Habitat associations of estuarine species: Comparisons of intertidal mudflat, seagrass (Zostera marina), and oyster (Crassostrea gigas) habitats

The complexity of habitat structure created by aquatic vegetation is an important factor determining the diversity and composition of soft-sediment coastal communities. The introduction of estuarine organisms, such as oysters or other forms of aquaculture, that compete with existing forms of habitat structure, such as seagrass, may affect the availability of important habitat refugia and foraging resources for mobile estuarine fish and decapods. Fish and invertebrate communities were compared between adjacent patches of native seagrass (Zostera marina), nonnative cultured oyster (Crassostrea gigas), and unvegetated mudflat within a northeastern Pacific estuary. The composition of epibenthic meiofauna and small macrofaunal organisms, including known prey of fish and decapods, was significantly related to habitat type. Densities of these epifauna were significantly higher in structured habitat compared to unstructured mudflat. Benthic invertebrate densities were highest in seagrass. Since oyster aquaculture may provide a structural substitute for seagrass being associated with increased density and altered composition of fish and decapod prey resources relative to mudflat, it was hypothesized that this habitat might also alter habitat preferences of foraging fish and decapods. The species composition of fish and decapods was more strongly related to location within the estuary than to habitat, and fish and decapod species composition responded on a larger landscape scale than invertebrate assemblages. Fish and decapod species richness and the size of ecologically and commercially important species, such as Dungeness crab (Cancer magister), English sole (Parophrys vetulus), or lingcod (Ophiodon elongatus), were not significantly related to habitat type.     

Fish and invertebrate assemblages in seagrass, mangrove, saltmarsh, and nonvegetated habitats

Many studies compare utilization of different marine habitats by fish and decapod crustaceans; few compare multiple vegetated habitats, especially using the same sampling equipment. Fish and invertebrates in seagrass, mangrove, saltmarsh, and nonvegetated habitats were sampled during May–August (Austral winter) and December–January (Austral summer) in the Barker Inlet-Port River estuary, South Australia. Sampling was undertaken using pop nets in all habitats and seine nets in seagrass and nonvegetated areas. A total of 7,895 fish and invertebrates spanning 3 classes, 9 orders, and at least 23 families were collected. Only one fish species,Atherinosoma microstoma, was collected in all 4 habitats, 11 species were found in 3 habitats (mangroves, seagrass, and nonvegetated), and 13 species were only caught in seagrass and nonvegetated habitats. Seagrass generally supported the highest numbers of fish and invertebrates and had the greatest species richness. Saltmarsh was at the other extreme with 29 individuals caught from two species. Mangroves and nonvegetated habitats generally had more fish, invertebrates, and species than saltmarsh, but less than seagrass. Analyses of abundances of individual species generally showed an interaction between habitat and month indicating that the same patterns were not found through time in all habitats. All habitats supported distinct assemlages although seagrass and nonvegetated assemblages were similar in some months. The generality of these patterns requires further investigation at other estuaries. Loss of vegetated habitats, particularly seagrass, could result in loss of species richness and abundance, especially for organisms that were not found in other habitats. Although low abundances were found in saltmarsh and mangroves, species may use these habitats for varying reasons, such as spawning, and such use should not be ignored.     

Nekton of new seagrass habitats colonizing a subsided salt marsh in Galveston Bay, Texas

Subsidence and erosion of intertidal salt marsh at Galveston Island State Park, Texas, created new areas of subtidal habitat that were colonized by seagrasses begining in 1999. We quantified and compared habitat characteristics and nekton densities in monospecific beds of stargrassHalophila engelmanni and shoalgrassHalodule wrightii as well as adjacent nonvegetated substrates. We collected 10 replicates per habitat type during April, July, October, and December 2001. Most habitat characteristics varied with season. Water temperature, salinity, and dissolved oxygen were similar among habitat types. Turbidity and depth were greatest inH. engelmanni beds and least inH. wrightii beds.H. engelmanni exhibited shorter leaves and higher shoot density and biomass core⁻¹ thanH. wrightii. Densities of almost all dominant species of nekton (fishes and decapods) were seasonally variable, all were higher in seagrass habitats than in nonvegetated habitats, and most were higher in one seagrass species than the other. Naked gobyGobiosoma bosc, code gobyGobiosoma robustum, bigclaw snapping shrimpAlpheus heterochaelis, and blue crabCallinectes sapidus, were most abundant inH. engelmanni. Brown shrimpFarfantepenaeus aztecus, brackish grass shrimpPalaemonetes intermedius, and daggerblade grass shrimpPalaemonetes pugio were most abundant inH. wrightii. PinfishLagodon rhomboides and pink shrimFarfantepenaeus duorarum were equally abundant in either seagrass. Most dominant nekton varied in size by month, but only two (L. rhomboides andC. sapidus) exhibited habitat-related differences in size. Nekton densities in these new seagrass habitats equaled or exceeded densities associated with historical and current intertidal smooth cordgrassSpartina alterniflora marsh. Continued seagrass expansion and persistence should ensure ecosystem productivity in spite of habitat change.     

