In the Mediterranean sea, the problem is invasive tropical species of Caulerpa algae, primarily Caulerpa taxifolia and Caulerpa racemosa. The mentioned algae, due to intentional or unintentional introduction into the sea, brought by ballast waters, attached to vessel's hull or anchors, by fishing nets, are considered to be one of the greatest threats to the biodiversity of the sea.
Caulerpa is sea green alga, known as the largest single organism that can grow up to several meters. They are made of the stem, leaves and roots, and depending on the type of algae they have a different shape. What is characteristic of these algae is rapid regeneration, because if damage occurs, it creates rapidly a cytoplasmic cap that closes the wound. Due to the rapid growth and absence of natural enemies in these areas, these algae are a significant threat to the marine ecosystem of the Mediterranean sea.
Known as the "Tumor of the Sea," Caulerpa taxifolia is a fluorescent green macroalga, built of crawling trees and leaves from 5 to 65 cm in length. It is one of the world's 100 worst invasive species. It was first spotted in the Mediterranean in 1984, and it is assumed that it was accidentally released from the Aquarium Oceanographic Museum in Monaco. Alga Caulerpa taxifolia is most often transmitted on ship anchors or fishing nets. Due to the possibility of rapid adaptation to different ecological conditions, this alga has the capacity to develop and survive on all types of bottom: sandy, rocky and muddy bottom. The most drastic changes occur on the rocky bottom because in this case, the indigenous species will withdraw completely.
The dark green alga Caulerpa racemosa, like all the algae of the Caulerpa genus, is recognizable by the tree with leaves with tiny balls. These algae came from the Red Sea to the Mediterranean where they spread very quickly. In relation to alga Caulerpa taxifolia, which is exclusively transmitted by anchors and fishing nets, this alga has an additional more efficient way of spreading. Its main spreading mechanism is with the help of waves and strong sea currents. Caulerpa racemosa releases certain substances that negatively affect the biological diversity of the sea. It is equally well developed by a dense network of twisted trees on the rocky, sandy or sandy bottom, and the most densely populated settlements are on the rocky bottom.The proliferation of algae at long distances is most often the result of human transmission. Removing invasive algae species is a delicate task performed by trained divers, since unprofessional removal can lead to the spread of algae and even more damage. The most common methods of removing algae from the areas affected by these invasive species are manually collecting talus, underwater suckers, covering with black plastic foil. As a small part of the alga is needed for reproduction, so none of these removal methods is ultimate. However, the most effective method is to cover algae with a black plastic film that prevents light penetration into the algae and causes its death.
The biggest problem in removing these invasive algae species is the lack of natural enemies. The only recorded natural enemie of these species is the Mediterranean snail, Oxynoe olivacea and Lobiger serradifalci, which feed on these algae. However, these snails don't have a large population, so they can't prevent the spread of these algae to the Mediterranean Sea.
Improper anchoring, discharged ballast water, littering, noise and various human activities are very harmful to the natural environment. It is necessary that each individual takes responsibility for their actions in order to prevent irreparable damage. Some of the precautionary measures:
Monitoring the development of algae and controlling impacts on indigenous species and the ecosystem, should be the main task of modern ecology and aquaculture. It is necessary to raise awareness of the individual, to work on international cooperation and to make more efforts in order to find a concrete solution for this problem.