OCEAN 320 Lecture Notes - Lecture 5: Moss Landing, California, Northern Hemisphere, Counterargument
Unit 5B
Changes to California Current
River of ocean water running down CA coast is shifting with climate
oUnsure about “tipping point” where progressive physical changes cause abrupt
biological changes
Decreases in zooplankton, mid-water fishes, seabirds along coast linked to global
warming
Average surface water temperature has increased by 3 degrees since 1950
Coastal waters become more stratified by temperature; limits movement of species
Dissolved oxygen concentrations have decreased in parts of Southern CA Current, and
low-oxygen zone have spread along Oregon coast
CA Current one of richest marine areas in world; commercial fisheries haul 373 million
lbs worth $150 million in 2009, along with noncommercial species
oCurrent generally flows south, driven by winds parallel to coast; runs 1,600 ft
deep within 600 mi of shoreline from British Columbia to Baja CA
oKey to productivity-upwelling: winds push surface water offshore and it is
replaced from below; moves deep water to surface, circulates nitrates, phosphates,
and trace metals to top layers where they can be taken by phytoplankton (which
feed food chain)
Challenge: distinguishing between short-term variations (such as El Nino/La Nina)
weather phenomenon vs those that span decades/centuries
oResearches collect samples up coast 4 times a year to document changes
Complex interactions of air and water currents have held sea-level rise along west coast
far below global average
oPrediction: major shift in dynamics will end upwelling and surface water will heat
and expand; rising the sea level
oAlteration of upwelling will destroy phytoplankton population, eventually climb
up food chain
2002: “dead ones” in Oregon coast; oxygen levels too low for marine organisms to
survive; climate models suggest more low-oxygen zones due to rising water temps and
changes in mixing patterns
Acidification: result of CO2 from atmosphere being absorbed by ocean; seas become
more acidic, less hospitable to sensitive organisms important o food web
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oShelled animals most threatened
Toxic Bloom-Monterey Bay
Spring 2015: toxic algal bloom in North America affects wildlife and closes commercial
fisheries from CA to WA
oConsisted of diatoms in the genus Pseudo-nitzschia, became toxic because of
unusually low ratio of silicate to nitrate in waters of Monterey Bay
Some species of Pseudo-nitzschia produce potent neurotoxin called domoic acide (causes
seizures and death in mammals)
oPrevious blooms (1991 and 1998) sickened/killed seabirds and sea lions in MB
oStill not sure why some blooms are more toxic than others
2015 bloom coincided with experiment in MB: Ecology and Oceanography of Harmful
Algal Blooms
oScientists from MBARI, UC Santa Cruz, Moss Landing Marine Labs, Natl Ocean
& Atmospheric Admin measure oceanographic conditions and concentrations of
Pseudo-nitzschia and domoic acid throughout MB
oSend underwater robots through bay; sensors reveal extremely high
concentrations of toxic Pseudo-nitzschia diatoms below surface
oAlso anchored two robotic molecular biology instruments near north and south
ends of bay
oFound that bloom consisted mainly of Pseudo-nitzschia australis (more toxic
species) and the diatoms contained unusually high concentration of domoic acid
oDense population of highly toxic diatoms=bad combo
What factors led to growth and toxicity of 2015 bloom in MB
oMust examine physical and cchemical conditions leading up to bloom and
compare with earlier conditions
oNot because of warming; waters in MB in 2015 were not particularly warm in
comparison to what they should be; did affect bay before/after bloom, but spring
2015 was cooled by upwelling
oUpwelling brings up nutrients that act as fertilizer for marine algae, often lead to
diatom blooms; common in MB during spring
Strong upwelling event in March 2015 initiated bloom; followed by several milder events
that revived diatom populations and allowed drifting algae to persist and accumulate in
bay
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