Variability in drift macroalgal abundance in relation to biotic and abiotic factors in two seagrass dominated estuaries in the Western Gulf of Mexico

We examined the spatial and temporal variability in drift macroalgal abundance in two seagrass dominated estuarine systems on the Texas coast: Redfish Bay (in the Copano-Aransas Estuary) and Lower Laguna Madre. Measurements of benthic macroalgal variability were made in conjunction with a suite of biotic (seagrass biomass, percent cover, blade width and length, shoot density, epiphyte biomass, seagrass blade C:N ratios, and drift macroalgal abundance and composition) and abiotic (inorganic nitrogen and phosphorus concentrations, chlorophylla, total suspended solids, light attenuation, salinity, temperature, total organic carbon and porewater NH₄ ⁺) indicators. All parameters were measured at 30 sites within each estuary semiannually from July 2002 to February 2004. Principal components analysis (PCA) was used to examine relationships between drift macroalgal abundance and biotic and abiotic parameters. In both Redfish Bay and Lower Laguna Madre, drift macroalgal distribution was widespread, and during three of four sampling periods, abundance was equal to abovegro und biomass ofThalassia testudinum, the dominant seagrass. Drift macro algal abundance was highly variable within sites, between sites, and between seasons in both estuaries. No significant differences in drift macroalgal abundance were found between Redfish Bay and Lower Laguna Madre. In Redfish Bay, drift macroalgae (90.1±10.2 gm⁻²) tended to accumulate in bare patches within seagrass beds. In Lower Laguna Madre, drift macroalgae (72.7±10.7 gm⁻²) tended to accumulate in areas of dense seagrass cover rather than in bare areas. We found no relationship between drift macroalgal abundance and low (<2μM) water column nutrient concentrations, and although several of our measured parameters were related to drift macroalgal abundance, none alone sufficiently explained the variability in abundance noted between the two estuarine systems. The contrasting patterns of macroalgal accumulation between Redrish Bay and Lower Laguna Madre likely reflect differences in water circulation characteristics between the two regions as dictated by local physiography, in cluding the shape and orientation of the lagoons, with seasonal variations in macroalgal abundance related to changes in freshwater inflow and nutrient loading.     

Latitudinal patterns in seagrass epifauna: Do patterns exist,and can they be explained?

Seagrass-associated epifauna of several taxa constitute a major parallel element of seagrass communities over a range of latitudes. Hypotheses relating to latitudinal variation of several factors (e.g., predation, competition, primary production, habitat structure, stability and time) have been proposed to explain geographic variation in the structure of biological systems. We have summarized available information to firstly determine whether any latitudinal patterns exist for the seagrass-associated epifauna, and secondly to examine hypotheses which might explain observed patterns. Diversity and density of various seagrass epifaunal groups showed inconsistent latitudinal patterns. Diversity of decapod and amphipod crustaceans increased significantly with decreasing latitude, while diversity of isopods and fishes showed nonsignificant trends with latitude. Amphipod diversity was highly correlated with seagrass biomass over the range of latitudes. However, density of amphipods showed no pattern with either latitude or seagrass biomass; large within-site differences may have overwhelmed latitudinal patterns. For seagrass-associated amphipods, two parameters presumably related to predation intensity showed contradictory patterns. Size of individuals generally decreased toward the tropics, yet susceptibility to predators showed weak trends of increasing in the tropics. We found little support for the assumed gradients of those hypotheses proposed to explain latitudinal patterns in biota. Only a weak trend of increasing seagrass production toward the tropics was found; there was no relationship between latitude and seagrass biomass (=habitat complexity in part), epiphyte species richness (=habitat heterogeneity in part), or predator abundance. No data were available comparing actual intensity of predation on seagrass fauna or on proposed gradients of stability and competition. The patterns found were not consistent with the predictions of any single hypothesis. Contrary to evidence from other biological systems, it appears that latitude is, in general, an inconsistent predictor of differences in structure of the epifaunal component of seagrass communities. Although we did find some latitudinal patterns of increasing diversity and susceptibility to predators and decreasing size of individual amphipods toward the tropics, we were astonished by the lack of data supporting the assumptions of hypotheses concerning primary productivity, stability, time, competition, predation and habitat heterogeneity and complexity.     

