Motivation
Questions
Approach
Field Sites
Findings
Data
PISCO’s physical oceanographic research focuses on how physical processes in the marine environment, such as ocean currents, waves and winds, affect ecological dynamics in the coastal zone. We are particularly interested in the nearshore region, also known as the inner-shelf (the area approximately 5-10 km from shore), which is home to most of the communities we study.
The physical environment has both immediate and long-term effects on many organisms and populations. For example, many species grow faster in warmer waters, waves from winter storms can rip-up entire kelp beds, and fish can be swept out of their feeding areas by currents. These are some examples of immediate physical effects at the level of the organism. But the ocean's physical processes also have more subtle and long-term effects on entire marine populations.
Most shallow-water, rocky-shore organisms have open-water larvae that disperse well beyond their near-shore birthing-areas, but later return to settle into adult habitats. A principal hypothesis of the PISCO project is that ocean temperatures and coastal currents control larval transport, settlement, and retention, as well as species range boundaries. These influences may eventually dictate the fate of entire populations. We are particularly interested in the role of coastal circulation processes, which differ greatly along the coast.
PISCO's physical oceanography program is designed to answer the following two fundamental questions:
- What are the nearshore (or inner-shelf) oceanographic patterns and processes along the U.S. West Coast?
- How do inner-shelf oceanographic conditions affect the dynamics of shallow subtidal and rocky intertidal communities?
For example, the intensity of large surface waves created by severe winter storms may dictate the geographic extent of kelp forests. Or a predominant direction in ocean currents may limit the extent of a fish population by inhibiting larval transport in one direction, and enhancing it in another.
All of the PISCO units use similar methods to observe the physical processes believed to be important to nearshore communities, larval transport and settlement. These processes include winds, coastal currents, eddies, water mass variability, and internal waves. We use moored instruments, small-boat operations and land-based high frequency radars (called CODARs) to study nearshore physical oceanography.
We have dozens of semi-permanent stations (see maps) along the inner shelf of the U.S. West Coast, where we measure ocean temperatures and other physical variables, such as ocean currents. Our physical oceanography stations are clustered about the OSU, UCSC and UCSB campuses, i.e., along the Oregon coast, in Monterey Bay and the central California region and in the Channel Islands and the Southern California Bight, respectively.
Typically located in water depths of 10-20 meters, the stations consist of a mooring and several 
temperature sensors, or thermistors (see photo at left). The stations are often supplemented with other instruments, such as bottom-mounted ADCPs (Acoustic Doppler Current Profilers), which can measure water velocities throughout the water column (see photo at right).
Most of our moorings have a similar design. A subsurface float is moored to the bottom. This float's buoyancy provides enough tension on the mooring line to keep it vertical even is strong currents. Thermistors are then hung on the taught line, measuring temperatures at at least three points in the vertical. Many moorings also have a surface float that, when combined with a thermistor, allows us to measure the temperature just below the water's surface. ADCPs are mounted to the bottom near the mooring using hard or soft-bottom mounts, depending on the bottom-type. The moorings are serviced approximately every three-months, when the instruments are swapped with replacements. Most instruments are programmed to a sampling-frequency of two minutes, which allows us to resolve high-frequency internal waves propagating in the thermocline. The ADCPs have a vertical resolution of one meter.
Our moored observations are supplemented by vertical profiles of water properties (temperature, salinity, and density) taken during small-boat surveys with CTDs (Conductivity, Temperature, Depth profilers).
PISCO has dozens of physical oceanographic stations spaced along the inner shelf of the US West Coast. Use the clickable map at right to see closer views of most of our sites. For more detailed information on sites and available data click here to be taken to our physical oceanographic data search page.
We are currently developing the data-access portion of our Webpage. If you are a scientific user and are having any trouble locating or downloading the data you need, please contact Patrick Drake at drake@biology.ucsc.edu.
In 2004, PISCO partnered with the National Marine Sanctuary Program to expand our physical oceanographic research and monitoring. We now have many partnership PISCO/NMSP stations. Data from these stations are also available online though a NOAA Website at the following address, http://portal.ncddc.noaa.gov/wco/.
