Dr. Sala is a marine ecologist actively engaged in research, teaching, and communicating scientific information. Enric examines scientific solutions for marine biodiversity and coastal ecosystems using a historical context. He co-leads the innovative IGERT Ph.D. program on marine biodiversity and conservation that incorporates natural sciences, economics, social sciences, marine policy and law, and communication. Enric is author of numerous publications, is a 2005 Aldo Leopold Leadership Fellow, a 2006 Pew Fellow in Marine Conservation, and Wildlife Conservation Society Research Fellow. Enric serves on scientific advisory boards of several international conservation organizations. He is Associate Professor of Marine Ecology and Conservation at Scripps Institution of Oceanography, and co-founder and Deputy Director of the Center for Marine Biodiversity and Conservation.
- Coral reef fish feeding behavior in the Caribbean
- Marine microbial loop
- Marine biodiversity
- Arctic marine environment
- Coastal and marine environments in Africa
- Marine biomes
- Marine Protection, Research, and Sanctuaries Act, United States
- Judge says farmed fish can’t be counted
- BIODIVERSITY-PHILIPPINES: Warmer Seas Threaten Rich Marine Life
- Guyana Environment and biodiversity
- NOAA Coral Reef Conservation Program
- ReefBase: A Global Information System For Coral Reefs
- Understanding Marine Biodiversity book
- Center for Marine Biodiversity and Conservation (CMBC)
- UNEP’s Regional Seas Programme
- WWF Marine Conservation
Introduction
Although marine species richness may only total 4% of global diversity, life began in the sea, and much of the diversity in the deep branches of life’s tree is still primarily or exclusively marine. For example, 35 animal phyla are found in the sea, 14 of which are exclusively marine, whereas only 11 are terrestrial and only one exclusively so. Our understanding of major changes in marine diversity over deep time is comparatively good, thanks to the excellent fossil record left by many marine organisms, although considerable sampling problems limit the potential for accurate fine grained analyses. In contrast, our knowledge of marine diversity in the present is poor compared to our knowledge for terrestrial organisms, and an appreciation for the dramatic changes in marine ecosystems that have occurred in historic times is only just beginning to emerge.
What then can we say about recent trends in the state of marine biodiversity and what they imply for its future? How have and will these changes in marine biodiversity affect the provision of essential ecosystem services? In this review, we synthesize the current state of knowledge on global marine biodiversity, discussing composition and function, as well as patterns across time, space and levels of complexity ranging from populations to ecosystems. Our specific goals are to (a) define marine biodiversity, (b) describe the historic trends in biodiversity unrelated to human activities, (c) review recent biodiversity trends and the role of human drivers, (d) assess the functional consequences of recent and future change, and (e) synthesize the unknowns and the unknowables of marine biodiversity and suggest priorities for marine biodiversity research and conservation.
What is marine biodiversity?
Vibrant coral reefs harbor diverse communities of life in the tropical oceans. Like trees, corals produce annual rings that store a record of past conditions. Chemical analyses reveal details about past temperature, nutrient availability, salinity, and other information. (Photograph courtesy NOAA Photo Library)
Marine biodiversity is the variety of life in the sea, encompassing variation at levels of complexity from within species to across ecosystems. Biodiversity is not a simple concept like temperature or volume but rather multidimensional. It can thus be measured in different and complementary ways and have different units. Any single measure of diversity (so-called inventory diversity) has four conceptual components: the numbers of entities (or compositional diversity, the most common measure being species richness), the distribution of abundances of these entities in communities [or structural diversity, the most common measures being evenness or equitability and ecodiversity (which combines evenness and richness)], the degree to which the entities differ (e.g., divergence when measured genetically, disparity when measured morphologically), and the functional role (trophic, metabolic, habitat forming) these entities play in ecosystems.
The complexity of units and scale makes it impossible to assess the state of marine biodiversity using a single measure. Most studies dealing with biodiversity patterns report the simplest measure of biodiversity, that is, species richness. Although species richness may be useful for comparison of taxonomic diversity between ecosystems or within ecosystems over time, it may not give us a good measure of the structure or function of these ecosystems. Moreover, different measures can suggest different conclusions. For example, areas with low α-diversity can have high β-diversity; thus it may be risky to use single measures for management or conservation purposes. Similarly, patterns of species diversity and diversity measured at higher taxonomic levels are not always concordant. To obtain a measure of the current state and the dynamics of ecosystems, data on evenness of species abundance or functional measures of biodiversity are usually more appropriate.
Estimating marine biodiversity today
There are approximately 300,000 described marine species, which represent about 15% of all described species. There is no single listing of these species, but any such listing would be only an approximation owing to uncertainty from several sources. As a consequence, the total number of marine species is not known to even an order of magnitude, with estimates ranging from 178,000 species to more than 10 million species. The two biggest repositories of marine biodiversity are coral reefs (because of the high number of species per unit area) and the deep sea (because of its enormous area). Estimates for coral reefs range from 1 to 9 million species, but they are very indirect as they are based on a partial count of organisms in a large tropical aquarium or on extrapolations stemming from terrestrial diversity estimates. Estimates for the deep sea are calculated using actual field samples, but extrapolations to global estimates are highly controversial. The largest estimate (10 million benthic species) was based on an extrapolation of benthic macrofauna collected in 233 box cores (30 × 30 cm each) from fourteen stations, although others suggested 5 million species as a more appropriate number. Briggs argued that these enormous figures are excessive extrapolations from small-scale samples, and May suggested instead a total of 500,000 living marine species.