SYMPOSIUM on Marine Accidental Oil Spills
Monitoring spatial patterns and temporal changes in trophic
ecology of seabirds in relation to the Prestige oil spill
CAROLA SANPERA1*, , ROCÍO MORENO1, XAVIER RUIZ1, and LLUIS
JOVER2
1
2
Dep. Biologia Animal, Fac. Biologia, Universitat de Barcelona, Avgda. Diagonal 645, 08028 Barcelona
Professor, Dep. Biologia Animal, Fac. Biologia, Universitat de Barcelona, Avgda. Diagonal 645, 08028
Barcelona
* e-mail: csanpera@ub.edu
ABSTRACT
Mortality of oiled seabirds in relation to oil spills is one of the main focuses of public
environmental concern. Nevertheless, oil spills can also bring about medium and long-time
effects on seabird populations as a consequence of habitat degradation, decrease of some key
prey species, or through trophic cascades and/or other ecosystem disturbances. At which point
these factors are responsible of detrimental effects on populations remains an elusive question,
although its knowledge is keystone because of their importance in modeling the recovery of
populations.
Shags (Phalacrocorax aristotelis) and yellow-legged gulls (Larus michahellis) are the main
seabirds reproducing in the Atlantic islands off the Galician coasts, so they are key species to
monitor the status of underlying food webs. For shag, demographic studies have shown that
their populations had suffered a decrease in recent years in which the lower abundance of
sandlance, one of shag’s preferred prey species, cannot be ruled out (Velando et al. 20051). On
the other hand, yellow-legged gulls show great trophic plasticity which allows them to exploit
several food resources including refuse dumps resulting from human activities (Munilla 19972).
Since the Prestige shipwreck we’ve collected several types of samples from both, shags
and yellow-legged gulls with the aim of assessing spatial patterns and monitoring temporal
changes in the trophic ecology of their populations. Soft tissues and feathers from corpses of
animals which dead indirectly by the Prestige (provided by Conselleria de Medio Ambiente,
Xunta de Galicia) have been analysed for stable isotopes and trace elements. In these animals,
comparisons between feathers grown at different times provide clues about trophic status
before and after the Prestige oil spill. On the other hand, stable isotope signatures and heavy
metal content of soft tissues were compared with data from healthy individuals which fell
trapped in gillnet gears later on. Since 2004 onwards we have focused efforts on sampling four
breeding colonies along the Galician coast which were affected to a different degree by the
spilled oil: Cies, Ons, Sálvora (Parque Nacional de las Islas Atlánticas) and Ansarón Island
(Lugo). In 2004 we analized feathers of chicks from both species, as well as adults, which were
considered jointly with feeding data obtained from pellets at the same locations (provided by A.
Velando and I.Munilla, University of Vigo) to track feeding patterns amongst colonies. Moreover,
in the samples obtained during the breeding season of 2005 we combined the analysis of stable
isotopes with fatty acid composition of chick’s blood plasma to test for interspecies and intercolony differences. Continuing sampling in 2006 and 2007 must allow tracing temporal variation
in feeding ecology from both species and, subsequently, to assess the recovery of the
ecosystem.
1Velando
2
A, Munilla I & Leyenda, P (2005). Mar. Ecol. Progr. Series 302: 263-274
Munilla I (1997). PhD. Thesis. Universidade de Santiago de Compostela. 328 pp.
PROYECTO: Las aves marinas como indicadoras del cambio ecológico en el sistema natural costero
afectado por el vertido del Prestige: isótopos estables como biomarcadores.
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