Constantino Stefanescu

Deep-sea fish assemblages in the Catalan Sea (western Mediterranean) below a depth of 1000 m

Abstract The analysis of 48 bottom trawl collections from the Catalan Sea below a depth of 1000 m has allowed the identification of two distinct demersal fish assemblages, occurring on the middle and lower slope. The Middle Slope Assemblage (MSA) and Lower Slope Assemblage (LSA), restricted to the middle (1000–1425 m) and lower (1425–2250 m) slope, respectively, each consist of two groups with distinct structures. While one group is relatively homogeneous, the other can be considered as comprising a faunal transition. Each assemblage is dominated by species possessing very different characteristics. The preponderance of middle and large size fish with high energy requirements in the MSA is replaced, in the LSA, by smaller and more passive species with lower energy requirements. These differences are reflected in a series of ecological parameters such as abundance, biomass, mean fish weight, species richness and mean species richness. A pronounced decrease in the value of these parameters is generally seen with increasing depth, reflecting the increasingly oligotrophic conditions. Furthermore, the highly stable environmental conditions of the western Mediterranean (where water temperature and salinity rarely change below a depth of 150 m), suggest that the observed zonations may be determined by biological factors. It is possible to relate the observed faunistic changes with the vertical distribution of mesopelagic organisms. These organisms play a fundamental role in the feeding ecology of demersal fish species of the slope, either directly as prey or indirectly by enriching the sediments, and thus determining the distribution of sedimentivorous invertebrate species.

Deep-living demersal fishes in the Catalan Sea (western Mediterranean) below a depth of 1000 m

An extensive survey of the deep-living fishes of the Catalan Sea (western Mediterranean) recorded 31 species in 19 families and 29 genera from 100 samples at depths between 960 and 2251 m. Chlorophthalmidae, Moridae and Macrouridae accounted for nearly 85% of all specimens taken. In biomass terms, Hexanchidae, Moridae, Alepocephalidae and Chlorophthalmidae were the most important families. A quantitative model of the bathymetric distribution of the species is presented. The ‘centre of gravity’ of species’ distribution and the habitat width, a measure of the distribution heterogeneity, are also given. Out of the 31 demersal species caught, the distributions of only 13 are centered below 1000 m. The Mediterranean deep-sea ichthyofauna is very impoverished in comparison with the adjacent Atlantic Basin fauna.

Rapid changes in butterfly communities following the abandonment of grasslands: a case study

Abstract.  1. Abandonment of grasslands is a major threat for the conservation of biodiversity in Europe. The response of butterflies towards secondary succession has been studied in northern temperate grasslands, but always by comparing sites at different seral stages.