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A biological survey of Baha de Los Angeles, Gulf of California, Mexico. 4. Benthic Amphipoda (Crustacea)

1969; Volume: 15; Linguagem: Inglês

10.5962/bhl.part.12057

0080-5947

J. Barnard,

Marine Biology and Ecology Research

The gammaridean fauna of a bay in the disjunct, warm-temperate zone of the Gulf of California is discussed.Of the 70 species encountered, 13 represent new species and 5 new subspecies.Two new genera are proposed.In 1962 and 1963 a sharp decline in diversity and abundance occurred in autumn in depths between 6 and 46 m.The diversity of Gammaridea is about half that of similar depths in southern California.Approximately 70 per cent of the amphipods have warm-temperate affinities; at least 9 cognates of Californian species occur in BLA.Shallow, sandy bottoms, in 2-8 m depth, are dominated by Ericthonius brasiliensis and Podocerus fulatius; middepths of 7-36 m on fine sands by Ampelisca compressa, A. cristata and Platyischnopus metagracilh; and the deepest zone, 37-46 m on brown silts, by Hetcrophoxus oculatus, Ampelisca cristata and A. compressa.None of the dominant species is endemic, but in the Californian warm-temperate zone Podocerus fulanus is confined to lagoons.Resumen.-Se estudian los Anfipodos Gammaridos de una bahia situada en la zona limitrofe de la region calido-templada del Golfo de California.Se describen setenta especies, de las cuales 13 son especies nuevas y ademas 5 nuevas subespecies.La bahia esta bajo la influencia del conocida fenomeno del efecto del verano en la densidad faunistica, de modo que esta es pobre en relacion con la que presenta el mar abierto.Un 70% de los Anfipodos, aproximadamente, presentan afinidades con los de las regiones calido-templadas; por lo menos 9 especies son cognatos a las que aparecen en regiones calido-templadas; todo lo cual indica en cierto modo, el aislamiento de esta fauna de sus fuentes originales.Las regiones poco profundas (de 2 a 8 metros de profundidad) con fondos arenosos, estan dominadas por Ericthonius brasiliensis y Podocerus fulanus; las zonas de profundidad media (de 7 a 3 6 m) sobre arena fina, aparecen pobladas por Ampelisca cristata, A. compressa y Platyiscbnopiis metagracilh; mientras que las zonas profundas (de 36 a 46 m) con fondos de fango marron, estan habitadas por Hetcrophoxus oculatus, Ampelisca cristata y A. compressa.Ninguna de las especies dominantcs refleja una dislocacion de la fauna al hacerse endemicas; a excepcion de Podocerus fulanus que puede funcionar en mar abierto como una reliquia confinada a las pequefias lagunas litorales.This paper describes the gammaridean fauna of a small bay, Bahia de los Angeles, on the east shore of Baja California, in the northwestern part of the Gulf of California.Amphipoda from the gulf have been recorded previously by Shoemaker (1925).Bahia de los Angeles is presumably within the disjunct, warm-temperate, upper gulf region discussed by Beltran (1960) in the "Symposium: The biogeography of Baja California and Adjacent Seas."Collection of this fauna was undertaken as part of a survey to assess the simple mud and sand-bottom communities and the general environment of that bay.Barnard and Grady (1968) have outlined the thermal regime, water characteristics, and benthic sedimentary structure of the bay and have reported on the phenomenon of "summer-kill" as a dominating influence on the warm-temperate fauna in 1962 and 1963.The amphipodan fauna of Bahia de los Angeles is impoverished, in terms of both species and abundance of individuals, in comparison with southern California, the only other quantatively studied region of the eastern Pacific Ocean.Approximately 70 per cent of the Amphipoda have warm-temperate affinities, and at least 9 cognates of warm-temperate species occur in Bahia de los Angeles (BLA).