Our shared sea

Mechanisms of ecosystem change in the Western Channel

Context and objectives

This part of the program concentrates on the ability of endogenous marine species to cope with modifications to their environment. The work functions at a different level, focusing on selected model species rather than working at a broader ecosystem level. This approach, which is possible because endogenous species tend to be better characterised than species that have recently arrived in the Western Channel area, enables us to investigate specific physiological and genetic processes that play a key role in the responses of populations of marine organisms to changes in their environment. Work  focus on selected organisms from both coastal and open water ecosystems. For the former, we concentrate on macroalgae and address two main questions:

- the underlying genetic mechanisms that regulate their life cycles

- their ability to adapt to stress.

For open water ecosystems, we investigate the genomic parameters which are related to the ability of coccolithophores to adapt to modifications to their environment, in particular to acidification caused by increased levels of atmospheric carbon dioxide (CO2).

The coastal ecosystems of the Channel are subjected to a broad range of anthropogenic influences, including both the indirect effects of climate change and the direct effects of pollution and maritime commercial and leisure activities. The responses of coastal ecosystems to such perturbations are difficult to predict, and this is in part due to a lack of understanding of the basic biology of the organisms that make up these ecosystems. Marine macroalgae, or seaweeds, are keystone species in the rocky shore environments that make up most of the coastline along both sides of the Channel, and these organisms provide habitats for a wide range of other species. One objective is to investigate key biological processes in macroalgae of direct relevance to their ability to respond to modifications to their environment. This involves work both on the model seaweed Ectocarpus siliculosus and on Fucus and Laminaria species, which are major components of coastal eccosystems in the Western Channel.

Coccolithophores (haptophyte microalgae) are an important component of the phytoplankton of the open waters of the Western Channel and these organisms have a significant impact, globally, on the cycling of carbon between the different compartments of the biosphere. Coccolithophores are protected by tiny calcium carbonate (CaCO3) plates and the biomineralisation process that produces these plates is responsible for ~50% of global pelagic carbonate production. Biomineralisation traps carbon in an insoluble form, a large proportion of which is sequestered on the ocean floor after the death and sedimentation of the algae. This process is sensitive to the current rapid rise in the concentration of CO2 in the atmosphere because this gas diffuses into surface waters, provoking a decrease in pH and carbonate ion (CO32-) concentration. In consequence, biomineralisation is inhibited, with negative feedback effects on regional and global climates. It is therefore crucial to estimate the capacities of coccolithophores to adapt to these changing conditions and to understand their mechanisms of adaptation.

What are we doing?

The ability of a wild population to adapt to changes in its environment depends on the structure of the population and its mode of reproduction. It is therefore crucial, when studying the effects of environmental modifications on populations in the field, to take into account an organism’s life cycle and to understand how this life cycle is regulated. We are developing molecular markers to investigate population structures at several sites on both sides of the Western channel. Laboratory based experiments are being undertaken to investigate the life cycle of Ectocarpus. Physiological and genetic studies of the response of macroalgae to stress will focus on Ectocarpus and another brown algal species, Fucus serratus. Responses to changes in several parameters such as salinity, temperature, light and pH, tested individually and in combination are being measured using Pulse Amplitude Modulation Fluorometry (PAM) together with imaging of embryos in response to stress using reporter fluorescent dyes. These experiments are expected to provide information about the resilience of brown macroalgae to stress due to modifications to their environment and allow insights into the genetic processes that underlie this resilience.

Additionally, the collection of Ectocarpus strains from different sites on both sides of the Channel is being analysed for the presence of the lysogenic virus EsV-1. These analyses provide complementary data about the extent to which these organisms are subjected to a second type of stress, biotic stress due to viral infections. Field isolates of Laminaria spp. are also being analysed for the presence of virus to determine whether other macroalgae are also subject to this type of biotic stress.

Work on coccolithophores uses a comparative genomics approach to correlate genomic variations (e.g. genome sizes determined by flow cytometry and gene complements determined using microarrays) with phenotypic traits at both the inter- and intra-specific levels. The aim is to identify “adaptive” genes, or at least genes under positive selection pressure, and to study the expression of these genes under different environmental conditions particularly with respect to acidification.

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