PISCO has developed an extensive research program to characterize patterns of the coastal ocean. From north to south, there are several major oceanographic discontinuities along the California Current System. In Oregon, efforts have initially focused on the discontinuity represented by the Heceta-Stonewall Banks, which force the California Current offshore and generate a large eddy over these banks. We suspect that this discontinuity is linked to differences observed in rocky intertidal communities along the central coast of Oregon. As a result, we have focused our efforts on this region and the region to the north where the California Current is closer to shore and exhibits a simpler north-south flow. In California, Point Conception is a major biogeographic boundary. Traditionally oceanographers have assumed that the warmer waters of the Santa Barbara Channel to the south and colder waters of the Santa Maria Basin to the north provide suitable habitats for different species. PISCO is investigating whether coastal currents control larval transport and retention, thereby determining settlement locations and species range boundaries.
Distinct regions within the California Current System
Substantial new insights have resulted from the first three years of PISCO research. Specifically, we have developed an emerging working model for the California Current ecosystem: The West Coast may be divided into three distinct regions that are dynamically quite different:
- North: Washington/Oregon border to Cape Blanco
- Central: Cape Blanco to Point Conception
- South: Point Conception south
The North region is characterized by intermittent, weak summer upwelling with periods of relaxation. Within this region we have found that: 1) Recruitment of invertebrates is very high; 2) Growth rates of sessile filter feeder are high but variable, depending on nearshore productivity; and 3) Predation rates on mussels are high. In contrast, the Central region experiences longer, more persistent, and stronger upwelling than the North region. Within this Central region, we have found that: 1) Recruitment is very low (relative to the north); 2) Growth of filter-feeders is low; and 3) Predation rates are lower but variable. We hypothesize that the distinct oceanographic regimes bear directly on the biological differences between these two sections of coast. The South region has strong offshore upwelling, weak nearshore upwelling, and a gyre between the mainland and the Channel Islands. Here we have found that: 1) Recruitment is very low; 2) Growth of sessile invertebrates is relatively high; and 3) Predation rates are very low. Thus, we predict that the onshore dynamics that drive much of the patterns and distribution of species link directly to the very different nearshore dynamics.
Critical transition zones
In addition to these distinct regions, we are learning that the transition points are more biologically abrupt than previously thought. PISCO scientists are studying the connections between water transport mechanisms and larval recruitment along the coast of Oregon and California. Combined with PISCO's nearshore oceanographic measurements, recruitment data have shed new light on recruitment patterns and processes along the west coast. For example, comparisons across the PISCO study range have shown that recruitment rates of invertebrates are much higher in Oregon than in central and southern California. Large-scale shifts in recruitment rates coincide with oceanographic discontinuities at prominent topographic features like Cape Blanco in Oregon and Point Conception in California. These discontinuities also mark the northern or southern range limits for some marine species
suggesting that these features inhibit the north-south movement of larvae. Support for this hypothesis comes from research at UCSB that shows abrupt changes in the recruitment rates of some species at Point Conception and modeling studies that demonstrate the potential for ocean currents to generate these patterns.
A new understanding of nearshore oceanography
PISCO's oceanographic sampling of the inner shelf is documenting important oceanographic patterns that run contrary to conventional wisdom. Specifically, we have observed that: 1) Recently upwelled water is carried further inshore than previously documented; 2) The nearshore water column is often strongly stratified; and 3) Internal waves propagate inshore to depths as shallow as 4 meters. Our measurements indicate that offshore transport in shallow water due to upwelling is much less than predicted by existing theories and that current speeds over the inner shelf are much lower than those offshore. PISCO scientists have also observed nearshore responses to upwelling relaxation, including current reversals, that may be important for delivering invertebrate and fish larvae to subtidal and intertidal habitats.
Food inputs and community structure
A primary goal of PISCO research is to link the dynamics of the nearshore ocean with those in intertidal and subtidal communities. In 2001, PISCO pioneered the deployment of an array of oceanographic instruments in Oregon to measure chlorophyll fluorescence (an indicator of phytoplankton concentration) and light in the intertidal zone. We can now quantify the delivery of phytoplankton and light, two fundamental resources for benthic animals and plants, to intertidal communities. Through continuous, high frequency measurements we are able to make both from moorings and on shore provide us with a new tool for opening the black box of nearshore processes that deliver resources and larvae to the shore.
By Libe Washburn, Research Fellow, Cynthia Cudaback, Postdoctoral Researcher, Renee Davis-Born, and Lydia Bergen, Policy Coordinators, and Patrick Drake, Research Technician.
