II. HABITAT AND
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
In the Indian River Lagoon, A. spicifera is commonly found attached
to rocks and oyster rubble. Dead or dying specimens can be found smothering Thalassia
III. LIFE HISTORY AND POPULATION BIOLOGY
Age, Size, Lifespan:
Typical size for this species, under conditions of minimal disturbance, is
approximately to 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
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.
Sessile. Fragments are carried and dispersed by local currents.
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.
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 some 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 was required for A. spicifera fragments to attach to
hard substrata, conspecifics, or to other species of plants.
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.
IV. PHYSICAL TOLERANCES
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
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).
V. COMMUNITY ECOLOGY
A. spicifera is autotrophic.
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, and somewhat insulated from dessication. One such
beneficial 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
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.
Grows attached to rocks and oyster rubble in shallow (1 m) areas of the
Indian River Lagoon. Elsewhere, it commonly inhabits reef flats where it
attaches to hard bottoms, grows as an epiphyte on other algae, or is free living
as drift algae.
An association refuge sometimes occurs
when A. spicifera grows in association with the soft coral Sinularia
sp. Kerr and Paul (1995) have shown that predation upon A. spicifera
by fish decreases with its proximity to Sinularia.
VI. SPECIAL STATUS
Notes on Special Status:
Providing food, habitat and refuge for
many fish and invertebrates, Acanthophora spicifera and other drift algae
play an integral part in many pelagic and benthic by increasing
Notes on Endemism:
Though a native to Florida and the Caribbean, Acanthophora spicifera
is an invader to Hawaiian waters, probably as the result of its colonizing boat
hulls and being transported throughout the Hawaiian Islands during the late
1940's and early 1950's (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).
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Report by: K. Hill,
Smithsonian Marine Station
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