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Management Strategies of Invasive Species

Invasive species are non-native species that are introduced to an ecosystem through a variety of pathways such as: intentional introductions, accidental releases, and natural events like tsunamis. The most common pathways are said by researches to be ballast water exchange of oceangoing vessels and the marine ornamental trade.Many species that are introduced into non-native areas either die out because they are not able to adapt to their new environment fast enough or they do survive but don’t alter the ecosystems enough to cause any damage. However, invasive species are given their name because they are able to adapt and thrive in non-native ecosystems causing significant damage to their new ecosystems, the food-web and the environment itself which why it is necessary to develop these management strategies to control them.

Invasive species affect coral reefs both directly and indirectly, corallivore's like the Crown of Thorns Starfish directly consume corals while Pterois pose a threat through their over consumption of native species within coral reef ecosystems. However, most management strategies are the same for both. Outbreaks of these invasive species have become more frequent over the past century and are adding to the frequency at which coral cover is being lost.

Crown of Thorns Starfish

Native to the Indo-pacific these marine invertebrates feed on coral and play a critical role in the coral reef ecosystem, regulating the diversity of corals and maintaining balance within the reefs. However, the crown of thorns starfish (Acanthaster sp., COTS) is also a natural boom-and-bust species which mean that their population dynamics are characterized by the extreme fluctuations in adult abundance, followed by population collapse as coral food levels decline, leaving a swath of dead coral behind.COTS outbreaks were first discovered in the 1960’s on the the GBR, occurring under natural conditions as frequently as every 50-80 years. However, unnaturally there has been an increase in the frequency of outbreaks to every 15 years has led to further research that still hasn’t been answered.

Manual COTS control

Manual control is the process in which experienced COTS control divers remove COTS from reefs either by lethal injections or hand collections and disposal on shore. This method has been around from the 1960s, since then 17 million starfish have been killed or removed as a collective by 84 manual control programs at an estimated cost of $15-44 million USD. Due to the large cost and limited success in preventing COTS outbreaks and coral loss, scientists doubt the effectivity of this method. Sites are selected by the national governments of individual countries with coasts based on the potential significance in the overall pattern of coral and COTS larval spread for example: economically important for tourism, or located on reefs that oceanographic modeling suggested were highly connected to other reefs. Selected sites including permanent survey marked sites are used to precisely relocate RHIS survey sites for continuous measurements of coral cover. . All sites are GPS mapped to make it easy for researchers, volunteers and the marine protection groups to find.

Marine Protected Area zoning

Marine Protected Area zones are areas created by Marine National Parks or other management operators of a country. There are two components to a Marine protected area, zoning and the degree of protection for each zone. Marine zoning has in previous studies been highly successful in minimizing outbreaks of COTS when it is paired with manual control. There are three different types of zoning, ‘no-take’, ‘limited-take’ and ‘take’ zones on COTS numbers and coral cover.

Water quality in minimizing the outbreaks of COTS

Increasing water quality has the ability to increase or decrease COTS outbreaks. According to earlier studies, controlling the quality of the water can help prevent breakouts to some extent but this is not always tangible. Exposure to flood plumes variables and the presence of COTS indicated a positive threshold type response at low levels, highlighting the significance of larval nutrition availability for the establishment of COTS populations. Excess nutrients run-off from agricultural land uses (grazing, grain, sugar cane, and horticulture) create phytoplankton blooms in reef waters that can be carried to COTS populations. Water quality can be managed by controlling how catchments discharge water, but this requires intensive land management employing best management practices.