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Distribution of Liocarcinus depurator along the western Mediterranean Coast

AuthorsRufino, Marta M.
AdvisorAbelló, Pere
Issue Date2004
PublisherUniversity of Wales
AbstractThe distribution of L. depurator has been analysed through classical statistics, linear models and geostatistics. Density was obtained from a ten-year time series of bottom, otter trawl surveys in eight areas along the Mediterranean coast of Spain. Two peaks of L. depura-tor occurrence were observed. The first (80% occurrence) between 51 and 150 m, and the other (66% occurrence) between 301 and 400 m. Below 500 m, crab occurrence was negligi-ble (<8%) and densities fell sharply. The pattern shown by crab densities closely shadows that of occurrence, although a second abundance peak was barely evident, and was located at 201-300 m. From 200-400 m, crab abundance appeared fairly evenly distributed but showing lower densities than in shallower waters. Analysis through linear modelling showed that L. depurator density decreased signifi-cantly with depth and year, but no effect of sample location was evident. The decrease of L. depurator density was most pronounced at shallower depths (depths < 150 m, declining at ~8±1 % per annum), than in deeper waters (depths > 150 m, declining at ~4±1 % per annum). Geostatistical analysis of L. depurator densities showed that the crabs distributions ex-hibited varying degrees of spatial structure with patch sizes varying between 19 and 75 km among the sampled years. When average densities were low, crabs were most abundant in Ebro River Delta area and Western Alborán Sea, areas showing permanent high-density popu-lations. The virtues and drawbacks of each approach are discussed. On a smaller scale, off the Ebro Delta L. depurator distribution (numbers and biomass) was related to sediment characteristics using geostatistics. Smaller crabs were found preferen-tially in shallower water, whereas larger crabs, in deeper ones. Given the presence of at least two distinctive aggregations (possible populations) of L. depurator on the Spanish coast, a series of morphometric studies were undertaken. A combi-nation of traditional dimension analysis and geometric morphometry (whole shape analysis) was used to compare crab morphology. Differences in carapace shape were identified between genders and geographic location that largely appeared to involve the abdomen width
DescriptionMemoria de tesis doctoral presentada por Marta M. Rufino para obtener el título de Doctora en Philosophy por la University of Wales, realizada bajo la dirección del Dr. Pere Abelló Sala del Institut de Ciències del Mar (ICM-CSIC).-- 215 pages, 80 figures, 29 tables
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