 1980. Greater than 90% of the catch comprised 10 species. The four dominant species,Cymatogaster aggregata, Leptocottus armatus, Phanerodon furcatus, andEmbiotoca jacksoni, occurred during most or all seasons and were classified as residents or partial residents. Several abundant species were marine immigrants that seasonally use the slough as spawning and nursery grounds; this resulted in higher abundance and species richness during summer. Species collected during winter largely were slough residents. Species compsosition and richness varied with distance from the slough entrance. The ocean assemblage was most different, and its similarity to other stations decreased progressively with distance inland and into the tidal creeks. During our study, 5,074 fishes were collected by beach seine in Bennett Slough, a remote shallow marsh basin adjacent to the entrance of Elkhorn Slough. Species richness was relatively low and three euryhaline species accounted for >80% of the total catch. The species assemblage was most similar to those at the tidal creek and most shallow stations of Elkhorn Slough. Resident species numerically dominated assemblages in Bennett Slough and the most inland areas of Elkhorn Slough. The high relative abundance of marine-related fishes (classified as marine, marine immigrant, and partial resident), entering Elkhorn Slough early in life or as spawning adults indicates the importance of this habitat to nearshore fish assemblages.     

Seasonal and spatial distribution of planktonic crustacea in the lower Saint John River,a multibasin estuary in New Brunswick,Canada

Five stations on the lower Saint John River, a complex multibasin estuary, were sampled semiquantitatively for zooplankton at biweekly intervals for one year, and qualitatively over a 4-year period. Planktonic Crustacea were dominated by the true estuarine copepods,Acartia tonsa andEurytemora affinis and the euryhaline marine copepodsOithona similis andPseudocalanus minutus. Atypical estuarine forms, confined to a lower fiord-like basin with salinity of 20‰, were the amphipod,Parathemisto abyssorum and the mysidErythrops erythrophthalma. River flows were highly variable from year to year. Certain basins function as lakes in some years and estuaries in other years, causing extreme zooplankton community fluctuations, and succession patterns dependent on salinity rather than season. On occasion freshwater zooplankters maintained viable populations at unusually high salinities (ca. 5‰). Vertical and horizontal distributions of zooplankters indicate that the estuary in fact comprises two systems: a true estuary in the upper reaches and the surface waters at the lower end, and a fiord in a subsidiary basin in the lower end.     

Spatial and temporal patterns in coastal macrobenthos of Samborombon Bay, Argentina: A case study of very low diversity

The benthic community structure of the southernmost part of Samborombon Bay was studied at 13 stations for 2 yr. A detailed examination of the zoobenthos, using similarity indices and cluster analysis, is presented. The area was characterized by low diversity. The Shannon-Weaver information diversity index H′ showed low values of 0.28–1.60. The brackish part of the area was dominated by two opportunistic polychaetes species,Heteromastus similis andLaeonereis acuta. The only species found in the transitional marine zone was the bivalveMesodesma mactroides. Variability in benthic community has been interpreted in terms of spatial and temporal changes. Depending on the area, abundance appeared to be controlled by pollution and intense predation during the warmer months. The observed gradient in species composition and dominance of these benthic communities are compared with some other North and South Atlantic estuaries.     

Tropicalization of the Northern Gulf of Mexico: Impacts of Salt Marsh Transition to Black Mangrove Dominance on Faunal Communities

The tropically associated black mangrove (Avicennia germinans) is expanding into salt marshes of the northern Gulf of Mexico (nGOM). This species has colonized temperate systems dominated by smooth cordgrass (Spartina alterniflora) in Texas, Louisiana, Florida and, most recently, Mississippi. To date, little is known about the habitat value of black mangroves for juvenile fish and invertebrates. Here we compare benthic epifauna, infauna, and nekton use of Spartina-dominated, Avicennia-dominated, and mixed Spartina and black mangrove habitats in two areas with varying densities and ages of black mangroves. Faunal samples and sediment cores were collected monthly from April to October in 2012 and 2013 from Horn Island, MS, and twice yearly in the Chandeleur Islands, LA. Multivariate analysis suggested benthic epifauna communities differed significantly between study location and among habitat types, with a significant interaction between the two fixed factors. Differences in mangrove and marsh community composition were greater at the Chandeleurs than at Horn Island, perhaps because of the distinct mangrove/marsh ecotone and the high density and age of mangroves there. Infaunal abundances were significantly higher at Horn Island, with tanaids acting as the main driver of differences between study locations. We predict that if black mangroves continue to increase in abundance in the northern GOM, estuarine faunal community composition could shift substantially because black mangroves typically colonize shorelines at higher elevations than smooth cordgrass, resulting in habitats of differing complexity and flooding duration.     