The response of fishes to submerged aquatic vegetation complexity in two ecoregions of the mid-Atlantic bight: Buzzards Bay and Chesapeake Bay

Estuarine seagrass ecosystems provide important habitat for fish and invertebrates and changes in these systems may alter their ability to support fish. The response of fish assemblages to alteration of eelgrass (Zostera marina) ecosystems in two ecoregions of the Mid-Atlantic Bight (Buzzards Bay and Chesapeake Bay) was evaluated by sampling historical eelgrass sites that currently span a broad range of stress and habitat quality. In two widely separated ecoregions with very different fish faunas, degradation and loss of submerged aquatic vegetation (SAV) habitat has lead to declines in fish standing stock and species richness. The abundance, biomass, and species richness of the fish assemblage were significantly higher at sites that have high levels of eelgrass habitat complexity (biomass >100 wet g m^?2; density <100 shotts m^?2) compared to sites that have reduced eelgrass (biomass <100 wet g m^?2; density <100 shoots m^?2) or that have completely lost eelgrass. Abundance, biomass, and species richness at reduced eelgrass complexity sites also were more variable than at high eelgrass complexity habitats. Low SAV complexity sites had higher proportions of pelagic species that are not dependent on benthic habitat structure for feeding or refuge. Most species had greater abundance and were found more frequently at sites that have eelgrass. The replacement of SAV habitats by benthic macroalgae, which occurred in Buzzards Bay but not Chesapeake Bay, did not provide an equivalent habitat to seagrass. Nutrient enrichment-related degradation of eelgrass habitat has diminished the overall capacity of estuaries to support fish populations.     

Short-Term Effects of an Oil Spill on Marsh-Edge Fishes and Decapod Crustaceans

On 19 April 2005, an oil spill occurred in southeastern Louisiana’s Barataria Bay estuary. We used a drop sampler to characterize the marsh-edge nekton community. Thirty-six locations were sampled in pre- and post-spill time frames from March through May 2005. Before–after control–impact (BACI) analyses of the total number of individuals (fishes + decapod crustaceans), total fishes, and sensitive species found significant interactions between the temporal (before/after) and spatial (control/impact) treatments and indicated an effect of the oil spill. Nonparametric analyses detected varied faunal assemblages across temporal treatments, but were similar in species composition among spatial treatments. While the BACI analyses showed event effects, differences were not strongly detected in nonparametric analyses of community structure. Fish are mobile and left the spill area after the disturbance, whereas the less mobile but more numerous benthic decapod crustaceans remained. The overall community structure appears to be robust and quickly recovered from the localized spill event.     

The fish community of a shallow tropical lagoon in Belize,Central America

Trawl collections indicate that the fish community of the Belize barrier reef lagoon is dominated numerically and in biomass by grunts (Haemulidae), especiallyHaemulon sciurus andHaemulon flavolineatum. Although the gear selected for small sizes, length frequency analysis indicated seasonality in recruitment of the dominant species of grunts. Apogonids and tetraodontiform fishes were also dominant components of the community. Most fishes collected were juveniles of species that occur as adults on the main reef, or were small species that are resident in the lagoon. Of three habitats sampled, the mangrove creek had the greatest relative abundance and biomass of fishes, followed by the seagrass bed and the sand-rubble zone. There were no significant seasonal differences in fish relative abundance or biomass. Community structure analysis indicated a uniqueness in the mangrove fish community. Diversity (H′) was high, and was due to high species richness and evenness of distribution of individuals among species. The Belize barrier reef lagoon serves as an important nursery habitat for juvenile fishes.     

