Nursery areas of red mullet (Mullus barbatus), hake (Merluccius merluccius) and deep-water rose shrimp (Parapenaeus longirostris) in the Eastern-Central Mediterranean Sea     

Roberto Carlucci  Lembo Giuseppe  Maiorano Porzia  Capezzuto Francesca  Marano Chiara Alessandra  Sion Letizia  Spedicato Maria Teresa  Ungaro Nicola  Tursi Angelo  Gianfranco D'Onghia 《Estuarine, Coastal and Shelf Science》2009,83(4):529-538

The spatial pattern of the nursery areas of red mullet (Mullus barbatus), hake (Merluccius merluccius) (Linnaeus, 1758) and deep-water rose shrimp (Parapenaeus longirostris) (Lucas, 1846) was studied in the South Adriatic and North Ionian Seas (Eastern-Central Mediterranean) applying geostatistical techniques and data from time series trawl surveys conducted in the area. The analysed variables were: R (number of recruits/km²) and R/Tot (fraction of recruits on the total sampled population). The structural analysis showed a spatial pattern of both variables characterized by continuity on a small scale. Predictions of nursery area localization with probability of finding recruits at different threshold values were obtained through median indicator kriging. For the red mullet the nurseries were mainly identified in the South Adriatic Sea off the Gargano peninsula and between Molfetta and Monopoli within 50 m in depth. The main concentration of hake juveniles was found to be between 100 and 200 m in depth along the Gargano peninsula and between Otranto and Santa Maria di Leuca, where a nursery of deep-water rose shrimp was also detected. An overlapping depth, between 100 and 200 m, was identified for hake and deep-water rose shrimp nurseries. Protection of these areas through limitations of fishing pressure is discussed.  相似文献   

Intersexuality incidence, sex ratio fluctuations and intersex reproductive output as factors affecting the temporal variation of intersexed populations of the marine amphipod Echinogammarus marinus     

Irene Martins  Alex T. Ford  Teresa F. Fernandes 《Marine environmental research》2009,68(4):163-169

The occurrence of intersexuality in populations of the marine amphipod Echinogammarus marinus has been related to several causes, including anthropogenic contamination, microsporidian parasites and environmental sex determination (ESD). At the individual-level, the costs of intersexuality in E. marinus are reflected in reduced reproductive output of intersexes compared to normal specimens. The impacts of intersexuality and other reproductive disorders in nature will only be fully understood when individual-level effects are upscale to the population-level, which can be achieved through ecological models. The aim of the present work is to simulate the density variation of real populations of E. marinus with different intersexuality incidence, proportions of phenotypes and intersex female reproductive rates. To achieve that, we have incorporated empirical data obtained at the individual-level from three intersexed populations of E. marinus into a population dynamic model. The original model was calibrated and validated for a long-term stable population without intersexuality and sex ratio 1. In the present version, the model includes an extra population group, intersex females, but the total sum of flow rates from juveniles to adults was kept the same as in the original model to respect the previous validation. In these circumstances, results indicate that the male-biased population is very sensitive to intersexuality, even at low incidence levels, and exhibits significant density decrease if conditions do not change. On the contrary, the two populations with a preponderance of female-biased sex ratios, low or moderate intersexuality incidence (up to an average value of 9% of the population) and with intersex reproductive rates corresponding to 80% the value of normal specimens, exhibit long-term persistence.The model is highly sensitive to adult female parameters (e.g. mortality), indicating that small variations on its values can significantly change population responses.Overall the present results suggest that, in spite the costs of intersexuality in E. marinus, the temporal variation of intersexed populations depend on intersex incidence level, sex ratio fluctuations and reproductive output of intersexes. Simulations also suggest that other processes (e.g. mortality rates of normal females) may play important roles in the maintenance of populations with intersexuality. In the future, it will be crucial to improve and validate this type of models with long-term observations and monitoring of intersexed populations.  相似文献   

Pockmarks, collapses and blind valleys in the Gulf of Cádiz   总被引：2，自引：2，他引：0  

Ricardo León  Luís Somoza  Teresa Medialdea  Francisco Javier Hernández-Molina  Juan Tomás Vázquez  Victor Díaz-del-Rio  Francisco Javier González 《Geo-Marine Letters》2010,30(3-4):231-247

Herein we describe a suite of fluid escape depression features, including pockmarks and collapse structures, discovered in the Gulf of Cádiz (Spain) during several recent cruises. We also establish an evolutionary model for these depressions and discuss the generation of bottom undercurrent furrows from fluid-flow structures, considering the oceanographic and tectonic framework and gas expulsion mechanisms. We describe for the first time blind valleys, which we define as giant, elongated (3 to 10 km long), collapsed and complex fault-strike features comprising mega-collapses and mega-pockmarks, generated in gas-venting areas and not associated to the collapse of mud-volcano complexes. We detected the blind valleys above diapiric structures. The collapse processes associated to blind valleys result from fluid escape through migration pathways which, in turn, are created by distension due to diapiric activity or to later tectonic reactivation of these diapirs. The evolution of these blind valleys, and their present-day morphology as furrows, derives from progressive fluid migration as well as from interaction of Mediterranean Outflow Water with the seafloor.