Distribution and population biology of pelagic decapod crustaceans of the western Mediterranean
- Autores: Daniela Silveira Simão
- Directores de la Tesis: Vicente Gracia García (dir. tes.), Pere Abelló Sala (dir. tes.)
- Lectura: En la Universitat Politècnica de Catalunya (UPC) ( España ) en 2013
- Idioma: inglés
- Tribunal Calificador de la Tesis: Joan B. Company (presid.), Manuel Espino Infantes (secret.), Ferran Palero (voc.)
- Materias:
- Enlaces
- Tesis en acceso abierto en: TDX
- Resumen
The present thesis provides new information about pelagic decapod crustaceans, specially so concerning the Mediterranean pasiphaeids. Remarkable differences in the pattern of distributions of the pasiphaeids were observed according to the influence of Atlantic waters. Overall both abundance and biomass of the pasiphaeids in Alboran Sea was higher than in the rest of the Iberian Mediterranean populations. The depth on which the pasiphaeids started to occur in appreciable density was also shallower in the Alboran Sea where the P. sivado presented the widest depth range of distribution as well as the biggest size of first maturity of females. This size was progressively smaller with increasing distance from the Atlantic water source, i.e the Gibraltar Strait area. Overall the two species presented a size structure that changed with depth, with younger individuals occupying shallower depths and biggest adults occupying deeper bathymetries. P. multidentata juveniles were only observed in the Catalan Sea while they were absent in the Alboran Sea. Size and morphological dimorphism of P. sivado were reported for the first time in the present thesis. All the five pleopods of females were thinner and more elongated than male pleopods, which in turn were rounded anteriorly and had robust shapes. A critical size from which the population sex ratio biases changed from females to males dominance was found in all P. sivado populations of the Mediterranean Iberian coast. This critical size was different and progressively larger again from populations nearest the Gibraltar Strait versus those placed in the Catalan Sea, in concordance with the female first maturity size gradient. The present thesis also provides a first attempt to investigate the influence of the Gibraltar Strait on the genetic population structure of the species by using congener benthopelagic shrimps that dwell in different depth strata. The Gibraltar Strait was shown to be a strong and unique geographical barrier to the genetic flux of both P. sivado and P. multidentata, due the presence of a marked genetic structure characterized by two main haplotypes: one Atlantic and another one Mediterranean. Other new information related to the phylogeny of the genus Pasiphaea was that P. sivado a much higher genetic divergence when compared to the rest of pasiphaeid species analysed, indicating that several genetic subgroups do occur within the genus Pasiphaea. The study of the pelagic decapod community in the waters around the island of Mallorca, placed between the Algerian and the Catalano-Balearic basins, showed the occurrence of two main assemblages: one above the shelf break and another one above the middle slope. The shelf community was characterized by the dominance of almost transparent species, such as Sergestes arcticus, the species that reached the greatest abundances, and P. sivado that was omnipresent in all pelagic strata. The novel registration of Chlorotocus crassicornis and Plesionika heterocarpus in the pelagic realm were restricted to the shelf-break at the Deep Scattering Layer. The red body species Gennadas elegans, Pasiphaea multidentata, and Sergia robusta, were restricted to the middle slope. No significant differences concerning the sampling geographic area or seasonality were found. Actually, the decapod pelagic community of the Balearic Sea was mainly structured by both the geomorphology (and associated hydrographic characteristics of the shelf/slope transition) and the influence of light in the water column. No decapod crustacean species occurred in epipelagic daytime samples. Size analysis showed the occurrence of species-specific patterns concerning the size/age movements into the water column throughout the day-night cycle. Moreover, the present work clearly confirms the presence of adult P. multidentata in the water column, evidencing that the adult fraction of the population has also the ability to perform vertical migrations.