Nekton use of submerged aquatic vegetation, marsh, and shallow unvegetated bottom in the Atchafalaya River delta, a Louisiana tidal freshwater ecosystem

We sampled nekton (fishes and decapod crustaceans) in submerged aquatic vegetation (SAV) (Potanogeton nodosus, Najas guadalupensis), in emergent marsh vegetation (Sagittaria spp. andScirpus americanus), and over unvegetated bottom associated with three islands in the Atchafalaya River Delta, Louisiana. The purpose of our study was to quantify nekton densities in these major aquatic habitat types and to document the relative importance of these areas to numerically dominant aquatic organisms. We collected a total of 33 species of fishes and 7 species of crustaceans in 298 1-m² throw trap samples taken over three seasons: summer (July and August 1994), fall (September and October 1994), and spring (May and June 1995). Fishes numerically accounted for >65% of the total organisms collected. Vegetated areas generally supported much higher nekton densities than unvegetated sites, although bay anchoviesAnchoa mitchilli were more abundant over unvegetated bottom than in most vegetated habitat types. Among vegetation types, most species showed no apparent preference between SAV and marsh. However, inland silversidesMenidia beryllina and freshwater gobiesGobionellus shufeldti were most abundant inScirpus marsh in summer, and blue crabsCallinectes sapidus were most abundant in SAV (Potamogeton) in spring. Several species (sheepshead minnowCyprinodon variegatus, rainwater killifishLucania parva, and blue crab) apparently selected the vegetated backmarsh of islands (opposite of riverside) over stream-sideScirpus marsh. Freshwater gobies, in contrast, were most abundant in streamsideScirpus marsh. Densities of juvenile blue crabs were high (up to 17 m⁻²) in vegetated delta habitat types and comparable to values reported from more saline regions of Gulf Coast estuaries. Shallow vegetated habitat types of the Atchafalaya River Delta and other tidal freshwater systems of the Gulf Coast may be important nursery areas for blue crabs and other estuarine species.     

Nekton use of subtidal oyster shell habitat in a Southeastern U.S. estuary

Subtidal accumulations of oyster shell have been largely overlooked as essential habitat for estuarine nekton. In southeastern U.S. estuaries, where oyster reef development is mostly confined to the intertidal zone, eastern oyster (Crassostrea virginica) shell covered bottoms are often the only significant source of hard subtidal structure. We characterized and quantified nekton use of submerged shell rubble bottoms, and compared it to use of intertidal reefs and other subtidal bottoms in the North Inlet estuary, South Carolina. Replicate trays (0.8 m²) filled with shell rubble were deployed in shallow salt marsh creeks, and were retrieved after soak times of 1 to 25 days from May 1998 to March 2000. Thirty six species of fishes, representing 21 families, were identified from the 455 tray collections. Water temperature, salinity, soak time and the presence of a shell substrate all affected the catch of fishes in the trays. Catches during the warmer months were two to five times greater than those during the winter. Fishes were present in 98% of the trays with an overall average of 5.7 fish m^?2. The assemblage was numerically dominated by small resident species including naked goby (Gobiosoma bose), oyster toadfish (Opsanus tau), and crested blenny (Hypleurochilus geminatus). Transient species accounted for 23% of all individuals and 62% of the total biomass due to the presence of relatively large sheepshead (Archosargus probatocephalus) and black sea bass (Centropristis striata). Both the transient and resident species displayed distinct periods of recruitment and rapid growth from April to October. Lower abundances of juvenile gobies and blennies during 1998 were attributed to long periods of depressed salinity caused by high rainfall associated with El Niño conditions in spring. Crabs and shrimps, which were often more abundant than the fishes, accounted for comparable biomass in the tray collections. In comparisons of subtidal tray and trawl catches, trays yielded 10 to 1,000 fold higher densities of some demersal fish groups. Comparisons of intertidal and subtidal gear catches indicated that many species remain in the subtidal shell bottom at all stages of the tide. This study suggests that subtidal shell bottom may be essential fish habitat for juvenile seabass, groupers, and snappers and that it may be the primary habitat for a diverse assemblage of ecologically important resident fishes and crustaceans. Given the high levels of nekton use and the areal extent of oyster shell bottoms in eastern U.S. and Gulf estuaries, increased attention to protection and restoration of these areas appears justified.     

