- Life in the ocean – species richness that counts
- > As a habitat, the ocean exceeds all dimensions. No other habitat on the planet is as vast, diverse and unexplored as the global ocean. The variety of shapes and colours displayed by marine life is unparalleled. Measuring, understanding and, above all, conserving and enhancing this diversity is a major challenge in an era of climate change and natural resource overexploitation.
A constant stream of new discoveries
The ocean: Diversity in every nook and cranny
The ocean is the largest habitat on planet Earth. It covers 71 per cent of the Earth’s surface and reaches depths of up to eleven kilometres. There is life everywhere in this vast space − even in places where nobody would have thought it possible.
The total number of marine species is un-known. Scientists estimate that there are between one and two million different species in the oceans, but there could be many more. Only a quarter of the estimated number has been scientifically described.
The large proportion of unknown marine species explains why researchers make new discoveries on almost every expedition. Identifying newly discovered species and assigning them to a group or family of organisms is a very complex process. It is time-consuming and requires tremendous expertise.
For this reason, experts are increasingly turning to molecular methods such as barcoding, metabarcoding and metatranscriptomics.
These methods analyse the genetic information of organisms or, more precisely, selected regions of their DNA molecules. This information can be used to uniquely identify species, infer their functions and phylogeny, and identify successful adaptation strategies.
This basic knowledge is needed to make statements about the biodiversity of a selected marine area − be it an individual ecosystem, a marine region or the entire ocean.
Scientists use “biodiversity” as a catch-all term embracing various kinds of diversity: within species, between species and between habitats and ecosystems. Diversity includes variation in genetic, morphological, phylogenetic and functional traits, as well as changes in abundance and distribution over time and space.
The concept of biodiversity is hence multidimensional and not easy to understand. As a further complication, researchers use a great variety of methods to quantify the biodiversity of any particular region. Such methods involve estimating or measuring the region’s species richness, calculating the total amount of biomass present and its distribution among species and species groups, examining the phylogeny of the organisms living in the region and analyzing the relationships between the different species.
Marine habitats displaying a high level of species richness as well as high functional and phylogenetic diversity are generally more resilient than low-diversity ecosystems. When the biodiversity of a marine region declines, the productivity of the biological communities affected tends to decline as well. These communities of organisms are then no longer able to deliver all the services they usually provide.
Experts are currently observing such a decline in performance as a result of drastic losses of biodiversity in many marine regions. In some places, populations are in decline, while in others species are vanishing altogether.
The drivers of these trends are man-made. Through climate change and the continued destruction and overexploitation of marine habitats, we are weakening marine ecosystems to the point where their survival and the many services they provide to us humans are no longer guaranteed.