Gaspar Soria

Spawning Induction, Fecundity Estimation, and Larval Culture of Spondylus calcifer (Carpenter, 1857) (Bivalvia: Spondylidae)

ABSTRACT In this study we describe spawning induction, fecundity estimation, and the early life history of the rock scallop Spondylus calcifer under laboratory conditions. We collected adults of S. calcifer from a natural stock in the Gulf of California, Mexico (28°37′N, 112°15′W). We induced spawning by means of thermal shocks (10°C magnitude) and estimated species fecundity as a function of size. We evaluated the effects on growth rate and final survival of larvae reared with 3 dietary treatments: (1) 30 cells/µL, (2) 50 cells/µL, and (3) 75 cells/µL. We reared larvae in 15-L containers at a density of 3 larvae/mL at 30°C, and renewed 100% of the water culture every 48 h. The diet comprised a combination (1:1) of Isochrysis galbana (clone T-ISO) and Chaetoceros calcitrans (clone C-CAL). Both females and males responded positively to thermal shock induction. Mean size of oocytes was 56.0 ± 4.2 µm (standard deviation; n = 30). Mean number of oocytes spawned was 48.9 × 106 ± 13.2 × 106 with the smallest female (shell height, 110.5 mm) spawning 28.95 × 106 oocytes and the largest (shell height, 180 mm), 71.76 × 106 oocytes. We observed the first group of throchophore and D-larvae at 7 h and 17 h after fertilization, respectively. At the beginning of the experiment, the mean shell height of D-larvae was 79.8 ± 8.54 µm (n = 35). Two weeks after fertilization, larvae reached the pediveliger stage and we ended the experiment. We found that S. calcifer larval growth rates were significantly different between diet treatments (F2.2.703 = 24.65; P < 0.001), with larvae reared at 50 cells/µL exhibiting the highest growth rate (12.42 µm/day) of all treatments. At the end of the experiment, larvae fed at 50 cells/µL attained a larger size (mean height, 234.01 ± 28.03 µm; n =115) than larvae from the other 2 treatments (30 cells/µL: mean height, 210.48 ± 30.81 µm; n = 107; 70 cells/µL: mean height, 221.81 ± 29.81 µm; n = 104). We did not find significant differences in larval survival between diet treatments at the end of the experiment (F2.6 = 0.63; P = 0.56). Our findings suggest that the minimum period for larvae of S. calcifer to begin settlement is approximately 15 days after fertilization under the experimental conditions assessed. The first appearance and the extension of the planktonic stage represent the minimum extension that the larvae can be subject to dispersion by oceanographic currents. Whether S. calcifer can delay settlement if no suitable substrate is found was not addressed in this study. These results will be used as an input for the development of a coupled biological—oceanographic model that can assist in management of the rock scallop fishery in the Gulf of California by predicting species larval dispersion patterns from known reproductive sources.

PANGAS: An Interdisciplinary Ecosystem-Based Research Framework for Small-Scale Fisheries in the Northern Gulf of California

Small-scale fisheries contribute about half of global fish catches, or two-thirds when considering catches destined for direct human consumption (FAO 2014). Small-scale fisheries play an important role in food security and nutrition, poverty alleviation, equitable development, and sustainable use of natural resources, providing nutritious food for local, national, and international markets. More than 90% of the world’s fishers and fish workers (those who work in pre-harvest, harvest, and post-harvest activities, including trade) are employed by small-scale endeavors that underpin local economies in coastal, lakeshore, and riparian ecosystems. This, in turn, generates multiplier economic effects in other sectors (FAO 2014). These activities may be a recurrent sideline undertaking or become especially important in times of financial difficulty. Small-scale fisheries represent a diverse and dynamic sector, often

Effect of Increasing Salinity on Weight-Specific Filtration Rate of Juvenile Scallop Argopecten purpuratus Reared at Two Temperatures: Is Any Effect Related to Ammonia Buildup?

ABSTRACT n Larvae of the northern Chilean scallop Argopecten purpuratus (Lamarck, 1819) can be produced in hatcheries in closed aquaculture systems (CAS), and then early juveniles transferred to the sea for further grow-out. A new scallop mass production method from larvae to early juveniles that applies recirculation aquaculture system (RAS) technology has been developed at Universidad Catolica del Norte. RASs might lose water by evaporation, which increases salinity. Water temperature will increase as well if it is not controlled. An experiment was performed to determine the effect of varying salinity and temperature over water quality parameters and scallop physiological processes. Feeding behavior of A. purpuratus was determined under CAS with daily water exchange for hatchery-produced juvenile scallops (mean shell height, 26.5 mm; SD, 1.9) reared at salinities of 34, 38, and 42 g/L, and temperatures at 16°C and 22°C. Weight-specific filtration rates (WFRs) were analyzed at day 12 and again at day 55. Scallops were fed Isochrysis galbana and Chaetoceros calcitrans (ratio, 1:1). Results shows that WFRs analyzed for a 24 h period had a tendency to be lower at 0 h than at 24 h, for both temperatures; WFRs were higher at 22°C than at 16°C. A significant positive regression was also found between final WFR and total ammonia nitrogen (both NH3-N and NH4+-N) levels. Results presented here should be interpreted with caution outside the shell height range of 26.5 ± 1.9 mm. These results are applicable to the management of A. purpuratus under controlled conditions, such as a RAS.