Impact of habitat edges on density and secondary production of seagrass-associated fauna

Species richness and abundance of seagrass-associated fauna are often positively correlated with seagrass biomass and structure complexity of the habitat. We found that while shoot density and plant biomass were greater in interior portions of turtle grass (Thalassia testudinum) beds than at edges, mean faunal density was significantly greater at edges than interior sites during 1994. This pattern was also observed in 1995, although differences were not significant. The four numerically dominant taxonomic groups showed varying degrees of elevated densitities at edges ofT. testudinum beds. Peracarids and polychaetes had significantly greater densities at edges oft. testudinum beds, while both decapods and gastropods showed dramatic temporal variability in density, with reversals in density between edge and interior occurring during the course of the study. This within-habitat variability in abundance may reflect both active accumulation of fauna at edges and settlement shadows for species with pelagic larvae. Active accumulation of highly mobile taxa seeking refuge in seagrass beds may explain the differences in density between edge and interior ofT. testudinum patches for peracarids in 1994 and in 1995. Active accumulation at edges may also explain differeces in density for some decapod taxa. Chauges in gastropod densities between habitats may reflect larval settlement patterns. Results showed a distinct settlement shadow for the gastropodCaecum nitidum whose densities (primarily second stage protoconch) increased by more than an order of magnitude in 1994. Settlement shadows and post-settlement processes may also explain density differences of polychaetes between the edge and interior ofT. testudinum patches. The differences in faunal densities between edge and interior habitat resulted in habitat specific differences in secondary production among the major taxonomic groups. On four of five dates in 1994 and in 1995, secondary production was greater at edge than interior locations. These unexpected results suggest that differences in faunal densities and secondary production between edges and interiors of seagrass patches represent a potentially vital link in seagrass trophic dynamics. If this elevated secondary production leads to increases in trophic transfer, then edges may serve as a significant trophic conduit to higher-level consumers in this system.     

The effects of eelgrass habitat loss on estuarine fish communities of southern New England

We studied the late June–August fish community in extant and former eelgrass (Zostera marina L.) habitats in 15 estuaries of Buzzards Bay, and in Waquoit Bay, Massachusetts, U.S. Our objective was to quantify the effects of eelgrass habitat loss on fish abundance, biomass, species composition and richness, life-history characteristics, and habitat use by examining the response of the fish community to eelgrass loss in Waquoit and Buttermilk Bays over an 11-yr period (1988–1999) and in 14 other embayments of Buzzards Bay during 1993, 1996, and 1998. Sampling sites were located in present-day or historical eelgrass beds and were classified according to eelgrass habitat complexity (zero complexity: no eelgrass; low complexity: <100 eelgrass shoots or <100 g wet weight m⁻²; high complexity: ≥100 shoots and ≥100 g wet weight m⁻²). Habitats that had lost eelgrass included a variety of substratum types, from bare mud bottom to dense accumulations of red, brown, and green macroalgae (up to 7,065 g wet weight m⁻²). Contemporaneous sampling of fish (by otter trawl) and vegetated habitat (by divers) was conducted at each site. Overall, fish abundance, biomass, species richness, dominance, and life history diversity decreased significantly along the gradient of decreasing eelgrass habitat complexity. Loss of eelgrass was accompanied by significant declines in these measures of fish community integrity. Ten of the 13 most common species collected from 1988–1996 in Waquoit and Buttermilk Bays showed maximum abundance and biomass in sites with high eelgrass habitat complexity. All but two common species declined in abundance and biomass with the complete loss of eelgrass.     

Seasonal and Spatial Variations in Fish and Macroinvertebrate Communities of Oyster and Adjacent Habitats in a Mississippi Estuary

In Grand Bay National Estuarine Research Reserve (Grand Bay NERR), Mississippi, we used quantitative drop sampling in three common shallow estuarine habitats—low profile oyster reef (oyster), vegetated marsh edge (VME), and nonvegetated bottom (NVB)—to address the dearth in research comparing nekton utilization of oyster relative to adjacent habitats. The three habitats were sampled at two distinct marsh complexes within Grand Bay NERR. We collected a total of 633 individual fishes representing 41 taxa in 22 families. The most diverse fish family was Gobiidae (seven species) followed by Blennidae and Poeciliidae (three species each). We collected a total of 2,734 invertebrates representing 24 taxa in 11 families. The most diverse invertebrate family was Xanthidae (six species) followed by Palaemonidae (five species). We used ordination techniques to examine variation in species relative abundance among habitats, seasons, and sampling areas, and to identify environmental gradients correlated with species relative abundances. Our resulted indicated that oyster provided a similarly complex and important function as the adjacent VME. We documented three basic trends related to the importance of oyster and VME habitats: 1) Oyster and VME provide habitat for significantly more species relative to NVB, 2) Oyster and VME provide habitat for rare species, and 3) Several species collected across multiple habitats occurred at higher abundances in oyster or VME habitat. We also found that salinity, temperature, and depth were associated with seasonal and spatial shifts in nekton communities. Lastly, we found that the relative location of the two marsh complexes we studied within the context of the whole estuary may also explain some of the temporal and spatial differences in communities. We conclude that oyster habitat supported a temporally diverse and spatially distinct nekton community and deserves further attention in research and estuarine conservation efforts.     

