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Invasive Species: Killer Algae (Caulerpa taxifolia)Archida Korat

BIOL 115 SPRING 2019

ABSTRACTCaulerpa taxifolia, famously known as “killer algae” is a strain of green algae native to the Indian Ocean. Due to its neat presentation and arrangement, it is often used in aquariums. As a result of an accident, the mutant form was introduced to the Mediterranean Sea. It grows at a rapid rate in undesirable conditions such as polluted waters, low light levels, and extreme temperatures. Though it does not possess any threat to human health, it can have a significant impact on economic and environmental health to the marine ecosystem. Due to its dense nature, reproduction through fragmentation, and rapid growth in covering the seafloor, many species lost food and shelter among the original biomass of seagrasses. Though many preventive measures were used in the process of eradicating it, chlorine bleach was the most effective. It was able to eradicate the algae with over 99% success rate in California. To prevent re-introductions to the sea, federal laws and regulations were passed from 2000-2001 to ban the possession, sale, and transport of the species.

INTRODUCTION

IDENTIFICATION

ESTABLISHMENT

There are many reasons the mutant form of C. taxifolia has survived for many years. In comparison to the native form which grows up to 5-65 cm in length, the mutant form can grow up to 10 feet in the Mediterranean Sea. It is able to grow in conditions such as “nutrient deprivation, heavily polluted waters, sandy bottoms, rocky outcroppings and mud” (Cotton 2005). It shockingly can “survive without water for up to 10 days” (Cotton 2005). It can tolerate temperatures low as 70 C and high as 320 C with the optimal growth temperature ranging from 20-300 C (Peichel 2001). It is also able to grow in low light levels and can cover the entire “sea bottom from the surface to a depth of 35 meters” (Cotton 2005).

ECOLOGYCaulerpa taxifolia colonizes the environment it lives in and becomes the “dominant form of plant life” (Cotton 2005). Since it creates a “dense algal expanse across the sea floor” as seen in Figure 3, the oxygen consumption in that particular area increases (Cotton 2005). As a result, the marine species (various fishes and invertebrates) that once thrived and relied on food and shelter in the Mediterranean have been greatly reduced. Additionally, it contains a toxin called caulerpenye that is lethal or distasteful to some marine organisms. The Mediterranean beam (Sarpa salpa) is one of the few fishes that eat C. taxifolia; however, the toxin accumulation in their bodies makes it “unsuitable for human consumption” (Schaffelke 2018 ). Consequently, predation is not a concern for this species as they have no natural predators in the environment (Agardh 2001). There is also a growing concern that this toxin gets transferred through the food chain and results in loss of species biodiversity. For example, a study illustrated that sea urchin, a herbivore, would rather starve than consume the algae (Cotton 2005).

PREVENTIVE MEASURESIn order to eradicate C. taxifolia, biological, chemical, and physical have been taken over the years. Although there is not a proven biological factor for the algae, Elysia suboranata, a Molluscs, is the most promising out of the four gastropods that have been examined. The issue with this Molluscs species is that “it is unable to survive below 15 oC (Schaffelke 2018).Another possibility is eradicating them chemically by covering them with PVC tarps and injective them with chlorine bleach (concentration of 125 ppm) (Ribera 2016; Schaffelke 2018). This method was successful in California, costing them $2.33 million in eradication alone. As a result, the Southern California Caulerpa Action Team (SCCAT) was able to eradicate over 99% of the biomass. Australia was moderately successful in eradicating by treating it with coarse sea salt. “The use of this method during cooler months was recommended and […] salting has so far only been successfully used on soft sediments in water <6m in depth” (Ribera 2016). The physical removal by scuba divers was successful in removing a small area of C. taxifolia in the Mediterranean. Other physical methods included covering the colonies with “black PVC plastic” in Croatia or using a “suction pump to remove all fragments” (Ribera 2016).

