The bathyal connections between the Mediterranean Sea and the Northeastern Atlantic Ocean: An assessment using deep-water sponges as a case study

Abstract

The general outline of this thesis was to assess the potential of the Mediterranean water masses to transport deep-sea fauna towards the Atlantic Ocean. By examining the effects that the bathyal water mases moving from the Eastern Mediterranean basin towards the Northeastern Atlantic Ocean may have on the relationships of the deep-water sponge fauna, a case study is provided. Prior to using the sponge fauna as a deep-water biogeographic tool, new collections of deep-sea sponges needed to be conducted in order to increase the faunal resolution at the two most important transitional areas across the bathyal trajectory from the Eastern Mediterranean to the Atlantic, the Strait of Gibraltar and the Strait of Sicily, which remained poorly studied. In this context, the specific objectives of this thesis were as it follows:

1. To complete the previous limited knowledge on the deep-water sponge fauna at key transition areas along the trajectory of the bathyal water mases.

1.1. To provide the missing qualitative and quantitative knowledge of the bathyal sponge fauna at the most Eastern-Atlantic side of the Strait of Gibraltar, focusing on a mud volcano system at the Gulf of Cádiz that spans the entire range of bathyal depths. 1.2. To underpin the qualitative knowledge of the deep-water sponge fauna at the most Western-Mediterranean side of the Strait of Gibraltar, focusing on the deep shelf and upper slope of the Alboran Island. 1.3. To underpin the qualitative knowledge of the deep-water sponge fauna at the Eastern-Mediterranean side of the Strait of Sicily, focusing on the deep shelf and slope of the Maltese Islands. 1.4. To put into practice basic genetic techniques to aid in the identification of species that remain unresolvable through the classical phenetic approach, providing an example case for a more integrative sponge taxonomy. 2. To assess the effects of local environmental variables on the qualitative and quantitative distribution of abundances of the sponges across a complete bathymetric bathyal range, focussing on the mud volcanoes of the Gulf of Cádiz as a case study.

3. To examine the affinities of the deep-water sponge fauna across the trajectory of the bathyal water masses running from the Eastern Mediterranean to the Northeastern Atlantic.