Epibenthic community monitoring in New Jersey coastal bays: a priority initiative of estuarine research programs.
An initial investigation of the temporal and spatial settlement patterns of epibionts on aluminum sampling panels at one of the study sites (i.e., Buoy 126 in Great Bay)found that blue mussels numerically dominated the epibenthic community from May to July and calcareous bryozoans predominated from September to November. Blue mussels exhibited the greatest variation in abundance, rapidly colonizing the panel surfaces in spring and early summer and then abruptly disappearing by mid summer. Other epifauna (i.e., barnacles, polychaetes, and mud crabs), while present during the study period, were not numerically significant. Among macroalgae, Agardhiella sp. was abundant in June, but absent thereafter. Results of this 6.5-month field experiment showed considerable variations in settlement, recruitment, and post-recruitment events of epibenthic organisms in the bay. Such results have important implications for the biofouling of hard substrates in the bay. An expansion of this epifaunal community study, incorporating seven additional sampling sites in Great Bay, Little Egg Harbor, and Barnegat Bay, commenced in June 2003, and the findings will be reported in 2004.
KEY WORDS: Great Bay, settlement panels, epibenthic organisms, population abundance, temporal variation, community development
The monitoring of water quality, biotic communities, and habitats is an integral component of both the Barnegat Bay National Estuary Program and the Jacques Cousteau National Estuarine Research Reserve Program. These two federally funded initiatives are dedicated to the maintenance, protection, restoration, and enhancement of natural resources in New Jersey coastal bays (Kennish, 2000, 2003). A well-designed and effectively implemented monitoring effort is necessary to accurately assess the status and trends of water quality, living resources, and habitats in the coastal bays of New Jersey. The long-term health and viability of these critically important estuarine systems depends on delineating environmental problems, mitigating anthropogenic impacts, and revitalizing damaged components. Monitoring is an essential part of identifying degraded estuarine environments, determining the effectiveness of abatement strategies, and addressing resource management concerns. As noted by the National Estuarine Research Reserve System (2002), a major goal of monitoring is to identify and track short-term variability and long-term changes in the integrity and biodiversity of representative estuarine ecosystems and coastal watersheds for the purpose of contributing to effective national, regional, and site-specific coastal zone management.
The Barnegat Bay National Estuary Program encompasses the waters of the Barnegat Bay-Little Egg Harbor Estuary. It overlaps a portion of the Jacques Cousteau National Estuarine Research Reserve, which extends from the southern part of Barnegat Bay (Manahawkin Bridge) to Absecon Bay, and includes Little Egg Harbor, Great Bay, Little Bay, and Reeds Bay. The two programs therefore cover most of the back-bay areas bordering the New Jersey mainland.
DESCRIPTION OF THE MONITORING PROGRAM
The Barnegat Bay National Estuary Program and Jacques Cousteau National Estuarine Research Reserve Program are currently supporting studies to monitor the epibenthic communities of the Barnegat Bay-Little Egg Harbor Estuary and Great Bay. Eight sampling stations have been established for long-term monitoring of the communities in these coastal bays (Figure 1, Table 1). The purpose of these investigations is not only to assess the taxonomic composition and temporal changes of the communities but also to determine if data collected on them are useful for delineating water quality changes in the two estuaries. The monitoring focuses on collecting data that will shed light on changes in ambient environmental conditions, ecological functions, and biological populations and communities. Once these changes are established and priority problems identified, corrective actions to detrimental anthropogenic impacts can be implemented to restore and maintain the chemical, physical, and biological integrity of the estuaries (Kennish, 2001).
