World Aquaculture December 2019

40 DECEMBER 2019 • WORLD AQUACULTURE • WWW.WA S.ORG lease located outside the lagoon in estuarine waters that are free of contaminants from urban and agricultural runoff. A pilot study was conducted to determine if we could use mangroves as a nursery area, collect spat using low-cost artificial collection substrates suspended frommangrove trees and successfully rear spat to market size in a mariculture lease. Study Sites in Boquerón Bay Mangrove oysters are currently abundant in Rincon Lagoon, associated with Boquerón Bay, in Cabo Rojo, southwest Puerto Rico (Fig. 4). This is one of the few remaining sites in Puerto Rico where mangrove oysters are sufficiently abundant to warrant harvesting. Oysters in this area grow on the prop roots of red mangroves and other structures located in the intertidal zone. This area is ideal for natural oyster recruitment because it is semi-enclosed and receives intermittent streamflow. Streams entering the lagoon receive urban and agricultural runoff and effluent from two secondary wastewater treatment plants. Water quality was monitored monthly at Rincon Lagoon (18 o 0’27.74” N, 67 o 10’41.51” W) and the Boquerón Bay farm site (18 o 0’16.54” N, 67 o 11’33.42” W) between June 2011 and June 2013. AYSI-85 meter was used to measure temperature (±0.1 C), dissolved oxygen (±0.03 mg/L) conductivity (±0.5 percent full scale) and salinity (±0.1 ppt). In addition, water samples were analyzed for total suspended solids (Crompton 1989), chlorophyll a , nutrients (nitrate, nitrite and phosphate), and turbidity (Strickland and Parson 1972). Rincon Lagoon had significantly lower dissolved oxygen, conductivity and salinity than the Boquerón farm site (Table 1), although all values were within the tolerance limits of mangrove oysters. There was a significant difference among dates for both TSS and chlorophyll a , the result of weather conditions prior to sampling in October and November. There were no significant differences between sites with respect to TSS or chlorophyll a , nitrate, nitrite or phosphate (Table 1). Both sites appear ideal for the growth of mangrove oysters. Evaluation of Spat Collection Structures Spat collection using artificial substrates to support oyster rearing has been practiced for hundreds of years (Wedler 1980, Buitrago and Alvarado 2005). Three techniques were evaluated for spat recruitment in Rincon Lagoon between April and August 2010: • Baskets —Oysters shells that are usually sent to an area landfill were collected from vendors and placed in plastic screen (“chicken fencing”) baskets (15 × 30 cm) with 2.5 × 2.5 cm openings and attached to mangrove roots (modified fromWatters and Prinslow 1975, Puerto Rico; Figs. 5 and 6). Each basket contained a minimum of 20 shells, each greater than 4 cm in length. • Dowels —Wooden dowels (50-cm length) were partially covered (30 cm from the bottom) with cement and hung from tree limbs (modified from Jory and Iversen 1985, Cuba). • Bottles —Plastic bottles were cut in half and hung horizontally from roots horizontally (Buitrago and Alvarado 2005, Venezuela; Fig. 7). Structures were installed in triplicate in three areas, all with oysters naturally present, and allowed to recruit spat between April and August 2010. Installation targeted the rainy season in this area because changes in salinity trigger mangrove oyster spawning (Nascimento 1991b). FIGURE 4. Sites historically used to harvest oysters in Puerto Rico. Today only Boquerón (oysters) and Santa Isabel (clams) are used. FIGURE 5. Recycling oyster shells collected from street vendors are used in baskets. These baskets are placed in the mangrove lagoon to recruit larva. FIGURE 6. Oyster baskets in the mangrove recruit larva. These baskets can be easily transferred to a farm site.