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

AUGUST 2005 FINAL REPORT
(Orote peninsula), Blue Hole (Orote peninsula), and Hap’s Reef (Agat Bay) (Birkeland 1997; Hanauer
2001). Vessel groundings (recreational and commercial vessels) are also a source of physical impacts on
reefs in the Marianas (Richmond and Davis 2002; Starmer et al. 2002).
Apra Harbor—Apra Harbor is a deep lagoon located at the western end of Guam (Paulay et al. 1997;
Figures 1-1, 2-7a, 2-7b, and 2-7c). Before 1944, the lagoon of Apra Harbor was delimited to the north by
Cabras Island, Luminao Reef, and Calalan Bank; to the east by the Piti area; and to the south by the
Orote Peninsula (Paulay et al. 1997). In 1944, the construction of the Glass Breakwater (limestone
boulders) on Calalan Bank altered the barrier reef system and restricted water exchange between Apra
Harbor and the open ocean. In addition, dredging of the Inner Apra Harbor (formerly a silty embayment of
the lagoon) and fill operations to develop Dry Dock Island, Polaris Point, and artificial shorelines of the
northeastern and southeastern boundaries altered the lagoon (Paulay et al. 1997).
Because of its depth (37 m; USGS 1978), the Apra Harbor lagoon is unique to the Marianas study area
(Paulay et al. 1997). It provides habitat for unique and diverse benthic fauna; for example, most of the
sponges and ascidians found in Apra Harbor; 48 species of sponges and 52 species of ascidians are
unique to Apra Harbor. Many of these species unique to Apra Harbor are indigenous. Some of the
species (1 sponge and 16 ascidians) were introduced via ship traffic. Indigenous species generally
occupy natural substrates while introduced and cryptogenic species (species whose origins cannot be
verified) generally occupy artificial substrata (e.g., wharf walls, concrete revetments, moorings, and
navigational buoys) (Paulay et al. 1997).
Corals are found in the Outer Apra Harbor where they thrive on shoals and fringing reefs (Paulay et al.
1997; DoD 1999; DoN 2003b; Paulay 2003; Smith personal communication). Coral cover in the outer
harbor is greater than what is depicted in Figure 2-7b. Figure 2-7b is based on the NCCOS/NOAA
(2005) delineation (Paulay personal communication; Smith personal communication); whereas, Paulay et
al. (1997) observed “well-developed reefs with some of the highest coral cover on Guam” within Apra
Harbor. Further, there are numerous deeper reef shoals in Apra Harbor that are missing from Figure 2-7a
(Paulay personal communication). The bottom of Apra Harbor is a complex environment that includes
substantially more reef than depicted in Figures 2-7b and 2-7c (Paulay personal communication).
Porites rus is the dominant coral species on the shoals in the center of the harbor outside Sasa Bay
(Western Shoals, Jade Shoals, and Middle Shoals) (Paulay et al. 1997). Other coral species associated
with these shoals include Porites lobata, P. annae, P. cylindrica, Millepora dichotoma, Acropora formosa,
and P. damicornis (Paulay et al. 1997). Coral cover on the shoals range from 50 to 90% (Paulay 2003;
NCCOS/NOAA 2005). There are mounds at deeper depths in the outer harbor. Paulay et al. (1997)
surveyed Sponge Mound located west-southwest of Western Shoals. They found that the top of the
mound (within 20 m of the sea surface) supported the highest diversity of sponges in all of Guam.
Along the southern boundary of Apra Harbor between Orote Point and Gabgab Beach including east and
west of ammunition pier or “Kilo Wharf”, coral cover on fringing reefs is high (DoD 1999; Smith 2004;
NCCOS/NOAA 2005). The areas to the east and west of Kilo Wharf support high coral cover (close to
100% cover) consisting mainly of P. rus (>90% of the cover) and other stony corals including P. lichen, P.
lobata, Platygyra pini, Leptoseris spp., Lobophyllia corymbosa, and Acanthastrea echinata (Smith 2004).
Reefs located further in the harbor (excluding the Inner Apra Harbor) have been severely impacted by
freshwater runoff, sedimentation, and polluted discharges (DoD 1999; Richmond and Davis 2002). Corals
in the Inner Apra Harbor (including P. rus and P. damicornis) encrust sheet pilings, rocks, and concrete
debris (DoD 1999).
There are no corals on the seafloor of the Inner Apra Harbor or the inner portion of the Entrance Channel
to the Inner Apra Harbor (Smith personal communication). The closest area to the Inner Apra Harbor
where corals occur on the seafloor is in the outer reaches of the Entrance Channel of the Inner Apra
Harbor. In this area corals consist of P. rus and P. cylindrica (Smith personal communication). Corals are
also found on sheet piles in the Entrance Channel of the Inner Apra Harbor and the outer reaches of the
Inner Apra Harbor.
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