Invasive seaweed species succeeds due to their rapid adaptability
The red alga Gracilaria vermiculophylla is an invasive marine alga. Although it was originally from the Pacific Ocean, it has managed to establish itself in the Kiel Fjord. We look into how it has been able to spread so effectively.
Global change is partly responsible for the increase in invasive marine species. This can lead to disastrous consequences and may permanently alter natural ecosystems. A large proportion of marine invasive organisms are marine algae, which may subsequently comprise up to 40 percent of a particular habitat. The invasive red alga Gracilaria vermiculophylla has proven to be highly successful in defending itself against bacterial pests in the environments it spreads to. In fact, it is one of the four most successful invasive marine algae worldwide, and is the subject of a recent study by a team of ecologists at the GEOMAR Helmholtz Centre for Ocean Research Kiel.
Publishing their research findings in the Journal of Ecology, the team believe that the answer lies in the alga's ability to adapt very quickly to changes in a hostile environment. This allows it to be well prepared to resist enemies and predators in its new environment.
Native to the north-eastern Pacific, the alga is now found in the coastal regions of the eastern and western Pacific, eastern Atlantic and the Mediterranean. It was first discovered in the Kiel Fjord, Baltic Sea in 2005, where it exhibited strong growth till 2007, after which it declined drastically. However, since 2012, the alga has experienced resurgence and is now regaining its foothold in the area once again.
During the period of the alga's sharp decline, there had not been any significant temperature changes or increased predator presence that could have been responsible for it. In any case, it has been demonstrated in previous studies that invasive species tend to possess a higher resistance to such factors when compared to the native species.
According to GEOMAR's Florian Weinberger, one of the study's co-authors, there was evidence that a bacterial infection could have caused the alga to almost disappear, and that as the alga population recovered, it developed a customised defence against the local bacterial pests.
To confirm their theory, the researchers conducted an elaborate experiment involving native alga from South Korea and invasive alga from Germany and Denmark. They measured both algae's resistance against bacteria from their own habitats and bacteria from other habitats. According to Dr Mahasweta Saha, the study's author, the results showed that the algae had adapted their defences based on their current habitat. The effectiveness of the algae's defences dropped when they were confronted with bacteria from other habitats.
In the short span of less than a decade, the invasive algae had adapted their defences to deal with the bacteria in their new environment, and lost their defensive capabilities against bacteria from their original habitats.
Further research is needed before the team can confirm the specific components (be it selection mechanism, genetics, etc) responsible for the red alga's rapid defence adaptation. Nevertheless, the results are highly significant, as they can be used as a model for other plants and systems, within a scenario of global change. "If we know more about the adaptation speeds, we can also answer these questions in greater detail: Why are some species more successful than others? What specific survival strategies help marine invasive species succeed?" said Dr Saha in German.
Further information: www.geomar.de