[FIGURE 1 OMITTED]
Our objective is to use detailed monitoring methods to characterize the species composition, diversity, and dynamics of the epibenthic community of organisms inhabiting the coastal bays of New Jersey, as well as to assess potential biofouling impacts on substrate surfaces of different contour, texture, and hardness. Table 1 lists the sampling locations, sampling periods, and type of substrates used for the monitoring work conducted to date. Initial work on epibenthic community monitoring was conducted at Buoy 126 in Great Bay from May to November 2002. The Buoy 126 (39[degrees]30.478'N, 74[degrees]20.308'W) study site is a long-term water quality monitoring station of the Jacques Cousteau National Estuarine Research Reserve. It is located on the eastern side of Great Bay about 3 km from Little Egg Inlet (Figure 1). Because of its close proximity to the inlet, Buoy 126 is characterized by relatively strong tidal currents (> 2 m/s). The bottom sediments consist of fine to coarse sand and various amounts of shell debris. An extensive blue mussel bed surrounds the site. The water depth averages 3 m and ranges from ~1.8-4.3 m. The water temperature varies widely over an annual cycle, ranging from ~1.0-29[degrees]C and averaging ~13.7[degrees]C. The mean salinity is 30 [per thousand], with minimum and maximum salinity values of ~19.0 [per thousand] and ~33.0 [per thousand], respectively. The pH typically ranges from 7.4-8.2 (Kennish and O'Dounell, 2002).
Epibenthic community sampling at Buoy 126 consisted of the deployment of aluminum panels (15 x 20 cm) on aluminum rods that were injected into the estuarine bottom such that the panels were positioned ~1.0 m above the sediment-water interface. Two panels were attached to each of six aluminum rods deployed at the site, although three of the panels were swept off the rods sometime during deployment, apparently due to strong tidal currents. Sampling panels were retrieved from June through November using SCUBA. However, only one sampling panel was recovered in July and none in September. The recovered panels were preserved in 10% buffered formalin for the first 24 hours subsequent to retrieval and then emersed in 90% ethanol until analyzed in the laboratory. Organisms were identified to species or genus level, when possible, and enumerated. The abundance and spatial cover of all sessile species were noted. The attachment site (bare substratum, calcareous bryozoans, mussels, etc.) was also documented. Observations were made on both sides of each monthly set of panels.
PRELIMINARY RESULTS AT BUOY 126
Results are presented for the first year of study (2002) involving monitoring of the epibenthic community at Buoy 126 in Great Bay. Monitoring efforts have been expanded in 2003 to incorporate the remaining seven sampling sites and, pending results of this expanded study, will be reported elsewhere in 2004.
All panels were deployed at Buoy 126 in Great Bay on May 4, 2002, and they were retrieved on the following dates in 2002: June 11, July 10, August 12, October 1, and November 27. Conspicuous change in the composition of epibenthic organisms on the panels was evident over the 6.5-month deployment period. The sampling panels and rod retrieved on June 11, 2002 only contained a cluster of blue mussels. About 250 mussels were enumerated on the sampling apparatus; they were found mainly adhering to the small space on the rod between the two panels. Individual mussels ranged in size from ~3 mm in length by 2 mm in height to ~12 mm in length by 6 mm in height.
The abundance of epibenthic organisms increased significantly during June as reflected by the number of organisms found on the sampling panel collected at the site on July 10, 2002. More than 1,500 blue mussels were attached to the one panel and aluminum rod recovered at this time; they ranged in size from ~10 mm in length by 5 mm in height to ~20 mm in length by 10 mm in height (Figure 2). However, the mussels were loosely attached to the panel surface and readily sloughed off the aluminum substrate upon shipboard retrieval. Two crabs inhabited the mussel cluster, including a male mud crab, Panopeus herbstii, which measured 23 mm in carapace width, and a gravid female mud crab, Panopeus herbstii, which measured 10 mm in carapace width. Five clam worms, Nereis virens, were also observed among the mass of epibenthic organisms. They ranged from ~40 to 50 mm in length. A clump of filamentous macroalgae (Agardhiella sp.) and a small amount of sea lettuce (Ulva lactuca) occurred on the panel as well. Divers observed the overwhelming predominance of blue mussels, which completely carpeted the estuarine floor at the field site during June.
[FIGURE 2 OMITTED]
The epibenthic community changed markedly during the July to early August period. Two panels retrieved on August 12, 2002 contained only a small amount (< 10%) of macroalgae (Polysiphonia sp.). No fauna was observed on these panels. Divers also reported the absence of blue mussels on the estuarine floor at this time.
No panels were retrieved during September. Both panels recovered on October 1, 2002, were blanketed by calcareous bryozoans (Figure 3). Colonies of encrusting calcareous bryozoans also covered a large area of the panels (~20-80%) retrieved on November 27, 2002. One barnacle (Balanus sp.), measuring 12 mm by 14 mm, was likewise attached to one of the panels.
