Spatial distribution and species diversity of Cephalopoda caught in ARSA bottom trawl
surveys were studied out during two different seasons (autumn and spring) in the Gulf of
Cadiz (Spain) from 2000 to 2007. Species composition of cephalopod assemblages was
analysed, using both clustering analyses and non-metric multidimensional scaling analysis
(nMDS). Spatial distribution of the assemblages identified and abundance of the main
species were mapped with Surfer 8.0 software, using kriging as the geostatistical gridding
method. A total of 35 cephalopod species belonging to 6 families were found at depths
between 20 and 700 m. In each season, Sepiolidae was the most abundant family in terms of
number of species, followed by Octopodidae. The species richness increased up to 100–120 m
depth, where it reached the maximum value. From 120 m, the species richness decreased
progressively with depth. In spring, the species with the highest occurrence was
Eledone moschata (34%) and in autumn it was Alloteuthis media
(70%). In both seasons, the most abundant species in terms of weight was
Octopus vulgaris, while Alloteuthis media showed the
highest yields in terms of numbers. Most species showed wide bathymetric ranges,
especially in autumn. Three different assemblages were found in both seasons during the
time period analysed (although 2003 and 2006 were not included in the cluster analysis):
shelf assemblage (20–160 m), deep shelf/upper slope assemblage (100–350 m) and middle
slope assemblage (320–700 m). The specific composition of these three assemblages was
similar between spring and autumn and an overlap could be observed between them, mainly in
the two continental shelf groups: shelf and deep shelf/upper slope assemblages.
Alloteuthis media and Alloteuthis subulata were the
most abundant species in the shelf assemblage as well as in the deep shelf/upper slope
assemblage. In the middle slope assemblage, Illex coindetii was the most
abundant species. The assemblages and their spatial distributions could be largely related
to a combination of physical and biological factors and their interactions.