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

AUGUST 2005 FINAL REPORT
during heavy rainfall) impacting coral cover and recruitment in Guam and the CNMI and is the main
source of human-induced impacts on coral communities and reefs in the study area (Richmond 1994;
Birkeland 1997; Houk 2001; Richmond and Davis 2002; Starmer et al. 2002; Paulay 2003; Abraham et al.
2004). Sedimentation affects both coral cover and diversity. Sedimentation-impacted sites can further be
degraded by the compounding effects of overfishing of herbivorous fishes and starfish (Houk 2001;
Abraham et al. 2004). Polluted runoff (nutrients from sewage, fertilizers, agriculture, and animal waste),
sedimentation, and overfishing have impacted reefs off the most urbanized areas.
2.7.2.2 Coral Communities and Reefs of Guam
Guam is almost entirely surrounded by fringing reefs, is entirely surrounded by fore reefs, and has barrier
reefs at Apra Harbor (Luminao Barrier Reef at the western end of Guam) and Cocos Lagoon (southern
end of Guam) (Eldredge 1983; Paulay personal communication). The depiction of benthic habitats
(including reefs) of Guam presented in Figures 2-7a, 2-7b, and 2-7c is approximate and would benefit
from higher resolution mapping and site-specific input on reef structure and coral coverage from local
experts.
Reefs in the southern half of Guam have always been subject to more naturally-occurring sedimentation
than in the northern half of the island because of the difference of erosional products (volcanic in the
south versus limestone in the north) (Richmond and Davis 2002). Coral cover and diversity are currently
higher on reefs located along the northeastern coast of Guam (Richmond and Davis 2002). Historical
surveys suggest that diversity was actually higher in the south before anthropogenic impacts severely
impacted those reefs (Paulay personal communication). The NCCOS/NOAA (2005) survey of shallowwater
benthic habitats of Guam determined that the overall coral cover around Guam ranged from 10 to
90% (Figure 2-7b). Most the reefs surrounding Guam have a coral cover ranging 10 and 50%.
NCCOS/NOAA (2005) delineates four of the areas of Guam where coral cover ranges from 50 to 90%: an
area off Mergagan Point on the northeastern end of the island, an area off Pagat Point on the eastern
side of the island, an area immediately south of Togacha Bay also on the eastern side of the island, and
Apra Harbor.
The fringing reef is interrupted in several locations along the coastline by bays, channels, and areas
where the insular shelf is colonized by seagrass (Figures 2-7a, 2-7b, and 2-7c). Along the northern coast
of the island between Achae Point and the Ritidian Channel, the fringing reef and fore reef area
transitions from a relatively wide swath of coral (less than 250 m wide) to an area populated by turf algae
(200 to 500 m wide). Similarly, turf algae and macroalgae cover the insular shelf (up to a 500 m width)
from Pati Point (northeastern tip of the island) to an area south of Mati Point on the eastern side of the
island. Turf algae and macroalgae also cover the insular shelf from Fadian to Lates, Talofofo Caves to
Paulicuc Bay, north of Toguan Bay to south of Cetti Bay, Apuntua Point to Orote Point, Amantes Point to
NCS Beach, and from Ague Point to Haputo Beach (NCCOS/NOAA 2005). Small coral-populated reef
areas (individual areas less than 1 ha occur within large stretches of turf algae and macroalgae cover off
of Jones Beach near Camp Dealy (eastern side of the island), at Asanite Bay (south of Jones Beach),
and in two areas off Togcha on the western end of the island south of Agat Bay (NCCOS/NOAA 2005).
Natural and human-induced disturbances affecting the reefs of Guam have caused a significant decline of
coral cover and recruitment since the 1960s (Richmond 1994). Coral cover on many fore reef slopes on
Guam has decreased from over 50% to less than 25% (Birkeland 1997). There are, however, several
reefs of Guam where coral cover remains high, including Apra Harbor, Agat Bay, Orote ERA, and Haputo
ERA.
Hagåtña and Tumon Bays are centers for tourism and incur a high level of tourism-related impacts on
water quality and marine resources. Polluted runoff has affected the inner areas of Hagåtña, Tumon, and
Piti Bays. Marine recreational sports (including SCUBA diving, snorkeling, fishing, underwater walking
tours, and jet skis) can cause physical damages on reefs (Richmond and Davis 2002; Starmer et al.
2002; Abraham et al. 2004). Anchor damage on reefs occurs at popular dive and fishing sites (Abraham
et al. 2004). It is estimated that over half a million SCUBA dives are done each year on Guam and
concentrated in five main dive sites: Tokai Maru (Apra Harbor), the Cormoran (Apra Harbor), The Crevice
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