Barnegat Bay Little Egg Harbor System: Use of SAV Biotic Indicators of Estuarine Condition

Seagrass is an important indicator of estuary condition. Results of a comprehensive investigation of the seagrass demographics in the Barnegat Bay-Little Egg Harbor (BB-LEH) Estuary during 2008 indicate ongoing degradation of seagrass habitat associated with increasing eutrophic conditions. Surveys of seagrass beds in BB-LEH from spring to fall in 2008 show that the seagrass (predominantly Zostera marina) beds have not yet recovered from the marked reduction of plant biomass (g dry wt m-2), density (shoots m-2), blade length, and percent cover recorded in 2006. Quadrat, core, and hand sampling, as well as digital camera imaging at 120 transect sites in 4 disjunct seagrass beds of the estuary during the June-November period in 2008, as in 2004, 2005, and 2006, reveal distinct changes in demographic patterns that can lead to significant shifts in ecosystem services. In 2008, seagrass was found at less than 50% of the survey sites (46.3%) during the June-July sampling period when the median aboveground and belowground biomass values were a maximum. The percent cover of seagrass was lowest in June-July (23%), highest in August-September (36%), and intermediate in October-November (27%). Seagrass biomass, density, and areal cover measurements in comparison to previous years, were higher at interior transect sampling sites closest to the seagrass bed margins (i.e. areas of seagrass beds away from margins) than at exterior transect sampling sites (i.e. outermost area of seagrass beds), which be attributed to edge effects and environmental conditions less optimal for overall survival. These values are consistent with those measured during 2004, 2005, and 2006. The percent cover of macroalgae was significantly lower than that of seagrass, declining markedly from June to November. The mean percent cover of macroalgae decreased from 20% during the June-July period to 10% during the August-September period and 5% during the October-November period. The nitrogen content of Z. marina blades measured at field transplantation sites ranged from 2.97% to 4.33%. Nitrogen Pollution Index values calculated for Z. marina in the estuary ranged from 0.58 to 2.55. Rutgers University Assessment of Eutrophication in the Barnegat Bay Little Egg Harbor System: Use of SAV Biotic Indicators of Estuarine Condition Introduction Eutrophication poses the most serious threat to the longterm health of the Barnegat Bay-Little Egg Harbor Estuary (Kennish et al., 2007a). Nutrient enrichment and associated organic carbon loading in this shallow, coastal lagoon have been linked to an array of cascading environmental problems such as increased microand macroalgal growth, harmful algal blooms (HABs), altered benthic invertebrate communities, impacted harvestable fisheries, and loss of essential habitat (e.g., seagrass and shellfish beds). The net insidious effect of progressive eutrophication is the potential for the permanent alteration of biotic communities and greater ecosystemlevel impacts. For example, hard clam (Mercenaria mercenaria) stocks in BB-LEH declined by two-thirds between 1986 and 2001, and the hard clam harvest declined by more than 95% between 1975 and 2005. Recurring brown tide (Aureococcus anophagefferans) blooms occurred between 1995 and 2002, with monitoring for brown tide being discontinued after 2004 (Olsen and Mahoney, 2001; Gastrich et al., 2004). The biomass of seagrass beds in the BB-LEH Estuary decreased by 50-87.7% over the 2004-2006 period (Kennish et al., 2007b). Since the BB-LEH Estuary is shallow, poorly flushed, and bordered by highly developed watershed areas, it is particularly susceptible to nutrient loading. Seagrass subsystems, which are excellent indicators of estuarine sediment and water quality conditions, have been on the decline not only in estuaries in the mid-Atlantic region but also in many other regions worldwide due to nitrogen and phosphorus loading associated with human activities (Nixon, 1995; Rabalais, 2002; Orth et al., 2006; Valiela, 2006). Most of the seagrass beds in New Jersey (~75%) occur in the BB-LEH Estuary. While more than 6,000 ha. of seagrass habitat have been re-