Idea Transcript
Groups of recurrent fish larvae on the West Coast of Baja California Sur and the central region of the Gulf of California ... summary:
The spatial and temporal variability of the species composition, as well as of the general patterns of distribution, and the associations of fish larvae in the Gulf of California and the western coast of Baja California Sur between 1984 and 1988 were studied. Biological, comes from 22 oceanographic cruisers, in which 1020 oblique trawls of plankton were made with bongo networks, from where fish larvae were extracted from the 505 um net. The study of the composition of species allowed the development of two systematic lists that included 283 taxa identified for the Gulf of California and 241 for the western coast of Baja California Sur. The analysis of the taxocenosis of fish larvae was elaborated using the technique of main components and the analysis of groups, which allowed the characterization of groups of species, defined by the spatial and temporal gradients of its distribution and abundance. Spatially, in the Gulf of California, the distribution gradients are mainly latitudinal, with a taxocenosis of temperate-subarctic affinity to the north, and a tropical-subtropical affinity in the south, whose distribution airs expand and contract coinciding with the general patterns Circulation of major streams and water bodies throughout the year. Temporally, the system presents two main states, the first one of summer characterized by the predominance of a tropical community, and the second one of winter, with a dominance of temperate-subarctic and subtropical species, between these there are two transition periods, in which A codominance of pelagic-coastal and mesopelágicas species that converge in the central region of the Gulf of California is observed. Although differences were observed between years, the most important variability in the composition and abundance of species is seasonal. The analysis of recurrent groups allowed the establishment of groups of species that define three faunal regions, coincident with the surface temperature gradients, and allowed to establish a criterion of division of the gulf, based on the isotherms of 18 ° C and 21 ° C . In contrast, on the western coast of Baja California Sur, the distribution gradients are mainly ocean-coast, and the distribution limits of the formed groups appear to be more defined by the spawning habitat of adults, consisting of an oceanic complex And a coastal one, that converge in the isóbata of 200 m, and that they cause a edge effect along this zone. Temporally, on the western coast of Baja California Sur, a period of winter is defined, one of spring, and one of summer-autumn, this last one is characterized by a high diversity of demersal species of shallow zones. Unlike the Gulf of California, on the western coast of Baja California Sur, the most important variations in fish larvae taxocenosis were between the years, which was reflected in the separation of a group of cold summer-autumn associated At low temperatures and lower species diversity, compared to the warm summer-autumn group in which positive thermal anomalies coincide with the presence of two El Niño phenomena (1982-1983 and 1987) and in the presence of tropical species Rare in the area. The El Niño phenomenon seems to be a fundamental factor that, on the western coast of Baja California Sur, determines the northern expansion of the southern tropical community, and its contraction towards the south during non-El Niño years. The comparative analysis of the recurrent groups in both systems shows that the associations of fish larvae reflect the environmental characteristics of the area and that their recurrence in space and time suggests that these can be used as biotic indicators of environmental change, And as decision elements in the delimitation of faunal regions.