4.5. Alien species

At the sea, the term alien can refer to animal and plant species that are not part of a given area, whose original habitat is far from where they were found.

Molluscs, crustaceans, jellyfish, fish, algae that have made long journeys from the oceans to settle in the Mediterranean, are the travelers of the sea that are colonizing new habitats and testify how the migrations are part of the natural flow of life in the environment, accelerated or not by the human action.

Alien species can also be invasive, with negative consequences on biodiversity and the ecosystem. Invasive alien species are species whose introduction and/or spread outside their natural past or present distribution threatens biological diversity. Ecosystems that have been invaded by alien species may not have the natural predators and competitors present in its native environment that would normally control their populations.

Some examples of invasive alien species in the Mediterranean are green algae from genus of Caulerpa and representative of ctenophore Mnemiopsis leidyi.

Caulerpa species are fast-growing green algae widely distributed in shallow temperate and tropical seas. They can reproduce vegetatively by fragmentation – when pieces of the plant get broken off they develop into new plants. Caulerpa species contain secondary metabolites that are toxic for most of Mediterranean animals deterring them from consuming it. Therefore, Caulerpa foulings are spreading fast suffocating other seaweed species and invading Mediterranean seafloors.

The invasive ctenophore Mnemiopsis leidyi also called warty comb jelly or sea walnut, due to its oval shaped body, lives in zooplankton forming gelatinous clusters in the sea column. Mnemiopsis are carnivores that consumes zooplankton including crustaceans, other comb jellies and eggs and larvae of pelagic fish. The number of Mnemiopsis colonies have increased globally owing to a number of human-mediated factors, including food web alterations and species introductions. In the early 1980s they entered the Black Sea and recently they started invading the Mediterranean Sea. In the Black Sea, Mnemiopsis leidyi caused a dramatic drop in blue fish populations, notably the commercially important anchovy, by competing for the same food sources and eating the young.

Where do these species come from into the Mediterranean? The possibilities are different:

1. Entry through the opening of artificial channels (ex. from the Suez Canal about 60 marine species have passed from the Red Sea and the Indian Ocean) or natural entrances (ex. from the Strait of Gibraltar 30 Atlantic species have entered);

2. Transport on the ship’s hull – especially larval forms of the animals;

3. Transportation with the ballast water – the water that is loaded to balance the cargo of a ship;

4. Importation for aquaculture;

5. Escaped from Aquariums during the cleaning or some other activities;

6. Climate changes that have led to the increase in temperature are causing geographical redistribution of Mediterranean species – species from the warmer southern regions today can be found in areas that were once too cold for them.

4.5.1 Define alien species in marine environment!

The alien species are all the species that man introduce, voluntarily or accidentally, into another environment that doesn't coincide with the original one. Their expansion can threaten the biodiversity causing profound changes in the biological process, but can have also great socio-economic impact. For example with direct damages to the health or to human activity. Infact, they have contributed for the 54% of total extinctions of the known animal species. One of the species that can cause damages at human health is the "Pterois miles" or "Scorpion fish", equipped with poisonous bones. Currently, there are 800 alien species in the Mediterranean Sea of which 200 are just on the italian coasts.
The best answer to this problem is prevention: it is much more efficient to limit access to new invasive species than fighting them when they are already established, as well as healthy and biodiverse ecosystems are able to naturally counteract the settlement of alien species much more effectively than polluted or impoverished ecosystems. In some countries it is strictly forbidden to enter a port with the hull encrusted boats with organisms (this is the case of Australia and New Zealand). In Europe at the moment there is no law that prevents it: waiting for national measures or EC regulations, however, it is necessary to sensitize those who practice recreational navigation and to promote "responsible" behaviors, such as frequent cleaning of the hull, which can help in countering the spread of harmful aliens .

4.5.2 What are the main reasons that some species are changing their habitat?

More and more areas of the Earth change as we build new cities, factories and roads.
The forests are cut down, the swampy areas are drained, the open fields disappear.
This means that living beings lose their habitat, ie the natural environment in which they lived.
Some manage to adapt, others do not.
Pollution is another serious problem.
The spilling of chemicals and oil poison the rivers and seas, and with them the organisme that live there, while pesticides and chemical fertilizers can destroy land animals and their food, and spread in the water.
Climate change can also make life impossible for animals; atmospheric conditions may become too hot or too cold, water reserves may dry up and plants that animals eat will not grow any more.
The natural environment that is particularly affected by the negative effects of human activities is the tropical rainforest: it contains more species of plants and animals than anywhere else on Earth, but every year more and more species are disappearing from it,
Unable to adapt to a new type of environment.
Many conservation experts agree that the best way to save animals is to protect the places they live in, that is, their habitats.
They are studying how to best develop nature reserves in areas such as rain forests and wetlands.
Some animals, however, need a very large area to live in and find food, and a reserve may not be big enough.
An answer to this difficulty is the development of natural corridors: narrow strips of land linking different reserves, through which the animals manage to move even though they pass through anthropized areas, ie in which man and his buildings are present.

