Leg 3 will use the ROV to
investigate the ecological and physiological adaptations of the Gulf’s
midwater fauna to three significant hydrographic features: the region of
oceanographic fronts at the mouth of the Gulf; the Gulf’s pronounced
oxygen minimum layer; and the hydrothermal plume above the Guaymas Basin
vents. This research will use the ROV’s video cameras, instruments, and
samplers to examine the composition of the midwater community over the
Mazatlan, Farallon, and Guaymas Basins, determine its vertical
distribution in the water column, and measure the characteristics of its
bioluminescent constituents. Scuba divers will collect open water
zooplankton in all three sampling regions. The leg 3 coordinator is Dr.
Bruce Robison from MBARI, and the Mexican collaborator is Rebeca Gasca
Serrano from ECOSUR-Chetumal.
goals are to investigate the influence of oxygen concentration, oceanic
fronts, and hydrothermal plumes on the composition, distribution, and
characteristics of the Gulf of California’s midwater fauna. Our approach
will be to make detailed measurements of midwater animals relative to
these parameters, and to compare them with our reference community in
water mass within the Gulf is a modified extension of the Eastern Tropical
Pacific water mass that has a pronounced oxygen minimum layer. Oxygen
concentrations of less than 0.2 ml/l encompass from 40 to 50% of the upper
kilometer of the water column. In contrast, the layer in Monterey Bay
covers only about 20% of the upper kilometer yet it acts as a lower
boundary for the vertical distribution of many midwater species and is a
defining parameter of the mesopelagic habitat. Based on our mesopelagic
time-series data in Monterey Bay, we expect that with increasing depth,
the number of gelatinous zooplankton in the Gulf will increase relative to
the number of micronekton (fishes and squid) because of the expanded
oxygen minimum layer.
mouth of the Gulf of California is a region of well-developed oceanic
fronts, which strongly affect the horizontal distribution of epipelagic
species. When these features are intersected by the diel vertical
migrations of mesopelagic animals, the resulting aggregation patterns
reflect the hydrographic preferences of the migratory species. Our studies
of fronts in Monterey Bay have shown distinct patterns of aggregation and
orientation. However, the ephemeral nature of the local fronts makes them
very difficult to study. The persistent fronts in the Gulf offer a very
promising venue for investigation. We will test the hypothesis that fronts
at the mouth of the Gulf help to define the composition of its midwater
fauna by creating spatially stable boundaries of prey abundance.
vents have strong biogeochemical effects on the adjacent benthic
environment, and they can also influence the overlying water column.
Previous work on zooplankton has suggested that vent plumes affect the
diversity and abundance of planktonic species above the vent fields. We
will investigate the water column around and within the
vent plumes in
Guaymas Basin to determine if they create atypical distribution patters of
gelatinous zooplankton and micronekton when compared with Monterey Bay and
with other regions of the Gulf. We will also look for physiological and
behavioral adaptations to plume chemistry as well as evidence of trophic
links to the vent community.
of bioluminescence will be an integral part of each of the regional
surveys. We will trigger bioluminescence during quantitative transects
with a low-light video camera, and determine the luminescent signatures of
key species in order to characterize the faunal composition in differing
hydrographic conditions and habitats. We will measure emission spectra and
the kinetics of light production at depth and in the lab. Given its
isolation, we expect to find novel bioluminescent systems in the Gulf’s
midwater fauna, particularly among the poorly known gelatinous species.
We will use the ROV’s main video camera to quantify the Gulf’s midwater fauna and to observe behavior patterns. A low-light video system will be employed to study bioluminescence in situ. Specimens for identification, genetic analyses, and laboratory-based physiology and behavior studies will be collected with the ROV’s suction sampler and detritus samplers. Scuba divers will make additional collections of zooplankton. In situ measurements of environmental parameters such as temperature and oxygen concentration will be made with the ROV’s CTDO instrument.