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Article Excerpt
ABSTRACT: High resolution, underwater videographic imaging coupled to differential global positioning system data has been employed to assess the distribution, abundance, and coverage of seagrass and macroalgae in Little Egg Harbor, New Jersey. The application of this innovative technique in conjunction with aerial imaging of the water body is an effective method of accurately characterizing the seagrass system and identifying benthic habitat types. A Seaviewer Sea Drop Camera and recorder unit deployed at randomly selected sampling sites along two transects in Little Egg Harbor during the summer of 2005 generated 317 images of bottom habitats. Analysis of these habitats showed that seagrass (Zostera marina) was the dominant component, with 84% of the images (N=267) containing seagrass, 48% of the images (N=152) containing macroalgae, and 44% of the images (N=138) containing both seagrass and macroalgae. Bare bottom (unvegetated) habitat was recorded in only 4% of the images (N=13). Seagrass covered a mean area of 62.8% of the sampling units along the transects compared to a mean area of 14.2% of the sampling units covered by macroalgae. The use of diver- and boat-based videographic imaging, together with aerial platforms, offers researchers one of the most effective methods of monitoring the status of seagrass and other benthic habitats in shallow coastal bay environments.
KEY WORDS: Underwater videography, aerial platforms, benthic habitat imaging, seagrasses, Little Egg Harbor.
INTRODUCTION
Eutrophication poses the most serious threat to the long-term ecosystem health of the Barnegat Bay--Little Egg Harbor Estuary (Kennish 2001a, 2002; BBNEP, 2005). Nutrient enrichment and associated organic carbon loading in this shallow, lagoon-type estuary have been linked to an array of cascading environmental problems such as increased micro- and macroalgal growth, harmful algal blooms (HABs), bacterial and viral pathogens, high turbidity, altered benthic invertebrate communities, impacted harvestable fisheries, and loss of essential habitat (e.g., seagrass and shellfish beds) (Kennish, 2001b). The net insidious effect of progressive eutrophication is the potential for the permanent alteration of biotic communities and ongoing ecosystem-level impacts. The Barnegat Bay--Little Egg Harbor Estuary is classified as a highly eutrophic estuary, and because it is shallow, poorly flushed, and bordered by highly developed watershed areas, it is particularly susceptible to the effects of nutrient loading and other anthropogenic stressors. Consequently, monitoring programs must continue to assess priority indicators of eutrophication and associated water quality changes for effective long-term management of the system.
Seagrass beds comprise critical habitat in the Barnegat Bay--Little Egg Harbor Estuary, supporting many benthic invertebrate populations, fish, waterfowl, and other organisms and serving as a key indicator of water quality conditions and ecosystem health (Kennish, 2001a), vital roles demonstrated in other coastal bays as well (Corbett et al., 2000). They form an important structural component in an otherwise barren sandy bottom of the estuary (BBNEP, 2005). These beds are also critical to the survival of bay scallops (Argopecten irradians) in the system. Recurring phytoplankton and benthic macroalgal blooms reduce light availability for seagrass growth (Dennison et al., 1989, 1993; Bricelj and Lonsdale, 1997; Lathrop et al., 2001), and acute light attenuation can markedly reduce seagrass survivorship (Bortone, 2000). In addition, brown tide (Aureococcus anophagefferans) blooms may significantly increase bay scallop mortality (Bologna et al., 2001; Gastrich and Wazniak, 2002). The result is often a substantial decline in seagrass areal coverage and the elimination of essential habitat for bay scallops, hard clams (Mercenaria mercenaria), and other organisms. During the past two decades, the Barnegat Bay--Little Egg Harbor Estuary has been the site of increasing frequency and magnitude of phytoplankton and benthic macroalgal blooms. Brown tide blooms have commonly occurred in the estuary since 1995 (Kennish 2001a; BBNEP, 2005).
Most of the seagrass beds in New Jersey (75%) occur in the Barnegat Bay--Little Egg Harbor Estuary, covering an area of more than 6,000 ha (Lathrop...
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