Invasive species sometimes known as marine pests are species that have migrated from their natural habitat to new foreign habitat. The movement of these species are usually a result of human activities by a wide range of means; including ballast water being discharged by commercial ships, aquaculture operations, bio-fouling on hulls and inside internal seawater pipes of commercial and recreational vessels, aquarium imports, as well as marine debris and ocean currents. Invasive species can cause threats towards our environment, human health and our economy (Australian Government Department of the Environment and Energy, n.d). In this blog I will be talking about how a strain of a marine macro-algae introduced into a foreign habitat is causing threat to our marine environment and our economy.
Killer Algae (Caulerpa taxifolia) is a native species to the tropical waters of Indian and Pacific Oceans. A cold-resistant strain of this algae was discovered in 1980 in an aquarium in Germany where it was then distributed to multiple aquariums and institutes. It was first detected in the Mediterranean Sea four years later in 1984 (Ocean Portal Find Your Blue, n.d), where it was observed a few meters from the public Oceanographic Museum in Monaco where it was used as a decorative alga, and where it was accidently released into the Mediterranean Sea (Meinesz et al, 2001). When the C. taxifolia was first discovered in the Mediterranean Sea in 1984 only a single square metre was present, after five years passed the algae had expanded to cover an area of 10,000m2. A year later in 1990 it was also found 5km east of Monaco. This killer alga is now found in many parts of the Mediterranean such as Spain, Italy, Croatia, Tunisia and France. In 2000 the ‘aquarium strain’ was also found in two other coastal locations situated in southern California (CABI, 03rd January 2018).
C. taxifolia can be introduced into a foreign environment through multiple ways. The cold-resistant strain was first introduced into the Mediterranean Sea through accidental release of this algae from an aquarium into a natural environment. Another way this species can be dispersed is through anchoring of vessels. When a vessel uses their anchor, it may remove parts of C. taxifolia from an estuary. Conditions inside the anchor are favourable for these parts to survive meaning when a boat reaches a location the C. taxifolia will also inhabit this area. Boats play a key part in the spreading of this invasive species and is thought to be how C. taxifolia spread around the Mediterranean Sea. Sport fishing is one other way that is thought to spread C. taxifolia locally through fragments of this algae getting stuck to fishing equipment and then getting released in a different location (CABI, 03rd January 2018).
The invasion of C. taxifolia has many negative economic and environmental impacts. The ‘aquarium strain’ of C. taxifolia grows at a rapid speed and will cover seagrass beds, changing the habitat of the area they invade. Organisms that live on the sea bed where the C. taxifolia is invading cannot withstand environmental disturbances causing sub lethal effects on the native species that were present. Due to the speed this species grows, large monospecific meadows are produced by out competing other species for food and light and therefore has reduced native species diversity and fish habitat. C. taxifolia also contains a caulerpenyne compound meaning when the small range of fish than can eat this species, such as Mediterranean bream (Sarpa salpa) feed on the algae they will accumulate toxins in their flesh. This makes them unsuitable for human consumption. As a secondary effect of the reduction in fish habitat, the catches by commercial fishermen has largely been reduced and the weeds are known to get tangled in the boats propellers and fishing nets which has an adverse effect on efficiency of these fisheries causing a large economic impact (CABI, 03rd January 2018).
The invasion of Caulerpa taxifolia in our oceans are having a negative effect on both marine life and also economically. It is down to us to ensure through multiple methods that we try to prevent and control this problem getting any worse in the future to protect our ocean planet. One method used is to inform the public with the risks to the environment through education and extension, to prevent the accidental release of Caulerpa taxifolia by aquariums into natural waters. Another method is through direct control where an eradication programme is carried out to eliminate Caulerpa taxifolia in a certain location. Chlorine bleach may be used to kill Caulerpa taxifoli. Caulerpa taxifolia is still causing many issues to marine habitats and diversity. However, with a growing knowledge of how we can manage and prevent this invasive species, there is hope that invaded habitats can return to normal and regain the rich biodiversity they originally had (CABI, 03rd January 2018).
If you would like to read further on Caulerpa taxifolia or the methods used to prevent invasion of these species follow the link provided below.
Australian Government Department of the Environment and Energy. n.d. Marine Pests. [ONLINE]. [12th February 2018]. Available from: http://ocean.si.edu/ocean-news/5-invasive-species-you-should-know
CABI. 3rd January 2018. Invasive Species Compendium. [ONLINE]. [12th February 2018]. Available from: https://www.cabi.org/isc/datasheet/29292#F17F5E85-4711-419C-9021-56A99EE16A87
Meinesz, A., Belsher, T., Thibaut, T., Antolic, B., Mustapha, K.B., Boudouresque, C.F., Chiaverini, D., Cinelli, F., Cottalorda, J.M., Djellouli, A. and El Abed, A., 2001. The introduced green alga Caulerpa taxifolia continues to spread in the Mediterranean. Biological invasions, 3(2), pp.201-210.
Ocean Portal Find Your Blue. N.d. 5 Invasive Species You Should Know. [ONLINE]. [Accessed 12th February 2018] Available from http://ocean.si.edu/ocean-news/5-invasive-species-you-should-know