CHAPTER 8. Estuarine Habitats of Narragansett Bay
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CHAPTER 8. Estuarine Habitats of Narragansett Bay CHAPTER 8. Estuarine Habitats of Narragansett Bay Malia L. Schwartz 89 An Ecological Profile of the Narragansett Bay National Estuarine Research Reserve Figure 8.1. Estuarine habitats of Narragansett Bay. Source: French et al., 1992. Image courtesy Applied Science Associates. 90 CHAPTER 8. Estuarine Habitats of Narragansett Bay Estuarine Habitats of Narragansett Bay Introduction This chapter provides an overview of the major habitat types of Narragansett Bay and, where ap- propriate, makes specifi c reference to those habitats Estuarine habitats support some of the most found on and around the islands of the NBNERR. It productive fl oral and faunal communities on Earth, also delves into the basic life histories and ecology and the habitats of Narragansett Bay are no excep- of the organisms found in these habitats that are then tion. Many different habitat types are found in and expanded on in subsequent chapters. And fi nally, it around the Bay, including open water, salt marshes, gives examples of habitat restoration efforts ongoing subtidal bottom habitat, brackish waters, a complex in several Bay habitats. intertidal zone of sandy beaches, mud and sand fl ats, and rocky intertidal areas, submerged aquatic vegetation with macroalgal and eelgrass beds, and human-modifi ed shorelines (Fig. 8.1). Open Water The productivity and variety of estuarine habitats foster an abundance and diversity of The open water, or pelagic, habitat is the wildlife. Shorebirds, fi sh, crabs and lobsters, marine dominant habitat in Narragansett Bay, based on area. mammals, clams and other shellfi sh, marine worms, The Bay itself is a phytoplankton-based ecosys- sea birds, and reptiles are just some of the animals tem with relatively little salt marsh or macroalgae. that make their homes in and around estuaries. The pelagic habitat is a dynamic environment with These animals are linked to one another, and to an tidally and wind-driven circulation and freshwater assortment of specialized plants and microscopic inputs (French et al., 1992). A wide variety of plank- organisms, through complex food webs and other ton, benthic communities (Chapter 9), and nekton interactions (EPA, 1998). (Chapter 10) are found in and under the open water In addition to serving as important habitat habitat of Narragansett Bay. In turn, this habitat pro- for wildlife, fringing estuarine wetlands also per- vides food for a diverse assemblage of birds, as well form other valuable services. Water draining from as for marine mammals and occasional sea turtles the uplands carries sediments, nutrients, and other (Chapter 11). The pelagic habitat also supports a pollutants. As the water fl ows through wetlands such number of commercial and recreational fi sheries and as swamps and salt marshes, much of the sediments shellfi sheries. and pollutants are fi ltered out. This fi ltration process creates cleaner and clearer water, which benefi ts both people and marine life. Wetland plants and soils also act as a natural buffer between the land Salt Marshes and ocean, absorbing fl oodwaters and dissipating storm surges. This protects upland habitats as well While only covering a small surface area as economically valuable real estate from storm and in Narragansett Bay, estuarine emergent wetlands, fl ood damage. Salt marsh grasses and other estuarine or salt marshes, are some of the most ecologically plants also help prevent erosion and stabilize the valuable habitats in the Bay (Fig. 8.2). Salt marshes shoreline (EPA, 1998). protect coastal areas Narragansett Bay from erosion, remove is one of the best-studied nutrients from overen- estuaries in the world riched waters, provide (Ely and Crist, 2001), sheltered habitat for key and its habitats have been resource species, serve the subject of in-depth re- as nursery grounds for search for over 30 years. fi sh and shellfi sh, and are a major food source Figure 8.2. Salt marshes, such for the organisms that as Round Marsh in Jamestown, live there (Tiner, 1984). R.I., are some of the most A primary ecologically valuable habitats source of food in in Narragansett Bay. Photo by Malia Schwartz. salt marshes is in the form of decomposing 91 An Ecological Profile of the Narragansett Bay National Estuarine Research Reserve plant material, or detritus. Detritus is the base of the organisms that inhabit the low marsh, S. alterni- an aquatic food web supporting higher consumers fl ora has also been shown to be an effective nutrient and commercial species. Animals such as shrimp, sink, able to capture and hold available inorganic snails, clams, worms, and killifi sh consume plant nutrients, such as nitrogen and phosphorus and trace breakdown products, graze on microscopic organ- elements, then slowly release them as the plants isms growing on the surface of the detritus (Beck die, decay, and are carried into the estuary to serve and Beck, 1998), or