From the land to the sea: towards a redefinition of biodiversity?

Biodiversity has been defined as the variability among living beings from all sources and at different taxonomic and spatial scales, with specific reference to genes, species and ecosystems. This definition automatically includes terrestrial and marine organisms and ecosystems on the same level. However, to a closer look, the characterisation of biodiversity in terms of static entities is less suitable for the marine context. Not surprisingly, terrestrial environments were the original target of the first conservation strategies, such as the establishment of national parks at the end of the 19th century. Many authors still underline the importance of protecting biodiversity by identifying and delimiting relevant places, and this idea has been transposed to the conservation of the sea through the creation of Marine Protected Areas. But do these entities – especially species, ecosystems and places – account for the specific nature of the marine environment?

This question is extremely important since the fundamental ecological role of the ocean for essential ecosystem services such as climate regulation and resource provision is now widely recognised. This contribution aims to compare the characterisations of marine and terrestrial biodiversity in order to show the limits of the traditional categories employed to describe biodiversity and to highlight the potential of new alternative or complementary concepts.

As regards the first point, species and ecosystems only allow for a partial comprehension of marine biodiversity. As an example, the identification of marine species can hardly be based on morphological criteria since many marine organisms (such as jellyfish) significantly change their morphology during their life cycle. Moreover, a great part of marine species diversity is still unknown, due to the ocean's reduced accessibility: this epistemic limitation may help to explain why biodiversity concepts are implicitly associated with terrestrial – and more familiar – living entities despite the longer evolutionary history of marine diversification. Also, although marine species richness seems to be lower compared to terrestrial one, diversity among marine phyla is higher. Shifting from the taxonomic to the ecological level of biodiversity, marine ecosystems' boundaries are hardly separable based on merely geographic criteria, because of the dynamic nature of the water.

Concerning the second point, marine organisms undergo biological processes which develop in a particularly close relationship with the surrounding physical environment. This aspect suggests that a deeper consideration of the processes and environmental interactions which shape biodiversity is needed. Rather than considering marine life forms as merely different from terrestrial ones, we could think of the ocean as a new paradigm to better understand biodiversity in a broader sense, shifting from a compositional view to a process-based conceptualisation. This theoretical redefinition could promote the integration of new efficient approaches to marine conservation management.