|
|
|||||
|
Sancutary Program Accomplishments Open Ocean & Deep Water Systems Endangered & Threatened Species
|
|
The Year of the Ocean inaugurated an era of expanding research cooperation in the Monterey Bay National Marine Sanctuary. From partnerships forged between regional institutions to international collaborations, interdisciplinary investigations revealed details of the complex physical, chemical, and biological forces at work in the Sanctuary. Researchers from the Naval Postgraduate School and Stennis Space Center used computer models to simulate water circulation in the Monterey Bay region and Monterey Canyon, which features some of the steepest undersea topography anywhere. Other scientists at the University of California Santa Cruz (UCSC) and the U.S. Geological Survey investigated the role of topography on the distribution and transport of sediments in the central region of the Sanctuary.
Researchers from Moss Landing Marine Laboratories (MLML) and the Monterey Bay Aquarium Research Institute (MBARI)measured iron concentrations in Sanctuary waters during March of 1997 and 1998. Conditions in 1997 favored coastal upwelling: strong winds from the northwest pushed surface waters offshore and allowed deeper nutrient-rich water to upwell. The scientists measured high coastal concentra-tions of nutrients, iron, and chlorophyll from plankton blooms. However, early 1998 - the peak of the El Niño event - revealed very different conditions. Winds favorable to upwelling were rare; ocean surface waters were nearly 3° C warmer than in 1997; and very low levels of iron, nutrients, and chlorophyll were measured near the coast. The source of iron appears not to be coastal runoff, but rather, dissolved iron resuspended from sediments on the continental shelf and then upwelled into surface waters. This raises the possibility that primary production in water that upwells over narrow shelf regions (or further offshore at the shelf break and along jets and filaments) may be iron limited. Researchers at UCSC reported that primary production in water from the Point Sur region, where the shelf is particularly narrow, is iron limited. During late 1997 and in 1998 when upwelling was greatly reduced, the extremely high ocean temperatures and extremely low levels of nutrients, chlorophyll, and primary production were the greatest anomalies ever recorded in MBARI's ten-year records on coastal water properties. Far from Monterey Bay, along the equator, water temperatures during mid-1998 changed from abnormally warm to abnormally cold. Researchers expect these conditions to spread to the Central California coast beginning in 1999, resulting in the resumption of periodic high levels of primary production in the Sanctuary's coastal waters. Associated with this high productivity we may see the recovery of typical fisheries of the region and the replenishment of marine food webs on which the fishes and many marine mammals depend. Also, there are some indications that the climate oscillation is shifting the Pacific from the warm phase that has prevailed since 1976 to a cold phase, which would enhance the return to more normal oceanographic conditions in Central California's coastal waters. Harmful Algal Bloom The year marked the first recorded episode of marine mammal illness and mortality strongly linked to a documented bloom of Pseudo-nitzschia australis and associated toxic poisoning by domoic acid. During May 1998 a bloom of P. australis, a pennate diatom that produces domoic acid, occurred in the waters of the Sanctuary. Researchers detected the organism - using DNA-targeted molecular "probes" developed at MBARI - and tracked the bloom in near real-time as it spread. The toxic diatoms were found in plankton and in the stomachs of anchovies collected and dissected at the time of the bloom. Coincident with the toxic algal bloom, sea lions suffered from a neurological disorder, now attributed to domoic-acid poisoning. Marine mammal rescue agencies reported treating seventy stranded sea lions, forty-seven of which died. This may represent only a fraction of affected animals, as the victims were collected only from accessible beaches; large stretches of coastline were unmonitored and not all sick animals land on the beaches. Following the spread of the bloom in Monterey Bay, the National Marine Fisheries Service conducted surveys from Half Moon Bay south to Point Conception and detected more harmful organisms related to P. australis. In October a similar algal bloom occurred further offshore, and again a number of sea lions died from domoic-acid poisoning. Midwater Explorations and Discoveries
MBARI's investigations have also revealed new information about the abundance of the siphonophore Nanomia bijuga, the most commonly observed of all the gelatinous animals in the midwaters of Monterey Bay. This fragile animal, ranging up to about one-third of a meter in length, turns out to be one of the Bay's most important predators, feeding on krill and other zooplankton. Researchers determined that abundance of N. bijuga is cyclical, regularly occurring about three months after the onset of upwelling and the consequent surge in primary production. Deep-Sea Experiments on Clathrate "Ice" Formation The Sanctuary was also the setting for novel field experiments on the behavior of carbon dioxide (CO2) in the deep ocean. During 1998 ROV-based experiments were conducted in part to evaluate the potential for eventual disposing of fossil-fuel CO2 in the ocean as a way of curtailing its increase in the atmosphere. MBARI chemists injected several liters of liquid CO2 into a glass laboratory beaker on the Bay seafloor at a depth of 3,650 meters. At this depth liquid CO2 becomes denser than seawater, so the researchers expected to see it form a stable pond with a thin "skin" separating it from the seawater, like a layer of ice on a winter lake. Instead, to the surprise of