[FIGURE 3 OMITTED]
Species richness was low on the settlement panels. Less than 10 taxa were found on the panels during the spring to fall period (Table 2). A conspicuous successional pattern was evident, however, with blue mussels predominating from May to July and calcareous bryozoans dominating from September to November. These two taxa controlled much of the physical structure of the epibenthic community. Although mobile taxa (i.e., clam worms and mud crabs) were also present, they were not numerically significant. Blue mussels maintained early dominance by dense and early colonization, and rapid growth. However, they abruptly disappeared as the temperature increased above 25[degrees]C during the summer months.
Settlement patterns of epifaunal organisms such as bryozoans (Walters, 1992), barnacles (Wethey, 1986), schyphozoans (Keen, 1987), and foraminiferas (Mullineaux and Butman, 1990) have been shown to be correlated with various aspects of field flows, inferring the influence of currents on larval settlement and recruitment patterns on hard surfaces (Mullineaux and Garland, 1993). Thus, hydrodynamic processes must be considered in studies of epibenthic community development on hard substrates in shallow estuarine habitats. Bay sites in close proximity to tidal inlets (i.e., Little Egg Inlet and Barnegat Inlet) in the Barnegat Bay-Little Egg Harbor system have historically harbored dense accumulations of blue mussels, whose larvae enter the estuary on flooding tide (Kennish, personal observation). The flow characteristics, notably velocity and boundary shear stress, are major factors affecting larval dispersal, deposition, and settlement in these areas (Eckman, 1983; Wethey, 1986; Butman, 1987; Mullineaux, 1988; Abelson and Denny, 1997). The ability of the larvae to colonize discrete hard surfaces, rather than competition or predation, may exert the greatest control on the species composition and structure of the developing epibenthic community (Keough, 1984; Mullineaux, 1988).
Larval behavior and the duration of the planktonic stage are also important factors affecting larval settlement on suitable hard surfaces (McEdward, 1995). Various physical, chemical, and biological factors can induce settlement (James and Underwood, 1994; Keough and Raimondi, 1995; Keough, 1998; Pech et al., 2002). Larvae actively explore substrate surfaces in search of settlement sites (Bourget and Harvey, 1998). Substratum topographic heterogeneity and complexity significantly affect the abundance and development of epibenthic assemblages in estuarine and marine environments (Bourget et al., 1994; Lemire and Bourget, 1996; Blanchard and Bourget, 1999; Lapointe and Bourget, 1999; Pech et al., 2002). Epibenthic assemblages in estuarine and coastal lagoons typically exhibit considerable temporal and spatial variation in recruitment and development (Benedetti-Cecchi et al., 2001).
Flood tide currents, which are strongest near Little Egg Inlet and along the northern part of Great Bay, transport large numbers of planktonic larvae across the Buoy 126 site toward the head of the bay. The Buoy 126 site, therefore, is in the direct pathway of larvae transported landward from the nearshore ocean and mouth of the bay. Because of rapid current flow at Buoy 126, larval settlement of some species may be significantly hindered, although this does not appear to be the case for blue mussels which attain highest abundances on hard substrates at the site. The duration of larval life of Mytilus edulis ranges from about one to four weeks, being a function of temperature, salinity, food supply, and other factors. Previously settled mussels stimulate larval settlement and metamorphosis. The larvae readily attach to the byssal threads of juveniles and adults, but may also settle on bryozoans, hydroids, filiform algae, and other filamentous substrates (Lutz and Kennish, 1992).
Biogenic heterogeneity was limited on the sampling panels. The relatively impoverished assemblage is attributed to two causes: (1) the rapid settlement and spread of the blue mussels and calcareous bryozoans; and (2) the smooth surface of the aluminum panels which does not appear to provide a favorable attachment site for many other larval forms. The settlement patterns of blue mussels on the sampling panels at Buoy 126 clearly reflect larval abundance of this species during the spring to early summer period in Great Bay. The dense and early colonization of blue mussels on the panels are circumvented by rising temperatures, and the bivalve cannot maintain its dominance of the epibenthic community in the summer months. As the blue mussels disappear from the hard substrates, other epibionts settle on the surfaces. The most successful are calcareous bryozoans, which eventually cover most of the metal surfaces by late summer, precluding the attachment of many other forms.
