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Warming Waters Identified as Cause of Marine Life Depletions off California

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  • npat1@juno.com
    In the mid-1970s, the abundance of marine life along the western coast of the United States began a momentous decline, the start of a trend that today has yet
    Message 1 of 1 , Nov 9, 2003
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      In the mid-1970s, the abundance of marine life along the western coast of
      the United States began a momentous decline, the start of a trend that
      today has yet to rebound. Numbers of fish, seabirds, kelp beds, and
      zooplankton-the critical base of the oceanic food web-plummeted.

      A recent study led by a scientist at Scripps Institution of Oceanography
      at the University of California, San Diego, has found warming ocean
      temperatures as the likely driving force behind the 25-year

      Scripps's John McGowan and his colleagues used data recorded by the
      California Cooperative Oceanic Fisheries Investigations (CalCOFI) to
      examine the mechanism behind the changes seen in the California Current,
      the large current originating in the northern Pacific Ocean that passes
      along the western coast of North America.

      "We had seen a big change in the California Current ecosystems since the
      late 1970s, and in this report we looked at the possible mechanisms
      accounting for that change. We found that the most likely cause is a
      change in the upper-ocean heat content," said McGowan, who published the
      results in Deep Sea Research Part II, in a special
      edition that focused on the California Current and CalCOFI. The paper was
      coauthored by Steven Bograd and Ronald Lynn of the National Marine
      Fisheries Service and Arthur Miller of Scripps.

      The authors caution that similar forces impacting ecosystem populations
      could emerge elsewhere, especially if ocean temperatures continue to
      rise. They say their results demonstrate that significant changes in
      sea-temperature balances can "greatly alter the marine community
      ecosystem structure and productivity, sounding the alarm to the potential
      impacts of a global warming trend." They further note that the ability to
      distinguish between human-caused and climate-caused changes will be
      necessary in the future in order to model marine population trends for
      conservation and management decisions.

      In coming to their conclusion, McGowan and his coauthors looked at two
      other possible causes for the ecosystem decline, testing and ultimately
      showing that those are not likely. McGowan also shows that fishing
      pressure cannot be blamed solely for the decline. "The massive declines
      we've seen in fish eggs and larvae population after
      1976 cannot be due entirely to fishing pressure because many of the
      larvae are from species that are simply not harvested, and they too have
      decreased," said McGowan.

      Rather, the paper places the spotlight squarely on a "regime shift" to
      warmer upper-ocean temperatures. This led to a disturbance in the method
      in which lower, nutrient-rich water mixes with the upper ocean.
      Essentially, a thickening of the warmer water layer caused the
      nutrient-rich waters to deepen, disrupting the food supply for plankton
      and other sea life in the upper layers.

      "After this regime shift we saw the massive changes take place, not just
      in plankton but in fish, seabirds, kelp beds, and nearshore
      invertebrates," said McGowan. "In the larger sense this paper confirms
      and reaffirms the notion that there are large-scale
      environmental changes happening on land, lakes, and in our ocean. It's
      uncertain how long it's going to continue and whether it will increase in
      velocity or decrease. It's fear of the unknown, but something big is
      happening. I think an awful lot has to do with
      global warming and that's going to continue."

      The conclusions reached in the paper are one example of the value and
      importance of the CalCOFI program, launched more than 50 years ago to
      explore the dynamic California Current. Although initially focused on the
      disappearance of the sardine off the California coast, the data collected
      by the CalCOFI program-from recordings such as ocean circulation,
      temperature, oxygen levels, and salinity to observations of marine
      life-have become invaluable.

      "There are a lot of principles of interactions that can be derived from
      this magnificent 50-year data set," said McGowan. "It's been called a
      'national treasure' because it's so highly interdisciplinary and so
      accurate, so trustworthy."

      Says Bograd: "CalCOFI is the world's longest-running multidisciplinary
      field program. The accumulation of physical, chemical, and biological
      data spanning more than five decades now allows us to explore the
      dynamics of the California Current and its
      ecosystems across a range of temporal scales. CalCOFI also has been
      instrumental in training numerous students and young scientists over the

      McGowan believes the value of CalCOFI will increase in the years ahead as
      science and government continue to pursue questions of human-produced
      versus naturally produced changes. He says that since its beginning, the
      CalCOFI program has focused on distinguishing this separation.

      The value of CalCOFI surfaced as far back as the 1950s, when a 1958-59 El
      Nino event was identified as having a profound effect on marine
      populations. That event was, as McGowan puts it, an "eye-opener" for
      future El Nino events.

      Volume 50 of Deep Sea Research Part II, published this fall, was devoted
      to CalCOFI and the California Current. Fourteen research papers in the
      issue highlight various aspects of the California Current, including
      "CalCOFI: a half century of physical, chemical, and biological research
      in the California Current System" by Bograd and his colleagues and
      "Long-term change and stability in the California Current System: Lessons
      from CalCOFI and other long-term data sets" by Ginger Rebstock.

      "It seemed fitting to present a sample of research papers from CalCOFI in
      a special volume, as a celebration of more than 50 years of successful
      scientific endeavors," said Bograd. "Hopefully it will also reinforce the
      notion that long-term sampling programs such as CalCOFI are absolutely
      necessary if we are to understand how marine
      ecosystems respond to climate change. As oceanographic sampling programs
      go, CalCOFI is the crown jewel."

      Scripps Institution of Oceanography November 7, 2003

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