Spatial and Temporal Variation of Epiphytic Growth on Zostera marina

1. Spatial and Temporal Variation of Epiphytic Growth on Zostera marina Tara Seely* and Mike Kennish** *Department of Earth and Planetary Science, Washington University in St. Louis, Saint Louis, MO. **Institute of Marine and Coastal Sciences, Rutgers University, New Brunswick, NJ. Abstract Detailed investigations of eelgrass epiphytes in the Barnegat Bay-Little Egg Harbor Estuary reveal important temporal and spatial patterns linked to specific environmental forcing factors. Epiphytic growth was significantly different between June and July sampling periods in 2010. Peak epiphytic biomass in 2009 was recorded at transect 7 because of the high abundance of mussels at that location. Much lower epiphytic biomass was observed in 2010 at transect 7 because of the absence of mussels. A statistically significant difference in epiphytic biomass was found between summer 2009 and summer 2010 because of temperature differences between the two years. In 2010, no statistically significant difference was found in epiphytic biomass in Barnegat Bay compared to Little Egg Harbor. The differences in eelgrass biomass documented in this study are attributed to variations in temperature, nitrogen concentration, and epiphyte composition in the estuary during the study periods. • Methods • 120 sites were sampled during period 1 (June 2010) and 60 sites sampled during period 2 (July 2010) (Figure 2). • At each site a diver collected a handful of eelgrass blades. • The 5 longest blades in each sample were measured. Length and width (mm), percent epiphyte coverage, and types of epiphytes were noted for all 5 blades. • Epiphytes were scraped from blade surfaces. Epiphytes and blades were dried for 48 hours. Biomass (g) was recorded for each blade and corresponding epiphytes. Figure 3. Boxplot results of Wilcoxon rank test for epiphytes in BB and LEH Figure 4. Boxplot results of Wilcoxon rank test for epiphytes in June and July 2010 • Background • Barnegat Bay -Little Egg Harbor (BB-LEH) is a highly eutrophic estuary with peak concentrations of nitrogen in the northern and southern segments of BB. • Eelgrass (Zostera marina) beds form essential habitat that cover extensive shallow areas (~1.5 m) along the eastern side of the estuary. • The eelgrass functions as a source of primary production, stabilization of sediment, a buffer against waves, currents, and erosion, critical habitat for many organisms, and an indicator of water and sediment quality as well as ecosystem health. • Epiphytic growth on eelgrass blades attenuates light and can significantly reduce photosynthesis, thereby adversely affecting abundance and biomass of eelgrass beds (Figure 1). Figure 1. Eelgrass epiphytes. Clockwise from top left: calcareous tubeworms, finger sponge algae, orange sheath tunicate, and golden star tunicate block light to eelgrass blades reducing plant photosynthesis. Figure 5. Boxplot of epiphyte biomass by transect in 2009 Figure 6. Boxplot of epiphyte biomass by transect in 2010 • Objectives • Assess temporal and spatial changes in eelgrass epiphytes between: • Barnegat Bay and Little Egg Harbor • June 2010 and July 2010 • Summer 2009 and Summer 2010 Figure 2. Epiphyte samples were collected along 12 transects (10 sites each). Northern 6 transects were located in BB; southern 6 in LEH. Note high nitrogen concentrations in northern and southern segments of BB. • Results • No statistically significant difference in epiphytic biomass was found between LEH and BB in 2009 (Figure 3). This may be explained by similar levels of nitrogen in both basins (Figure 2). • A statistically significant difference in epiphytic biomass was found between sample period 1 and 2 (Figure 4). Warmer temperatures in July are more conducive to epiphytic growth in BB-LEH. • Epiphyte results for 2009 show peak biomass values at transect 7 (Figure 5) because of high abundance of blue mussels. • Epiphyte results for 2010 show low biomass values at transect 7 (Figure 6) because of the absence of blue mussels. Variable epiphyte biomass exists at the other transects. • A statistically significant difference in epiphytic growth was found between summer 2009 and summer 2010 (Figure 7) because of temperature differences between years . • Figure 7. Boxplot results of Wilcoxon rank test for epiphytes in summer 2009 and summer 2010 • Conclusions • Epiphytic growth on eelgrass blades varied temporally and spatially in BB-LEH primarily because of different temperatures, nitrogen concentrations, and epiphyte species composition across the estuary. • Observed differences in epiphyte biomass at transect 7 during 2009 vs. 2010 was because of the abundance of mussels in 2009. • Absence of mussels in summer 2010 was attributed to high water temperatures in the estuary. • Higher salinity and lower water temperature at transects near ocean inlets may be responsible for the increased epiphytic biomass observed there in 2009. • Greater precipitation in summer 2009 vs. 2010 may also have contributed to the observed differences in epiphytic biomass between years. Acknowledgments Gregg Sakowicz, Gina Petruzzelli, Chris Huch, and Sarah Wolfson for their assistance with field work and sample processing, Dr. Mike Kennish for guidance throughout the entire project, and Scott Haag for statistical analysis. This RIOS project was funded by NSF.