Tuesday, April 6, 2010

Los Angeles HAB superstar (Pseudo-nitzschia)

Previous blog entries have hinted at our interest in understanding toxic or harmful algal blooms. The global rate of harmful algal blooms (HABs) has been increasing for decades with longer bloom duration, increased toxicity, and greater geographic coverage. HABs are simply defined as significant increases in phytoplankton biomass with harmful consequences. HABs cause harm by producing toxins or because the accumulated biomass negatively impacts food-web dynamics and ecosystem structure, such as decreasing the oxygen content in the water when they die. The negative impacts of HABs make understanding the physical, chemical, and biological variables influencing the growth of the phytoplankton community a scientific priority. And that’s what we are trying to do here in the lab. This posting has a special focus on one of the local Los Angeles HAB superstars, Pseudo-nitzschia, a diatom that contributes to HABs in the Southern California Bight.

HAB Background – Toxic Blooms and Pseudonitzschia australis

Pseudonitzschia australis, a local diatom, is one of the HAB species here in Southern California. Diatoms are unicellular phytoplankton that have a cell wall made of silica, the same substance that makes up window glass. Diatoms are phytoplankton that often bloom under cool water and nutrient rich conditions. There are an estimated 100,000 species of diatoms that come in a variety of shapes. Interestingly, since the Victorian Age art has even been created from arranging diatoms into intricate patterns (see image above). Pseudo-nitzschia's long narrow shape places it in the pennate diatom group (see image above left).

Domoic acid produced by the diatoms Pseudo-nitzschia causes domoic acid poisoning (DAP) also known as amnesic shellfish poisoning (ASP). DAP poisoning negatively impacts a wide range of wildlife including mussels, crabs, marine mammals, cormorants, and pelicans. Blooms of Pseudo-nitzschia can be expansive with a 1991 bloom establishing from Washington State to Southern California. In addition to the health threats the economic implications of these blooms is great, because high levels of domoic acid have lead to the closure of shellfish collection and have caused millions of dollars of economic losses.

Pseudo-nitzschia is a typical member of the phytoplankton community off the Southern California coast. However, the numbers are typically so low that Pseudo-nitzschia does not present any harmful threats to the ecosystem or human health. When conditions are right Pseudo-nitzschia can bloom and dominate the phytoplankton community. Once these blooms occur domoic acid can often be measured in the water. Our lab is working to better understand the ocean physical dynamics and conditions that lead to blooms, especially the toxic blooms, of Pseudo-nitzschia in our urban ocean. We collaborate closely with the Caron Lab at USC who are working to understand details about the biology and genetics of Pseudo-nitzschia. More about our collaborative group and our approaches to observing the ocean can be found at http://cinaps.usc.edu.