Deep-sea community dynamics
Co-investigators: Kurt Buck, Mario Tamburri, Tim Pennington, Kim Reisenbichler
With its varied underwater topography, sinuous depths, and complex of currents, Monterey Canyon encompasses a wide range of habitats. In surface waters above this mosaic of habitats, phytoplankton blooms occur episodically. The patchy availability of this staple food of the ocean, and the resulting fall-out of carbon-rich material to the seafloor, creates spatial and seasonal patterns of nutritional abundance and scarcity for midwater and seafloor animals. Ultimately, the interactions between ocean physics and biology govern the workings of marine communities. In this project MBARI researchers are studying how the physical environment shapes and regulates deep-sea ecosystems in Monterey Bay. There are five components to the program:
P2A Deep-sea benthic biology and ecologyInvestigations of seafloor ecology will concentrate on defining patterns and processes that influence three types of communities: soft-sediment communities, brachiopod assemblages living on the continental shelf, and animals attached to rock surfaces. Questions driving this research are: What is the distribution, throughout the water column and down to the seafloor, of carbon-rich material manufactured by photosynthesizing algae in surface waters? And, what other environmental factors regulate where and how benthic communities thrive?
Soft sediment layers much of the Monterey Canyon floor, and the fates of animal communities living on and in the sediment are directly linked to the widely ranging supply of organic carbon, i.e. food. One sampling strategy used in exploring their world is the collection of cores of sediments from many types of sites. In the laboratory biologists identify the worms, bacteria, and other organisms present at various depths in the cores and measure their respiration rates (oxygen uptake), which tells researchers their metabolic levels, that is, how much of the food they take in is converted to energy. Researchers are devising a respirometer that can be deployed by an ROV, for use at the seafloor. With the deeper diving capabilities of the ROV Tiburon, they look forward to exploring seafloor areas and collecting samples in depths below the oxygen minimum layer, where oxygen increases with depth, rather than the opposite condition.
Institute ecologists also will conduct experiments in which they observe the effects of artificially enhancing food supply at the seafloor with kelp. Other studies will focus on chemoreceptionthe marine equivalent of smellwhich is thought to be a crucial sensory ability for scavengers in the dark depths. Using the ROV to pump out different attractants (for example, water in which a dead fished has been soaked), researchers will be able to observe, via the ROVs video camera, animals that use chemical cues to home in on food sources.
The second community type, brachiopods, represents an ancient group of shelled animals, most varieties of which died off about 60 million years ago. The dense communities found on the floor of Monterey Bay are rare in nature, and little is known about their survival advantages. They may have high rates of reproduction or long lifespans, or possibly they lack predators. To begin to unravel the details of brachiopod life, MBARI researchers have set out "recruitment" trays of different kinds of substrates at sites on the seafloor. In 1998 they will collect the trays and, from the number of brachiopod larvae that have settled on the tray surfaces, they hope to identify factors influencing brachiopod habitat requirements. In other experiments with brachiopods raised in the laboratory, they will place trays of juvenile animals at diverse seafloor sites, where conditions such as food supply and currents vary. Subsequent comparisons of the brachiopods' survival and growth rates at the different sites will help biologists evaluate their survival needs.
The third target community, sessile animals on rocky surfaces, have been monitored in video surveys of fixed transects on the canyon floor for two to three years. In 1998 researchers will summarize their findings on animal population changes along the transects and the associated environmental conditions.
P2B Harbor seal acousticsAs common as the Pacific harbor seal (Phoca vitulina) is in Central California waters, little is known about the importance of vocalizing in their behavior patterns. In this specialized study, researchers are using an array of underwater microphones (hydrophones) to record the repertoire of underwater calls among a group of harbor seals near Hopkins Marine Station on Monterey Bay. The vocalizations are recorded on shore and sorted out from background noise by computer. Familiarized through underwater observations, the researcher is able to associate various behaviors with different vocalizations (made primarily by males) in analyzing the recordings. The findings have revealed that the quality and volume of seal sound emissions vary with season, tidal stage, and water temperature. Also, there are acoustic differences between the calls of individuals. For example, an older, bigger male makes distinctive noises when he is "attended" by subservient animals gathering around him. In 1998 the researchers will increase the number of hydrophones to 16, significantly enlarging the area of underwater sound monitoring. They will attempt to determine how external noise levels affect seal vocalizations and what significance male calls play in attracting females.
