Narrator: This is Science Today. One of the most pressing issues of ocean health is a naturally occurring phenomenon in which toxin-producing marine phytoplankton cause harmful algal blooms. Ocean scientist Mary Silver of the University of California, Santa Cruz, says the concern is when organisms eat the toxic algae; the toxins can move from the marine food web and accumulate in shellfish that may be harvested for human consumption.

Silver: So our job here is to identify them, know what the toxin levels are and then we work with the state health department and we also measure these toxins as they enter shellfish. So we coordinate our findings with those of the public health department. And just about every part of the developed world has monitoring programs to detect this when it gets into shellfish.

Narrator: Silver stresses that in almost all cases, these phytoplankton are not harmful to swimmers or surfers.

Silver: At low levels, they're not a problem, so it's entirely a dose problem.

Narrator: For Science Today, I'm Larissa Branin.