40 DECEMBER 2023 • WORLD AQUACULTURE • WWW.WAS.ORG abundance of grass shrimp at the floating cages is differential food availability or protection provided by increased algal growth on the floating cages which receive more sunlight than the bottom cages. Previous work from another group has found macroalgal growth on shellfish aquaculture gear can support high abundances of motile invertebrates (Powers et al. 2007) such as seagrass and coral/oyster/polychaete reefs, threaten coastal fisheries worldwide. We tested the hypothesis that macroalgae and epifauna growing upwards from protective plastic mesh used in bottom clam culture substitutes for seagrass as a nursery habitat for mobile invertebrates and juvenile fish. By quantifying biomass of epibiota in each season and by seining both day and night on 11 occasions from August 1997 to April 1999, biogenic habitat structure and habitat use by mobile invertebrates and juvenile fishes were quantified on hard clam Mercenaria mercenaria aquaculture leases that were using 2 alternative grow-out methods and on 2 natural habitats, a seagrass bed (Zostera marina and Halodule wrightii). While the sandy-area floating cage did support high numbers of grass shrimp, this cage was likely not an accessible habitat readily used by a wide variety of species based on lower invertebrate diversity at this cage. We think this may be related to limitations of some species, which would prevent them from swimming up in the water column. For example, hermit crabs or non-swimming crabs might find it difficult to reach a floating cage which does not have additional vegetative structure nearby. Grass shrimp in contrast are able to swim in the water column so they would not be limited in this way. Plans for Future Work Our experiment has demonstrated how different aquaculture gear designs variably influence oyster growth and the ecosystem services provided by oyster farms using these gears, thereby supporting our initial hypotheses. Bottom cages supported faster oyster growth in both shell length and shell depth, as well as higher levels of abundance and diversity of fishes. Our work has identified new questions that will need to be explored in order to fully understand the influence of gear type on oysters and other animals. For example, how do rates of fouling by barnacles, algae, and sediment change with depth and oyster bag mesh size? What influence might these fouling organisms or sediment have on oyster growth in a controlled setting? Would low levels of fish abundance and diversity trends at isolated floating cages continue with additional replication at other sites? Our project demonstrated variance in the growth of eastern oyster between cage types, while documenting some of the key habitat provisioning provided by aquaculture farming. We look forward to continuing to explore how anthropogenic activities such as oyster farming affect coastal environments in the future. Acknowledgments We thank members of the University of Delaware-Lewes campus community who played a crucial role in data collection including Ms. Lenna Wood, Ms. Madison Windsor, Mr. Anthony O’Toole, Ms. Kaylin Regan, Ms. Caroline Bowers, Mr. Nicholas Whaley, Mr. Sam Hankinson, Ms. Maddie Reifsteck, and Mr. Randy Feris. Additionally, we would like to recognize Dr. Adam Marsh for statistical advisement of the analyses for this project and Steve Friend for his guidance on the installation and operation of the oyster cages. Notes Timothy J. Smoot, University of Delaware, College of Earth, Ocean & Environment, Newark, DE, USA; tjsmoot@udel.edu Edward A. Hale, University of Delaware, College of Earth, Ocean & Environment, Delaware Sea Grant, School of Marine Science & Policy, Lewes, DE USA; ehale@udel.edu References Dealteris, J.T., B.D. Kilpatrick and R.B. Rheault. 2004. A comparative evaluation of the habitat value of shellfish aquaculture gear, submerged aquatic vegetation and a non-vegetated seabed. Journal of Shellfish Research 23(3):867–874. Marenghi, F., G. Ozbay, P. Erbland and K. Rossi-Snook. 2010. A comparison of the habitat value of sub-tidal and floating oyster (Crassostrea virginica) aquaculture gear with a created reef in Delaware’s Inland Bays, USA. Aquaculture International 18(1):69– 81. https://doi.org/10.1007/s10499-009-9273-3 Powers, M.J., C.H. Peterson, H.C. Summerson and S.P. Powers. 2007. Macroalgal growth on bivalve aquaculture netting enhances nursery habitat for mobile invertebrates and juvenile fishes. Marine Ecology Progress Series 339:109–122. https://doi.org/10.3354/meps339109 Theuerkauf, S.J., L.T. Barrett, H.K. Alleway, B.A. Costa-Pierce, A. St. Gelais and R.C. Jones. 2022. Habitat value of bivalve shellfish and seaweed aquaculture for fish and invertebrates: Pathways, synthesis and next steps. Reviews in Aquaculture 14(1):54–72. https://doi. org/10.1111/raq.12584 FIGURE 9. Grass shrimp (Palaemon sp.) captured in one of the oyster aquaculture cages. Photo by Timothy Smoot.
RkJQdWJsaXNoZXIy MjExNDY=