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Acanthophora spicifera (Vahl) Børgesen

Description: Plants to 25 cm, 2-3 mm wide, sparingly to repeatedly branched, with lateral spinose determinate branches, no spines on main axes; base a thickened crust, coalescing at times with lower axes apices pyramidal, with incurved trichoblasts. Pericentral cells corticated densely, the central axial cells usually evident. In older axes, ventral axial filaments surrounded by small-celled adventitious filaments. Tetrasporangia ca. 75 micrometer diam. in short, determinate, spinose branches. Spermatangial heads plate-like, on single-celled stalks near branch apices. Cystocarps on adaxial sides of spines (Abbott, 1999 p.355)

Introduction and Origin: A. spicifera first inoculation occurred at the arrival of a fouled barge from Guam in 1950. In the following years, it spread along O'ahu and eventually to all the Hawaiian islands. A. spicifera is able to outcompete the majority of native species, the most affected species being the native Laurencia sp. The successful occupation of Hawaiian habitats by A. spicifera can be attributed to three factors: its capacity for vegetative reproduction, high production of tetraspores, and human-induced enrichment of outflowing waters. The thallus of A. spicifera is easily fragmented. Most often the fragments remain viable and take hold further down current. A large number of the specimens brought to the Bishop Museum have tetraspores present, showing there is always a high recruitment pressure. Due to agricultural practices and urbanization, most of the water effluents in the Hawaiian islands contain high amounts of dissolved nutrients. This has caused the coastal environments to change from originally oligotrophic conditions to eutrophic, creating more favourable conditions for the establishment of new algae.

Hawaiian Distribution: Found on all substrates from reef to mudflats on all islands. Well established on Maui, Molokai, Lanai, Kahoolawe, Oahu, and Kauai. Recently identified on Hawaii Island.

Habitat: Saxicolous, epiphytic, or epizooic. Intertidal and subtidal, also as free-floating fragments. Ofter dominant intertidal species.

Environmental Effects: Due to its high recruitment rate, Acanthophora spicifera has displaced many native Hawaiian algae and has become one of the dominant algae species in the islands (Russel, 1992).

World Distribution: Type locality: St. Croix, Virgin Islands. Widely distributed throughout the tropics and into warm temperate areas.

Commercial Interests: By displacing many native Hawaiian algae, A. spicifera may affect the availability of species of commercial interest, or indirectly, the abundance of certain herbivorous fish and invertebrates .

Rate of Spread / Method: Dispersal rate due to vegetative propagation and sexual reproduction varies from one area to another. A strong current can carry viable fragments for long distances, creating a larger dispersal range. Boats are often the main agents of dispersal by carrying along fragments, or even whole individuals growing attached to their hulls.

Factors likely to influence Spread and Distribution: Highly adaptable, it was found to grow best in places with high water motion, in a temperature range of 25-27°C, being sensitive to temperatures lower than 23.5°C (Russell, 1992). Boats are often the main agents of dispersal, by carrying along fragments, or even whole individuals growing attached to their hulls. A.spicifera has been repeatedly documented to grow on the hulls of boats, which are likely to carry viable propagules to new and remote locations. Boat anchors will lift and disperse the basal portion of the plant.

Reasons for Success: Acantophora spicifera disperses easily through fragmentation, and shows a high recruitment rate (Russell, 1992).

Control Methods: Nothing has been done to control the spread of A. spicifera. Possible strategies to diminish its growth rate will include increasing the herbivorous fish populations by regulating fishing activities, and implementing strict freshwater management measures to prevent nutrients runoff.

References: Jokiel, P. J,Morrissey. 1986. Influence of size on primary production in the reef coral Pocillopora damicornis and the macroalga Acanthophora spicifera. Marine Biology. 91:15-26. Kilar, J. J,McLachlan. 1986. Branching morphology as an indicator of environmental disturbance:testing the vegetative fragmentation of Acanthophora spicifera and the turf morphology of Laurencia papillosa. Aquatic Botany. 24:115-130. Kilar, J. J, Mclachlan.1986. Ecological Studies of the alga, Acanthophora spicifera. J. Exp. Biol. Ecol. 104:1-21. Russell, D. 1992. The ecological invasion of Hawaiian reefs by two marine red algae, Acanothophora spicifera (Vahl) Boerg. And Hypnea musciformis (Wulfen) j. Ag., and their association with two native species, Laurencia nidifica J. Ag. and Hypnea cervicornis J. Ag. ICES mar. Sci. Symp. 194:110-125.