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Urban Marine Habitats—Spotlight on Gloucester Harbor By Dr. Todd Callaghan and Anthony R. Wilbur, CZM Amidst an undulating mass of eelgrass, a snail moves along a single green strand, gently grazing on a thin slime of algae. Beneath the thicket of eelgrass blades, a juvenile lobster cautiously pushes its way out of its sandy burrow to forage on small worms and clams. Suddenly, the shadow of what appears to be a large fish passes over the lobster. With a kick of its tail, it retreats to shelter. The shadow moves over and abruptly changes direction. Several hundred small mirrors turn at the same moment in a silvery flash. It isn't one fish, but a school of juvenile menhaden feeding on a patch of nutritious plankton. In an instant, two more shadows pass over the lobster's burrow and it wisely stays inside. A pair of hungry striped bass propel themselves toward the trailing edge of the school of menhaden, isolating a few stragglers and quickly swallowing them whole. Remnants from the feeding frenzy fall lightly to the bottom. The juvenile lobster hurries out of its burrow and secures an easy meal. Is this a scene from the Discovery Channel? Feeding time at the New England Aquarium? No, this is an example of some of the ecological interactions that occur beneath the surface in any one of the Bay State's many busy harbors. Televised nature programs have made us aware of the diverse and colorful life swimming, burrowing, eating, and being eaten in remote locations across the globe, but how many of us know and appreciate the diversity and tenacity of aquatic life right here in local ports? Many commercial ports along the Massachusetts coast (including Gloucester, Salem, Boston, Plymouth, Provincetown, Hyannis, Nantucket, New Bedford, and Fall River) have been active for centuries. Together these ports provide the Commonwealth with waterways and dockage for fishing fleets, tankers, container ships, recreational boats, and ferries. While many of these man-made additions to natural harbors and their associated environmental impacts are obvious, what is less known is that these ports contain viable habitats (albeit fragmented, sometimes polluted, and frequently disturbed) that continue to provide ecological value to a number of species. The key to continued aquatic diversity in high human impact areas such as ports is the persistence of a variety of habitat types in which organisms can forage, seek shelter, and reproduce. This article focuses on specific habitats in Gloucester Harbor, which supports nearly 3,000 full-time and 800 part-time employees and generates $720 million in sales, largely in the commercial fishing and frozen seafood sectors. Dramatic changes to Gloucester's inner harbor resulted from the filling and armoring the entire inner harbor, especially around Five Pound Island with the creation of the State Pier. While these changes had unavoidable environmental impacts, the port of Gloucester continues to harbor several habitat types that support a variety of species. Seafloor Even with dozens of recreational and commercial boats passing through the harbor every day, the mud, sand, and rock of the seafloor, and the waters above continue to provide habitat for numerous organisms. For example, trawl surveys in 1998-1999 revealed that some commonly known fish species, such as winter flounder (Pseudopleuronectes americanus), skates, and Atlantic cod (Gadus morhua), were the fish species of greatest abundance on the Gloucester Harbor seafloor throughout the year. Some other well-known species such as hake (Urophycis chuss and U. tenuis), pollock (Pollachius virens), cunner (Tautogolabrus adspersus), windowpane (Scophthalmus aquosus), and butterfish (Peprilus triacanthus) were also present, but in lower numbers. The survey also turned up some fish that sound more like they belong in a science fiction novel than on a dinner plate: lumpfish (Cyclopterus lumpus), longhorn sculpin (Myoxocephalus octodecemspinosus), rock gunnel (Pholis gunnellus), grubby (Myoxocephalus aenaeus), snailfish (Liparis spp.), radiated shanny (Ulvaria subbifurcata), ocean pout (Macrozoarces americanus), sea raven (Hemitripterus americanus), and pipefish (Syngnathus fuscus). Interestingly, while skate and winter flounder dominated the catch from June to October (60-80 percent of total abundance), winter flounder enjoyed the number one spot without rival from November to January (30-80 percent of total abundance) and then was surpassed by cod from March to May (20-50 percent of total abundance). The appearance and disappearance of species in the survey record is at least in part determined by the different habitat needs of those species. Species that prefer cool water for spawning or foraging, (e.g., winter flounder and cod) move into Gloucester Harbor during the cooler months, while others like skate find their niche in the harbor in the warmer months. In addition to this temporal variability, these species also have spatial preferences. According to a 2001 survey, 63 percent of the Gloucester Harbor seafloor is silt (soft mud), while the remainder is a combination of silt, sand, and hard bottom. The silty seafloor attracts juvenile and adult fish of many species that feed upon the abundance of polychaete worms and small bivalves burrowed into the sediments. Silty seafloor habitat is attractive to hermit crabs, green crabs (Carcinus maenas), and lobsters as well. Estimates of lobster abundance in this area based upon dive surveys in 1999 and 2001 range from 0.06-0.20 lobsters per linear meter, indicating good lobster habitat. The number of lobstermen fishing Gloucester harbor waters confirms the existence of a substantial lobster population. 