GOVERNMENT REGULATIONS

REFERENCES

Many countries around the world have been affected by the killer algae as demonstrated in Figure 4. In order to reduce the risk of re-introduction in eradicated areas, the public was educated and made aware of the potential risk and threats of the killer algae to the marine ecosystem. Additionally, under the Noxious Weed Act (1999) and Plant Protection Act (2000), the sale and transport of the aquarium strain Caulerpa is prohibited (Hoddle and NOAA Fisheries). In 2011, possessing, selling and transporting of the strain and species similar to it is banned in California under the Assembly Bill 1334 (NOAA Fisheries). San Diego under the city limits too cannot possess, sell or transport “the entire genus of Caulerpa” (NOAA Fisheries). Lastly, no new infestations have been observed in California since its original eradication due to the efforts of SCCAT and NOAA Fisheries Service.

Agardh, V., 2001, Algae: Native, Invasive Elsewhere: Caulera taxifolia.University of Hawaii: Botany

Cotton, K. 2005. Killer Algae (Caulpera taxifolia). Columbia University.

Hoddle, M. Killer Alga, Caulerpa taxifolia. Center of Invasive Species Research, University of California Riverside.

Internet source at https://www.westcoast.fisheries.noaa.gov/habitat/aquatic_invasives/caulerpa_taxifolia.html, accessed 05/15/19

Makowka, J. 2000. Monterey Bay National Marine Sanctuary Fact Sheet: Caulerpa taxifolia. Report to the Monterey Bay National Marine Sanctuary.

Pierre., Maricela. 2005. Literature Review of Caulerpa taxifolia. University of Salzburg.

Ramey, V., Peichel, B., 2001, Caulerpa taxifolia, University of Florida: Center for Aquatic and Invasive Species.

Ribera, A. 2006. Caulerpa taxifolia. Global Invasive Specie Database. University of Nice.

Schaffelke, B. 2018. Invasive Species. CRC Reef Research Centre, James Cook University, QLD, Australia

Schofield P.J., Brown M.E., 2016. Reference Module in Earth System: Invasive Species.

An invasive species is a type of a non-native organism that causes economic or ecological harm to the environment. One example is the Caulpera taxifolia, famously known as “killer algae” is a strain of green macroalgae. They are a photosynthetic organism native to the Indian Ocean and the Caribbean Sea. It is widely used as an ornamental plant in saltwater aquariums due to its neat arrangement of brightly green color fronds complementing the coloring of tropical fish as seen in Figure 1 (Makowka 2000; Schofield and Brown 2016).

Mode of Introduction: In 1984, scientists were trying to breed an attractive form of the Caulpera taxifolia strain to be used in aquariums. After exposing the seaweed to abiotic stressors such as UV lights and aquarium tank chemicals, the current form of the strain was created. It eventually was leaked into the environment along the coast of the Mediterranean Sea where it grew from one square meter to 2.5 acres in under five years. (Cotton 2005). Currently, it is found in the Adriatic Sea, Southern coast of California and Australia. (Cotton 2005).

Its classification is as follows: Phylum Chlorophyta, Class Ulrophycea, Order Caulerpales, Family Caulerpaceae, Genus Caulpera, and Species Caulperataxifolia (Agardh 2001). It is a siphonalean alga (coenocytic morphology) which can grow up to 5-65 cm in length. As it is illustrated in Figure 2, the non-vascular algae are anchored to the substrate with root-like structures called rhizoidal bouquet which gives rise to rhizoid pillars. Rhizoidal bouquet functions in absorbing inorganic and organic nutrients from the substrate it’s attached to. This structure gives rise to stolons (stems) that has the fronds, photosynthesizing “feather-like leaf blades”, attached to them. (Peichel2001). Lastly, pinnules are the leaf-like structures that grow from the fronds. They have a monoecious lifecycle; however, the form of reproduction varies between the native and mutant forms. The native plant reproduces sexually with the fusion of the male and female gamete and forming a zygote which eventually grows into an adult. In contrast, the mutant form reproduces asexually through fragmentation and can grow as fast a centimeter a day (Ribera 2006).

Figure 1: Mutant form of Caulerpa taxifoliademonstrating its neat arrangement and bright-green coloration. (Hoddle).

Figure 2: Illustration of the Caulerpa taxifolia’s morphology (Pierre 2005).

Figure 3: Illustration of the dense nature of Caulerpa taxifolia’s across the sea floor (Agardh 2001).

Figure 4: Map showing the distribution of Caulerpa taxifolia across the world (Schaffelke 2018).