The Sea Bottom — a Mosaic of Substrates

Abstract

In contrast to pelagic environments, the benthic realm is characterized by two physicochemical subsystems below and above the bottom-water interface. Both subsystems work according to different mechanisms, but are closely interrelated. The organisms living on the bottom depend thus not only on the properties of their watery medium, but also on the nature of their substrate of sediment or rock. On the shelf at least, the substrates are changing over short distances, restricting the ecosystems to surface extensions in the order of some hundreds of meters to a few kilometers. These small-scale ecosystems cannot be surveyed by methods of remote, “blind” sampling or measuring from surface ships, as currently used to explore the much larger-scale planktic systems or the benthos of the deep sea. In order to explore the shallower benthic realm, visual control of the bottom must provide adequate accuracy to select samples or implant measuring devices at locations relevantly positioned with respect to ecosystem boundaries. Mapping under water by extensive SCUBA diving to 70 m assisted by grab sampling with the small research vessel Arnona and the use of the research submersible GEO down to 200 m depth revealed on selected parts of the Sinai “shelf” a mosaic of hard and soft substrates. The use of an underwater, sand-sucking “vacuum cleaner” device and sampling with the submarine’s artificial arm provided ample evidence for early diagenetic processes progressing below soft surfaces of the sea bottom and participating in the evolution of the substrate.