Fiji’s extensive pastures of seagrass are also a significant resource for green turtles in the central south Pacific region. Green turtles spend most of their adult life foraging in Fijian waters, occupying home ranges averaging 27 km2, taking only brief migrations (up to 1066km) to French Polynesia, American Samoa, Tonga and Cook Islands to nest⁶. The seagrass foraging areas in Fiji may well be providing foraging habitat for over half of the adult greens in the central South Pacific. This is possibly a consequence of lower availability of turtle food east of Fiji where most islands are small, steep and have limited areas suitable for seagrass. The need to protect such foraging areas is becoming widely recognized as a critical part of sea turtle conservation.

Six seagrass species and one subspecies are reported from the Fiji Islands: Halodule pinifolia, Halodule uninervis, Halophila ovalis,, Halophila decipiens Syringodium isoetifolium and Ruppia maritima⁷. Records of Thalassia hemprichii, Cymodocea serrulata, Halophila minor, and Halophila ovata credited to Fiji are possibly erroneous.

Halodule pinifolia is generally found in the high intertidal to upper subtidal areas of sheltered bay, reef platforms and in high energy locations. H. pinifolia often forms homogenous patches or occasionally intermixes with other seagrass species including H. uninervis⁷. They are easily distinguishable in the field by their much narrower blade size compared with that of H. uninervis (1 mm versus 4 mm)⁸. Waycott et al.¹⁰ suggested that H. pinifolia and H. uninervis are conspecific, recognising that the plasticity of blade size is attributed to local conditions. Nevertheless, in Fiji they are retained as separate entities, as there is no sufficient evidence from Fijian material to support this merger⁸.

Halodule uninervis is found from intertidal to 6m in sheltered or exposed coral reefs, in creeks and mangroves. H. uninervis often forms dense meadows at some sites, or is patchy and intermixed with other seagrass species (eg H. pinifolia, S. isoetifolium, or Halophila spp.)⁷.

Halophila ovalis is the most eurythermic of all seagrasses in Fiji and extends from the intertidal to 10-12m deep. First reported in Fiji in 1874 from Viti Levu, there are both bullate (blister or pucker-like) and smooth leaf forms^7,11. The bullate form is recognized as a subspecies H. ovalis ssp. bullosa because it appears sufficiently distinct⁹. However the synonymy adopted here follows Waycott et al.¹⁰ who consider H. ovalis to be a complex of closely related entities whose leaves are highly plastic especially in relation to blade size, shape, colour, and texture¹². The bullate forms have only been reported from Samoa, Tonga and the Fiji islands. H. ovalis forms dense meadows in some locations, but is frequently encountered in small patches. It tolerates a wide variety of substrata from fine muddy sand to coarse sand, mixed sandy-rubble or large boulders with sandy patches.

Halophila decipiens is a recent addition to the seagrass inventory in Fiji. It is no surprise that it occurs in Fiji, as the species is pan tropical and has been reported in New Caledonia and Tahiti from the mid-late 1800’s¹¹. Globally, H. decipiens is a sciophilous species which occurs from the water surface to a depth of 85m (Cargados Carajos Shoals, Mascarene Islands in the Indian Ocean). In the Fiji Islands it occurs from 10–25 m depth and has only been found growing in the fine muddy/sandy substratum along the reef channels of the Great Sea Reef ⁸. The plants form sparse patches and grow to 40 mm tall. H. decipiens is distinguished from H. ovalis and its subspecies bullosa by the presence of marginal serrations and hairs on either side of the leaf blade.

Syringodium isoetifolium is usually found in the shallow subtidal areas (1–6 m depth), with some meadows are occasionally exposed during extreme low tide on reef flats. Earliest records are from 1926 in Suva Bay¹¹. Syringodium is known to be more tolerant of oxidized substrata than other seagrass species and it has been reported that Syringodium will take over as a pioneer after a disturbance¹³ S. isoetifolium also has the ability to utilise a very high proportion of the available dissolved inorganic carbon compared to other seagrass species. Such an environment provides S. isoetifolium with a competitive advantage, especially when combined with disturbances that remove existing seagrass species.

Ruppia maritima only occurs in estuarine habitats in Viti Levu and is reported from brackish water pools or along the banks of the Rewa, Penang and Sigatoka Rivers⁷

A number of general parameters are critical to whether seagrass will occur along any stretch of coastline. These include physical parameters that regulate the physiological activity of seagrasses (temperature, salinity, waves, currents, depth, substrate and day length), natural phenomena that limit the photosynthetic activity of the plants (light, nutrients, epiphytes and diseases), and anthropogenic inputs that inhibit the access to available plant resources (nutrient and sediment loading). Various combinations of these parameters will permit, encourage or eliminate seagrass from a specific location. In Fiji, seagrasses are distributed throughout the Islands and local conditions may often determine which seagrass species are present.