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

AUGUST 2005 FINAL REPORT
area once supported a large aggregation of Bumphead parrotfish (Bulbometopon muricatum) (Davis
personal communication).
Paulay et al. (2001) defined the Orote reef slope as a depth zone between the Orote cliff reef and the
Orote drop-off. This is the largest macrohabitat of the Orote peninsula ERA. The pavement of Orote reef
slope has a gentle slope, is barren, and supports a low diversity biota including clumped macroalgae,
corals (Montipora foveolata, Leptastrea, Astreopora, Pocillopora), and the large boring sponge
Spirastrella vagabunda. Yet, there are three microhabitats that support unusual biota: boulder fields,
rubble fields, and the Blue Hole.
Boulders detached from and clustered along cliffs provide habitat for highly diverse reef communities.
Individual boulders are up to 15 m in diameter. Large clusters of boulders are located off Neye Island,
Apuntua Point, and Barracuda Rock and support higher coral diversity, higher fish diversity and biomass
compared to typical locations of Guam, and many soft corals rarely observed on Guam. In this
microhabitat, Paulay et al. (2001) found the largest population of Plerogyra sinuosa (bubble coral) and the
only sighting of Madracis kirbyi known on Guam.
The fore reef pavement on the western half of the Orote peninsula is covered with large areas of rubble
(10 to 100 cm in size). The rubble fields contain diverse cryptofauna including a new species of lobster
(Paraxiopsis sp.), a new species of a swimming crab (Carupa sp.), a rare crab (Aethra edentata), the only
observation of a spider crab (Acheus lacertosus), and many species of pagurid hermit crabs.
The other microhabitat on the reef slope is the Blue Hole, a cave formed during low sea stands. The
bottom of the cave is 91 m deep with a collapsed roof at 18 m and a “window” at 37 m. The Blue Hole is
the most popular dive spot on Guam (Hanauer 2001). This cave contains sessile species and fishes
known only to this location on Guam. In the 1970s, the Blue Hole contained many more gorgonians and
much more macrofauna than it does today. Since then, recreational divers have taken much of the
gorgonians as souvenirs (Birkeland 1997). The cave contains the gorgonians Viminella sp., Keroides sp.,
Heliania spiniescens, and Briareum excavatum which have only been observed around the lip of the cave
and on the Orote Drop Off (Paulay et al. 2001). Other significant observations include the undescribed
minute false oyster (Dimyella sp.) and an undescribed hard coral (Leptoseris sp.).
The Orote dropoff on the southwestern margin of the Orote peninsula is a steep vertical face that begins
at 25 to 35 m and extends down to >100 m. This region of the reef is exposed to strong currents, and
large gorgonians and black corals can be found on the reef face (Annella mollis, Annella reticulata,
Astrogorgia sp., Subergorgia suberosa, Antipathes sp., and Cirripathes sp.). The rare encrusting
gorgonian B. excavatum and the hard coral Favia rotumana inhabit the drop off. Paulay et al. (2001) has
also identified an undescribed sponge Callyspongia aff. carens.
Agat Bay—Agat Bay is located at the eastern end of Guam (Figures 1-1, 2-7a, 2-7b, and 2-7c). Paulay et
al. (2001) recently surveyed coral reefs from Orote Point to the northern half of Agat Bay. This survey
contains information on the reefs specific to the MRA study area, i.e., the coastal area contained between
Togcha Beach and Apuntua Point (Agat Bay area).
The Agat Bay shoreline is characterized by sandy beaches and small limestone outcrops. The sand on
Agat Bay consists of dredge spoils from the Inner Apra Harbor deposited on the shore here following
World War II (WWII). As a result, the sand contains abundant shells of Timoclea sp., a bivalve specific to
Apra Harbor.
There is a silty sand plain found in the middle of Agat Bay at water depths ranging from 5 to 30 m (Paulay
et al 2001; NCCOS/NOAA 2005). Sand channels and reef substrate interdigitate with patch reefs and reef
substrate rising more than 2 m above the sand channels. At 30 m, few patch reefs are found on the
dominant sand cover. The epifauna on the sand substrate has a low diversity.
The reef flat from Tipalao Bay through Dadi Beach contains silty intertidal and nearshore areas covered
with macroalgae and some seagrass. Paulay et al. (2001) found that the silt cover and macroalgae and
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