chapter  8
36 Pages

Seagrass Decline in New Jersey Coastal Lagoons

Abstract .......................................................................................................................................... 168 8.1 Introduction .......................................................................................................................... 168 8.2 Study Area ............................................................................................................................ 170 8.3 Materials and Methods ......................................................................................................... 170

8.3.1 Sampling Design ....................................................................................................... 170 8.3.2 Sampling Methods .................................................................................................... 172

8.3.2.1 Quadrat Sampling ...................................................................................... 172 8.3.2.2 Macro algae Sampling ................................................................................ 173 8.3.2.3 Core Sampling ........................................................................................... 173 8.3.2.4 Sediment Sampling .................................................................................... 173 8.3.2.5 Water Quality Sampling ............................................................................ 173 8.3.2.6 Videographic Imaging ............................................................................... 173

8.4 Results: Physicochemical Conditions ................................................................................... 174 8.5 Biotic Indicators .................................................................................................................... 175

8.5.1 Seagrass Distribution ................................................................................................ 175 8.5.2 Aboveground Biomass .............................................................................................. 176 8.5.3 Belowground Biomass .............................................................................................. 179 8.5.4 Seagrass Density ....................................................................................................... 184 8.5.5 Seagrass and Macro algae Cover ............................................................................... 184 8.5.6 Seagrass Blade Length ............................................................................................. 186 8.5.7 Macro algae Composition .......................................................................................... 187 8.5.8 Brown Tide ............................................................................................................... 190

8.6 Discussion ............................................................................................................................. 190 8.7 Summary and Conclusions ................................................................................................... 196 Acknowledgments .......................................................................................................................... 198 References ...................................................................................................................................... 198

Results of a comprehensive 3-year (2004 to 2006) investigation of the seagrass (Zostera marina L.) demographics in the Barnegat Bay-Little Egg Harbor Estuary, a lagoonal system located along the central New Jersey coastline, reveal a dramatic decline in plant biomass (g dry wt m-2), density (shoots m-2), blade length, and percent cover of bay bottom associated with increasing eutrophic conditions. Quadrat, core, and hand sampling, as well as digital camera imaging, at 120 transect stations in four disjunct seagrass beds of the estuary during the June to November period in 2004, 2005, and 2006 indicate distinct changes in demographic patterns leading to significant shifts in ecosystem services provided by the beds, such as the loss of habitat for bay scallops (Argopecten irradians), blue mussels (Mytilus edulis), blue crabs (Callinectes sapidus), and seatrout (Cynoscion nebulosus). Of all the metrics analyzed, seagrass biomass exhibited the most significant decrease over the study period, which was evident estuary-wide. For example, the mean aboveground biomass and belowground biomass of Z. marina decreased by 50.0% to 87.7% between 2004 and 2006, with the greatest decrease occurring in Little Egg Harbor. Shoot density of Z. marina also decreased from a mean of 292 shoots m-2 in 2005 to 241 shoots m-2 in 2006. The mean blade length of Z. marina was relatively consistent during 2004 (31.83 to 34.02 cm) and 2005 (25.89 to 32.71 cm), but decreased greatly during 2006 (18.61 to 19.37 cm), thereby reducing overall plant biomass. A progressive seasonal reduction in the percent cover of seagrass in the estuary was apparent during each year of the study and correlated well with diminishing eelgrass biomass. The percent cover of seagrass in the study area over the June to November period dropped from 45% to 21% in 2004, 43% to 16% in 2005, and 32% to 19% in 2006. The reduced growth and spatial cover of Z. marina during 2006 correlated with lower shoot density and biomass measurements. Declining seagrass abundance and biomass in the coastal lagoons of New Jersey signal an ongoing negative response to nitrogen over-enrichment, which has also been correlated with the occurrence of phytoplankton and benthic macroalgal blooms which are detrimental to seagrass habitat. Macro algae completely cover extensive areas of the bay bottom during blooms, particularly when comprised of sheet-like forms such as Ulva lactuca. These blooms appear to cause significant dieback of seagrass in some areas of the estuary. Recovery of seagrass beds in the estuary will depend on management intervention, including an accelerated remediation program involving a reduction of nitrogen loading from coastal watershed areas.