Until 1984 hardly anybody knew the neat alga with its feathery leaves and fresh green color giving shelter to tropic fishes in many public and private aquaria. But then this tropical alga could somehow manage to escape through the sewage waters from the public aquarium of the oceanographic institute of Monaco into the Mediterranean Sea. Unnoticed in the beginning, later scarcely attended, it survived in the new environment tolerating the prevailing completely non-tropical temperatures with below 12°C during winter and began to spread slowly.
The first alerts by single experts warning about the new alien where smiled at and died away. But then the rapid spread began. Caulerpa taxifolia, the "yew - foliated" is able to regenerate from smallest ragged pieces and suddenly appeared at diverse sites near the french riviera. And new patches even enlarged: the alga was growing so fast that it virtually overran native plants and thus even replaced them.
Nowadays every expert seriously concerned with the issue agrees that this means an ecological danger for nearshore habitats the more as since now all efforts to fight the plants populations failed.
Since the alga is so resistant to even survive days after days in dark moist air a spreading mechanism is supposed within the anchor boxes of sport and sailing boats as well as with fishing nets. This seems to be the only possible explanation for its patchy spreading over hundreds of kilometers.
There is light slowdown to be noted until the year 2010. However - an end of the spreading is not yet in sight and there is no known means to stop the spreading.
The consequences for the domestic fauna and flora is yet unknown. At high abundant overgrown areas a decrease in biodiversity has being observed. If the toxic of the alga enriches in the food chain thus raising a potential danger for humans is not yet clear as well.
First records of Caulerpa taxifolia were communicated in 1993. Presumably the alga was introduced here by anchors of sailing and motor yachts.
Since then the divers of the Institute for Marine Sciences were engaged tracking and exactly documenting the spread of the invasive seaweed within the bay of Marina di Campo.
Therefore regularly SCUBA dives were accomplished in order to measure the individual colonies and transfer their position to a map of the area. Additionally the density was counted and samples for biomass measurement were taken. The results are frightening: the alga was spreading rapidly during the last fifteen years within the bay of Marina di Campo and the area of the affected seafloor add up to several hectares.
Beneath the monitoring of Caulerpa taxifolia in the waters around Elba we also accomplished analyses of the physiology and ecology of the seaweed. Due to the vicinity of the affected spots to our field station direct in situ experiments and analyses are easy to accomplish.
C. taxifolia is able to settle on a wide range of different seafloor types like wave exposed rocky shores, in shallow waters as well as on deep silty seafloor in bays with low water movement.
Quite contrary to other, domestic, sessile macroalgae this siphonal seaweed lives in intense interaction with the respective seafloor.
In field experiments different types of substrate were offered to the plant in order to achieve informations about growth rates depending on the quality of the substrate. The result was a clear avoidance of plain stone material and a preference of sandy seafloor.
 Design for substrate preference at the beginning of the experiment |
 State after a experimental period of 4 months |
During its unrestricted expansion Caulerpa taxifolia was able to invade also the native seagrass meadows of Posidonia oceanica, being of great ecological value for the nearshore habitats of the mediterranean sea.
There where several observations of a change in growth forms of the alga while invading the seagrass meadows leading to a gigantism which is not known of the alga within its natural habitat in tropical seas. Single phylloids (leaf like parts of the alga) naturally reaching a mean height of about 10 cm, where reaching a height up to 80 cm.
The reasons for the observed gigantism are controversially discussed by experts and mainly explained by the better nutritional features within the seagrass meadows. To analyze possible influences of other abiotic parameters on the growth of Caulerpa taxifolia we tested the light depending growth. Therefore black and transparent plastic stripes were knit together to create an artificial seagrass meadow and brought to the border of an existing Caulerpa taxifolia population growing on a shallow sediment area. Thus the invading of the alga into the physical structure of a seagrass meadow could be simulated without a change in nutrient availability.
The results of the 4 months experiments are clear: In spite of equal sediment conditions the shading of the artificial seagrass meadow causes a significantly higher growth in length of Caulerpa taxifolia.
The origin of Caulerpa taxifolia in the Mediterranean Sea can be tracked down via several public aquaria up to Germany, were it primarily emerged in 1972 as ornamental plant for tropical aquaria. However its provenance was unknown so far. In cooperation with Jörg Wiedenmann from the UNiversity of Ulm scientists of HYDRA Institute for Marine Sciences searched for answers to the following questions:
Here we present the abstract of the publication of Jörg Wiedenmann et al.:
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