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.