Mediterranean Deep-Sea Biogenic Habitats: Imperiled Oases of Biodiversity

Abstract

Marine biogenic habitats formed by non-motile faunal species, including corals, bivalves, tube-building polychaetes, bryozoans, and sponges, are ubiquitous in shallow coastal areas and in the deep sea, worldwide. Their biophysical complexity provides a multitude of niches and additional surface area for colonization that are exploited by numerous species including sponges, anemones, gastropods, worms, crustaceans and echinoderms, resulting in habitats that support a high biodiversity. They also provide ecosystem goods and services, for example, by serving as a global carbon sink, while corals have been exploited in the jewelry trade since time immemorial. The most familiar and extensive marine biogenic habitats are tropical coral reefs, which occur in shallow coastal waters and whose ecological importance and associated high biodiversity are well known and studied. Less familiar are the several different types of marine biogenic habitats that occur worldwide on the deep-sea floor, including in the Mediterranean, where they are subjected to a plethora of adverse impacts resulting from the intense human activities that characterize this sea. Adverse impacts include direct and indirect effects resulting from large objects and litter deposited on the seabed, fishing activities that lead to overexploitation of natural resources and to lost and discarded non-biodegradable gear, interventions on the seabed such as oil and gas exploration and extraction, mining, laying of infrastructure such as cables and pipelines, and pollution and climate change. As a result, deep-sea Mediterranean biogenic habitats are imperiled. The present chapter provides an overview of the main ecological characteristics of biogenic habitats in the deep Mediterranean, their importance as oases of biodiversity, the pressures and threats they are subject to, and the conservation measures that can be implemented to ensure their continued health and existence.