The environmental setting of the other seven sampling sites is considerably different than that of Buoy 126 (Figure 1). Current velocities are generally much lower at these other sites, which are located within protected marina habitat along the estuarine shoreline away from tidal inlets and open bay channels. Characterized by significantly different circulation patterns and other factors, the array of marina sampling sites likely supports epibenthic communities with highly variable structure. Larval settlement is greatly affected at these sites by suitable hard substrates and local physical, chemical, and biological conditions.
Future epibenthic studies in the estuary will deploy a variety of recruitment panels, because it has been demonstrated that considerable variation exists regarding larval preferences for artificial substrates in estuarine and marine environments (Connell and Glasby, 1999; Glasby and Connell, 1999). Hence, the development of epibiotic communities can differ substantially on wood, metal, plastic, concrete, and other types of hard surfaces in these environments. It is also necessary to expand the epibenthic studies by sampling multiple sites in estuarine waters over a protracted period (i.e., several years). Such an effort is currently underway by the authors at the aforementioned marina sites in the Barnegat Bay-Little Egg Harbor Estuary. Settlement panels of uniform size deployed in a variety of habitats will enable investigators to better understand the complexity of epibenthic community development over time and the dynamics of the community under different environmental conditions. This method of study will also enable more accurate assessment of epibiotic population ecology in the estuary.
Table 1. Sampling stations for long-term monitoring of epibenthic communities in New Jersey coastal bays. LOCATION SAMPLING PERIOD SUBSTRATE Buoy 126 May-November, 2002 Aluminum (Great Bay, NJ) Rutgers University Marine June-October, 2003 Plastic Field Station (Great Bay, NJ) First Bridge Marina June-October, 2003 Plastic (Tuckerton, NJ) Cedar Grove Marina June-October, 2003 Plastic (Tuckerton, NJ) Margo's Inn June-October, 2003 Plastic (Manahawkin, NJ) Sun Harbor Marina June-October, 2003 Plastic (Barnegat, NJ) Berkeley Yacht Basin June-October, 2003 Plastic (Seaside Park, NJ) Winter Yacht Basin June-October, 2003 Plastic (Mantoloking, NJ) Table 2. List of taxa found on settlement panels deployed at Buoy 126 in Great Bay, New Jersey from 4 May to 27 November 2002. SPECIES OR GROUP DESCRIPTION Mytilus edulis Thick cluster of small mussels (>1,500 on settling panels and poles) attached to the panels and each other (~3 unit in length by 2 nun in height to ~12 mm in length by 6 mm in height). Panopeus herhstii Single male, dark green (above) to yellowish-brown (below) in color (23 mm in carapace width), mobile within the mussel mass. Single gravid female (10 mm in carapace width), mobile within the mussel mass. Nereis virens Solitary worms, elongated with well-developed parapodia. Measures ~40-50 mm in length. Balanus sp. Solitary barnacle, ivory color, with smooth plates. Measures 12 turn by 14 met at the base. Calcareous bryozoans Hard encrusting colony, relatively thin and irregular shape. White in color. Forms oval patchwork covering extensive areas of the panels. Agardhiella sp. Bushy, filamentous plants surrounding mussels and attached to the panels Polrsiphonia sp. Small cluster of light brown, bushy plants adhering to the panel surface. Ulva lactura Leaf-like plant mass attached to blue mussels and panels
This is Publication Number 2003-27 of the Institute of Marine and Coastal Sciences, Rutgers University, and Contribution Number 2003-26 of the Jacques Cousteau National Estuarine Research Reserve. Work on this project was conducted under an award from the Estuarine Reserves Division, Office of Ocean and Coastal Resource Management, National Ocean Service, National Oceanic and Atmospheric Administration, Silver Spring, Maryland.
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MICHAEL J. KENNISH
INSTITUTE OF MARINE AND COASTAL SCIENCES
NEW BRUNSWICK, NEW JERSEY 08901
SCOTT M. HAAG
CENTER FOR REMOTE SENSING AND SPATIAL ANALYSIS
NEW BRUNSWICK, NEW JERSEY 08901
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|Author:||Kennish, Michael J.; Haag, Scott M.|
|Publication:||Bulletin of the New Jersey Academy of Science|
|Date:||Sep 22, 2003|
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