Seagrass Abundance and Productivity in Pensacola Bay and Santa Rosa
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Seagrass abundance and productivity in Pensacola Bay and Santa Rosa Sound Final Technical Report Submitted to Florida Fish and Wildlife Conservation Commission Fish and Wildlife Research Institute Photo credit: B. Albrecht Jane M. Caffrey, Barbara Albrecht, Rachel Capps Center for Environmental Diagnostics and Bioremediation University of West Florida January 31, 2017 Deliverable 1 - Historical Perspective A variety of information related to seagrasses in Pensacola Bay and Santa Rosa Sound has been collated. This includes available seagrass data, publications, maps and imagery and was included in the Progress report and Appendix 1. The results from the workshop conducted on January 29- 30 were reported in the Progress report and are included in Appendix 2. The Pensacola Bay System (PBS) is located in the extreme western panhandle of Florida. The PBS covers 372 km2 and receives drainage from 18,130 km2 in northwest Florida and southern Alabama. The PBS encompasses the Escambia, Blackwater, East, and Pensacola Bays. It is a drowned river valley with a small outlet into the Gulf of Mexico at the western end of Santa Rosa Island. A 1948 survey of the PBS reported extensive seagrass beds, followed by reports of seagrass die off beginning in 1955 with the most rapid loss in Escambia Bay near industry.Historically, the PBS has had problems with anthropogenic inputs, both point and non- point source, discharging into its waters (Olinger 1975). Large areas of submerged aquatic vegetation (SAV) and oyster reefs were lost in the late 1960’s and early 1970’s. After the implementation of regulatory standards in the 1970’s, the condition of the system improved. Current priorities for the PBS include; sediments traveling downstream into the bays, and the potential eutrophication of portions of the system due to changes in nutrient loadings. (USEPA 2004). A 1960 survey of Santa Rosa Sound identified roughly 10,000 acres of seagrass beds (Lewis et al. 2008).The last comprehensive survey in 2010 survey identified 1,053 acres in Pensacola Bay and 2894 acres in Santa Rosa Sound (Harvey et al. 2015). Seagrass coverage in 2014 declined following high rainfall and runoff (Harvey et al. 2015). As part of this project, a reanalysis of data collected as part of a project on the impact of seagrasses on sediment biogeochemistry was conducted and is described below. Most of the sediment biogeochemistry results are presented in Devereux et al. 2011, but we present some additional unpublished data (Devereux, pers. Comm.). Several sites were visited in Santa Rosa Sound between 2002 and 2005 (Fig.1). Figure 1 – Location of sampling sites in Santa Rosa Sound from Deverereux et al. (2011) study. Reproduced from Devereux et al. (2011) Salinity during the sampling period ranged from 18 to 28 with lowest values occurring during late Jul 2004 (Fig. 2). This high frequency data suggests that while daily variation in salinity is generally low, rain events can 2 lead to declines in salinity in Santa Rosa Sound. Daily variations in salinity appear to be tied to local circulation with higher salinity at high tide (Figure 3). Figure 2 – Continuous 40 Temp 4 Salinity measurements of 35 Depth 3.5 temperature, salinity and 30 3 water depth at experimental locations. 25 2.5 Unpublished data from R. Devereux 20 2 or or Salinity Depth, Depth, m 15 1.5 Temp 10 1 5 0.5 0 0 1/18/05 4/21/05 5/15/04 6/15/04 7/16/04 8/16/04 9/16/04 2/18/05 3/21/05 10/17/04 11/17/04 12/18/04 28.5 Salinity Depth 1.8 Figure 3 – Salinity and water depth in Santa Rosa 1.5 28 Sound between March 10, 1.2 2005 and March 25, 27.5 2005.Unpublished data 0.9 from R. Devereux Salinity 27 m Depth, 0.6 26.5 0.3 26 0 3 Above Ground Biomass 400 300 shallow 200 mid deep 100 grams/square meter grams/square 0 Jun-02 Jul-02 Sep-02 Jun-03 Jul-03 Sep-03 Nov-03 Apr-04 Jul-04 Oct-04 Feb-05 sampling months Figure 4 – Aboveground biomass (g dw/m2) of Thalassia testudinum in Santa Rosa Sound between June 2002 and February 2005 at 3 water depths. Unpublished data from R. Devereux Aboveground biomass of Thalassia testudinum ranged from 50 to 300 g dw/m2. Biomass was generally highest during the summer. There were no consistent differences between biomass from different water depths (R. Devereux, pers. Comm.). Leaf production was also measured at these sites. Highest rates of production occurred during June and were positively correlated to salinity (Fig 5). Shallow Mid Deep 5 Shallow Mid Deep 4.5 Linear (Shallow) Linear (Mid) Linear (Deep) 5 4 