World Aquaculture December 2019

WWW.WA S.ORG • WORLD AQUACULTURE • DECEMBER 2019 43 ISCC = TWW - DSW CI = (AFDTW × 1000) / ISCC where total wet weight (TWW), dry shell weight (DSW), and ash-free dry tissue weight (AFDTW) are determined in grams, making CI unitless. The L:W ratio and CI varied significantly by sites (Fig. 10, Table 3). Environmental impacts of these structures on the benthic community were measured by seagrass percent cover and shoot density, blade length, and growth rate (Zieman andWetzel 1980). The benthic assessment was conducted monthly beginning in January 2013 (before the floats were deployed) through June 2013, when the floats were removed. Percent cover declined but the difference was not significant. There was no significant difference in growth rate of seagrass (Table 4). Seagrass shoot length decreased and shoot density increased between the beginning and end of float deployment (Table 4). Discussion In Puerto Rico, traditional artisanal oyster harvesting and sale practices have been passed down over generations to the current group of fishers. Current practices of harvesting mangrove oyster in Puerto Rico are arduous, pose a risk of personal injury to fishers and damage the roots of the islands remaining mangroves. Mangrove oyster populations have declined precipitously and the oyster is now only abundant in Rincon Lagoon, where current harvest pressure will further limit the oyster’s abundance in Puerto Rico’s coastal waters. These harvesting practices are not sustainable and have resulted in the depletion of oysters and mangroves. This pilot study was initiated to determine if mangrove oyster populations can be refocused to serve as a nursery resource, rather than a primary harvest site for market-size oysters. Mangrove oyster veliger larvae are released into the water column, locate intertidal structures, then attach (set) on that structure. When a hatchery is not available to purchase oyster juveniles (seed), farmers collect the juveniles on hard substrate (tiles, plastic rods, sheets) then relocate the collected juveniles and rear them in the water column. If the substrate is placed out before the optimal period of larval availability and attachment, the substrate becomes fouled, and only a small proportion of larvae attach. The presence of larvae in the water may be monitored to enhance the timing of substrate placement as seen with similar species (Dupoy et al. 1977). The availability of hard substrate for veliger larvae to set is typically the limiting factor in this environment. By providing recycled material as surface area for spat recruitment; we are not depleting the natural population and protect mangroves from destructive harvesting practices. Recycled shell and artificial substrates have been used for hundreds of years to collect spat to support oyster farming (Wedler 1980, Buitrago and Alvarado 2005). We examined three low- cost methods of deploying substrates for spat recruitment. Shell deployed in hanging baskets from the mangroves had the highest initial recruitment. The baskets when suspended from the mangrove, just below the high tide water line, did not damage the mangroves or detract from their overall appearance. We used the construction and deployment of the baskets as an opportunity to introduce local fishers to how they can use the baskets to collect oyster spat and potentially farm oysters. Appropriate site selection for grow-out is also critical. Shoreline surveys and water quality assessments were essential in determining the location of the farm site. Many coastal areas serve as repositories for sewage and agricultural and industrial runoff (Hunter and Arbona 1995). In a previous study, microbial indicators of fecal contamination and Salmonella spp. were found in Rincon Lagoon water, oysters and sediments (Ramirez-Toro et al. 2013). The farm site was similar to the lagoon site with respect to all water quality parameters except TSS and chlorophyll, indicators of food quality and quantity. Oyster condition indices were not different among sites, suggesting that this may not be a health factor for the oysters. Condition index also provides information on the reproductive cycles of the organisms and thus strategies for recruitment and farming. In general, condition index tends to decrease during the breeding season, reaching lowest levels after spawning takes place (Kennedy et al. 1996). Following this, the condition index gradually increases, usually through the winter. However, different patterns have been observed in different oyster populations (Nascimento 1991b). Length to weight ratio, also an indicator of oyster physiological condition, decreased from farm baskets to lagoon baskets to oyster collected from the mangroves. This may be a factor of oyster life stage; oysters collected from mangrove roots were typically mature. Growth rate is initially very high but slows down very quickly once a critical size is reached. Oysters in baskets never reached the ideal market size of 45 mm or greater that was historically self- imposed by fishers and accepted by local consumers. However, the duration of these studies was limited to six months by the local permits obtained to support establishment of the lease. We anticipate that extended deployment in the baskets would have facilitated the growth of oysters to market size in the baskets held at the farm site. A number of potentially parasitic invertebrates were observed associated with the oysters at all sites. As these parasites were identified at all sites, further investigation is needed to identify alternative sites for oyster grow-out. We observed a decrease in percent cover, shoot length and growth rate and an increase in shoot density under the floats; however, this could be attributed to the patchy nature of seagrass systems. Oyster farming may also improve benthic-pelagic coupling in these areas. Additional and longer term data collection would increase the understanding of the impact of such floats on seagrasses. FIGURE 10. Oyster size (length x width) in baskets from Rincon Lagoon and the farm site. Baskets were installed in the mangroves in July 2012 and measurement began after spat recruitment and continued until July 2013. ( C O N T I N U E D O N P A G E 4 4 )