Presentation on theme: "Preliminary analysis (2 cages, 24 clams/cage) showed that the ranking of sites in terms of clam growth over 5 wks in 2013 was: Tuckerton > HC = Sedge >"— Presentation transcript:
Preliminary analysis (2 cages, 24 clams/cage) showed that the ranking of sites in terms of clam growth over 5 wks in 2013 was: Tuckerton > HC = Sedge > IBSP. Low growth at IBSP in 2013 is attributed to low salinities during early-mid June (minimum = 16, Table 1) approaching the low tolerance limit for hard clams . Clams ceased growing during this period, which coincided with high precipitation (cumulative levels of ~10”, compared to 5” in 2012). Harvey Cedars (HC) Sedge Is. (Marine Conservation Zone) Island Beach State Park (IBSP) Tuckerton Cove Little Egg Inlet Barnegat Inlet The optimum temperature range for hard clam growth is ~20 o to 24 o C, with growth rates declining above and below this range . Despite consistently lower temperatures and markedly greater temperature variation at Sedge (up to 16 o C day -1 ) than at other sites (<6 o C day -1 ), time-integrated clam growth rates over 7 wks were highest at this site in 2012 (not shown). There was highly significant variation both spatially and temporally in clam growth rates. Maxima in BB-LEH in 2012 and 2013 were comparable to those reported in other mid-Atlantic coastal lagoonal ecosystems (up to ~200 µ m day -1 ) . Low clam growth at IBSP was associated with low salinities and high contribution of picoplankton to the phytoplankton, resulting from influence of the Toms River plume. A 2nd deployment will be initiated August 12 th, completing a 2 yr-dataset of clam growth rates, and providing the first characterization of growth of hard clam juveniles in BB-LEH. Multiple regression analysis will be used to further investigate the relationship between clam growth and environmental factors in this estuary. Conor MacDonnell 1, Ryan Fantasia 2 and Monica Bricelj 2 1 William and Mary, Williamsburg, VA 2 Institute of Marine and Coastal Sciences, Rutgers University, New Brunswick, NJ Hard Clams as Indicators of Suspended Particulates in BB-LEH, NJ Populations of the hard clam (Mercenaria mercenaria), a commercially important shellfish species, have suffered a decline in the mid-Atlantic region, including Barnegat Bay-Little Egg Harbor (BB-LEH). BB-LEH (Fig. 1) is an EPA-designated National estuary, exhibiting strong north to south gradients in eutrophication/human development and salinity. Hard clams do not occur north of the Toms River, where salinities are < 15. Conclusions/Future Research Methods Juvenile clams were deployed at 4 sites in cages, off-bottom to exclude predators and confounding effects of substrate type (n=4 cages per site, 600 clams per cage in 4x4 mm mesh bags). Clams were deployed twice between June and Sept. 2012 and in June-July 2013 to determine weekly shell & tissue growth and survival. Seston samples were filtered in situ and analyzed for total and < 5 µm-Chl a, photopigments as indicators of phytoplankton functional taxonomic groups (FTGs) determined by HPLC, POC/PON, and POM/PIM. Fig. 1: The BB-LEH Estuary and its Watershed, indicating Study Sites Table 1 : Salinities at BB-LEH Study Sites- Deployment I IBSP has lower salinities than the other study sites, due to influence of the Toms River plume. Sedge shows higher salinities due to oceanic exchange via Barnegat Inlet Objectives The goal of this project is to investigate the relationship between seston characteristics and juvenile clam growth in BB-LEH, to determine whether current environmental conditions can support production of hard clams. This project will serve to guide shellfish restoration efforts in BB-LEH.. Acknowledgements We especially thank Carola Noji for technical support, and Lisa Izzo for processing of 2012 clam samples. We also acknowledge participation of co-PIs John Kraeuter (Haskin Lab) and Gef Flimlin (NJ Cooperative Extension). Jeffrey Silady provided boat access to Sedge Is., Larry Murphy access to his property in HC, and the IBSP Forked Interpretive Center with space for in situ processing of water samples. References Diagnostic pigments: Fucoxanthin= diatoms, Zeaxanthin= cyanobacteria, Chl b= chlorophytes, Alloxanthin= cryptophytes. IBSP had a unique phytoplankton assemblage with high contribution of picoplankton (especially cyanobacteria), often associated with low salinities and high organic nutrient levels in other estuaries . Picoplankton (cyanobacteria and chlorophytes), known to be poorly retained and of low nutritional value for hard clams  were negatively correlated with weekly clam growth rates (Fig. 4). The dominant chlorophytes at BB-LEH are within the picoplankton size range [3 & unpub. data 2012]. Concentrations of diatoms, considered a high quality food source for hard clams, were typically high at Sedge, where clams had the highest growth rates (ranking Deployment II= Sedge > Tuckerton > IBSP > HC ). Fig. 3: Contribution of Phytoplankton FTGs to Chl a and Clam Soft Tissue Growth Rates- Deployment II 2012 Background Fig. 5: Mean Shell Growth Rates – Deployment I 2013 Fig 2: Water Temperatures (daily means) during Deployment I Toms River  Grizzle R., V.M. Bricelj, S.E. Shumway. 2001, Physiological ecology of Mercenaria mercenaria, Chapter 8 In: Kraeuter, J. & M. Castagna (eds.). Biology of the Hard Clam. Amsterdam: Elsevier, New York, pp. 305-382.  Paerl, H. W., L. M. Valdes, J. L. Pinckney, M. F. Piehler, J. Dyble, P. H. Moisander. 2003. Phytoplankton photopigments as indicators of estuarine and coastal eutrophication. BioScience 53.10: 953  Mahoney and Olsen 2001, Phytoplankton in the Barnegat Bay-Little Egg Harbor system: Species composition and picoplankton bloom development. Journal of Coastal Research 32: 115-143 LE H Fig. 4: Relationship between Picoplankton & Clam Growth (IBSP)
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