Species Description: The green feather alga, Caulerpa sertularioides, is among approximately 35 species and varieties of Caulerpa found in the Caribbean and western Atlantic Oceans (Littler & Littler 2000). The alga obtains its name from the feather-like fronds rising from a common stolon. Each frond is upright, branched and light to dark green in color (Littler & Littler 2000, Littler et al. 2008, Taylor 1979). Branchlets are opposite, cylindrical and needle-shaped with upcurved or straight apices or tips that are bluntly pointed. Each branchlet, measuring 180-330 µm in diameter and 3-11 mm long, is connected to a central, cylindrical axis measuring 1.0-1.5 mm in diameter. These axes connect each frond to a creeping stolon, 2.0-2.5 mm in diameter and up to 2 m long. Stolons branch to slender points and rhizoids stem from the ventral or bottom surface of each stolon to hold the alga to the substrate.
Potentially Misidentified Species: Caulerpa sertularioides contains two additional varieties, C. sertularioides f. farlowii and C. sertularioides f. longiseta. The range of f. farlowii overlaps with the original variety described above. However, it is more commonly found on reef flats, rocks and coral fragments (Littler & Littler 2000). Further distinction can be made by examining the branchlets of f. farlowii, which are at least twice as thick, crowded and radially arranged on each frond. The range of the remaining variety, f. longiseta, is most likely confined to the Greater and Lesser Antilles. Although similar in appearance to C. sertularioides, this form is characterized by branching fronds. Three other similar species occur in Florida waters: C. ashmeadii, C. mexicana and C. taxifolia. The branchlets and fronds of C. ashmeadii are usually much larger than those of C. sertularioides, and are often club-shaped. Branchlets of both C. mexicana and C. taxifolia are broader and flattened.
Regional Occurrence: The range of C. sertularioides extends from North Carolina to Florida, Bermuda, Bahamas, Greater and Lesser Antilles (Rodríguez-Prieto et al. 1999), Gulf of Mexico, throughout the Caribbean (Littler & Littler 2000, Littler et al. 2008) and in the southern Atlantic Ocean to Brazil (Taylor 1979). The species also occurs in many locations worldwide, including: the Great Barrier Reef in Australia (Benzie et al. 1997), Papua New Guinea (Coppejans & Meinesz 1988), Philippines (Meñez & Calumpong 1982), Palau (Santoso et al. 2004), and along the northern Pacific coast of Mexico (Scrosati 2001). In addition, C. sertularioides is considered to be an invasive alga along the northern Pacific coast of Costa Rica, where it is spreading rapidly over coral reefs (Fernández & Cortés 2005). The green feather alga is mostly found in coastal and estuarine environments, growing in sandy areas, seagrass beds or on mangrove prop roots (Littler et al. 2008). It is commonly a shallow-water species, occurring to 10 m deep, although sparse individuals have been dredged from depths of up to 110 m (Taylor 1979).
Age, Size, Lifespan: Information concerning the lifespan and age of C. sertularioides is limited, and growth may vary with water temperature, light and nutrient availability, salinity and other factors. As mentioned above, stolons of the green feather alga can reach up to 2 m in length. To form algal mats, they often overlap and entwine with other stolons. Fronds originating from the stolons can grow up to 20 cm high and 2 cm wide (Littler & Littler 2000).
Abundance: Abundance of C. sertularioides can vary depending on environmental conditions and other factors. Single stolons supporting a few fronds can be found in between seagrass blades, on rocks and shells, and attached to mangrove prop roots. However, carpets of the alga can grow as large as several square meters in certain habitats.
Reproduction: Like most other macroalgae, C. sertularioides can reproduce sexually or asexually. Asexual reproduction occurs via fragmentation of the parent plant. These pieces of the original alga can drift through the water column before settling and starting a new population. Sexual reproduction occurs by the release of both male and female gametes. While details on the specific reproductive strategies for C. sertularioides are lacking, studies on other Caulerpa species have shown that entire reproductive events may last no longer than 36 hours. Algae become fertile, release gametes during spawning events that occur around sunrise, and die after discharging all cellular contents into the water column (Clifton 1997).
Temperature: Although information on the temperature tolerance for C. sertularioides is lacking, the current tropical and subtropical range of the species suggests that it thrives best in warm waters.
Salinity: The green feather alga is found in a wide range of salinities in tropical and subtropical estuaries, and coastally on coral reefs. However, this species is a marine alga, and mortality most likely occurs in salinities lower than those in which populations naturally occur.
Trophic Mode: Like other macroalgae, C. sertularioides is autotrophic, obtaining energy through photosynthesis. As a photosynthetic organism, it is most commonly found in shallow waters with high light intensities. In the Indian River Lagoon, the photosynthetic rates associated with these light levels are elevated when compared to other species of Caulerpa (Gacia et al. 1996). Although optimum light and temperature values likely exist for each species, some studies suggest that C. sertularioides and other macroalgae have the ability to adapt to a wide range of environmental conditions (Gacia et al. 1996).
Special Status: Habitat structure
Benefit to the IRL: With its well developed fronds and carpet-like growth pattern, C. sertularioides can provide habitat structure for a variety of fishes and invertebrates in the IRL. Algal cover can act as a refuge from predators and create a nursery habitat that provides juvenile organisms with food sources. In one example, aquaculture studies in Mexico on the yellowleg shrimp, Panaeus californiensis, show that the growth and survival of the crustacean increased significantly in the presence of C. sertularioides (Porchas Cornejo et al. 1999).
Economic Importance: In addition to being grazed upon by the predators listed above, C. sertularioides is an edible crop consumed by humans in some parts of the world. In the Philippines, the alga is used for dietary and medicinal purposes (Trono 1998). As a food source, C. sertularioides may provide important anti-oxidants. In fact, studies on the extracts from populations in Palau showed the highest anti-oxidant activity of any alga examined (Santoso et al. 2004). The green feather alga has also been sold, along with other macroalgae, to aquarium hobbyists in retail shops and via internet sites throughout the United States and overseas (Stam et al. 2006). Though little information is available on the negative impacts of C. sertularioides, similar species of Caulerpa can carpet reefs and reduce coral cover, especially species that have invaded new ranges.
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