Kenneth W. Able

The Identification, Conservation, and Management of Estuarine and Marine Nurseries for Fish and Invertebrates

Michael W. Beck, Kenneth L. Heck, Jr., Kenneth W. Able, Daniel L. Childers, David B. Eggleston, Bronwyn M. Gillanders, Benjamin Halpern, Cynthia G. Hays, Kaho Hoshino, Thomas J. Minello, Robert J. Orth, Peter F. Sheridan and Michael P. Weinstein

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

A comparison of eelgrass, sea lettuce macroalgae, and marsh creeks as habitats for epibenthic fishes and decapods

Densities of epibenthic fishes and decapod crustaceans (excluding xanthids and pagurids) were quantified with daytime throw trap sampling in shallow water habitats of New Jersey estuaries. We compared eelgrass (Zostera marina), sea lettuce macroalgae (Ulva lactuca), unvegetated sand/mud substrates adjacent to these vegetation types, and saltmarsh creeks. The highest total density of fishes occurred in marsh creeks, due primarily to high abundances of Menidia menidia. The highest total decapod density was also in a marsh creek, but only slightly surpassed the density in Zostera. Results of apriori comparisons tests for individual species demonstrated that vegetation (either Zostera or Ulva) was superior in quality (based on fish and decapod densities) to adjacent unvegetated substrates. Sites with Zostera as the dominant vegetation had higher densities of most fish species than sites with Ulva as the dominant vegetation, but only one decapod, Hippolyte pleuracanthus, was more abundant at eelgrass sites. Ulva lactuca, therefore, was an important habitat in areas lacking Zostera marina; for the decapods the two vegetation types were comparable in habitat quality, but for fishes Ulva did not provide an equivalent substitute for Zostera. Marsh creeks supported very high densities, but only for a few species that were also common in other habitats. Comparison of recruitment patterns suggested many species do not begin exploiting these estuarine habitats until relatively late in the summer, perhaps as result of peak spawning in mid-summer.

Fishes and Decapod Crustaceans of Cape Cod Eelgrass Meadows: Species Composition, Seasonal Abundance Patterns and Comparison with Unvegetated Substrates

Bimonthly trawl samples from eelgrass and nearby unvegetated areas on Cape Cod, Massachusetts, showed greater species richness in eelgrass meadows relative to unvegetated areas, and greater summer abundance in vegetation for decapod crustaceans and fishes. The composition of eelgrass-associated decapods and fishes was dominated by cold-water taxa and was strikingly different from that of the better studied eelgrass meadows of the mid-Atlantic coast. Four of the eight decapod species collected, including the second and third most abundant taxa, do not even appear in collections reported from Chesapeake Bay eelgrass meadows. Similarly, 10 of the 22 fish species taken, including the first and sixth most abundant species, are not reported from Chesapeake Bay eelgrass samples. Cape Cod eelgrass beds seem to play a nursery role for several commercially important fish species, although the nursery function is less obvious than in previously studied mid-Atlantic eelgrass meadows.

Estuarine and habitat-related differences in growth rates of young-of-the-year winter flounder (Pseudopleuronectes americanus) and tautog (Tautoga onitis) in three northeastern US estuaries

Instantaneous growth rates of young-of-the-year winter flounder Pseudopleuronectes americanus (Walbaum) (12.0-60.4 mm standard length, SL) and tautog Tautoga onitis (Linnaeus) (21.4-73.8 mm total length, TL) from three estuarine systems in New Jersey (Great Bay-Little Egg Harbor and Navesink River) and Connecticut (Hammonasset River) were used in an attempt to assess the relative quality of selected nominal habitats. A series of short-term field caging experiments were conducted during 1994 and 1995 in: macroalgae (primarily, Ulva lactuca), eelgrass (Zostera marina), unvegetated areas adjacent to macroalgae and eelgrass and tidal creeks in Spartina dominated marsh. Growth rates varied with habitat, estuary and year. Comparisons across nominal habitats within and among estuaries did not show any one habitat with consistently higher growth, and growth was relatively independent of whether a habitat was vegetated or adjacent to vegetation. The growth rates of winter flounder and tautog from the Hammonasset River were not different among habitats in either year of the study. In the Great Bay-Little Egg Harbor, both winter flounder and tautog had higher growth rates in macroalgae with growth in eelgrass varying significantly between years. Conversely, in the Navesink River both species had higher growth rates in eelgrass. Environmental changes associated with temperature and dissolved oxygen appeared to influence growth rates. Winter flounder growth rate and survival was depressed in tidal marsh creeks in the three estuaries and in vegetated macroalgae habitats in the Navesink River where dissolved oxygen levels were often very low (<2 mgl(-1)) for extended periods. In summary, the growth rates of the young-of-the-year of these two species varied temporally and were dependent on the interaction of both the specific estuary and habitat in which the experiments took place. Further, habitat quality, as defined by relative growth rate, was difficult to evaluate because it can be variable and nominal habitat designations are often not sufficient to define the boundaries of a species habitat requirements.

