Eelgrass Habitat and Faunal Assemblages in the City and Borough of Juneau, Alaska

摘要

Eelgrass (Zostera marina) is an ecologically important nearshore habitat and is susceptible to degradation and loss due to coastal development and natural environmental changes. The distribution, areal extent, health, and faunal use of eelgrass habitat within the City and Borough of Juneau (CBJ), Alaska are unknown. We sampled eelgrass and faunal assemblages at 15 locations in the CBJ from 2004 to 2007 to establish a baseline of information to track long-term and large-scale biotic changes. Eelgrass was present on approximately 3% of the estimated 235 km of shoreline surveyed and occupied a total of 20.4 ha. Repeated sampling over 4 years found that most eelgrass beds were stable in size. Eelgrass characteristics (i.e., above-ground stem density, biomass) varied among years and locations and were generally lower than in other Pacific Northwest eelgrass beds. Diverse species were found in the eelgrass beds, underscoring the importance of eelgrass as fishery habitat. A total of 18,134 fish, representing 42 species, were captured with a beach seine. The five most abundant species in decreasing order of abundance were chum salmon (Oncorhynchus keta), tubesnout (Aulorhynchus flavidus), crescent gunnel (Pholis laeta), threespine stickleback (Gasterosteus aculeatus), and Pacific herring (Clupea pallasii). Juvenile fish dominated our catches, indicating that eelgrass may be important nursery habitat in the CBJ for some species. The most ubiquitous invertebrate species epiphytic on eelgrass was the variegated chink snail (Lacuna variegata), whereas the most common invertebrates captured with a seine were juvenile shrimp (Crangonidae and Pandalidae), hermit crabs (Pagurus spp.), and juvenile Dungeness crabs (Cancer magister). We identified five locations representing a wide range of geographic locations and potential development for long-term monitoring. Limited distribution of eelgrass in the CBJ and its importance for many commercially important species warrant the monitoring and protection of this valuable habitat.