4.5.4 Caulerpa sp. - invasive green algae

Caulerpa is a genus of seaweeds in the family Caulerpaceae native to the Caribbean Sea and the Indian Ocean. It consists of only one cell with many nuclei, in fact, It is the biggest single cell in the world.
Caulerpa algae have the capability to thrive in temperate waters, along with their freedom from natural predators.
Most Caulerpa species evolved in tropical waters, where herbivores have immunity to toxic compounds within the alga.
Temperate water herbivores, instead have no natural immunity to these toxins, allowing Caulerpa to grow unchecked if introduced to temperate waters.
In the Mediterranean Sea, Caulerpa has infested thousands of acres of seafloor since its introduction in 1984.
It created ecological and economic devastation by overgrowing and eliminating native sea grasses, reefs, and other native communities.
The Caulerpa strain in the Mediterranean Sea is extremely invasive and smothers sessile invertebrate communities. It does this by either out-competing species for food and light or due to the toxic effects of its caulerpenyne compounds. Its large monospecific meadows have vastly reduced native species diversity and fish habitat.
It has harmed tourism and recreational diving and had a costly impact on commercial fishing by altering the fishery.
This alga is used in aquariums and it's recommended to put Caulerpa in the trash and not into marine waters.
There were a lot of studies to understand where Caulerpa came from and after the extraction of DNA they discovered that this alga came from the Western Australian species.

4.5.5 Why is ctenophore Mnenopsis leidyi considered as invasive species in the Mediterranean sea?

Mnemiopsis leidyi is a ctenophore belonging to the Bolinopsidae family. Mnemiopsis leidyi originates from the Atlantic coasts of the American continent, but during the 1980s it was introduced into the Black Sea by means of ballast water from oil tankers. There he found an environment favorable to its development, mainly thanks to the abundance of food and the lack of competitors and predators. It began to produce large aggregations that, feeding upon mainly eggs and larvae of fish. In 2001 it was sighted in the Aegean Sea and in 2006 it was also reported in the Baltic Sea. After some sporadic sightings in the Adriatic Sea, probably of specimens coming from the Aegean, the first signs of its presence have arrived also in the western Mediterranean. Mnemiopsis is one of the 100 most invasive species in the world. The damage is due to its proliferation and its zooplankton diet. The harmfulness derives from the consequences of its development (it adapts very easily to new environments, withstanding wide variations in temperature), since the decrease of zooplankton directly or indirectly reduces the local fish populations. The great tolerance of this species to the different environmental factors (it supports salinity ranging from 4 to 38 and temperatures between 4 and 32 ° C) makes it able to adapt to the conditions of the Mediterranean with the risk of compromising fish stocks and through a competition for resources, both because of the diet consisting mainly of eggs and fish larvae. All this means that Mnemiopsis leidyi is able to strongly modify entire ecosystems and drastically reduce the ichthyofauna of the areas it manages to colonize. Its impact on habitats can be summarized briefly: structural changes in ecosystems, including hybridization with indigenous species; competition with native organisms for food and habitat and they can carry parasites or pathogen vectors.

4.5.6 Mnenopsis leidyi in the Black sea

Mnenopsis leidyi is a chenophore which belongs to the Bilonopsidae family. Mnenopsis leidyi can be mistaken for a jellyfish, but it is biologically very far from it.
Its body is oval and transparent and is composed of six lobes on which there are rows of ciliate combs that light up blue or green when exposed to light or touched. It also possesses the tentacles it uses to feed himself. Its body is 97% water and is about 7 to 12 cm long.
It is a species native to the Atlantic see introduced with ballast water from tankers in the Black Sea, the Baltic and the Caspian see.
It lives in deep and eutrophic waters and is very resistant to environmental changes, which makes it suitable to live in many seas and oceans of the planet. This animal is carnivorous and feeds on zooplankton, crustaceans, larvae and fish eggs. It is a hermaphrodite animal therefore capable of self-fertilizing, it is a very dangerous animal for marine ecosystems, in fact it is thought that because of its zooplankton-based diet it is responsible for the 80% decrease of zooplankton found in the Caspian Sea.
In the Black Sea it was introduced involuntarily by merchant ships, it was and is a drama for the ecosystem and for the economy of the area.
In 1989, the population in the Black Sea had reached very high levels with about 400 specimens per m³ of water, this had a strong impact on the anchovy trade, given that Mnemiopsis leidyi feeds on the eggs of these fish and also the two animals are competing for other food sources. The biological control was tried with Beroe ovata, another comb jelly, with some degree of success; it appears as if fairly stable predator-prey dynamic has been reached.

