Recursos Marinos y Pesquerías

Habitat use and stable isotopes in spider crab juveniles [Working paper]

11/02/05 ,

Freire J, S Carabel, P Verísimo, C Bernárdez & L Fernández (2005). Complex patterns of habitat use by juvenile spider crabs Maja brachydactila revealed by stable isotope analyses. Working paper (v.2, Jul 2005) [pdf]. (v.1, Feb 2005, pdf]

Patterns of habitat use by spider crab juveniles, Maja brachydactyla,
from two geographic areas in the NW coast of the Iberian Peninsula, were analyzed
through the analysis of Carbon and Nitrogen stable isotope relations in two
tissues (muscle and hepatopancreas). The main organisms that constitute the
diet of spider crab juveniles in rocky and sandy habitats and the different
organic matter sources in coastal food webs were analysed too. The isotopic ratios
of C and N did not show any difference between rocky and sandy habitats. The
use of carapace colour and epibiosis as an indicator of habitat use was not
supported by our data. These results suggest much more frequent movements
between both types of habitats than those suggested by former studies (carried
out using behavioural observations and sampling distributions) that
hypothesized seasonal and ontogenetic changes. In the coastal food web, two
main trophic compartments were identified according to the organic matter
source: one based in plankton and seaweeds, that corresponds, mainly, with
rocky habitats, and another based in sedimentary particulate organic matter
that correspond with sandy bottoms. The relationships observed between the C
and N isotopic ratios and the proportions of lipids and proteins in muscle and
hepatopancreas seem to indicate a clear relation between the trophic origin of
the food consumed by the spider crab juveniles and its energetic condition, and
the individuals that spent more time feeding in sandy areas would show a better
energetic condition. Juveniles of Maja brachydactyla, independently of the
habitat of capture, would consume in average approximately two thirds of the
preys in rocky habitats and a third in sedimentary habitats. The results
obtained indicate that, in exposed environments, large juveniles spend most of
the time in sedimentary bottoms, where they find more refuge, but they move
frequently (probably at night) to the nearby rocky substrates to feed.