Isolation and characterization of microsatellite loci in the rock scallop (Spondylus calcifer) (Bivalvia: Spondylidae) from the Northern Gulf California, Mexico

Twelve microsatellite loci were isolated from an enriched genomic library of the rock scallop (Spondylus calcifer). One locus was monomorphic. Overall polymorphic loci, the mean numbers of alleles per locus at one locality was 9.6 (range 3–16), and the average observed and expected heterozygosities were 0.650 and 0.707, respectively. Three loci deviated from Hardy–Weinberg equilibrium, and from these, one locus had and excess of heterozygotes and the other two loci showed deficits of heterozygotes likely due to the presence of null alleles. No evidence of linkage disequilibrium was found among loci. These loci are the first microsatellites ever reported for the monotypic family Spondylidae, and will be useful to validate the predictions of oceanographic larval transport models and connectivity between patchy reefs within fishing areas and marine reserves in the northern Gulf of California, Mexico.

Spondylids of Eastern Pacific Ocean

ABSTRACT n Members of the bivalve molluscan family Spondylidae were very important elements in the world view of pre-Hispanic cultures of America, and today remain as symbols of culture heritage in contemporary society. In recent decades, given the importance they have for crafts and jewelry, as well as for fisheries and gastronomy, their exploitation has caused a drastic decrease in natural populations leading to restrictions in fishing. In the present review, data about Spondylus species of eastern Pacific Ocean, describing the symbolism, taxonomy, distribution, biology, and ecology, their status as exploitable resources, the advances in aquaculture of these species, as well as management experiences and conservation efforts are presented.

Ammonium Removal During Laboratory Culture of the Tehuelche Scallop Aequipecten tehuelchus

ABSTRACT n Laboratory-scale research involving marine bivalves maintained in recirculating or closed aquaria requires control of seawater quality parameters. Among them, the total dissolved ammonium nitrogen (TAN), NH4+ + ammonia (NH3) nitrogen, concentration is a critical parameter because of its potential toxicity, mainly in closed systems. This study assessed the efficacy of two macroalgal species collected in Golfo Nuevo (Patagonia, Argentina) in removing TAN from the seawater of experimental systems containing the Tehuelche scallop (Aequipecten tehuelchus). The use of the traditional nitrifying bacterial biofilter was also explored. Scallops were collected from the Gulf of San José (Patagonia, Argentina) where they support an artisanal fishery of great socioeconomic importance. This resource is currently threatened by declining landings observed in the previous years, and experimental research is needed to explore the best conditions for ex situ cultivation. A 14 day-experiment was conducted in 3-L beakers containing an adult scallop with addition of a biofilter (treatment T1: containing Ulva spp.; T2: Undaria pinnatifida; T3: bacterial biofilter; and T4: mechanical filtration before Ulva spp. addition). Negative controls (NC) (no scallop or biofiltration) and positive controls (PC) (without biofiltration) were also performed. The concentration of TAN was measured at the beginning of the experiment and every 48 h, and temporal patterns were described by regression models. Removal efficiency relative to PC was calculated on days 8 (Rd8%) and 14 (Rd14%). Ammonia concentration was estimated as a function of seawater temperature, pH, and salinity. In PC, TAN increased at a rate of 0.03 mg·L-1·h-1, reaching a final mean value of 9.85 mg·L-1 for total dissolved NH4+-N +NH3-N (TAN-N) (12.69 mg·L-1 TAN) and 0.15 mg·L-1 for NH3. In T1, TAN ranged from 0.02 to 0.22 mg·L-1 TAN-N during the first 10 days of the experiment (below those measured in PC, T2, and T3), and Rd8 and Rd14 were 98% and 84%, respectively. The highest TAN concentrations observed in the whole experiment were measured in T2, exceeding those in PC. In T3, TAN-N mean concentrations on days 8 and 14 were 1.45 mg·L-1 (Rd8 73%) and 0.45 (Rd14 95%), respectively. In T4, a linear increase of TAN was observed during the mechanical filtration period; after Ulva spp. addition, TAN decreased to levels as low as those measured in NC (<0.025 mg·L-1 TAN-N) until the end of the experiment (Rd14 100%). These results show that Tehuelche scallops may be relatively resistant to TAN and that NH3 concentrations were higher than several safety standards. The seaweed Ulva spp. provided the most efficient biofilter between both tested seaweeds, and its usage would represent a good alternative for the traditional bacterial biofilter in small-scale aquaculture experiments, including long-term acclimation. This information is useful for conducting experimental assays of this overexploited artisanal scallop resource from the Patagonian coast.