4.5 y = 0.1272x - 0.9424 R² = 0.4287 3.5 4 y = 0.107x - 0.5053 3 3.5 R² = 0.3638 2.5 3 y = 0.0937x - 0.1991 2.5 2 R² = 0.3365 2 1.5 Leaf production Leaf production mg shoot/d 1.5 Leaf production Leaf production mg shoot/d 1 1 0.5 0.5 0 0 0 2 4 6 8 10 12 10 15 20 25 30 35 Month Salinity Figure 5 – Leaf production by month (left panel) and leaf production versus salinity. Unpublished data from R. Devereux 4 Porewater sulfide concentrations were highest during July, with higher concentrations in the shallow and mid beds compared to the deeper beds (Devereux et al. 2011, Figure 6). Several profiles throughout the year show concentrations in excess of 1 mM (Figure 6), a concentration which can be toxic to Thalassia testudinum. Sulfide (mM) 0 1 2 3 4 5 6 0 1 2 3 4 5 6 0 1 2 3 4 5 6 0 1 2 3 4 5 6 0 Dec Shallow Feb Shallow 2 April Shallow July Shallow 4 6 8 10 12 14 16 0 July Mid Dec Mid Feb Mid 2 April Mid 4 6 8 10 12 14 16 0 July Deep Dec Deep Feb Deep 2 April Deep 4 6 8 10 12 14 16 Figure 6 – Porewater sulfide concentration in Thalassia testudinum from shallow, mid and deep beds in April, July, December, and February. Reproduced from Devereux et al. (2011). Deliverable 2 - Seagrass composition, abundance and growth rates Visual assessment of seagrass species composition in the Pensacola Bay System During this study, over 121 locations were visited in the Pensacola Bay system including Santa Rosa Sound to determine the seagrass species composition. Fifty-eight percent of the sites visited had seagrass or SAV species. The species identified at different locations are shown in Figure 7 and Table 1. Vallisneria americana and Ruppia maritima were found in the freshwater and brackish reaches of Escambia and East Bay. Not surprising given its wide salinity tolerance, Ruppia had a cosmopolitan distribution, occurring in all subestuaries of the Pensacola Bay system, including Santa Rosa Sound.We were surprised to find beds of Halodule wrightii in Escambia Bay between Indian and Trout Bayous. As previous recent surveys have shown, seagrasses are rare along the northern shore of the Gulf Breeze Peninsula. However, a bed of Ruppia was located in East Bay near Navarre and in numerous small un-named sloughs along the north shore of the Gulf Breeze Peninsula and in sloughs some along the south shore that feed into Santa Rosa Sound. In addition, there is some indication that seagrasses may be present in Butcherpen Cove in Gulf Islands National Seashore, although this could not be definitely 5 confirmed. Thalassia testudinum and Halodule were abundant in Santa Rosa Sound with Ruppia occurring at isolated locations as well. Figure 7 – Map of seagrass composition in the Pensacola Bay system including Santa Rosa Sound. Table 1 – Summary of seagrass species found in Pensacola Bay system subestuaries Subestuary # sites # sites with Seagrass/SAV species found surveyed seagrasses East Bay 35 15 Ruppia & Vallisneria Escambia Bay 27 17 Ruppia, Halodule, Vallisneria Pensacola Bay 9 2 Unknown & Ruppia Bayou Grande 18 9 Ruppia & Halodule Santa Rosa Sound 33 28 Thalassia, Halodule, Ruppia Total 121 70 Percent cover The seagrass species composition and basal cover of seagrasses and macroalgae was estimated at 68 sites in Santa Rosa Sound in May and June (Figure 8). On average, basal cover of Thalassia was 29% and Halodule was 7%. Macroalgae were predominantly red and represented 20% of the cover, with the remaining area as bare. At 7 sites in East Bay with seagrass beds, basal cover was 18% of Vallisneria, 14% Ruppia and the remainder was bare. The remaining sites in East Bay were 100% bare. Most sites in Escambia Bay were bare, except those in and near Indian Bayou, Trout Bayou and many smaller un-named bayous on the Garcon Peninsula where cover of Ruppia was estimated to be about 40%. 6 Figure 8 – Average percent basal cover of seagrasses and macroalgae in Santa Rosa Sound. Number in bar represents the number of quadrats analyzed. Seagrass Growth Rates Growth rates of Thalassia were estimated at 6 locations in Santa Rosa Sound using the leaf punch method. Three sites were along the north side of Santa Rosa Sound at Shoreline Park, Naval Live Oaks (NLO) and Oriole Beach and three were along the south side at the EPA facility, Big Sabine Point (BSP) and Opal Beach. Productivity quads were established at all 6 locations in June and September. In addition, two sites were revisited in July. Biomass at the different locations was variable, but generally higher in September compared to June (Figure 9). Opal Beach had the lowest biomass in June, 240 g/m2 and the highest biomass in September, 780 g/m2.