Similar to forests, shrubs and perennial meadows on land, habitats formed by long-lived macrophytes are important components of the marine environment. Large stands of algae and seagrass meadows provide a permanent livelihood as sources of food, substrate, or oxygen for numerous other marine organisms on all coasts worldwide. In many countries, there is also a growing interest in the economic use of algae as a source of raw materials or food.
However, these habitats are increasingly under threat. Eutrophication, climate change, species introductions, and other changes in the marine environment have led to a decline in kelp forests and seagrass beds worldwide in recent decades. At the same time, an increase in short-lived, opportunistic, and often free-drifting macrophytes has been observed along many coasts, causing ecological and economic problems when they form large aggregations of dying and decaying biomass.
Better management of macrophyte habitats is clearly needed: The multiple ecological challenges posed by environmental changes and land-use interests must be addressed in the future in a way that restores, rather than further reduces, the ecosystem services provided by algal and seagrass beds.
Changes in macrophyte habitats - targeted management actions as well as uncontrolled environmental changes - usually lead to shifts in the structure of the species communities associated with the algae. As a result, pathogens, herbivores, epiphytic organisms, or competitors may become prevalent or symbionts may decline. In all these cases, the algae may be permanently damaged. A detailed understanding of the interactions between algae and these accompanying organisms is therefore necessary if management measures are to be successful.
Communication through molecular signals is a fundamental principle that structures the coexistence of marine organisms. Such signals regulate behavior and thus determine the ecological functions of bacteria, protists, algae and animals alike.
This becomes particularly clear when we look at sessile organisms: Their sedentary lifestyle forces them to develop efficient strategies to ensure protection from consumers, epibionts, competitors, and pathogens, and to attract symbiotic organisms and the gametes of mating partners. A plethora of different deterrents, attractants, and molecular cues are used to achieve such goals. In addition, many of the numerous microorganisms found in seawater can colonize the surfaces of marine organisms, forming biofilms and influencing the exchange of metabolites and chemical signals between their host and the environment.
The production and release of signaling compounds by marine organisms is regulated by various environmental triggers. Many of these triggers are, in turn, molecular signals generated by synergistic or antagonistic organisms. Others are abiotic factors, such as light or water temperature. These can be sensed by specific perceptual mechanisms (example: light receptors), but they can also cause shifts in the interaction networks between organisms when they alter the availability of resources (example: light limiting photosynthesis) or when they cause stressful physiological conditions (example: damage from too much light).
The production and release of signaling compounds by marine organisms is regulated by various environmental triggers. Many of these triggers are again molecular signals, generated by synergistic or antagonistic organisms. Others are abiotic factors, such as light or water temperature. These may be perceived through specific sensing mechanisms (example: light receptors), but they may also cause shifts in the interaction networks among organisms if they change the availability of resources (example: light limitation of photosynthesis) or if they cause stressful physiological conditions (example: damage by excess light).
- the interactions of marine macrophytes (seaweed and seagrass) with pathogens, symbionts, herbivores, fouling organisms and competitors, and
- the influence of environmental change on these interactions.
Our short-term goal is the identification of ecologically important signal substances and the elucidation of molecular regulatory mechanisms.
Our long-term goal is to develop new approaches for the management of natural and artificial macrophyte habitats, for example
- biological plant protection in seaweed aquaculture,
- more successful restoration of damaged habitats,
- environmentally friendly suppression of invasive seaweeds.
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(1) Interactions with pathogens, symbionts, epiphytic organisms and predators
(a) in Gracilaria vermiculophylla, an invasive red alga from East Asia,
(b) in seagrass Zostera marina and bladderwrack Fucus vesiculosus, two important
habitat formers in the Baltic Sea.
(2) Innate immunity and regulation of defense in
these three model organisms and other species
(3) Seaweed invasion ecology
- Plasticity of stress resistance in native and non-native populations,
- Interactions between native and non-native species.
(4) Biodiversity and management of Baltic Sea seaweed habitats - A project in collaboration with the agency for agriculture, environment and rural regions of the state of Schleswig-Holstein. It includes, among other things
- the development of new eDNA-based monitoring methods for algae and neobiota and
- the development of new methods for the management of drifting algal populations on Schleswig-Holstein's coasts.
(5) CLIMALG-SN, a project adressing biodiversity and management of macrophyte habitats in Senegal.