Marine Resources Assessment for the Marianas Operating ... - SPREP

AUGUST 2005 FINAL REPORT
outer slope rocks, lagoons of barrier reefs, trenches of rocks at the reef-flat edge and beach rocks,
reef flats, and patch reefs (Sorokin 1995). The prosobranch (Trochus niloticus) occupies a welldefined
habitat from the intertidal and shallow subtidal zones on the seaward margin of coral reefs at
depths ranging from 0 to 24 m (Nash 1993; Paulay personal communication). Nudibranchs or sea
slugs are predatory opisthobranchs inhabiting a variety of substrates including the surface of soft
corals (alcyonaceans and gorgonaceans) and sponges (Colin and Arneson 1995; Paulay personal
communication). Sea slugs prey on diverse taxa including soft corals and sponges (Colin and
Arneson 1995; Paulay personal communication).
Life History—Sea snails generally have separate sexes, whereas sea slugs are unisexual.
Fertilization may be external or internal in sea snails. Sea snail species that undergo internal
fertilization produce eggs that may be enclosed in protective layers of gelatinous mucus or corneous
capsules. The majority of sea slugs deposit eggs in ribbon-like clusters. In sea snail species, embryos
hatch as free-swimming planktonic larvae or as crawling young (Poutiers 1998a).
♦ Bivalves (Oysters and Clams)
Status—Bivalves, consisting of oysters and clams, are managed in Micronesia as part of the PHCRT
by the WPRFMC (2001). At least 339 bivalve species occur in CNMI and Guam (Paulay 2003b) and
have EFH designated within the boundaries of the study area (WPRFMC 2001; NMFS 2004c). Both
the commercially harvested black-lipped pearl oyster (Pinctada margaritifera) and giant clams
(Tridacnidae) occur on Guam (Paulay 2003a). About 15 bivalve species (three of which are tridacnid
clams) are harvested on Guam (Hensley and Sherwood 1993) and at least one of the giant clams
(Hippopus hippopus) was extirpated (Paulay 2003b).
Distribution—Oysters and clams are found in all tropical and temperate seas of the world except for
the giant clams, which are confined to the Indo-West Pacific region (Briggs 1974). The overall
biodiversity of the malacological fauna is probably the greatest in the western central Pacific (Poutiers
1998b).
Habitat Preferences—Bivalves comprise 10% to 30% of the coral reef malacofauna utilizing rocky
hard substrates for sessile and boring species and soft-bottom areas for vagile species (Sorokin
1995). Sessile bivalves inhabit reef areas such as rocky surfaces of reef-flats, dead coral heads,
patch reefs, walls of trenches and channels, and on coarse sands and rubble substrates on flat and
littoral areas (Sorokin 1995). Boring bivalves are extremely widespread in areas of the rocky flat and
in areas of profuse coral growth hidden in coral colonies (Sorokin 1995). The sandy bottom of
channels crossing the reef-flat and its outer slopes as well as on silty coral sands in the lagoons of
barrier reefs are inhabited mainly by vagile bivalves (Sorokin 1995). The black-lipped pearl oyster
occurs in lagoons, bays, and sheltered reef areas to around 40 m depth, but is most abundant just
below the low-water (Sims 1993). Giant clams use various habitats including high- or low-islands,
sandy atoll lagoon floors, fringing reefs, or exposed intertidal areas to depths less than 40 m (Munro
1993).
Life History—In the majority of bivalves, sexes are separate. Fertilization is external, giving rise to
free-swimming larvae followed by a metamorphosis leading to a benthonic mode of life (Poutiers
1998b). Some species may be unisexual. If planktonic, the larval stage is reduced or totally absent,
young hatch directly as benthic organisms (Poutiers 1998b).
♦ Cephalopods (Nautiluses, Cuttlefishes, Squids, and Octopuses)
Status—Cephalopods are managed in Micronesia as part of PHCRT by the WPRFMC (2001).
Twenty-four species including one cuttlefish, one squid, and 22 octopuses have been reported from
the CNMI and Guam (Ward 2003) and have EFH designated within the boundaries of the study area
(WPRFMC 2001; NMFS 2004c). Currently, no data are available to determine if cephalopods of the
PHCRT are approaching an overfished situation (NMFS 2004a). Cephalopods are of considerable
ecological and commercial fisheries importance in the Western Central Pacific where the squid,
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