The development of global trade and the increase in international travel at the beginning of the twentieth century significantly influenced the rise in the number of invasive species in our area. Numerous organisms were allowed to “travel” on cargo ships, in ballast water, or on transport vehicles. The transportation of plant and animal species, as well as microorganisms to distant places, often unintentionally, allowed species to overcome barriers that would otherwise be insurmountable, such as mountains, rivers, and oceans which resulted in unexpected ecological consequences.
Along with pollution, habitat loss, overfishing, and climate change, invasive species are considered one of the most important threats to biodiversity.
In the twentieth century, due to global trends, the problem of invasive foreign species became even more serious. Various strategies and regulations have been put in place for better control of the number of invasive species. However, despite legislative measures, monitoring, education, and control, invasive species remain a major problem. And as usual, cooperation at the global level is often key to solving it.
Foreign vs. invasive species
It is important to know the difference between foreign and invasive species. Not every foreign species is invasive and vice versa. A foreign species is a non-native species that does not naturally inhabit a certain ecosystem but has arrived there through intentional or unintentional introduction. Terms used in the literature for such species include “alien,” “non-native,” “exotic,” “introduced,” or “imported species.” If the spread of a foreign species has a negative impact on biodiversity, and human health, or causes economic damage in the introduced area, that foreign species is classified as invasive. Competition for food and habitat, spread of diseases, and hybridization with local species are some of the threats that invasive species can pose to a new area. These threats are especially pronounced in sensitive ecosystems and geographically isolated areas, such as islands.
Reasons for arrival
- Any change in nature, whether it involves dredging, land reclamation, modifications, or larger interventions, leaves a mark on the environment. Projects like the construction of canals have a particularly significant impact. The best example of this is the Lessepsian species, named after Ferdinand de Lesseps, who received the concession for the construction of the Suez Canal in 1854. These are species that migrate from the Red Sea, through the constructed canal into the Mediterranean Sea, and later into the Adriatic Sea. An example of a species that reached the Adriatic Sea this way is the silver-cheeked toadfish (Lagocephalus sceleratus).
- Transmission often occurs through ballast water as well. Ballast is any material used to regulate the weight or balance of a vessel. Although other materials were used in the past, since the end of the 19th century, water (sea, river, brackish) has been used. When a ship unloads cargo, ballast is taken on, and vice versa, when cargo is loaded, ballast is discharged. It is estimated that between 10 and 12 billion tons of ballast water are transported worldwide annually. Studies conducted in many countries have shown that certain living organisms can survive in the water and sediment transported in ship ballast tanks. The discharge of such water and the organisms living in it can pose a significant threat to the coastal state, with unpredictable consequences for the marine environment.
- The International Maritime Organization (IMO), as a specialized agency of the UN, recognized the potential danger, and in November 1997, IMO Resolution A.868(20) – Guidelines for the Control and Management of Ships’ Ballast Water to Minimize the Transfer of Harmful Aquatic Organisms and Pathogens was adopted. The recommended application of the Guidelines applies to all coastal states. Currently, the IMO has 175 members, and the Republic of Croatia has been a member since 1992.
- Global warming also has an increasing impact, and “climate migrants” are already being mentioned. Changing temperatures create unfavourable conditions for many species in warmer regions, causing them to migrate to cooler areas. Although climate change is one of the main reasons for migration, it usually occurs in combination with another negative impact (such as the construction of canals).
- Free anchoring not only disrupts habitats but also allows for the transfer of species from one area to another. This is particularly the case with algae species that have the ability to reproduce vegetatively (reproducing by breaking, fragmentation, and so on). The best example of this impact is the species Caulerpa cylindracea, which can be found along the entire Adriatic Sea.
- Accidental releases of species when changing aquarium water is another reason. In 1984, during the cleaning of an aquarium in Morocco, the species Caulerpa taxifolia was introduced into the Mediterranean Sea, which was first recorded in the Adriatic Sea in 1994.
A new threat
The lionfish (Pterois miles), an invasive Indo-Pacific fish species, is notorious for its consumption of large quantities of native fish species, high reproductive capacity, and venomous spines and causes significant problems in the Mediterranean Sea. In the Adriatic Sea, it was first recorded in 2019.
The silver-cheeked toadfish (L. sceleratus) is considered one of the most dangerous invasive species of the Mediterranean Sea. Due to the toxin in its body, which is thermoresistant, it poses a threat to biodiversity and human health. It is a carnivore with an extremely strong jaw and sharp teeth. A Japanese species related to this one, although highly toxic, is considered a delicacy and can only be prepared by specially trained chefs. This species was first recorded in the Adriatic Sea in 2012.
What to do?
What is specific to most invasive species, including the lionfish and the silver-cheeked toadfish, is that they are more resilient and adaptable than native species. Many countries have significant problems with invasive species, whose numbers have increased significantly due to weak or no regulation, almost completely displacing native species. To prevent such a scenario, it is necessary to act in time. Here’s how:
- record and report the locations of foreign species to the relevant authorities;
- participate in workshops and seminars on invasive species to become informed about species that could enter the Adriatic Sea;
- gather expert advice and examples of good population regulation practices from other areas for possible application in our region;
- raise awareness about the dangers that can arise from any intervention in nature;
- according to the experience of countries already dealing with species like the lionfish, timely regulation of laws and enabling the fishing of the species to reduce population numbers is essential. It should be noted that this is a species whose migration is facilitated by climate change, and its re-entry into the Adriatic Sea is inevitable;
- the lionfish (once its venomous spines are removed) and many other species, such as the blue crab (Callinectes sapidus), are very tasty and should be considered for inclusion in the daily diet.
Having already overfished many native species to the brink of extinction, why not follow the same logic and eat the invasive species… at least those that can be eaten?