2.3.1 The NWHI are influenced by a wide range
of oceanographic conditions that vary on spatial and temporal scales.
Ocean currents, waves, temperatures, nutrients, and other oceanographic
parameters and conditions influence ecosystem composition, structure,
and function in the NWHI. Ocean currents play an important role in
the dispersal and recruitment of marine life in the NWHI. Surface
currents are highly variable in both speed and direction (Firing et
al. 2004), with long-term average surface flow from east to
west in response to the prevailing northeast trade wind conditions.
The highly variable nature of the surface currents is due in large
part to eddies created by local island effects on large-scale circulation.
Marine debris accumulation in shallow water areas of the NWHI also
is influenced by large and small-scale ocean circulation patterns.
These eddies might also result in pollution from vessels accumulating
in the coral thus damaging resources.
2.3.2 Ocean waves also play an important role
in the NWHI. The distribution of corals and other shallow water organisms
is influenced by the exposure to waves. The size and strength of ocean
wave events have annual, inter-annual, and decadal time scales. Annual
extra-tropical storms (storms that originate outside the tropical
latitudes) create high energy large wave events from five to over
ten meters which approach largely from the northwest during the winter.
During this time, the average wave power increases substantially and
extreme wave events of over ten meters pound the shallow water coral
communities, thus posing a hazard to the coral reef communities and
to navigation. Decadal variability in wave power is possibly related
to PDO events (Manutau et al. 1997). The number of extreme
wave events has been recorded during the periods from 1985 to 1989
and from 1998 to 2002, and anomalously low numbers of extreme wave
events occurred during the early 1980s and during the period from
1990 to 1996 (Friedlander et al. 2005).