Modern shallow- to deep-water bivalve death assemblages in the Red Sea — ecology and biogeography

Abstract

This study provides quantitative comparisons of modern bivalve death assemblages between shallow marine, deep shelf and bathyal settings. Cluster- and discriminant analyses of the bivalve fauna distinguish four sample groups which are primarily separated by water depth (shallow marine vs. deeper shelf vs. bathyal) and sedimentological features (fine-grained shallow marine vs. coarse-grained shallow marine). The four groups consist of taxonomically and/or ecologically distinct faunal associations. Association 1 from fine-grained shallow marine environments (6–40 m) is characterized by the infaunal chemoautotrophic Lucinoidea and suspension-feeding Corbulidae and Veneroidea. Association 2 from coarse-grained shallow marine environments (1–19 m) is dominated by the infaunal suspension-feeding Cardioidea, Glycymerididae and deposit-feeding Tellinoidea, but the importance of epifaunal (cemented and byssate) suspension-feeding Ostreoidea, Chamoidea, Arcoidea, Spondylidae and Mytiloidea increases. Association 3 from deeper shelf (mainly 50–100 m) is strongly characterized by suspension-feeding epifauna (diverse Pteriomorpha — mainly Limopsidae, Spondylidae and Mytiloidea), and association 4 from bathyal settings (mainly 300–1900 m) consists mainly of infaunal carnivorous Cuspidariidae, suspension-feeding Limopsidae and deposit-feeding Nuculanidae. The two shallow-water associations and the association from the deep shelf show considerable overlaps in taxonomic composition. They also show a south to north alteration in their faunal composition, which probably reflects their common post-Pleistocene immigration from refuge areas in the Gulf of Aden or Gulf of Oman. The bathyal fauna, in contrast, is very distinct and homogeneous in all investigated respects throughout the Red Sea basin. The dominance of endemic faunas, the presence of bivalves with clearly Tethyan origin and significant differences to deep-sea faunas from the Mediterranean basin and the Gulf of Aden indicate that in some deep-water parts of the Red Sea, Pliocene faunas have survived during the Pleistocene.