the scientists, who observed the experiment via the ROV's video camera, the CO2 appeared to expand in volume, then overflowed the container in huge droplets that bounced to the seafloor and were carried away by the current. In fact the reaction between liquid CO2 and water had produced large volumes of clathrate "ice," which sank to the bottom of the beaker and pushed the remaining liquid over the top. The chemists are working with biologists to conduct further experiments to determine whether the presence of CO2 in this form has any measurable effects on deep-sea animals. New Perspectives on Monterey Bay Seismicity Researchers from MBARI, UCSC, the University of California Berkeley, Institut de Physique du Globe in Paris, and other institutions continued the first-ever ROV deployments of seismic instruments at five sites in various parts of the Monterey Bay seafloor. During 1998, the second year of this multi-year study, the sensitive, state-of-the-art sensors measured seismic waves for hundreds of earthquakes, both large and small, including many events not recorded by the permanent onshore seismic network. To complement the seafloor array, other instruments loaned to UCSC by the Incorporated Research Institutes for Seismology were installed at coastal sites around the Bay. The researchers used data from all these stations to locate seismic events more accurately than was previously possible from land measurements alone. These results have helped to derive a new model for the travel times of seismic waves beneath the Central California seafloor, which has led to a better understanding of the structure of the offshore faults and their associated earthquake mechanisms. Using this information and historic seismic data, the collaborators reanalyzed earthquakes from the past seventy-two years, uncovering strong evidence that all major earthquake activity in the Bay occurs along the San Gregorio and Monterey Bay faults. Discoveries on the Deep Seafloor In spring 1998 surveys along part of the continental margin in Central California's offshore waters were completed using a state-of-the-art multibeam sonar system. In sonar images from the surveys, MBARI scientists saw what looked like areas of mineral deposits formed on the seafloor, possibly due to the seepage of sulfide- and methane-rich fluids. Using an ROV to investigate, researchers discovered at 2,310 m an underwater spring, or cold seep, they named "Tubeworm Slump." Like the other cold seeps in Monterey Bay, it supports an oasis of life in total darkness; in this location the prominent residents are vestimentiferan worms, cousins to the tubeworms of hydrothermal vents. Like hydrothermal-vent residents, most cold seep animals depend on chemosynthesis - the conversion of fluid chemicals into nutrients - rather than photosynthesis, which requires sunlight. Tubeworms had previously been found at only one other site in the canyon, and with lengths of up to one-half meter, Tubeworm Slump's worms are significantly larger than those previously observed. This was also the first discovery in the Bay of barite deposits. The researchers suspect that fluids rich in barium from the underlying, organic-rich Monterey Formation are flushed through the sediments, where they mix with seawater containing sulfate and then precipitate out as barite at the seafloor. Noreen Parks and Judith
Connor |
|||
The
1997-98 El Niño event, now recognized as the
strongest of the century, probably affected our
Sanctuary ecosystems more than any other single
natural phenomenon. Studies of that event
contributed to our understanding of the
biogeochemical effects of El Niño in coastal
ecosystems. The California Current System, which
dominates the circulation in the Sanctuary,
normally conveys upwelled nutrients such as
nitrate, phosphate, and silicate to the sunlit sea
surface from late winter to early spring. At the
surface, the nutrients support phytoplankton
growth, also called primary production because it
is the primary basis of most ocean food webs. UCSC
scientists demonstrated that iron is key to this
primary productivity, by adding iron to water
samples from the California Current and measuring
the resulting increase in phytoplankton
production.
Researchers
continued extensive midwater video surveys using
MBARI's remotely-operated vehicles (ROVs) during
1998. These systematic studies, conducted over the
past five years, have deepened scientific
understanding of both individual species and the
mesopelagic community of Monterey Bay. MBARI's
regular research missions in Sanctuary waters have
provided opportunities to observe species and
animal behaviors new to science. During the last
year researchers discovered a half dozen
undescribed varieties of larvaceans. These
tadpole-like animals secrete filters of mucous that
function to strain larger particles from their
watery surroundings. A scientific description was
published of Mesochordaeus erythrocephalus, the
"red-headed" larvacean, which produces filtering
structures up to the size of a basketball and
typically populates waters 200-750 m deep. Midwater
scientists also found an unusual new doliolid (a
tunicate) and a pair of medusae, likewise suspected
to be new to science.
Using
ROVs to observe residents of the dimly-lit
midwaters over hundreds of hours has allowed
ecologists unprecedented glimpses into their
characteristic behaviors. One such behavior,
witnessed in a variety of mesopelagic animals -
including certain marine worms, eelpout fishes, and
"houseless" larvaceans - is a curling of their
elongate bodies into a circular shape when
threatened. MBARI ecologists hypothesize that this
action represents protective mimicry, the imitation
of an unpalatable animal for the sake of escaping
predation. By assuming a curled profile, elongate
animals resemble round gelatinous animals such as
medusae, comb jellies, and salps, which make poor
meals for active predators.