The genus Amphibolis C. Agardh (Cymodoceaceae).

Author:

Species:

Two species of Amphibolis are currently recognised:

• Amphibolis antarctica (Labill.) Sonder & Aschers. ex Aschers.
• Amphibolis griffithii (J.M. Black) den Hartog

Life history:

Amphibolis plants are dioecious and viviparous, seedlings developing on the female plant and shed once mature. Mature seedlings possess a unique grappling device, sometimes referred to as a "comb anchor" because of its shape. Flowering times vary depending on location and between species (Ducker et al., 1977).

Distribution:

Both species of Amphibolis (common name: "sea nymph" or "wire weed") are endemic to Australia; distribution is restricted to southern Australia, and Western Australia (Figure 1).

Epiphytes:

A notable characteristic of both Amphibolis species is the large number and density of epiphytes which grow on them. Epiphytic species colonize both stems and leaves of the plants. Ducker et al. (1977) and Borowitzka and Lethbridge (1989) have recorded over 100 species of epiphytes growing on Amphibolis plants across their range.

Amphibolis antarctica (Labillardière) Sonder and Ascherson ex Ascherson.

Distribution and ecology:

Den Hartog (1970) and Ducker et al. (1977) list the distribution of A. antarctica from Carnarvon, Western Australia along the south- west and southern coast as far east as Wilsons Promontory, Victoria, and south to the north and north-east coasts of Tasmania. Walker and Prince (1987) recorded this species as far north as Exmouth Gulf, Western Australia (Figure 1).


Figure 1. Distribution map of Amphibolis antarctica based on Ducker et al. (1977), den Hartog (1970), Walker and Prince (1987).

This species is found sublittorally to depths of over 27 m (although rarely forming meadows below 13 m (Walker, 1989)), and in well-drained lower eulittoral pools. Although found growing in very shallow conditions, with the leaves floating on the surface, Ducker et al. (1977) noted that the leaves can become damaged and black, being lost over summer. The most extensive growth occurs in the sublittoral where it can form extensive meadows, such as in Shark Bay, Western Australia.

Amphibolis antarctica has been observed to grow on a variety of substrates, from sand-covered rock and gravel, to sandy bottoms and even clay (den Hartog, 1970; Ducker et al., 1977). Although usually described as occurring in areas of high water flow, Walker (1989) observed the species growing under "a wide range of current regimes", ranging from 0-4 knots, in Shark Bay. A. antarctica has been shown to be very tolerant of high salinity levels. Walker (1989) collected seedlings from areas of salinities up to 50 ppt. Although percentage cover was much reduced at the higher salinities, A. antarctica was observed growing at salinities of greater than 60 ppt, with an optimal range of 40-50 ppt (Walker, 1989).

An interesting aspect of the distribution of Amphibolis antarctica is its eastern limit. Wilson's Promontory in Victoria marks an oceanographic boundary, and it is possible that the seasonal easterly currents prevent colonization of seedlings east of this point. An alternative explanation is the sedimentological differences east and west of this location: east of Wilson's Promontory the sediments tend to be siliceous sands, while to the west calcareous sediments predominate (Ducker et al., 1977).

Amphibolis griffithii (J.M. Black) den Hartog.

Distribution and ecology:

A. griffithii occurs from Geraldton/Oakajee, Western Australia to Victor Harbour, South Australia (Ducker et al., 1977; Kirkman and Walker, 1989; personal observations). The considerably reduced range of this species compared to A. antarctica suggests a reduced temperature tolerance (Ducker et al., 1977). The northern limit of this species in Western Australia may be related to a lack of appropriate habitat between Geraldton and Shark Bay; the coastline in this region is dominated by high cliffs which are exposed to oceanic swell (Kirkman and Walker, 1989).


Figure 2. Distribution map of Amphibolis griffithii based on den Hartog (1970) and Ducker et al. (1977).

Den Hartog (1970) suggested that A. griffithii is more tolerant of rough conditions than A. antarctica.