Stacy M. Hagan

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.

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.

Impact of common reed,Phragmites australis, on essential fish habitat: Influence on reproduction, embryological development, and larval abundance of mummichog (Fundulus heteroclitus)

The invasion ofSpartina marshes by the common reed,Phragmites australis, along the east coast of the United States over the last several decades has been well documented, although we know little about the impact of this invasion on the fish fauna and the few published papers seem contradictory. During 1999–2000 (May–September) we evaluated the fish response to vegetation type (Phragmites australis veersusSpartina alterniflora) by monitoring several aspects of fish early life history (egg deposition, embryonic development, hatching success, and larval and juvenile abundance) in low salinity marshes in the Mullica River in southern New Jersey. The dominant fish species using the marsh surface,Fundulus heteroclitus (93% of total catch, n=996 individuals), reproduced in both vegetation types with eggs deposited in leaf axils near the base of the plant inSpartina and in broken stems ofPhragmites during both years. These eggs also undergo successful embryonic development to hatching in both vegetation types. Larval and juvenile (5–75 mm total length, but 95% < 34 mm TL) abundance of this species is much reduced onPhragmites-dominated (mean CUPE=0.02, n=7 ind) marsh surface relative toSpartina (mean CPUE=2.31). These findings, and similar results for fish abundance in 1997 and 1998, indicate that theSpartima marsh surface is likely essential fish habitat for this species because it provides habitat for larvae and small juveniles, whilePhragmites does not. ThePhragmites invasion in brackish marshes may be having deleterious effects on fish populations and possibly on predators that prey uponF. heteroclitus, and as a result, marsh secondary production.

Long-term assessment of settlement and growth of juvenile winter flounder (Pseudopleuronectes americanus) in New Jersey estuaries

Abstract We examined patterns of metamorphosis, settlement, and growth for young-of-the-year winter flounder over a ten year period (1990–1999) in four estuaries spanning the coast of New Jersey, USA, with the objective to determine the spatial and temporal coherence in these processes. We hypothesised that these processes could be influenced by large-scale climatic factors such as temperature and small-scale, local factors such as predator and prey abundances and differences associated with the localised population structure of winter flounder. Newly settled juveniles were collected in late May/early June each year. Increment counts on sagittal otoliths were used to determine the date of metamorphosis, and increment widths were used to estimate growth rates at two times, just after settlement and just prior to capture. A high level of consistency in spatial patterns among four individual estuaries was evident, and was largely driven by the northernmost site, Sandy Hook, which had higher fish densities and later metamorphosis than the three other sites, and faster growth rates than the two mid-coast sites (Barnegat Bay and Great Bay). In contrast to spatial patterns, consistent temporal patterns were evident only in the timing of metamorphosis, which was delayed in colder years at all sites. Weekly plankton sampling over the same ten year period at one site (Great Bay) yielded winter flounder larvae during a relatively narrow period in spring, with a later peak of abundance in colder years, in agreement with back-calculated dates of metamorphosis for settled juveniles. These patterns suggest that the timing of settlement is driven by large-scale climatic factors that influence the timing of spawning and/or larval development. Interannual variability in densities and growth rates, however, appeared to be independent at each site, indicating control by local environmental factors or genetic differences among local populations. The spatial consistency of growth rates suggests that appropriate nursery areas can be readily identified for juvenile winter flounder. However, subsequent recruitment needs to be verified at the level of local populations to identify contributing source habitats.

Variability in habitat use by young-of-the-year winter flounder,Pseudopleuronectes americanus, in three northeastern U.S. estuaries

We compared distribution and abundance by habitat for age-0, young-of-the-year (YOY) winter flounder,Pseudopleuronectes americanus, in three estuaries (Hammonasset River, Navesink River, and Great Bay-Little Egg Harbor) in the northeastern United States to better define essential fish habitat (EFH). Two replicates of five representative habitats were sampled in most estuaries: eelgrass (Zostera marina), unvegetated areas adjacent to eelgrass, macroalgae, (primarilyUlva lactuca), unvegetated areas adjacent to macroalgae, and tidal marsh creeks. Fish were sampled every two weeks, May through October 1995 and 1996, with a beam-trawl (1-m width, 3-mm mesh net). Abundance of YOY winter flounder was highest in the Navesink River estuary and similar between years, but was significantly lower and differed between years in the Great Bay-Little Egg Harbor and Hammonasset River estuaries. Annual temperature differences appear to influence estuary use by YOY. In the years and estuaries studied, where habitat-related differences in abundance were significant, YOY were found in higher densities in unvegetated areas adjacent to eelgrass. The exception was in the Hammonasset River in 1995 when densities were higher in eelgrass. We conclude that the type of habitat most important to YOY winter flounder varies among estuaries and as a result, care should be taken in defining EFH, based only on limited spatial and temporal sampling.

