I found this dead harbor seal pup at the foot of a makeshift cross at Surfer’s Knoll in Ventura yesterday. Dead seals are fairly common on these beaches, particularly this time of year when algae blooms produce high levels of domoic acid, a neurotoxin that can kill sea mammals. Several groups are working to locate and rehabilitate poisoned animals before they die.
Last week I found a number of dead birds along this beach: a seagull, commorant, pelican and a tern. These animals share one thing in common–besides being dead, they eat fish that in turn feed on the toxic algae.
This marine life die-off is part of a natural cycle. “Oh yeah, the Circle of Life,” a co-worker said when I told her I spent the early moring beachcombing for dead seals. But what’s surprising about the whole thing is the high-than-usual numbers of mammals washing up. According to UCSB’s Daily Nexus there have been daily strandings of whales and dolphins along California’s central coast for the past month or so. NOAA calls this kind of situation an Unusual Mortality Event.
According to NOAA biotoxins have been responsible for worldwide marine mammal die-offs over 9 of the past 17 years, with increasing frequency. In California biotoxins caused die-offs in 1998 and 2002–or roughly a four to five year cycle.
There’s a lot of chatter on the internets about fertilizer runoff being responsible for these harmful algae blooms. Marine scientists seem to think organic nitrogen, a component of sewage and agricultural runoff, might be a factor. But the mechanisms behind the blooms are very complex (pdf). Notably the harmful algae blooms only seem to happen in years when there is an upwelling current. But where is the algae bloom coming from? This type of algae doesn’t survive well at great depths, so it’s not likely that organisms are being churned up from the ocean floor. Or do they have some secret way of surviving without sunlight?
There’s not a lot of science writing being done on the subject–possibly because research into these blooms is limited.
So many end-of-the-planet scenarious to research, so little time…