Search

Two annual immigration cycles (1969-1970 cycle I; and 1981-1982 cycle II) of postlarvae (Pls.) of the white shrimp Litopenaeus vannamei (Boone, 1931) recorded at the same recruiting inlet and employing comparable sampling procedures, were analysed to examine interannual variability. The annual and monthly density values of both cycles were tested to infer a predictable immigration model that can be applied to assess the abundance and availability of shrimp Pls. at recruiting sites. A sustainable Pls. extraction programme must rely on a sound knowledge of the variability patterns of these parameters. Significant differences were noted in the annual density of Pls. between cycles. In cycle I, the annual mean density of postlarvae (μ d-3/yr-1/Pls.) was 3.1, while in cycle II it was 1.3. Successful reproduction and spawning of the offshore shrimp stock and coastal circulation conditions are invoked as possible sources of variability between cycles. The parameter μ d-3/yr-1/Pls. is recognized as a good estimator for assessing yearly immigration success of Pls. among cycles and localities. This parameter becomes statistically more robust, minimizing the above differences, when the numbers of days of Pls. absence detected in the two cycles are incorporated in the calculations. The monthly mean density of Pls. (μ d-3/month-1/Pls.) underwent significant interannual fluctuations (Mann-Whitney U-test, p = 0.001). While in cycle I there were three monthly abundance peaks, in cycle II only one peak was recognized. The correlation coefficient of this parameter in both cycles was low and inverse (r = -0.203). Nonetheless, both cycles exhibited similar values of maximum monthly mean Pls. density. The penaeid immigration process is a complex phenomenon, governed by physical factors and interspecific variability, that is further augmented when assorted sampling methodologies are applied in its study. The results here presented indicate the convenience of implementing long-term Pls. assessment in shrimp recruiting sites, and employing standardized methodologies in order to achieve a sustainable exploitation of this valuable resource. [ABSTRACT FROM AUTHOR]

Newly discovered hydrothermal systems in the Pescadero Basin (PB) and the neighboring Pescadero Transform Fault (PTF) at the mouth of the Gulf of California disclosed a diverse macrofauna assemblage. The trophic structure of both ecosystems was assessed using carbon (δ13C), nitrogen (δ15N), and sulfur (δ34S) stable isotopes. The δ13C ranged from -40.8 to -12.1‰, revealing diverse carbon sources and its assimilation via Calvin-Benson-Bassham and the reductive tricarboxylic acid cycles. The δ15N values were between -12.5 and 18.3‰, corresponding to primary and secondary consumers. The δ34S values fluctuated from -36.2 to 15.1‰, indicating the sulfide assimilation of biogenic, magmatic, and photosynthetic sources. In PB high-temperature vents, primary consumers including symbiont-bearing, bacterivores and filter-feeders predominated. The secondary consumers within the scavengers/detritivores and predator guilds were scarce. The siboglinid Oasisia aff alvinae dominated the macrofauna assemblage at PB, but rather than playing a trophic role, it provides a substrate to vent dwellers. In PTF low-temperature vents, only symbiont-bearing primary consumers were analyzed, displaying the lowest δ34S values. This assemblage was dominated by the coexisting siboglinids Lamellibrachia barhami and Escarpia spicata. δ34S values allowed to distinguish between PB and PTF vent communities, to exclude the presence of methanotrophic organisms, and the detection of photosynthetic organic matter input., Competing Interests: The authors have declared that no competing interests exist.