Northwest Fisheries Science Center

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A gateway to oceanographic adventures from the Newport Line and beyond

Blog on ocean conditions along the Newport Line and the northern CA Current.

Phytoplankton and HABs

By Xiuning Du
Posted on July 23, 2015

Marine phytoplankton are a group of single-celled algae that are the primary producers in coastal and oceanic waters. Like terrestrial plants, the majority of the species of phytoplankton are photosynthetic. Under optimal combinations of sunlight, nutrients and temperature, some species grow rapidly forming “blooms” which, in most cases, has a positive influence on the marine ecosystem by enriching the entire food-web. However, some blooms produce phytotoxins which disrupts ecosystem function, can cause mortalities of birds, fish, and marine mammals, and can disrupt the local economy and human health by contaminating shellfish. These toxic phytoplankton blooms are termed Harmful Algal Blooms (HAB) and they are actually caused by only a few species of phytoplankton.

Timing of phytoplankton blooms
In the coastal waters off Oregon, phytoplankton can be productive from February through October/November. The richest blooms occur from April through October, because wind-driven upwelling brings nutrient-rich deep water to the upper water column which fuels large phytoplankton blooms. The timing, magnitude, and species composition of a bloom determines its subsequent effects on other organisms and the food web. We track the progress of phytoplankton blooms through our biweekly sampling cruises off Newport, Oregon.

The phytoplankton species off Newport Oregon cover a broad size range from nano- (2-20μm) to micro- (20-200μm) algae. Diatoms are the most dominant micro-sized taxa responsible for nearly all of the bloom events that occur during upwelling, but occasionally dinoflagellates dominate. In the ocean, diatom species are most commonly present in the shape of long chains (e.g. several mm in length) or colonies (Figures 1-4).

Harmful Algal Blooms (HABs)
The major phytoplankton taxa that cause HABs in the Pacific Northwest are the diatom Pseudo-nitzschia (PN, Figure 5) and the dinoflagellate Alexandrium catenella (Figure 6). Domoic acid (DA) produced by PN can cause Amnesic Shellfish Poisoning (ASP). Saxitoxins (STX) are produced by several dinoflagellates, including Alexandrium, and they cause Paralytic Shellfish Poisoning (PSP).

Although PN blooms can occur annually with the onset of the upwelling season, these PN blooms aren’t always toxic. This year, we have seen the spatially largest PN bloom and DA toxin production along the west coast, spanning from central California to British Columbia, leading to extended shellfish closures and deaths of marine mammals.


The mechanisms triggering significant DA production are attributed to both external environmental stress and internal biophysiological reactions, which varies by strain/species and region. In contrast, while Alexandrium are mostly found in lower numbers, once their cells are present in the water, their toxic effects can be directly apparent.

Tagged: HAB, NH Line

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