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

AUGUST 2005 FINAL REPORT
nutrient rich layer (Rodier and LeBorgne 1997). As such, standing stocks of phytoplankton biomass
(Radenac and Rodier 1996) and concentrations of chl a are low throughout the study area (less than 0.1
mg per cubic meter [m 3 ]) (NASA 1998; Figure 2-6). In regions in which overall nutrient concentrations are
low, the phytoplankton communities are dominated by small nanoplankton and picoplankton (Le Bouteiller
et al. 1992; Higgins and Mackey 2000). This is true for the study area, as phytoplankton communities in
the western Pacific are dominated by cyanobacteria (Synechococcus spp.), prochlorophytes,
haptophytes, and chlorophytes (Higgins and Mackey 2000). These cells are less than one micron (µm) in
size and comprise 60% of the total chl a measured (Le Bouteiller et al. 1992).
Two regions of enhanced chl a (up to 0.06 mg/m 3 ) can be identified in the study area off the southwest
coast of Guam and in the region surrounding the islands of Tinian and Saipan (Figure 2-6). These
regions of enhanced chl a persist through both the rainy and dry seasons, with higher chl a
concentrations occurring during the rainy season. Reasons for these regions of higher chl a levels are not
completely understood but may be a product of the island mass interacting with currents. This island
mass effect has been previously observed for other islands located in oligotrophic or stratified regions
including the Scilly Isles in the Celtic Sea (Simpson et al 1982), the Marquesas islands (Martinez and
Maamaatuaiahutapu 2004), and the islands of Hawai’i (Gilmartin and Revelante 1974) in which currents
passing by the islands or through channels in island chains created turbulence mixing bringing more
nutrient rich waters to the surface. This mixing may be capable of occurring along the Mariana island
chain creating isolated areas of increased production. In addition, an anticyclonic eddy is formed off the
southwestern coast of Guam in the same region as the increased chl a (Wolanski et al 2003; Figure 2-6).
It is likely that phytoplankton is becoming trapped within the eddy and is not advected to the west,
allowing for an accumulation of biomass and chl a in the region. The remainder of the study area
experiences chl a levels below 0.045 mg/m 3 throughout the year (NASA 1998; Figure 2-6). ENSO
appears to have little, if any, effect on primary production in the western tropical Pacific (Mackey et al
1997; Higgins and Mackey 2000).
2.5.1.2 Chemosynthesis
Another potentially significant source of biological productivity does not occur in the light of the surface,
but rather at great depths within the ocean. In some locations, including the Mariana Trough,
hydrothermal springs can support vast benthic communities (Hessler and Lonsdale 1991; Hashimoto et
al. 1995; Galkin 1997). Many organisms live in association with bacteria capable of deriving energy from
hydrogen sulfide that is dissolved in the hydrothermal vent water (Thurman 1997). Since these bacteria
are dependant upon the release of chemical energy, the mechanism responsible for this production is
called chemosynthesis. Little is known regarding the significance of bacterial productivity on the ocean
floor on a global scale. Hydrothermal indicators and vents have been found within the study area (Embley
et al. 2004) and locations are described in further detail in subsequent sections.
2.5.2 Secondary Production
Secondary production refers to the production (change in biomass) of organisms that consume primary
producers, i.e., the production of bacteria and animals through heterotrophic processes (Scavia 1988;
Strayer 1988). Detailed descriptions of protected species as consumers of primary production including
marine mammals and sea turtles, as well as species such as corals and seagrasses are found in later
sections of this chapter or later chapters of this MRA. In this section, marine zooplankton is discussed.
Marine zooplankton are aquatic organisms ranging in size from 20 µm to large shrimp (>2,000 µm)
(Parsons et al. 1984), and can be separated into two distinct categories based upon their dependence to
coastal proximity. Oceanic zooplankton includes organisms such as salps and copepods typically found
at a distance from the coast and over great depths in the open sea. Neritic zooplankton (found in waters
overlying the island shelves), include such species as fish and benthic invertebrate larvae, and are
usually only found short distances from the coast (Uchida 1983).
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