Harrington Sound

The Shallow Sandy Zone

The shallow sandy zone is narrow with the exception of shallow banks along the median ridge. The zone lies close to the shore. It extends to a depth of about 10 m. In this zone, the distribution of organisms is more variable than in other zones. In shallow, well lit regions down to 5 m many sea grasses, algae and sponge species occur. Algae such as Penicillus, Halemeda, Neomeris and more recently Cladophora are common. Various bivalves such as Arca and Pinctada live free or are attached to exposed surfaces. The large holothurian Isostichopus is umbiquitous in this zone. Below 5 m fewer algae or sea grass beds and more sandy open areas are found. Penicillus is more common in the upper parts of the lower 5 m and Arca is abundant. Toward the 10 m depth frequent worm burrows are found. The predominantly medium to fine grain sand sediments are mainly rock and pelecypod mollusc fragments with lesser amounts of algae, worm tubes, and foraminifer fragments. Much of the shallow nearshore sand is derived from the disintegration of the surrounding sea cliffs, while sediments farther from shore and in deeper water are predominantly pelecypod shell fragments.