The transition from traditional species identification based on morphological diagnostic characters to full molecular genetic identification of marine assemblages is illustrated in a recent review paper from members of ICES Working Group on Integrated Morphological and Molecular Taxonomy (WGIMT). The crossover from microscopy to genes in marine diversity: from species to assemblages in marine pelagic copepods outlines past, present, and forward-looking perspectives on identifying and recording plankton diversity.
One of the characteristics of the marine planktonic community is the high biodiversity they hold. In a single sample from the ocean, hundreds to thousands of animal species can be found thriving together. Under pressure - driven by global change, invasive species, and other factors - these communities might be undergoing changes in their species composition and diversity, however due to their complexity, a proper assessment of their past and present state is difficult, extremely time-consuming, and demands a high number of trained personnel. Historically, this work was based on morphological characters unique to each species, allowing each of the thousands of individuals to be teased apart into separate taxa. This often required the involvement of several researchers to analyze each sample, with each of them specialized into different taxonomic groups.
In the last decades, there has been a transition to add molecular tools to better understand the limits between species, especially those very close to each other, to accelerate the identification of rare taxa, and to alleviate the dependency on those unique taxonomic experts. Each method has its own advantages, and the authors explain the process of how molecular tools can be integrated in the study of biodiversity in the oceans.
This integrated process of species recognition, discrimination, and identification by morphological and molecular tools to understand changes in community structure and species diversity is a focus of the ICES Working Group on Integrated Morphological and Molecular Taxonomy (WGIMT). The taxonomic group chosen were planktonic copepods, likely the most abundant metazoans on earth. Copepods are an essential link between the marine unicellular organisms and the higher trophic levels that are key for human society such as fish, both at larval stages and as adults. They play a major role in the biogeochemical cycles of the ocean, by consuming primary production and by transporting the acquired carbon and nitrogen to the deep ocean where it will stay away from active exchange with the atmosphere (which makes them an important carbon sink). However, not all copepod species have the same behaviour or impact and even subtle changes in species composition in a community can have a cascade effect with significant consequences in, for example, fisheries recruitment.
With this review, the authors wanted to highlight how molecular tools could aid in cases where morphological approaches were not enough to properly understand species limits, distribution, community composition or even community ecology processes. Molecular tools are very powerful and have provided answers to questions that would have not been possible without them, but they are not without other challenges and limitations for investigators. It is important to integrate both approaches since, despite both methods have a common objective, results are not easily interchangeable, and new molecular data cannot be seamlessly integrated with the old morphological data and studies without bridging them with integrative studies.
Silke Laakmann, co-author, Helmholtz Institute for Functional Marine Biodiversity at the University Oldenburg (HIFMB), states, “We hope to provide other researchers with background information to think about the advantages and caveats of molecular tools. We emphasize the need to keep morphological studies and to avoid jumping from one to the next without carefully considering transitions that will allow time series and historical data, and new molecular data, to be studied as a whole".
Read the full paper The crossover from microscopy to genes in marine diversity: from species to assemblages in marine pelagic copepods in Philosophical Transactions B.
ICES Working Group on Integrated Morphological and Molecular Taxonomy (WGIMT) promotes and provides new tools for species-level taxonomic analysis of the pelagic ecosystem. The group's work addresses Ecosystem Science, Observation and exploration, Emerging techniques and technologies, and Conservation and management science, four of ICES scientific priorities. Discover all seven interrelated scientific priorities and how our network will address them in our Science Plan: “Marine ecosystem and sustainability science for the 2020s and beyond".