Composition,abundance, biomass,and production of macrofauna in a New England estuary: Comparisons among eelgrass meadows and other nursery habitats

Quantitative suction sampling was used to characterize and compare the species composition, abundance, biomass, and secondary production of macrofauna inhabiting intertidal mud-flat and sand-flat, eelgrass meadow, and salt-marsh-pool habitats in the Nauset Marsh complex, Cape Cod, Massachusetts (USA). Species richness and abundance were often greatest in eelgrass habitat, as was macroinvertebrate biomass and production. Most striking was the five to fifteen times greater rate of annual macrofaunal production in eelgrass habitat than elsewhere, with values ranging from approximately 23–139 g AFDW m² yr^?1. The marsh pool containing widgeon grass (Ruppia maritima) supported surprisingly low numbers of macroinvertebrates, probably due to stressfully low dissolved oxygen levels at night during the summer. Two species of macroinvertebrates, blue mussels (Mytilus edulis) and to a lesser extent bay scallops (Argopecten irradians), used eelgrass as “nursery habitat.” Calculations showed that macroinvertebrate production is proportionally much greater than the amount of primary production attributable to eelgrass in the Nauset Marsh system, and that dramatic changes at all trophic levels could be expected if large changes in seagrass abundance should occur. This work further underscores the extraordinarily large impact that seagrass can have on both the structure and function of estuarine ecosystems. *** DIRECT SUPPORT *** A01BY070 00006     

Use of Multiple Chemical Tracers to Define Habitat Use of Indo-Pacific Mangrove Crab, <Emphasis Type="Italic">Scylla Serrata</Emphasis> (Decapoda: Portunidae)

The mangrove or mud crab, Scylla serrata, is an important component of mangrove fisheries throughout the Indo-Pacific. Understanding crab diets and habitat use should assist in managing these fisheries and could provide additional justification for conservation of the mangrove ecosystem itself. We used multiple chemical tracers to test whether crab movements were restricted to local mangrove forests, or extended to include adjacent seagrass beds and reef flats. We sampled three mangrove forests on the island of Kosrae in the Federated States of Micronesia at Lelu Harbor, Okat River, and Utwe tidal channel. Samples of S. serrata and likely food sources were analyzed for stable carbon (δ¹³C), nitrogen (δ¹⁵N), and sulfur (δ³⁴S) isotopes. Scylla serrata tissues also were analyzed for phosphorus (P), cations (K, Ca, Mg, Na), and trace elements (Mn, Fe, Cu, Zn, and B). Discriminant analysis indicated that at least 87% of the crabs remain in each site as distinct populations. Crab stable isotope values indicated potential differences in habitat use within estuaries. Values for δ¹³C and δ³⁴S in crabs from Okat and Utwe were low and similar to values expected from animals feeding within mangrove forests, e.g., feeding on infauna that had average δ¹³C values near −26.5‰. In contrast, crabs from Lelu had higher δ¹³C and δ³⁴S values, with average values of −21.8 and 7.8‰, respectively. These higher isotope values are consistent with increased crab foraging on reef flats and seagrasses. Given that S. serrata have been observed feeding on adjacent reef and seagrass environments on Kosrae, it is likely that they move in and out of the mangroves for feeding. Isotope mixing model results support these conclusions, with the greatest mangrove ecosystem contribution to S. serrata diet occurring in the largest mangrove forests. Conserving larger island mangrove forests (> 1 km deep) appears to support crab foraging activities.     

