Direct and indirect effects of Gracilaria vermiculophylla on native Fucus vesiculosus

The perennial red macroalga Gracilaria vermiculophylla (Ohmi) Papenfuss has recently been introduced to the Baltic Sea and is a potential competitor to Fucus vesiculosus, the most common native perennial alga in large parts of the Baltic Sea. Gracilaria might interfere with Fucus through direct competition for resources. In addition, Gracilaria is a favoured refuge for mesograzers, which prefer to feed on Fucus. Mesocosm-experiments were conducted over one year in the Kiel Fjord in order to test the direct and indirect effects of Gracilaria on Fucus. Fucus was incubated with Gracilaria at three different densities and grazers in high or low abundances. High densities of Gracilaria inhibited the growth of Fucus adults and also reduced the half-life-time of Fucus germlings. Associated grazers also had a negative effect on Fucus adults. Our results suggest that Gracilaria is able to influence Fucus in the Baltic Sea through direct competition for resources and by exposing it to higher grazer pressur

Invasion ecology of marine macroalgae: the relevance of stress resistance for the invasion success of Gracilaria vermiculophylla and consequences of its spread

Originating from East Asia, the perennial red macroalga Gracilaria vermiculophylla (Ohmi) Papenfuss has successfully invaded several temperate areas of the Northern hemisphere and continues to spread. In its new range, the seaweed tends to form local mass appearances and to dominate the native community. A high tolerance towards both abiotic and biotic environmental stressors could explain the invasion success of this species. I therefore compared the stress resistance of G. vermiculophylla from six native populations from South Korea and China and eight invasive populations from Europe and NW-Mexico. In short-term experiments G. vermiculophylla individuals were exposed to 1) heat shock, 2) UV-C-radiation and 3) elevated copper concentrations in the water. In a long-term experiment the seaweed had to cope with depletion stress (darkness in combination with low temperature and dryness) for several months. All experiments were carried out twice - one time in the native range in Qingdao, China and one time in the invaded range in Kiel, Germany - to rule out local acclimation effects. In order to compare the resistance against herbivory individuals of native and invasive G. vermiculophylla populations were fed to snails from the native (Littorina brevicula) and the invasive (Littorina littorea) range. In the Baltic Sea, G. vermiculophylla might threaten the habitat-forming native brown alga Fucus vesiculosus through direct competition for resources and by providing a shelter for mesograzers, which prefer to feed on F. vesiculosus. Mesocosm-experiments were conducted over one year in the Kiel Fjord in order to test the direct and indirect effects of G. vermiculophylla on F. vesiculosus

Invasionsökologie mariner Makroalgen: Die Bedeutung von Stressresistenz für den Invasionserfolg von Gracilaria vermiculophylla und Folgen ihrer Ausbreitung