P2C Midwater ecologyFor nearly a decade MBARI's ROV-based midwater surveys have provided an unprecedented video chronicle of marine animals that inhabit the upper kilometer of Monterey Bay. This continuous series of observations has allowed researchers to compare animal distribution, abundance, and behavior from season to season and correlate them with fluctuations in the physical environment. In 1998 scientists will continue the time-series surveys and add another dimension: In night-time missions they will record and observe the massive migration of marine organisms from ocean depths toward the surface and backor, for some animals the reverse sequencewhich occurs between dusk and dawn. Presumably their vertical journeys are related to feeding and/or avoiding predators, but few details of this most regular of marine events are known, though it represents the largest animal migration on Earth. For comparative purposes the researchers will track the night-time migrations in ROV dives during each of the three distinct seasons in the bay.
The life details of larvaceanstadpole-like animals who spin "houses" of mucus, which are periodically discarded and sink to the seafloorare not yet well understood. In 1998 institute scientists will focus on four species of this numerous group in the bay, to pin down their seasonal abundance and depth ranges, and the number of houses in the water column. In laboratory studies researchers will inspect larvacean stomach contents to see what the animals feed on and examine their houses to determine the organic carbon content. They also expect to conduct a novel experiment in which a stream of particles, color-coded by size, will be injected into the water surrounding a larvacean for the purpose of observing which sizes of particles are filtered into the house. Findings from the larvacean studies will provide information on the quantity of an important element of midwater carbona large amount of which is thought to end up on the ocean floor.
Investigations on gelatinous siphonophores, which institute scientists have discovered to be prominent predators in bay waters, will shift to important groups such as Praya and Apolemia. Some of these colonial animals are longer than a blue whale, and researchers would like to understand their ecological significance in greater detail. They are devising a laboratory respirometer to measure siphonophores metabolic rates, that is, how much of the food they take in is converted to energy. The results in these experiments also will contribute to estimates of another endpoint for carbon.
Ctenophores (comb jellies) will also be observed in the water column and in the laboratory, and several new species will be described. Other areas of research will go forward as the bioluminescence camera becomes operational and as dives with the ROV Tiburon makes it possible to compare animal communities in much deeper waters with patterns already identified.
P2D Zooplankton dynamicsMicrozooplankton, floating animals too small to be seen with the naked eye, represent a key link in marine food chains. They feed on phytoplankton, the primary producers, and in turn are consumed by larger animals. In Monterey Bay surface and midwaters, institute scientists are documenting the diversity and abundance of microzooplankton, their total biomass, and how it changes with the seasons. A valuable tool in this research is the optical plankton counter (OPC), an ROV-mounted device that that counts and measures the shadows of particles passing through a very narrow light beam. These particles are simultaneously collected by nets, so researchers can later compare the net's zooplankton with the information recorded by the OPC. In laboratory studies, they also will strive to determine growth and feeding rates of some of the important zooplankton groups, such as small larvaceans, copepods (tiny crustaceans), and euphausiids (krill). From this, researchers can begin to estimate the impact zooplankton grazing has on phytoplankton and the amount of food available to larger carnivores. These studies complement other institute research on primary production, midwater communities, the carbon cycle, and biogeochemical processes.
P2E Research on Atmospheric Variability and Ecosystem Response in the Ross Sea, Antarctica (ROAVERRS)The primary goals of this four-year, NSF-funded project are to increase scientific understanding of connections between climate variability and processes in the upper waters of the southwestern Ross Sea. As an area of very high and seasonal phytoplankton production, the Ross Sea supports huge numbers of marine animals. Variability in winds and currents govern the distribution and extent of sea-ice cover each year, creating broad stretches of open water, known as polynyas. The sizes of the open-water areas in turn directly affect levels of primary productivity. ROAVERRS is addressing meteorological, oceanographic, and ecological questions. Findings at the Ross Sea will help in predictions of what might happen in polar settings as a result of human-induced climate change. MBARI researchers are participating in investigations of the diversity and abundance of seafloor life, including bacteria, beneath the polynyas. Instruments at four moorings collect data on currents, salinity, and other water properties, and samples from sediment traps at the moorings provide information on the kinds of organisms in surface waters. Researchers are also using box corers to collect intact samples of seafloor sediment. From these samples they can measure chlorophyll content, which reveals plankton productivity levels, and respiration, which indicates metabolic rates of resident organisms. During the 19971998 research season they also employed a "mudscud"a camera sled towed just above the seafloor to record video images of the larger animals. The video images and laboratory analyses that will be completed at MBARI in 1998 will contribute to a better understanding of the relationships between physical and biological processes in the Ross Sea.
Last updated: 20 March 2005