The tubificidae (Annelida,oligochaeta) of a louisiana estuary: Ecology and systematics,with the description of a new species

Spatial and temporal variations in the abundances and distributions of oligochaetes of a southwestern Louisiana estuary were examined as part of a long term study of community structure of benthic macroinvertebrates. Quantitative samples were collected at monthly intervals from nine stations for two years and an additional 17 stations were sampled once. A tubificid oligochaete,Tubificoides denouxi n. sp., is described from the five species collected. The two predominant oligochaetes,Tubificoides heterochaetus andT. denouxi, were congeneric and exhibited completely allopatric distributions. Two oligochaete species with-restricted distributions,Monopylephorus helobius andLimnodriloides sp., were sympatric withT. denouxi, whileThalassodrilides belli, although less abundant, was sympatric with bothT. denouxi andT. heterochaetus. Sexually mature specimens ofT. denouxi andT. belli were collected only in the summer,T. heterochaetus was sexually mature in both winter and summer collections, andMonopylephorus helobius was sexually mature in spring and summer collections. Many of the studies of Oligochaeta have concluded that correlation exists between sediment grain size and species demography. Our data demonstrate a strong relationship between salinity and the abundance and distribution of estuarine species.Tubificoides denouxi was found only within the salinity range of 14.8 to 22.0‰ salinity,T. heterochaetus was found only within the range of 2.3 to 14.1‰, andT. belli had a salinity distribution intermediate between the previous species. No relationship was found between sediment grain-size analysis, water depth or hydrographic variables and species distribution.     

Seasonal abundance of aquatic diptera in two oligohaline tidal marshes in Mississippi

Nineteen species of Diptera (16 in each zone) from seven families were found in monthly collections (June 1979 through May 1980) in two Mississippi marsh plant zones dominated byJuncus roemerianus Scheele andSpartina cynosuroides (L.) Roth, respectively. TheJuncus zone was dominated by a species ofPalpomyia-Bezzia complex, two species ofBezzia (Ceratopogonidae),Paratendipes sp.,Limnophyes sp. (Chironomidae) andThinophilus frontalis (Dolichopodidae).Palpomyia-Bezzia sp.,Culicoides hollensis, Ormosia sp. (Tipulidae) andPelastoneurus abbreviatus (Dolichopodidae) dominated theSpartina zone. Total inset density and species richness were lowest in June and July in both zones, corresponding to a pulse of adult emergence. Overall, total density was significantly higher in theSpartina zone with mean values of 165 and 245 insects m^?2 for the {Juncus} and {Spartina} zones, respectively. In addition to total density, differences in abundance were apparent for a number of species between marsh zones. Patterns could be attributed to species-specific habitat preference., predation by aquatic predators, and/or by interactions of the infauna themselves.     

Benthic macrofaunal communities in partially impounded salt marshes in Delaware: Comparisons with natural marshes and responses to sediment exposure

This two-part study examined the benthic macrofaunal community in Delaware salt marsh impoundments having partial tidal restriction. The first part compared abundance, diversity, and taxonomic composition in three habitat types in impoundments—creeks, vegetated creek banks, and ponds—to those found in natural marshes. Impoundment effects were present but were habitat-specific. Abundances were higher in natural marsh creeks than in impoundment creeks, and diversities were higher in impoundment ponds than in natural marsh ponds. Vegetated bank communities in impoundments were about 50% insects and arachnids and 50% oligochaetes, while natural bank communities were primarily oligochaetes and the polychaeteManayunkia aestuarina. This is likely due to the decrease in flooding of the vegetated high marsh caused by partial impoundment. Pond and creek community composition also showed impoundment effects: in comparison with natural marshes, impoundments had higher proportions of the burrowing anemoneNematostella vectensis, nemerteans, andTubificoides sp. oligochaetes and lower proportions of the oligochaeteClitellio arenarius. The second part of the study compared benthic macrofauna in an impoundment before, during, and after the water level was lowered so that some bottom sediments were exposed and some covered with just a few centimeters of water for several weeks. During this event, macrofaunal abundances were reduced and the community shifted from being dominated by annelids, anemones, and nemerteans toward one dominated by annelids and insects. About 6 wk after reflooding, persistent effects of this disturbance were still suggested by greatly increased abundances and 96% dominance by one species of oligochaete,Paranais litoralis. Impoundment management plans calling for periods of sediment exposure or very low water may want to consider the potential for strong and persistent effects on the macrofaunal community.     

Structural components of eelgrass (Zostera marina) meadows in the lower Chesapeake Bay—Decapod crustacea

Otter trawl collections of eelgrass habitats in the lower Chesapeake Bay during 1976–1977 produced 14 species of decapod crustaceans. These collections were dominated by palaemonid shrimp (Palaemonetes spp.), blue crabs (Callinectes sapidus), and sand shrimp (Crangon septemspinosa), each of which exhibited unimodal seasonal abundance curves with large summer peaks. Decapod abundance was positively correlated with plant biomass throughout the year. Decapod densities on vegetated bottoms were greater than on unvegetated bottoms, and nighttime abundance on each bottom type was greater than corresponding daytime abundance. Total decapod abundances in Chesapeake Bay eelgrass meadows appear to be much greater than those reported in North Carolina eelgrass or Gulf of Mexico turtlegrass habitats.     

