The Sonoma Coast and other parts of the California Coast have been hit by quite an algal bloom. Those who spend time on the coast would probably agree with recent observations that being in this water is like traveling through chocolate milk, or for some people (surfers, divers), that it can be irritating to the skin or sinuses.
Algal blooms can happen anytime, depending on conditions, but they typically get attention at two distinct periods of the year; late spring/early summer and late summer/early fall. While happening at the right time of year, this particular bloom is a bit more intense than what we typically see at this time. It seems likely that conditions over the past ten days have set the stage for this bloom: there's been some late season upwelling followed by rain, both of which probably brought more nutrients to the neighborhood. Finally, a period of relatively calm seas and sunshine allowed the algae to quickly multiply at the sea surface.
Figure legend: The top graph shows that fluorescence (which is a good indication that algae are present) increased dramatically at the sametime as the bloom became visible from the shore. The center graph shows how the recent rainfall occurred just before the bloom and the lower graph shows calm winds on the 20th of October, as the bloom peaked (as well as northerly winds driving upwelling on the 18th of October and a brief burst of southerly rain-bearing winds on the 19th).
Algal blooms are exactly that - a population boost of planktonic algae (including diatoms or dinoflagellates) after they have been exposed to the right conditions. They can be toxic and cause Harmful Algal Blooms, or "Red Tides" (you know what they say about shellfish and months ending in "er"), or they can be completely harmless. Scientists in Santa Cruz have reported a bloom, beginning last week, and the two genera dominating that part of the coast are the diatom Pseudo-nitzschia, and the dinoflagellate Ceratium. A Ceratium-dominated bloom was also seen in the Gulf of the Farallones last week. We have seen Ceratium in some of our water samples here at BML, but no Pseudo-nitzschia sightings as of yet, which is good, depending on what mood they happen to be in (see link). Northward currents around Point Reyes carried the bloom north to Bodega Bay late on Monday (19th October), where it continued to grow due to the calm, nutrient-rich conditions.
Figure showing 8 day composite satellite image of sea surface chlorophyll levels, courtesy CeNCOOS Satellite Images of Ocean Temperature and Chlorophyll.
This 8-day composite shows high levels in the Gulf of the Farallones and up to Bodega. This average covers the time period 16-23 Oct, which includes dates before and after the bloom was transported northward around Point Reyes.
This bloom was extensive and some of our scientists observed it as far as 15 miles offshore, with very few birds or marine mammals sighted until after the bloom had passed. Water samples taken at sea also show high levels of dissolved oxygen, a sign of photosynthesis. The lab has had staff working hard to keep its filters from clogging, so that a clean sea water supply can be maintained for the lab's marine critters. The ocean is a dynamic place, and while phenomena like these are interesting, it will be nice when this particular "tide" has ebbed.
For more information on algal (phytoplankton) blooms, see: http://www.cencoos.org/sections/classroom/algal_blooms.shtml