Originating from East Asia, the perennial red macroalga Gracilaria vermiculophylla (Ohmi) Papenfuss has successfully invaded several temperate areas of the Northern hemisphere and continues to spread. In its new range, the seaweed tends to form local mass appearances and to dominate the native community. A high tolerance towards both abiotic and biotic environmental stressors could explain the invasion success of this species. I therefore compared the stress resistance of G. vermiculophylla from six native populations from South Korea and China and eight invasive populations from Europe and NW-Mexico. In short-term experiments G. vermiculophylla individuals were exposed to 1) heat shock, 2) UV-C-radiation and 3) elevated copper concentrations in the water. In a long-term experiment the seaweed had to cope with depletion stress (darkness in combination with low temperature and dryness) for several months. All experiments were carried out twice - one time in the native range in Qingdao, China and one time in the invaded range in Kiel, Germany - to rule out local acclimation effects. In order to compare the resistance against herbivory individuals of native and invasive G. vermiculophylla populations were fed to snails from the native (Littorina brevicula) and the invasive (Littorina littorea) range. In the Baltic Sea, G. vermiculophylla might threaten the habitat-forming native brown alga Fucus vesiculosus through direct competition for resources and by providing a shelter for mesograzers, which prefer to feed on F. vesiculosus. Mesocosm-experiments were conducted over one year in the Kiel Fjord in order to test the direct and indirect effects of G. vermiculophylla on F. vesiculosus.Die aus Ostasien stammende mehrjährige Rotalge Gracilaria vermiculophylla (Ohmi) Papenfuss hat erfolgreich zahlreiche Gebiete in den gemäßigten Breiten der nördlichen Hemisphäre neu besiedelt und breitet sich auch weiterhin aus. In den neu besiedelten Gebieten bildet die Alge oftmals lokale Massenvorkommen aus und neigt dazu, die heimischen Gemeinschaften zu dominieren. Eine hohe Toleranz gegenüber abiotischen und biotischen Umweltparametern könnte den Invasionserfolg dieser Art erklären. Ich verglich deshalb die Stressresistenz von sechs nativen Populationen von G. vermiculophylla aus Südkorea und China mit der Stresstoleranz von acht invasiven Populationen aus Europa und NW-Mexiko. In Kurzzeit-Experimenten wurden G. vermiculophylla-Individuen folgenden Stressoren ausgesetzt: 1) Hitzeschock, 2) UV-C-Strahlung, 3) erhöhte Kupferkonzentrationen im Wasser. In einem Langzeitexperiment musste die Alge mehrmonatigen Mangelstress (Dunkelheit kombiniert mit niedrigen Temperaturen und Austrocknung) erdulden. Alle Experimente wurden zweimal durchgeführt – einmal im nativen Gebiet in Qingdao, China und einmal im neu besiedelten Gebiet in Kiel, Deutschland, um lokale Akklimatisierungseffekte auszuschließen. Um die Resistenz gegenüber Herbivorie zu vergleichen wurden Individuen, die aus nativen und invasiven G. vermiculophylla-Populationen stammten, an Schnecken aus dem Ursprungsgebiet der Alge (Littorina brevicula) und aus dem neu besiedelten Gebiet (L. littorea) verfüttert. In der Ostsee könnte G. vermiculophylla die native Braunalge Fucus vesiculosus – die ein wichtiges Habitat für zahlreiche Arten darstellt – sowohl durch direkte Konkurrenz um Ressourcen bedrohen als auch dadurch, dass sie einen Lebensraum für Mesograzer bietet, die jedoch bevorzugt F. vesiculosus fressen. Über ein Jahr hinweg wurden Mesokosmen-Experimente in der Kieler Förde durchgeführt um den direkten und den indirekten Effekt von G. vermiculophylla auf F. vesiculosus zu untersuchen

Successful invaders are better defended: The example of Gracilaria vermiculophylla

To evaluate the importance of anti-herbivore resistance for algal invasion success we compared resistance traits among specimens of the red macroalga Gracilaria vermiculophylla from six native populations in Korea and China and eight invasive populations in Europe and Mexico that were maintained under identical conditions in the laboratory. Herbivorous snails both from the native range (Littorina brevicula) and from the invaded range (Littorina littorea) consumed significantly less of seaweed specimens originating from non-native populations. Metabolome profiling revealed that this preference was correlated with an increased woundactivated production of deterring prostaglandins and hydroxyeicosatetraenoic acids. Thus, invasive populations of G. vermiculophylla are more strongly defended against challenge by herbivores and other biological enemies that cause local tissue or cell disruption and activate oxylipin production. Anthropogenic distribution of genotypes adapted to resist elevated feeding pressure probably contributed to the invasion success of this species

Invasion success of the seaweed Gracilaria vermiculophylla correlates with low palatability

Differences with respect to anti-herbivore defense were investigated in invasive and native populations of the seaweed Gracilaria vermiculophylla. Specimens from 6 native populations in East Asia and from 8 populations invasive in Europe and the Mexican Pacific coast were maintained under identical conditions and offered to herbivorous snails from both the native range (Littorina brevicula) and Europe (L. littorea) in no-choice feeding assays. L. brevicula consumed in total significantly larger amounts of G. vermiculophylla tissue than did L. littorea. Further, both snail species least consumed the seaweed specimens originating from either non-native populations or from populations native to the Korean East Sea/Sea of Japan. The Korean East Sea/Sea of Japan had previously been identified as putative donor region of all the invasive populations of G. vermiculophylla. Thus, populations in the donor region as well as non-native populations in different invaded realms feature an increased capacity to resist feeding pressure. Differences in nutrient content did not account for the observed patterns of consumption, as palatability and carbon to nitrogen (C:N) ratio were not significantly correlated. Thus, mechanical or chemical defenses or the content of feeding cues influenced the behavior of the snails. We suggest that low palatability contributed to the invasion success of the species