Rocky Intertidal Along the edges of Gloucester Harbor, the rocky outcrops, boulders, and tide pools form niches where numerous species can find shelter in an otherwise turbulent and energetic tidal zone. For example, a survey by the Massachusetts Audubon Society of tide pools on Eastern Point in outer Gloucester Harbor found up to 24 species in a single tide pool, including 10 species of algae; six mollusks; two species each of starfish, sea squirts, and hydroids; one species of crab; and one species of sea urchin. Salt Marsh Salt marshes are relatively protected and highly productive areas that provide refuge for juvenile fish and crustaceans. Salt marshes also act as biofilters for removing excessive nutrients (like nitrogen) from the waters passing through them, absorbing as much as 30 percent or more of the waterborne nitrogen entering the system from upstream. Current research is aimed at determining if the small fish that inhabit the marshes impact nutrient levels in the water column. See http://ecosystems. mbl.edu/tide/ for a study funded by the National Science Foundation that is being conducted in the Plum Island watershed and is looking at whether removing mummichogs (Fundulus heteroclitus), an abundant fish species, makes marshes less resistant to the effects of nutrient loading. Sixteen acres of salt marsh occur on the western edge of Gloucester Harbor. Although the geology of the harbor shoreline is predominately exposed rock ledge and not conducive to salt marsh formation, port infrastructure such as roads and culverts have also limited its extent. To help address this issue on Eastern Point in the southeastern corner of the harbor, Massachusetts Audubon, the CZM Wetlands Restoration Program, the National Oceanic and Atmospheric Administration's Restoration Center, and the Natural Resources Conservation Service have replaced an undersized culvert to restore tidal flow to approximately six acres of formerly filled and buried tidal creek. Submerged Aquatic Vegetation Patches of eelgrass (Zostera marina—a flowering plant, not at all related to seaweed—see Spotlight on Eelgrass) occur on the northwestern and southeastern edges of Gloucester Harbor. Eelgrass is a productive nearshore marine habitat that supports diverse floral and faunal assemblages, absorbs nutrients, stabilizes sediments, and provides decayed matter that is consumed by species lower on the food web. A 1996 study of the eelgrass beds in Gloucester Harbor supports this characterization, finding up to 100 invertebrates, 25 bivalves, and 20 mysid shrimp per quarter of a square meter of eelgrass. This study also documented a preference of immature benthic fishes for eelgrass, finding three times as many immature fish in eelgrass beds than in unvegetated areas. The Gadidae family (pollock, cod, tomcod [Microgadus tomcod], and hake) made up the largest proportion of immature fish in eelgrass beds, although young winter flounder and tautog were also present. Coastal Beach Seine hauls along four Gloucester beaches in June 1999 revealed that many of the fish species found along the beaches were the same as those found in the deeper water trawls. The most noticeable and abundant addition was the Atlantic silverside (Menidia menidia, a common minnow), but an occasional stickleback (Gasterosteus aculeatus), puffer (Sphoeroides maculatus), or juvenile bluefish (Pomatomus saltatrix) was also found in the seine. These shallow areas are also visited by adult predatory fish, such as striped bass (Morone saxatilis), on the hunt for their crustacean or fish prey. Port Infrastructure as Habitat While active ports pose threats to natural habitats and the species that inhabit them, certain species of marine life continue to hang on, in some cases literally. Docks, piers, and jetties are settlement areas for a number of marine invertebrates. Walk out on a dock and take a look at the bright orange sponges and squishy sea squirts, notice the constellations of white barnacles and clumps of mussels woven together by their byssal threads. You may also see crabs or shrimp scuttling along algae-covered pilings. These encrusting and bottom-crawling communities originally inhabited only the boulders and ledges left by the receding glaciers thousands of years ago. However, these organisms can also be found on rock jetties, riprap, pilings, mooring lines, navigational aids, and some boat bottoms. The increased open space on new docks and piers creates settlement areas for entire aquatic communities. Not all new substrate has positive benefits, however. Recent scientific studies suggest that docks and piers may be unintentional promoters of invasive species. For example, a survey at the Gloucester State Pier identified at least 12 invasive species, including four tunicates, two shrimp, two crabs, a hydroid, an anemone, a bryozoan, and a red alga. Forward into the Future Ports are very important parts of the economic and historical landscape of Massachusetts. What is sometimes forgotten is that these busy industrial areas still contain intact and fragmented habitats that are populated by a wide variety of marine organisms. Ports do not have to be wastelands to sustain human uses, and can be managed with an eye toward maintaining and remediating the fragments of productive habitat that remain. | |||||||||||||||||||||||||||
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