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.

Fauna of polyhaline subtidal marsh creeks in Southern New Jersey: Composition, abundance and biomass

Three polyhaline subtidal marsh creeks in southern New Jersey were sampled with weirs and seines to determine seasonal patterns of utilization by fishes and macroinvertebrates. Sixty-four species of fish, 13 invertebrates, and the diamondback terrapin were collected in 69 weir and 57 seine samples from April to November 1988 and April to October 1989. Average abundance, biomass, and faunal composition were strongly seasonal with greatest abundances during spring and summer, and peaks in May and August. Sixteen species were represented by all life-history stages, including the five most important species by combined ranks of percent frequency, mean abundance, and mean biomass. These five species were important during spring, summer, and fall and included the fishes Menidia menidia and Fundulus heteroclitus, the shrimps Palaemonetes vulgaris and Crangon septemspinosa, and the crab Callinectes sapidus. In addition, there were distinct seasonal assemblages of other species which utilized the creeks primarily as young-of-the-year. Importnat species in spring collections included the fishes Clupea harengus, Alosa aestivalis, Alosa pseudoharengus, Pollachius virens, and Urophysics regia, while Leiostomus xanthurus, Pomatomus saltatrix, Paralichthys dentatus, Mugil curema, and Strongylura marina were important in the summer. Fall samples were best characterized by declining abundances of summer species. Thus, subtidal marsh creeks in southern New Jersey appear to be valuable nurseries for a variety of species which spawn over the continental shelf, as well as one of the most important habitats for estuarine residents.

VEGETATION TYPE AND THE INTERTIDAL MACROINVERTEBRATE FAUNA OF A BRACKISH MARSH: PHRAGMITES VS. SPARTINA

The responses of tidal marsh macroinvertebrate assemblages to the conversion of Spartina alterniflora marshes to marshes dominated by the invasive reed, Phragmites australis, are poorly understood Changes in edaphic, vegetative, hydrologic, and detrital conditions that attend conversion to Phragmites should produce changes in the intertidal fauna. We used core sampling (7.8-cm diameter, 4-cm deep) and litter packs to compare the intertidal macroinvertebrate fauna of Phragmites marshes and adjacent remnant Spartina marshes in a brackish reach of the Mullica River (0–17 ppt salinity during the study) in southern New Jersey, USA. Detrital and above-ground vegetative biomass and water velocity were greater in Phragmites marsh; stem density, microtopographic relief, and the density of standing-water microhabitats were greater in Spartina marsh. The intertidal assemblages varied between marsh types. Total macroinvertebrate density was greater in Spartina marsh (97,000 m−2) than in Phragmites marsh (82,000 m−2). Mean taxa richness (number of taxa per core sample) was greater in Spartina marsh (12.4 taxa sample−1) than in Phragmites marsh (9.4 taxa sample−1) and dominance (relative abundance of the three most abundant taxa) was lower. Oligochaeta, Nematoda, and the polychaete, Manayunkia aestuarina, dominanted the fauna (>75% of the total abundance) in both marsh types. Of these, oligochaetes were more abundant in Spartina marsh, and nematodes and polychaetes were slightly more abundant in Phragmites marsh. Most common subdominant taxa (100-4,000 m−2), including ceratopogonids, chironomids, mites, ostracods, isopods, and gastropods were more abundant in Spartina marsh. Collembolans were more abundant in Phragmites marsh; amphipods were about equally abundant in both marsh types. Invertebrate abundance and assemblage composition varied with distance from the edge of the marsh in both marsh types; overlap in assemblage composition between marsh types was greates at the edge of the marsh, where more frequent inundation may have moderated the influence of vegetation type on the marsh fauna. For mean taxa richness and for the density of most taxa, the effect of marsh type on density exceeded the effect of season, marsh position, or a local salinity gradient. We consider the greater density of intertidal standing-water microhabitats and probably of microalgal production as important sources of faunal variation between marsh types. Fewer refugia from predators during high tide in Phragmites marsh may also contribute to variation in faunal abundance and community structure between marsh types. Detritus biomass was probably a more important source of spatial variation in the fauna of the Phragmites marsh than in Spartina marsh.