scour epibenthic algae off the as a rich source of detrital food (Nixon and Oviatt, sediments. To illustrate the interwoven nature of this 1973b). food web, research by Nixon and Oviatt (1973a) in In contrast to the low marsh, the high marsh Bissel Cove reported that excretion and fecal pellets is a mosaic of species, the occurrence of each being produced by foraging grass shrimp provided nutri- precisely determined by the elevation and resultant ents for enhanced development of bacteria and algae amount of tidal fl ooding. The high marsh is char- on the detritus. In turn, forage fi sh (e.g., anchovies, acterized by salt-marsh hay (S. patens), spike grass silversides, sticklebacks, mummichogs) and small (Distichlis spicata), glassworts (Salicornia spp.), invertebrates (e.g., grass shrimp and worms) are sea lavender (Limonium nashii), salt marsh aster then consumed by commercial and recreational fi sh (Aster tenuifolius), black grass (Juncus gerardii), species, including winter fl ounder (Pseudopleuro- and hightide bush (Iva frutescens). Salt marsh pools nectes americanus), striped bass (Moroneorone saxatilis), and tidal creeks can also be vegetated with widgeon and bluefi sh (Pomatomus saltatrix) (Beck and Beck, grass (Ruppia martima), sea lettuce (Ulva lactuca), 1998). and other macroalgae (Beck and Beck, 1998). Salt marshes are characterized by two In Narragansett Bay, salt marshes cover general vegetative zones based on differences in about 1,120 ha (2,800 acres). There are also roughly tidal fl ooding—regularly fl ooded low marsh and ir- 80 km of narrow, fringing marshes—marshes that regularly fl ooded high marsh. In the low marsh—the line the edge of rocky shores or developed areas. area covered by each day’s high tides—vegetation is French et al. (1992) reported on the species compo- dominated by a single plant, the tall form of smooth sition and relative abundance of salt marsh plants cordgrass, Spartina alternifl ora, which typically in eight salt marshes around Narragansett Bay. The grows 90–180 cm (3–6 feet) high (Beck and Beck, surveyed marshes included: 1) Watchemoket Cove, 1998). In addition, fi lamentous algae and diatoms East Providence; 2) Hundred Acre Cove, Barrington; are found at the base of the grasses growing in the 3) Chase Cove, Warren; 4) Common Fence Point, fl ooded part of the marsh (Donaldson, 1995). Where Portsmouth; 5) Bissel Cove, North Kingstown; 6) the tall cordgrass meets the water’s edge, the mud is Round Swamp, Jamestown; 7) Weaver Cove (Mel- home to densely packed beds of ribbed mussels, and ville), Portsmouth; and 8) Emily Ruecker Wildlife around the plants’ roots, one can fi nd small holes Marsh, Tiverton. At the seven sites that could that form the openings to fi ddler crab burrows. Mov- be sampled (Weaver Cove was too degraded), S. ing away from the water, at the edge of the border alternifl ora dominated the low marsh and S. patens, marked by the high-tide line, the cordgrass is short, the high marsh. Both species are perennial grasses, less than 30 cm tall (Bertness, 1992). annually producing large amounts of organic matter In addition to providing food and shelter to that are exported from the marshes into the detrital Table 8.1. Relative coverage (%) of dominant high and low marsh species for seven salt marshes within Narragansett Bay. Sp = Spartina patens, Ds = Distichis spicata, Ap = Atriplex patula, Sa (t) = Spartina alternifl ora (tall), Sa (s) = Spartina alternifl ora (short), Jg = Juncus gerardii, If = Iva frutescens, Se = Salicornia europea, Ss = Solidago sempervirens, Lc = Limonium carolinianum, At = Aster tenuifolius, Pm = Plantago maritima. Data from French et al., 1992. 92 CHAPTER 8. Estuarine Habitats of Narragansett Bay food web or deposited within the marshes, contribut- Marsh (Newport), Walker Farm (Barrington), and ing to the underlying peat (Nixon, 1982; Teal and Silver Creek (Bristol). Teal, 1962). Table 8.1 shows the relative coverage of species found in the seven study sites that were examined. Benthic Habitat Within the boundaries of the NBNERR, salt marshes are found in the North Prudence Unit (102 acres) and Barre and Little units (48 acres), Occurring below the low-tide line, the sub- on the east shore of Patience Island (13 acres), tidal, benthic (bottom) habitat of Narragansett Bay is and in a small area on Dyer Island (3 acres) (see composed of soft, unvegetated sediments, predomi- Table 4.3, page 36; Fig. 4.11, page 34). As with the nantly clayey silt and sand-silt-clay. This habitat is previous examples, the salt marshes of the Reserve found throughout the mid- and upper Bay and in are dominated by S. alternifl ora and S. patens, and protected coves and embayments. Coarser, sandy are infl uenced by the adjoining Bay rather than sediments are found in the lower Bay (see Fig. 7.6, landward processes. They are laced with irregular page 84). Sub-tidal waters support a diverse benthic creeks, ponds, potholes, and man-made drainage community of molluscs, crabs, and worms that live ditches (Beck and Beck, 1998).