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Abstract
Polychaetes inhabiting deep-sea soft bottoms in the southeastern Gulf of California were collected during four oceanographic cruises in 2000 and 2001 at a depth range of 732-2110 m. A total of 84 taxa, representing 32 families, were collected. The relationships between density, species number and diversity and depth, dissolved oxygen, temperature, granulometry and organic matter content in sediments were analysed. Cluster analyses and MDS plots based on density allowed faunal assemblages to be established for each environmental variable: 700-1100 m, 1100-1600 m, 1900-2100 m and 2100-2200 m (depth); 0.00-1.20 ml/L, 1.20-2.00 ml/L and 2.00-2.40 ml/L (oxygen); 2.0-2.5°C, 2.5-4.0°C, 4.0-6.0°C and 6-6.5°C (temperature); 8-16%, 16%-18% and 18-20% (organic matter), 20-30%, 60-70% and 80-100% (mud). Polychaetes were not distributed according to gradients of any of these environmental variables. The dominant and frequent species of each group were not restricted to unique assemblages. Results of a canonical correspondence analysis indicated that depth, oxygen and temperature were the main environmental variables responsible for polychaete distribution. The dominance of muddy sediments with high organic matter content (8.26 to 18.78%) throughout the study area reduces the importance of these parameters for polychaete distribution, since the dominant and frequent species belong to the detritivore families Ampharetidae, Maldanidae and Cirratulidae.
Highlights
The southern Gulf of California connects with the Pacific Ocean at its mouth, where there are depths greater than 3000 m, while the northern part is relatively shallow (Parker, 1964; Alvarez-Borrego and Schwartzlose, 1979)
The present paper examines the relationships between some environmental variables and deepwater polychaete communities occurring at depths ranging from 732 to 2110 m in the southeast Gulf of California
It has been demonstrated that depth, oxygen and organic matter strongly influence the diversity of bathyal macrobenthos (Levin and Gage, 1998), depth being one of the most important factors affecting macrofauna distribution (Jumars, 1976; Grassle, 1989), as demonstrated by results obtained in the correspondence analysis (CCA)
Summary
The southern Gulf of California connects with the Pacific Ocean at its mouth, where there are depths greater than 3000 m, while the northern part is relatively shallow (Parker, 1964; Alvarez-Borrego and Schwartzlose, 1979). In the North Atlantic, the eastern Pacific and the Indian Ocean, organic carbon, bottom water oxygen concentration and depth strongly influence deepwater macrofaunal diversity. Effects of depth have been reported in the North Atlantic, where a mid-slope diversity maximum is found following a unimodal pattern with a peak at intermediate depths, and lower diversity occurs at upper bathyal and abyssal depths. This pattern, does not appear to be universal (Levin et al, 2001)
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