PRODUCTION OF MUMMICHOG (FUNDULUS HETEROCLITUS): RESPONSE IN MARSHES TREATED FOR COMMON REED (PHRAGMITES AUSTRALIS ) REMOVAL

The invasion of U.S. east coast salt marshes by common reed (Phragmites australis) and the efforts to remove it and restore marshes to their natural vegetation (Spartina spp.) can directly impact mummichog (Fundulus heteroclitus) as this abundant species is critically linked to marsh habitat. We estimated population density, growth, and biomass to determine production of mummichog in treated Phragmites (“Treated,” now dominated by Spartina), untreated Phragmites, and naturally occurring Spartina habitats in Delaware Bay using throw traps for small fish (mean = 24.1 mm standard length or SL, 95% CI = 10–38) and tag/recapture for large fish (mean = 36.5 mm SL, 95% CI = 18–64). Mean population density of small fish on the marsh surface was significantly higher in the Spartina (20.2 fish m−2) and Treated (14.1 fish m−2) habitats than in the Phragmites (0 fish m−2) habitat. Population density of large fish was similar among all three habitats (mean = 0.9–1.7 fish m−2). Mean absolute growth rates of large fish were significantly higher in the Spartina (0.24 mm d−1) and Treated (0.24 mm d−1) habitats than in the Phragmites (0.13 mm d−1) habitat. Mean monthly mummichog production during June to September varied among habitats with Spartina highest (1.22 g dw m−2 mo−1), Treated intermediate (0.51 gdwm−2mo−1), and Phragmites lowest (0.07 g dw m−2 mo−1). Small fish were the largest contributor to the production estimates in Spartina and Treated habitats. The Phragmites habitat had little or no standing water at low tide (i.e., optimal habitat for small fish was lacking), and thus, it had the lowest production for mummichog. These results also indicated that Treated marshes were more similar to Spartina than to Phragmites habitat; therefore, it appears that habitat quality and mummichog production can be increased with restoration.

Long-term response of fishes and other fauna to restoration of former salt hay farms: multiple measures of restoration success

This synthesis brings together published and unpublished data in an evaluation of restoration of former salt hay farms to functioning salt marshes. We compared nine years of field measurements between three restored marshes (Dennis, Commercial, and Maurice River Townships) and a reference marsh (Moores Beach) in the mesohaline portion of Delaware Bay. In the process, we compared channel morphology, geomorphology, vegetation, sediment organic matter, fish assemblages, blue crabs, horseshoe crabs, benthic infauna, and diamondback terrapins. For fishes we compared structural (distribution, abundance) and functional (feeding, growth, survival, reproduction, production) aspects to evaluate the restored marshes in an Essential Fish Habitat context. Marsh vegetation and drainage density responded gradually and positively with restored marshes approximating the state of the reference marsh within the nine-year study period. The fauna responded more quickly and dramatically with most measures equal or greater in the restored marshes within the first one or two years after restoration. Differences in response time between the vegetation and the fauna imply that the faunal response was more dependent on access to the shallow intertidal marsh surface and intertidal and subtidal creeks than on characteristics of the vegetated marsh. The fishes in created subtidal creeks in restored marshes responded immediately and maintained fish assemblages similar to the reference marsh over the study period. The intertidal creek fish assemblages tended to become more like the reference marsh in the last years of the comparison. Overall, these results document the success of the restoration and how marshes function for both resident and transient fauna, especially fishes.

Linkages Between Salt Marshes and Other Nekton Habitats in Delaware Bay, USA

Although the importance of salt marsh habitats for fishes and crabs has been accepted for nearly a half century, the linkages between marshes and adjacent estuarine habitats have been ill-defined. In this synoptic study (n > 19,000 samples, 14 species, 10 million individuals), we provide fresh insights into the patterns of fish and blue crab habitat use for the Delaware Bay and River (upstream to tidal fresh water) over 211 km of aquatic habitats. Our examination was based on 7 years (1998–2004) of sampling (with multiple gears) across 12 habitat types along the entire salinity gradient. While this study reinforces the importance of salt marsh creeks as fish and blue crab habitat, it also makes clear that there are few marsh-dependent species because almost all species simultaneously use a variety of other bay and river habitats. The pattern of use varies over seasons and with ontogeny. This facultative use of marshes, due in large part to the extensive migrations for many of the species, makes an improved focus on the linkages across this ecoscape critical to understanding the functional significance of marshes (and estuaries) to fishes and crabs and their continental shelf metapopulations.