What do Great White shark sightings near Santa Cruz, a toxic algae bloom from Santa Barbara to Seattle and the collapse of the salmon fishery have in common? They might all trace to a persistent blob of warm water that has been clinging to the west coast since last year, according to research conducted by NOAA and others.
It’s a complicated story, so I’ll try to unpack things with the help of Nate Mantua, a climate scientist based at NOAA’s Southwest Fisheries Science Center in Santa Cruz. First of all, the warmer-than-normal water has been with us since early 2014, but has been getting stronger and growing. From this map,
Daily ocean sea surface anomaly from July 7, 2015. Dark red areas show higher than normal ocean temperatures.
which shows temperature anomalies, or the areas where temperatures are warmer or colder than expected, you can see a very warm finger of water off Peru as well as warm patches of water extending into the Pacific between the West Coast and Hawaii and even up into Alaska. This warm water has brought with it lots of marine species that prefer the tropics this time of year, from sharks in Santa Cruz to pygmy killer whales seen for the first time off California last winter.
As Nate explained to me, each of these warm regions reflects persistent changes in atmospheric pressure, wind and ocean current patterns. Some of the changes are associated with El Nino, the periodic warming of the Eastern Pacific Ocean off South America that shifts weather patterns and could bring heavy rainstorms to California this winter, which would be a welcome relief to our drought-stricken state. But the warm water anomaly started last year, before this El Nino developed and grew, and is likely the result of large-scale shifts in atmospheric pressure resulting in weaker winds from the north. These winds, which typically strengthen in springtime, would normally push sun-warmed surface water off shore and bring up cold, nutrient-rich water from below, a phenomena known as upwelling.
Tiny marine invertebrates called copepods are critical components of the coast marine food web
Upwelling is an important feature for marine ecosystems all along the west coast. The cold, nutrient-rich waters support a bloom of phytoplankton, plant-like marine algae that thrive in upwelling conditions and support an entire rich food web from marine invertebrates called copepods to fish, seabirds and even whales. A highly productive salmon fishery depends on upwelling and fat, juicy copepods to feed the young fish as they travel from streams to the ocean. When upwelling is diminished, as a NOAA report warns is happening this year, young salmon can take a hit and never grow up to be big salmon for fishermen to catch.
Upwelling also affects the balance of marine algae along coastal regions. When nutrients are present, the “good“ algae species dominate the ecosystem. When the regime shifts to warmer, nutrient-poor conditions, “harmful” or toxic algae can gain a foothold and proliferate. This spring and summer, a toxic algae bloom has spread from Santa Barbara to Alaska to become the most severe in nearly two decades, according to Raphael Kudela of UC Santa Cruz whose lab helps monitor and map harmful algal blooms in California.
The harmful marine alga, Pseudo-nitzschia produces domoic acid, a neurotoxin that can harm marine life
The algae in this huge bloom, called Pseudo-nitzschia, produces domoic acid, a neurotoxin that accumulates in filter feeders, such as clams and mussels, and species lower in the food chain, such as crabs, anchovies and sardines which feed on plankton. The concentrations of domoic acid detected in Monterey Bay and along the coast of Oregon and Washington are some of the highest ever recorded and has resulted in the closure of shellfish harvesting and warnings about consuming recreationally-caught mussels, clams, and the internal organs of crabs taken from Monterey and Santa Cruz counties.
So while you might enjoy taking a dip in the ocean sans wetsuit this summer, this is all a good reminder that ecosystems and climate are intimately connected and that large changes in winds, ocean currents, and temperatures can have profound, long-term effects on marine life and communities that enjoy and depend on healthy oceans.
