Based on an extensive sampling regime from both nesting populations and bycatch, frequency analyses of mitochondrial (mt) DNA control region haplotypes in the Mediterranean were used to assess the genetic structure and stock composition of the loggerhead sea turtle, Caretta caretta, in different marine fisheries. The analyses show the following. (i) In drifting longline fisheries working in Mediterranean pelagic habitats 53-55% of turtles caught originated from the Mediterranean stock; (ii) In bottom-trawl fisheries all turtle bycatch is derived from this regional stock; (iii) This regional stock contribution to fishery bycatch suggests that the population size of the Mediterranean loggerhead nesting population is significantly larger than previously thought. This is consistent with a recent holistic estimate based on the discovery of a large rookery in Libya. (iv) Present impact of fishery-related mortality on the Mediterranean nesting population is probably incompatible with its long-term conservation. Sea turtle conservation regulations are urgently needed for the Mediterranean fisheries. (v) The significant divergence of mtDNA haplotype frequencies of the Turkish loggerhead colonies define this nesting population as a particularly important management unit. Large immature and adult stages from this management unit seem to be harvested predominantly by Egyptian fisheries. (vi) Combined with other data, our findings suggest that all the nesting populations in the Mediterranean should be considered as management units sharing immature pelagic habitats throughout the Mediterranean (and possibly the eastern Atlantic), with distinct and more localized benthic feeding habitats in the eastern basin used by large immatures and adults. (vii) Between the strict oceanic pelagic and the benthic stages, immature turtles appear to live through an intermediate neritic stage, in which they switch between pelagic and benthic foods.

The recent expansion of the Red Sea macroalga Caulerpa racemosa and its impact on the diversity and abundance of macrobenthos were examined and compared in the summers of 1992 and 1997, in Moni Bay, Cyprus. The phytobenthic community of the bay in 1992 was dominated by the seagrass Posidonia oceanica while, in 1997, the Lessepsian migrant C. racemosa became the most dominant, forming extensive mats. Changes in the vegetation system in Moni Bay have caused significant compositional changes in macrofaunal assemblages. A total of 178 individuals of 62 species are recorded. The composition of the macrofauna in 1992 was dominated by gastropods (44 %), crustaceans (22 %), bivalves (17 %), polychaetes (11 %) and echinoderms (6 %). In 1997, the gastropods and crustaceans had decreased to 13 % and 16 YO respectively, while, polychaetes had increased to 38 Yo becoming the most dominant taxon. Bivalves and echinoderms also increaseld to 22 % and 11 %, respectively, in 1997. The proliferative growth of C. racemosa imposed successional changes on the macrofaunal assemblages in Moni Bay, Cyprus, between 1992 and 1997. It remains to be tested whether the expansion of C. racemosa is related to the increase of water temperature associated with global warming or nutrient inputs or with the differences in the life history characteristics of this migrant vs. native algal species. 0 1999 Ifremer / CNRS / IIRD / Editions scientifiques et medicales Elsevier SAS Lessepsian migrant I Caulerpa racemosa I benthos I community composition I' Moni Bay, Cyprus Resume-Expansion de la macroalgue Caulerpa racemosa et variations de la ma.crofaune des fonds meubles dans la baie de Moni, Chypre. L'expansion recente de la macroalgue de mer Rouge Caulerpa racemosa et son impact sur la diversite et l'abondance du macrobenthos ont Cte compares dans la baie de Moni, a Chypre, entre les et& 1992 et 1997. La communaute phytobenthique de la baie Ctait dominee en 1992 par l'algue Posidonia oceanica, alors qu'en 1997, l'immigrant lessepsien C. .racemosa dominait, formant de vastes prairies. Les changements de vegetation dans la baie de Moni ont entrain6 des moldifications significatives dans la composition de la macrofaune. Au total, 178 individus de 62 espbces ont ttt examines. L,a composition de la macrofaune Ctait dominee en 1992 par les gasteropodes (44 Yo), les crustaces (22 %), les bivalves (17 %), les polychetes (11 %) et les echinodermes (6 %). En 1997, les gasteropodes et les crustaces Ctaient r&kits a 13 et 16 % respectivement, tandis que le polychbtes devenaient le taxon dominant (38 Yo) ; les bivalves et les Cchinodermes progressaient tgalement jusqu'a 22 et 11 % respectivement. La croissance proliferante de C. racemosa a provoque une s&L: de changements dans la macrofaune de la baie de Moni entre 1992 et 1997.11 reste a Ctablir si l'expansion de C. racemosa est due a l'tlevation de la temperature de l'eau associee au rechauffement global, a l'apport des nutriments, ou aux differences entre les caracteristiques de l'evolution de cet immigrant et c...

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