Do you want to understand cold-water coral ecosystems in the deep sea?
Are you up for the challenge of capturing this complex ecosystem in a mathematical model?

Background

Most people associate corals with warm tropical waters, but in the last decade it has become clear that also the deep sea harbors extensive coral reefs. Cold-water corals, like their tropical counterparts, form extensive 3-dimensional structures on the seafloor that provide a habitat for a very rich community of stony corals, soft corals, sponges, bivalves, polychaetes, shrimps and fish. Our understanding of these reefs and the interactions between the organisms in this community is still very rudimentary. In general, ecosystems in the dark deep sea are limited by the availability of food and cold-water corals are no exception. Trophic interactions, e.g. the competition for food, therefore play an important role in the cold-water coral community. However, recent experiments show that there are some intriguing interactions between a few components of the cold-water coral community that are non-trophic in nature. Cold-water corals create a carbonate skeleton that forms the basis of this deep-sea ecosystem, but a worm that lives between the living coral branches stimulates the formation of this skeleton. Sponges moreover, another key component of this community, appear to recycle an energy source, i.e. dissolved organic matter, that would otherwise get lost from the food web. These non-trophic interactions may be crucial in the functioning of a cold-water coral ecosystem, but so far they have not been considered in mathematical models.

In this project, the student is challenged to develop a mathematical model of trophic and non-trophic interactions between the key components of the cold-water coral reef ecosystem, i.e. cold-water corals, worms and sponges, and identify their importance for this unique deep-sea ecosystem.

Approach: Existing information on feeding by corals, sponges and worms will be used to setup a minimal model of trophic interactions in the cold-water coral community. The recently identified non-trophic interactions will be added to this minimal model to investigate the role and function of these interactions for the cold-water coral communities.

Are you fascinated by the deep sea?
Do you want to understand food web interactions in cold-water coral ecosystems?

Background

Corals and coral reefs are typically associated with tropical warm waters, but in the last decade, extensive cold-water coral reefs along the European margin have been discovered. These reefs are extensive 3-dimensional structures on the seafloor and provide habitat for a very rich community of corals, sponges, bivalves, polychaetes and shrimps. Food web studies of the reef community have shown that these are among the most productive benthic ecosystems in the deep sea and hence a comparatively large amount of secondary production is potentially available as food for higher trophic levels such as fish. Although fish stocks are reportedly higher in and around cold-water coral reefs, the question is whether this is related ‘simply’ to the presence of the 3-dimensional structure of the reef, or whether the high food availability also plays a role. Disentangling the strength of this food web relation will aid the development of management strategies of these fragile ecosystems.

Approach: Models of the food web structure of cold-water coral communities at various sites in the northeast Atlantic have been developed in our lab using food web modeling. These models will be extended with fish compartments to quantify the predation pressure of fish on the reef community. These food web models are developed within the CoralFISH project (http://eu-fp7-coralfish.net/).

Very recently, long filamentous bacteria have been discovered in marine sediments that are able to generate electrical currents and mediate the transport of electrons across centimeter-scale distances. These electrogenic bacteria let the ocean floor operate like a natural battery, and have an enormous potential for various bio-electric applications. These bacteria belong to the family Desulfobulbaceae and have been identified in sulphide-rich and fauna-poor environments. At NIOZ we have a specific culture facility dedicated to these bacteria. However, because they are only recently discovered, they remain enigmatic in many aspects. One particular feature is that these long filamentous bacteria are surrounded by a polymer sheath. Little is known about this sheath and its composition (proteins or rather polysaccharides?). In this project, we will study these sheaths using a novel technique – digital holographic microscopy (DHM), which is a new type of microscopy that allows the quantification of optical density information of particles and substances. We recently acquired the newest generation of such a microscope (D³HM instrument), which opens an exciting new way of studying cell morphology. The goal of this project is to use the optical density information to observe the polymer sheaths surrounding the filaments and combine this with classical staining methods, to gain a better understanding of its composition and role in these bacteria. The research activities will consist of field sampling (Dutch delta area), the cultivation of marine organisms (filamentous bacteria), sample preparation, microscopic imaging, and the processing and analysis of images.