Effects of common reed (Phragmites australis) invasion on marsh surface macrofauna: Response of fishes and decapod crustaceans

The tidally inundated marsh surface is an importnat site for energy exchanges for many resident and transient species. In many areas along the East Coast of the U.S. the dominant vegetation,Spartina alterniflora, has been replaced by the common reed (Phragmites australis). This shift has caused concern about the impact ofPhragmites on marsh fauna but research in this area has been limited. During 1997 and 1998, we examined the effect ofPhragmites on fish and decapod crustacean use of the marsh surface in the brackish water reaches of the Mullica River, in southern New Jersey, U.S. Fish and decapod crustaceans were sampled with an array of shallow pit traps (rectangular glass dishes, 27.5×17.5×3.7 cm) and with flumes (1.3 m wide×10 m long of 3.2-mm mesh). Fish (2–60 mm TL) dominated pit trap collections withFundulus heteroclitus andFundulus luciae significantly more abundant atSpartina sites.Fundulus heteroclitus was also the dominant fish (15–275 mm TL) collected in flumes but collections with this gear, including a number of species not collected in pit traps, showed no distinct preferences for different marsh vegetation types. Decapod crustaceans (1–48 mm CW) collected in pit traps were generally less abundant than fishes withCallinectes sapidus andPalaemonetes spp. most abundant inSpartina, whileRhithropanopeus harrisii was most abundant inPhragmites. The same decapod crustacean species (2–186 mm CW) dominanted the flume collections and, similar to the pattern of fish collected by the flumes, there were no distinct habitat preferences for different marsh vegetation types. As a result of these observations, with different sampling techniques, it appears there is an overall negative effect ofPhragmites on larval and small juvenile fish but less or no effect on larger fish and decapods crustaceans.     

Can oyster restoration reverse cultural eutrophication in Chesapeake Bay?

We investigated the hypothesis that effects of cultural eutrophication can be reversed through natural resource restoration via addition of an oyster module to a predictive eutrophication model. We explored the potential effects of native oyster restoration on dissolved oxygen (DO), chlorophyll, light attenuation, and submerged aquatic vegetation (SAV) in eutrophic Chesapeake Bay. A tenfold increase in existing oyster biomass is projected to reduce system-wide summer surface chlorophyll by approximately 1 mg m⁻³, increase summer-average deep-water DO by 0.25 g m⁻³, add 2100 kg C (20%) to summer SAV biomass, and remove 30,000 kg d⁻¹ nitrogen through enhanced denitrification. The influence of osyter restoration on deep extensive pelagic waters is limited. Oyster restoration is recommended as a supplement to nutrient load reduction, not as a substitute.     

Habitat Use by Nekton along a Stream-Order Gradient in a Louisiana Estuary

We examined patterns of habitat use by fishes and decapod crustaceans in a seemingly pristine tidal stream system that drains into southeastern coastal Louisiana, northern Gulf of Mexico. The study area centered on a relatively unaltered mesohaline saltmarsh nested within more heavily degraded conditions. Monthly sampling (February–November 2004) stratified along a stream-order gradient examined changes in nekton abundance, species richness, and community structure. Analyses were based on a microhabitat approach used to characterize nekton responses to spatial gradients of water depth, temperature, dissolved oxygen, salinity, turbidity, bottom slope, stream width, and distance to mouth. Thirty taxa were identified from 3,757 individuals collected in 82 seine samples. Seven fishes and three decapods constituted >95% of the community structure. Analyses detected the effects of stream order on fish community structure and associated environmental variables. Spatial differences of environmental variables across stream order were attributed to the geomorphology and hydrology of the study area. A factor analysis resolved eight environmental variables into four orthogonal axes that explained 80% of environmental variation. We interpreted factor 1 as a stream-order axis, factor 2 as a morphological axis, factor 3 as a seasonal axis, and factor 4 as a salinity axis. Differences in use of four-dimensional factor space by dominant species reflected habitat selection and species residency status.     

Estuarine Biotope Mosaics and Habitat Management Goals: An Application in Tampa Bay,FL, USA

Many types of anthropogenic stress to estuaries lead to destruction and conversion of habitats, thus altering habitat landscapes and changing the “arena” in which the life history interactions of native fauna take place. This can lead to decreased populations of valued fauna and other negative consequences. The Tampa Bay Estuary Program (TBEP) pioneered a system-wide management framework that develops estuarine habitat restoration and protection goals based on supporting estuarine-dependent species and the habitat landscapes they require (for example, the extent of seagrass beds, mangrove forests, oyster reefs, or oligohaline marshes) within an estuary. We describe this framework and provide related statistics as methods to help managers set system-wide ecological goals using larger conceptual approaches that are easily communicated to stakeholders and the public; we also discuss applications of the approach to existing and evolving paradigms of estuarine management. The TBEP and partners used this framework to combine a simple and unifying vision with a diverse and complex set of management tools, resulting in greatly improved environmental conditions within Tampa Bay.