Another travelogue for a Monday afternoon!
Our first official European stop on the Gracilaria vermiculophylla tour was in Germany and Denmark hosted by a colleague without whom we wouldn’t have been able to embark on this adventure!
I first met Florian Weinberger at a German phycological meeting in 2006 on the island of Helgoland (a phycologist’s dream apart from the weather). We’ve since shared many of the same model organisms, from Chondrus to Gracilaria, but only with this current project, were we able to finally start a formal collaboration!
I met up with Erik at the airport in Hamburg and we made our way to Kiel where we met up with Dr. Weinberger.
We were based at GEOMAR, one of Germany’s main research institutions in the field of marine research, employing about 900 people, of which perhaps 500 are scientists. GEOMAR is owned by the German ministry of education and research. It is a member of the Helmholtz society, a circle of federal research institutions that also includes the AWI (Alfred-Wegner-Institute for Polar Research) and DKFZ (German Center for Cancer Research), to name just two that are known to many life scientists.
The institute has four research divisions that focus on ocean circulation and climate dynamics, marine biogeochemistry, dynamics of the ocean floor and marine ecology. Most of the biologists – including me – belong to the ecology division that includes people working on various different aspects of evolutionary ecology, food web ecology, microbial ecology, global change biology, biodiversity research and marine biotechnology.
Dr. Weinberger links the biology of the macrophytobenthos and chemical ecology. He’s interested in the interactions of macrophytes with herbivores, epibionts or pathogens. One of the models in his lab is none other than Gracilaria vermiculophylla.
We spent several days collecting samples in northern Germany and southern Denmark.
Dr. Weinberger and his former student Mareike Hammann have done some very elegant analyses with Gracilaria vermiculophylla in which they found invasive populations were less consumed by periwinkles because they had a more pronounced activated defense through prostaglandins and related compounds. A new paper has just been published on their findings in Harmful Algae.
With his current student, Shasha Wang, they have found invasive thalli are also more defended against certain algal epiphytes, such as Ceramium species. The basis for this seems to be a more pronounced excretion of deterrent compounds.
With his postdoc Mahasweta Saha, the team is now exploring microepibiont communities – typically consisting of bacteria, fungi, protozoans, diatoms and other micro algae. These communities are extremely diverse and their different members all interact and can have quite different effects on their host. The effects could be detrimental when the microepibionts are opportunistic pathogens or when they attract macrofoulers, but the effects could also be beneficial when the microepibionts deter other microfoulers.
In Gracilaria vermiculophylla, potential microbial settlers from the native range are more deterred by non-native than by native populations and vice versa with potential microbial settlers from invaded ranges. The invasion process might have gone along with a shift in the communication interplay of host and settler communities.
What happens to the communities of associated microorganisms during the (perhaps stressful) transport and how can they recover? And how will they interact with new sets of non-coevolved microorganisms in the new environment? Dr. Saha’s work has shown there must be a relatively rapid adaptation in the interaction network.
In addition to Gracilaria vermiculophylla, Dr. Weinberger’s team also works with the green alga Ulva. Despite its abundance and ecological importance, the genus is extremely understudied due to its variable morphology, which complicates the identification of specimens. A PhD student in his group, Sophie Steinhagen, recently analyzed the distribution of Ulva in Germany and discovered that one of the most abundant species – Ulva compressa – has two very distinct morphologies in the Baltic Sea and the North Sea.
Two other models are the rockweed Fucus and the seagrass Zostera, the main perennial habitat forming macrophytes in the Baltic Sea. Fucus is currently declining in abundance, but the reasons are complex. On the one hand there is the problem of eutrophication that has resulted in a severe reduction in the penetration of sun light. Thus, suitable parts of the benthic zone have been considerably reduced. At the same time opportunistic filamentous epiphytes are increasing and Fucus is increasingly overgrown by them, as there are no tides. This, in turn, has caused a multiplication of mezograzers, which not only feed on filamentous algae, but on Fucus as well.
The Baltic is also warming. Before 1990, in normal years, water temperatures in summer usually reached 20°C, which was already relatively high for the latitude. Now the temperature peaks around 25°C on a regular basis. GEOMAR has a very cool benthocosm facility that is run by Martin Wahl.
This past summer, Dr. Weinberger and his colleagues conducted a heatwave experiment with three different treatments from May to September. They replicated benthocosms that were subjected to a simulated temperature regime, representing the conditions of 2009 (an average year without extremes) and then benthocosms that underwent either a single temperature increase by 3 °C for two weeks at the end of the experiment or three such heat wave periods over the course of the experiment.
Somewhat surprisingly, they detected very little effect of heatwaves at all. The capacity of Fucus for growth, reproduction and defense against consumers and epibionts was not reduced. Although the SW Baltic is rapidly heating up, the overall resilience to heatwaves seems relatively strong. For example, Zostera marina grew even better the more heatwave cycles that were applied.
Eelgrass is particularly interesting model due to the problem of wasting disease. In the 1930’s, many populations in the North Atlantic collapsed. The wasting disease was caused by a Stramenopile, Labyrinthula zosterae. Many populations have yet to fully recover. The wasting disease is inhibited by lower salinities, to a certain degree. This might be the reason why the Baltic Sea has some of the most intact stands of Zostera marina in the world.
Melanie Schulz from Dr. Weinberger’s group recently discovered that microorganisms other than Labyrinthula can modulate the wasting disease. Labyrinthula is known to feed on bacteria and yeasts and it seems conceivable that well fed pathogens could be more virulent. Alternatively, other pathogens that interact in a synergistic manner with Labyrinthula. This might explain the absence of major outbreaks in nearly 100 years: possibly not all the necessary pathogens were present.
If you are interested in Dr. Weinberger’s research, you can contact him at Weinberger, email@example.com.
Danke schön to everyone in Kiel that helped make our German and Danish leg a success, particularly Dr. Weinberger.