4.5.7 Where are alien species comming from in to the Mediterranean?

Tropical species arriving in the Mediterranean sea fall into two main classes according to their origin: in some cases these organisms passed through the Suez Canal from the Red Sea (this is called lessepsian migration named after Ferdinand de Lesseps, promoter and executor of the project of the Suez Canal) in other cases from the African coasts of the Atlantic Ocean, through the Strait of Gibraltar.
There is also a strong contingent of introduced species in the Mediterranean Sea, either voluntarily (for example, with the clam Tapes philippinarum), or by chance, especially through the ships' bilge water, which are often discharged into the sea without taking any precaution.
The alien species listed are 955 (of which 134 are considered invasive), representing 5.9% of Mediterranean biodiversity (by excluding phyto-plankton and microzooplankton); considring fish, this proportion increases to consider 27.9% of species as originally alien to the Mediterranean.
n addition to species from the bilge water a number of others comes from the cold waters of the North Atlantic.
This migration from the North is much smaller than from the tropical or subtropical regions (between 4% and 21%).
Many tropical species of new entrance are able to get perfectly acclimatized to the new environment, displacing native species, and they so far as to be commonly caught and marketed.
The rapid spread of lessepsians migrants in the Eastern Mediterranean is helped by climate change and the fact that the seo of origin presents harsher conditions than the Eastern Mediterranean Sea.

4.5.8 Name three main possibilities of entering alien species in new marine areas!

Alien species (formally called non-indigenous species) are a big issue in the marine environment. Normally we call alien species the ones that, thanks to humans or other reasons, move from their native place to another marine area. These animals are likely to cause a lot of problems in the environment and they are a big issue for the preservation of all the species in our marine ecosystem. For example, the Soft-shell clam (Mya arenaria), which is now very common in Europe, is a non-indigenous species introduced in the 16th or 17th century from the United States.

There are many ways of introducing non-indigenous species in a new marine area.
The most common cause of invasion, obviously, is the human sea commerce. Lots of goods every day move through water, that is the main connection for heavy portions of materials and food, from fuel or wood up to cereals. If a boat is not fully loaded water is used to maintain the draft, stability, and strength of the ship. This ballast water is usually taken up locally in harbours during unloading or en route on rivers and oceans and it can contain various organisms. They can also stick to a fuelling ship that usually travels around the world through every marine area and is likely to cause an invasion.

Another cause related to humans is the introduction of an alien species on purpose because there is a high demand for a certain animal in a specific area for food. For example, mussel seed is transported abroad for the purpose of aquaculture.

We also need to consider changes in the territory through time. The most common example is the opening of the Suez canal which led to the appearance of an overwhelming number of new species in the Mediterranean Sea.

Non-indigenous species are a real problem and we have to contain these invasions as much as we can, in order to save our environment.

4.5.9 Climate changes and distribution of marine species

In the last few years, climate change has been enormous. The temperature has risen considerably causing the melting of the glaciers. In climatology, the term climate changes indicates changes in the Earth's climate.
Climate change affects all regions of the world. The polar ice caps melt and the sea level rises. In some regions extreme weather phenomena and precipitation are increasingly common, while others are affected by droughts and unprecedented heat waves.
These changes have almost led to the extinction of some aniamals species, like the polar bear. Over the course of a century, from the end of the twentieth century to today, the earth's temperature has risen by around seven degrees. All the main factors attributed to climate change are related to human activities. The high consumption of fossil fuels has accelerated the process of global warming.

Climate change is occurring at such a rapid pace that many animal and plant species are struggling to adapt.
Many terrestrial, marine and freshwater species have already moved to other areas.
Some plant and animal species will be exposed to an increased risk of extinction if the world average temperature continues to rise uncontrollably.
With the current trends, without a decisive reduction in greenhouse gas emissions, half of the biodiversity of the Mediterranean Sea will be lost. The most endangered species are the sea turtles (they are three species, the most widespread is the Caretta Caretta) and the cetaceans, present in the Mediterranean.
Many animal species will concentrate in limited areas, with a strong extinction in places where these animals are regularly sighted.