Acanthophora spicifera is a Rhodophycean alga with wide distribution throughout the tropics and subtropics (Kilar and McLachlan, 1986). It occurs on a wide variety of substrata, from hard bottom, as an epiphyte on other algae, or as a free living drift alga. It is often a large component of drift algae biomass.
Growing upright to approximately 25 cm, A. spicifera has a large, irregularly shaped holdfast for attachment to hard bottoms. From the holdfast, erect fronds begin to branch out. The main branches have short, determinate branchlets that are irregularly shaped and spinose. Branchlets are hook-like, brittle and fragment easily under heavy wave action. Color is highly variable, and can be shades of red, purple, or brown (Littler and Littler, 1989).
Regional Occurrence: Acanthophora spicifera is one of the most abundant red algal species found on reef flats (Joikel and Morrissey, 1986). It has a wide distribution in both tropical and subtropical habitats, occurring primarily in the tidal and subtidal zones. It is found extensively on shallow reef flats throughout Florida, the Virgin Islands and Puerto Rico, to depths of 22 meters, although it typically inhabits more shallow waters from 1-8 meters in depth (Kilar and McLachlan, 1986; Littler and Littler 1989).
IRL Distribution: In the Indian River Lagoon, A. spicifera is commonly found attached to rocks and oyster rubble. Dead or dying specimens can be found smothering turtlegrass (Thalassia testudinum) beds.
Age, Size, Lifespan: A typical size for this species, under minimally disturbed conditions, is to approximately 250 mm. However, wave action is known to alter branching morphology depending on whether the alga inhabits a fore reef or a back reef habitat. In one study performed in Panama, A. spicifera populations in the heavily wave-influenced fore reef area had an average height of 38 mm, while those in the back reef grew to an average of 110 mm (Kilar and McLachlan 1986).
Abundance: A. spicifera is one of the most common and abundant red algal species to occur on reef flats. It is found at depths from 1-22 meters.
Locomotion: Sessile. Fragments are carried and dispersed by local currents.
Sexual: A. spicifera has a triphasic alteration of generations in which the tetrasporophytic and gametophytic generations are isomorphic, while the gametophyte is dioecious (Borgensen 1918; Taylor 1967; Kilar and McLachlan 1986).
Tetrasporophytes were the most common reproductive phase occurring on reef flats in Panama (Kilar and McLachlan 1986), with over 80% of the plants tetrasporic throughout much of the year. This percentage was reduced to only 5% during periods of prolonged tidal immersion.
Asexual: Fragmentation accounts for much of the distribution and standing crop of this species. On reef flats, as much as 26% of the standing crop can be lost to drift each month. Kilar and McLachlan (1986) showed that exported biomass of A. spicifera on a 1.0-1.3 ha sampling area of a plant-dominated fringing reef at Galeta Point, Caribbean Panama, was 3-74 kg per month. This equated to an estimated average of approximately 269 kg per year.
Turbulence in the fore reef zone causes A. spicifera to fragment. Currents often transport fragments across seagrass meadows to the back reef zone, where they snag on rocks, algae, or other substratum. Experiments conducted in Panama suggested that depending on the prevailing current direction and velocity, fragments broken off in the fore reef had a 49-93% chance of recruiting to the back reef zone. Higher currents tended to decrease the chances of snagging (Kilar and McLachlan 1986). Approximately 2 days were required for A. spicifera fragments to attach to hard substrata, conspecifics, or other species of plants.
A. spicifera is well adapted for recruiting into new areas after fragmentation because its branchlets are hook-like and easily snag onto other algae, or any substrate with an irregular surface. However, in experimental plots (Kilar and McLachlan 1986), A. spicifera was unable to recruit to plots of Thalassia testudinum, possibly because the hook-like branchlets of the algae were not able to snag onto the smooth, flexible leaves of Thalassia species.
Temperature: Kilar and Norris (1988) reported that maximum primary production for A. spicifera occurs at a water temperature of 25 °C. Taylor and Bernatowicz (1969) and Trono (1968), based on the observation that A. spicifera tends to disappear during mid-winter in the Caribbean, postulated that it may be limited to waters which remain above 23.5 °C. However, as the species is common throughout the topics and subtropics, its survival temperature range is thus significantly broader.
Salinity: Typical reef salinity in the Caribbean areas sampled for A. spicifera was between 32-35 ppt. Tabb and Manning (1961) observed that densities of this species generally increased when salinity decreased, but also found that it tolerated higher salinity levels relatively well.
Other Physical Tolerances: A. spicifera cannot withstand prolonged exposure to air (Russell 1992).
Trophic Mode: A. spicifera is autotrophic.
Acanthophora spicifera's survival on reefs is enhanced when it co-occurs with dense aggregates of other algal species that are more tolerant of wave exposure and are able to retain water when exposed to air. A. spicifera benefits from this association by being shielded from sunlight, as well as somewhat insulated from dessication. One such beneficial associated species is Laurencia papillosa. In some Caribbean habitats, A. spicifera is able to outcompete, but not exclude, Laurencia papillosa. The relative success of both species is heavily dependent on the duration and types of disturbance to the habitat area, as well as each species' ability to maintain space during competition, reproduction, and vegetative growth.
Predation upon A. spicifera: Along with reef fishes, the green turtle (Chelonia mydas) also ingests A. spicifera. An examination of the gut contents of dead turtles showed that they grazed tufts of A. spicifera. In a study conducted by Russell and Balazs (1994), A. spicifera appeared in 20% of the stomach content samples taken from green turtles.
Habitat: Grows attached to rocks and oyster rubble in shallow (1 m) areas of the Indian River Lagoon. Elsewhere, A. spicifera commonly inhabits reef flats where it attaches to hard bottoms, grows as an epiphyte on other algae, or is free-floating as drift algae.
Activity Time: An association refuge sometimes occurs when A. spicifera grows in association with the soft coral Sinularia spp. Kerr and Paul (1995) have shown that predation upon A. spicifera by fish decreases with its proximity to Sinularia.
Special Status: Habitat structure
Notes on Special Status: Drift algae like Acanthophora spicifera provide food, habitat and refuge for many fish and invertebrates, and play an integral part in many pelagic and benthic by increasing habitat complexity.
Notes on Endemism: A native to Florida and the Caribbean, Acanthophora spicifera is an invader in Hawaiian waters, probably as the result of its colonizing boat hulls and being transported throughout the Hawaiian Islands during the late 1940s and early 1950s (Russell 1992). Though this species, as well as another invader, Hypnea musciformis, have both been shown to compete with native species in Hawaii, they have added to the overall productivity of the areas they inhabit (Russell and Balazs 1994).Further, they have become a significant part of the diet for some fish species, and the green turtle (Chelonia mydas) (Russell and Balazs 1994).
Economic Importance: None
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