Mechanisms of Marsh Habitat Alteration Due to Phragmites: Response of Young-of-the-year Mummichog (Fundulus heteroclitus) to Treatment for Phragmites Removal

In recent decades, marshes naturally dominated bySpartina spp. have been replaced byPhragmites australis throughout the northeastern United States. We suggest that early in this invasion there was little effect on the fish fauna. As the invasion proceeds, the marsh surface habitat became more altered (i.e., elevated, flattened, reduced water-filled depressions, and reduced standing water), which resulted in a reduction of feeding, reproduction, and nursery function for fishes, especiallyFundulus spp. These potential changes in marsh habitat and function have resulted in numerous attempts to removePhragmites and restoreSpartina spp. To evaluate the response of marsh surface fishes toPhragmites treatment, we examined fish use in the brackish water reaches of Alloway Creek in the Delaware Bay estuary. ReferencePhragmites habitats were compared with referenceSpartina alterniflora-dominated habitats and sites treated (1996–1998) to removePhragmites to restore former vegetation (i.e., restored, now comprised of 100%Spartina). Fish were sampled with an array (n=9 at each site) of shallow pit traps (rectangular glass dishes, 27.5×17.5×3.7 cm). Small individuals (mean=17.5, 5–45 mm TL) dominated all pit trap collections. Fish abundance was highest at the restored (catch per unit effort [CPUE]=2.16) andSpartina (CPUE=0.81) sites with significantly lower values atPhragmites (CPUE=0.05) habitats. Samples were dominated by young-of-the-year mummichog,Fundulus heteroclitus (98% of total fish, n=631). The only other fish species collected was spotfin killifish,Fundulus luciae (2% of total catch, n=14), which was only present in restored andSpartina habitats. These observations suggest that the restored marsh is providing habitat (water-filled depressions on the marsh surface) for young-of-the-yearFundulus spp. These marshes are responding favorably to the restoration based on the much greater abundance of fish in restored versusPhragmites habitats and the overall similarity between restored andSpartina habitats.

Patterns of Seasonal Availability and Habitat Use by Fishes and Decapod Crustaceans in a Southern New Jersey Estuary

We examined the community structure of fish and selected decapod crustaceans and tested for within estuary differences among habitats at depths of 0.6 m to 7.9 m, in Great Bay and Little Egg Harbor in southern New Jersey. Several habitat types were identified a priori (e.g., eelgrass, sea lettuce, and marsh creeks) and sampled by trawl (4.9 m headrope, 19-mm mesh wings, 6.3-mm mesh liner), monthly, from June 1988 through October 1989. Repetitive (n=4) 2-min trawl tows were taken at each habitat type from 13 locations. The fishes and decapod crustaceans collected were typical of other Mid-Atlantic Bight estuaries but varied greatly inseasonal abundance and species. In the years sampled, bay anchovy (Anchoa mitchilli) was the dominant species (50.5% of the total number), followed by spot (Leiostomus xanthurus) (10.7%), Atlantic silverside (Menidia menidia) (9.7%), fourspine stickleback (Apeltes quadracus) (5.9%), blue crab (Callinectes sapidus) (4.6%), and northern pipefish (Syngnathus fuscus) (4.2%). The biota were examined by multi-dimensional scaling (MDS) for habitat associations and “best abiotic predictor” of community structure. Percent silt combined with salinity was the most important abiotic determinant of the faunal distributions among habitats. Temperature was a major factor influencing seasonal occurrence of the biota but had less effect on habitat comparisons. The analysis confirmed the distinct nature of the assemblages associated with the habitats, that is, eelgrass, upper estuary subtidal creeks, channels, and open bay areas. Several species were associated with specific habitats: for example,A. quadracus andS. fuscus with eelgrass, clupeids with subtidal creek stations,L. xanthurus with marsh channels, and black sea bass (Centropristis striata) and spotted hake (Urophycis regia) with sponge-peat habitat. Species richness appeared to be positively related to habitat structural heterogeneity. Thus, the best predictors for these estuarine fish and decapod crustacean assemblages were seasonal temperature, percent silt and salinity combined, and the physical heterogeneity of the habitat.