A portable suction dredge for quantitative sampling in difficult substrates

A lightweight, portable suction dredge has been used for five bottom types which usually present problems to benthic investigators. Water depth ranged from 0.25 m to 5 m. By use of a 0.25 m² quadrat or using the suction end as a probe with the depth of penetration limited by a collar, quantitative samples were taken in coarse sand, fine flocculent mud, dense turtle grass (Thalassia testudinum), sparse turtle grass over coralline rubble (Porites sp.) and carbonate rock with an overlay of shell rubble. The samples consisted of the material retained by a collecting bag attached to the suction dredge. None of the commonly used benthic sampling devices could obtain samples at all stations.     

The structure of two South Carolina estuarine tide pool fish assemblages

The fish assemblages of two South Carolina estuarine tide pools located in the North Edisto River were sampled from June to October 1977, and during June and July 1978, by haul seine, lift net and channel net. The nekton was dominated numerically byFundulus heteroclitus, Leiostomus xanthurus, Menidia menidia andAnchoa mitchilli. Oyster reef areas were dominated numerically byGobiosoma bosci andF. heteroclitus. The relative abundance of tide pool fishes differs from deep water areas of the North Edisto River as described from otter trawls, but is similar to that described by others for South Carolina tidal creeks.     

Identification of important primary producers in a Chesapeake Bay tidal creek system using stable isotopes of carbon and sulfur

The use of multiple stable isotopes in the study of trophic relationships in temperate estuaries has usually been limited to euhaline systems, in which phytoplankton, benthic microalgae, andSpartina alterniflora are major sources of organic matter for consumers. Within large estuaries such as Chesapeake Bay, however, many species of consumers are found in the upper mesohaline to oligohaline portions. These lower salinity wetlands have a greater abundance of macrophytes that use C3 photosynthesis to fix carbon, in addition toS. alterniflora, which fixes carbon via the C4 photosynthetic pathway. In a broad survey of the biota and sediments of a brackish tidal creek tributary to Chesapeake Bay, combined δ¹³C and δ³⁴S measurements disclosed a balanced contribution to secondary production from phytoplankton, C3 macrophytes,Spartina sp., and benthic microalgae. Surface sediment δ¹³C suggested that the organic matter from C3 plants was derived both from allochthonous sources (terrestrial runoff) and from autochthonous production (marsh macrophytes). Unlike most estuarine systems studied to date, which are dominated by algae (phytoplankton and benthic microalgae) and C4 macrophytes, C3 plants are of greater importance in the diets of consumers in this low-salinity creek system.     

Relationship between waterfowl and the seagrassRuppia maritima in a Southwestern Atlantic coastal lagoon

We evaluated the distribution of waterfowl in relation to a seagrass (Ruppia maritima) patch, to infauna, and on its relationship with substrate characteristics. An experiment performed in the Mar Chiquita coastal lagoon (37°46′S, 57°27′W; Argentina) was used to evaluate the effect of herbivory on widgeon grass,R. maritima. Control plots of equal size, located between bird exclosures, were exposed to herbivory. The experiment ran for 31 d, starting on December 1, 1994. Censuses showed that black-necked swan ( $\bar x = 50$ birds ha^?1, SD = 37, n = 10) and coots ( $\bar x = 42$ birds ha^?1, SD = 28, n = 10) were the most important (always present) of the waterfowl seen feeding onR. maritima. The results of the experiment showed greater leaf lengths, lower belowground (rhizomes and roots) biomass, greater aboveground (leaves and shoots) biomass, and greater abundance of the polychaeteHeteromastus similis in exclosure plots. There were no exclosure effects on total biomass (belowground plus aboveground), reproductive parts (fruits and pre- and postpollination flowers), or abundance of most benthic infauna. Topographic surveys showed that sediment surface was higher within theR. maritima patches, but there were no significant differences in granulometric composition. Surveys also showed that bird distribution was strongly associated with the presence ofR. maritima.     

Time series analyses of suspended sediment concentrations at North Inlet,South Carolina

Daily water samples have been collected at three stations in the North Inlet (South Carolina) marshestuary system since February 1981 as part of the NSF Long-Term Ecological Research (LTER) project. As a result of this sampling regime, nearly continuous time series of inorganic and organic suspended sediment, particulate organic carbon (POC), Secchi disk, salinity, and water temperature are now available. Power spectrum analysis of these data reveals that most of the explainable variance in the inorganic suspended sediment, POC, and Secchi disk data is related to a yearly cycle that is strongly coherent with water temperature such that high turbidity is associated with high water temperature. Only a small fraction of the explainable variance is associated with frequencies that can be related to the semidiurnal tide. Simple correlation analysis also indicates that turbidity is more closely associated with water temperature than with tide height or salinity. The ratio of POC to inorganic suspended sediment shows no discernible power spectra peaks and is weakly, but inversely, correlated with temperature. From these results we hypothesize that temperature-regulated bioturbation is the main factor controlling turbidity variations in the system. The lack of a strong inverse correlation between turbidity and salinity suggests that river runoff has little immediate impact on the suspended sediment of nearshore coastal waters in systems similar to North Inlet.