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

AUGUST 2005 FINAL REPORT
Corals also occur on reefs off the tip of the Orote Peninsula (Paulay et al. 2001). Paulay et al. (2001)
described two macrohabitats in this area, the Orote Point reef slope and the Orote Point fringing reef. The
Orote Point reef slope is found at the tip of the peninsula and extends from Spanish Steps to the western
end of Orote Island. This area supports higher coral and fish diversity and higher fish biomass compared
to other locations of Guam. The submerged terrace slopes gently down to a water depth of 12 to 15 m
followed by a steep fore reef slope that plunges down to 30+ m. The area of reef that is contiguous with
Apra Harbor is populated by the biota commonly found in the harbor (e.g., P. rus and sponges). The P.
rus dominated reef is limited to an area immediately adjacent to the harbor. Along the northern end of the
Orote Peninsula west from the harbor, the coral community is more diverse. Paulay et al. (2001) observed
19 species of corals in this area and noted that this was the most diverse coral area of the coastline from
Spanish Steps to Agat Bay. The diversity of fishes was also greatest in this area with 53 species
observed. In addition, in this diverse area, Paulay et al. (2001) may have found a new Acropora species
record for Guam. The coral species appeared to be similar to Acropora nasuta.
The Orote Point fringing reef is located between the tip of the Orote Peninsula and Orote Island. It has a
reef front facing the southern coast of the Orote Peninsula and another facing the southwestern end of
Apra Harbor (Paulay et al. 2001) intrinsically providing a connection between the north and south sides of
the peninsula. Karstic shores flank the other two sides of the reef. Paulay et al. (2001) found a “strong
gradient in species composition” on this reef. The middle and northern parts of the reef supported coral
species that are typical of Apra Harbor (including P. rus, P. cylindrica, Pavona venosa, Pavona divaricata,
Psammocora contigua, P. damicornis). Corals found on the southern end of the reef were characteristic
of an oceanic, reef front community with corals including A. digitifera, Galaxea fascicularis, and an
Acropora species similar to Acropora valida.
On the northern side of the harbor, the fringing reefs on either side of the Glass Breakwater, Luminao
Barrier Reef, the fore reef off Cabras Island, and the fore reef of Piti Reef have 10 to 50% coral cover
(NCCOS/NOAA 2005). Also, a narrow strip of seagrass borders the entire fore reef from the end of the
breakwater to Piti Reef (NCCOS/NOAA 2005). In addition to this data from the National Centers for
Coastal Ocean Science (NCCOS/NOAA 2005), Randall et al. (1982) surveyed three reef areas, the
Luminao Barrier Reef on the seaward side of Glass Breakwater, the fringing reef on the seaward side of
Cabras Island, and the Piti Reef (fringing reef east of Cabras Island). Randall et al. (1982) found that the
reef flat and the reef front were areas of the reefs where corals were concentrated. However, considering
the recent and severe impacts of corallivorous predators and storms on the corals of Guam, the surveys
of 1980 and 1981 are probably not representative of current reef conditions (coral diversity and cover)
(Birkeland 1997; Abraham et al. 2004). There is no new information to describe these reef areas;
therefore the following description from Randall et al. (1982) is discussed. Luminao Barrier Reef is
approximately 50 to 200 m long and less than 1 to 2 m deep. Coral cover on the reef flat ranged from 7 to
31% (Randall et al. 1982). Corals making up most of the cover were of the following genera: Porites,
Pocillopora, Leptastrea, Montipora, Millepora, Acropora, Psammocora, Leptoria, and Goniastrea. Coral
cover on the reef front slope ranged from 18 to 25% and was composed of the coral genera Pocillopora,
Acropora, Goniastrea, and Millepora. The reef off Cabras Island consisted of a narrow and wave exposed
reef pavement (0.6 m deep), a reef margin, and a reef slope. There were very few corals and coral cover
on the reef pavement and reef margin was minute (0 to 1.1% coral cover) with coral cover on the reef
pavement less than 0.3%. Coral genera on the reef pavement included Porites and Pocillopora. On the
reef margin, there were more coral genera including Goniastrea, Pocillopora, Acropora, Porites, and
Favites. Coral cover on the reef front (5 m water depth) ranged from 10 to 22% and was mostly
composed of Pocillopora, Goniastrea, Acropora, Millepora, and Montipora. The Piti Reef was located
seaward of the Tepungan Channel along the Piti shoreline. There were five physiographic zones on the
Piti Reef: the inner reef moat (approximately 50 m wide and 1 m deep), the outer reef moat
(approximately 150 m wide and 1.3 m deep), the outer reef flat pavement (approximately 60 m wide and
less than 1 m deep), the reef margin (approximately 50 m wide and exposed at low tide), and the reef
front slope (approximately 50 m wide and 5 m deep). Coral cover at Piti Reef ranged from 0.2 to 20% with
coral cover greatest on the outer reef flat (20%) and the reef margin (12%). The exposed outer reef flat
and the inner reef flat had the least amount of coral cover (0.2% and 0.4%, respectively). Corals on the
outer reef flat were of the genera Porites, Acropora, Pocillopora, and Millepora. On the reef margin and
reef front, the predominant coral genera were Pocillopora, Acropora, and Montipora. The little coral cover
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