Toxins released by harmful algal blooms (HABs) can poison and even kill humans who mistakenly ingest them, but at least some marine animals that regularly feed on the algae seem to experience a temporary high that causes them to swim faster and in an abnormal pattern.
The unusual reaction, reported in the journal Proceedings of the Royal Society B, suggests that HAB toxins affect animals differently. But, they can lead to similar, fatal consequences: However enjoyable the intoxication might be for marine animal consumers, the condition makes them more vulnerable to predation.
The study's lead author Rachel Lasley-Rasher, of the University of Maine's School of Marine Sciences, told Discovery News that the intoxication increases encounter rates with predators in two ways.
She explained: "First, they have a higher probability of encountering predators simply because they are covering more 'new ground.' If you walk around the block for 20 minutes, you are likely to encounter more neighbors than you would if you paced back and forth in your yard for 20 minutes."
"Secondly," she added, "when you move faster in the water you create a larger fluid wake. This is why you drive your boat slowly in a 'no-wake zone.'"
HABs are consumed by filter-feeding organisms such as certain fish, jellyfish, shrimp, clams, oysters and many other species. An HAB bloom recently parked off the coast of California for several months and ruined that state's crab season. Crabs ingested or were otherwise exposed to the toxins -- primarily domoic acid -- and became dangerous for people to eat.
For the study, Lasley-Rasher and colleagues Kathryn Nagel, Aakanksha Angra and Jeannette Yen focused on how HAB ingestion affects the common copepod Temora longicornis. Copepods are small aquatic crustaceans.
The researchers exposed the crustacean to Alexandrium fundyense, a microalgae that contains HAB toxins. They had no trouble getting the little animals to eat the algae. In fact, they "readily ingested" it.
Normally the crustaceans are rather low key, swimming back and forth at a slow rate. But the toxins in the algae seemed to affect them like caffeine, causing them to zip around in straight lines. (Intoxicated humans, on the other hand, are known to weave and have trouble walking in a straight line.)
The copepods remained in this state long after ingesting the microalgae. "Therefore, it appears to be a physiological response," Lasley-Rasher said, "but we still don't understand the mechanism at work."
It also remains unclear what precisely happens to the toxins as they are passed down the food chain, except that the outcome is not beneficial, especially for humans.
"Many commercially important fishes depend on copepods as a first food item when they are young," Lasley-Rasher said. "Copepods are also important in the diets of adult fishes such as herring and mackerel and also whales, such as the endangered North Atlantic right whale."
She added: "Copepods that have been feeding on harmful algal blooms can act as a vector, transferring HAB toxins to these predators."
Hans Dam, a professor with the University of Connecticut's department of marine sciences, has also studied HABs' effects on copepods in his own lab. He believes that the microalgae strain used in his studies had a higher toxin content: It caused his crustaceans to become lethargic.
"Instead [in the new study], the copepods swam faster, which can lead to increased encounter rates with their predators, and higher mortality," Dam told Discovery News. "This kind of indirect effect can actually lead to decreased fitness, and is something that is typically not considered in toxicological studies."
HABs are naturally occurring, but researchers at the National Oceanic and Atmospheric Administration and other organizations believe that human activities that disturb ecosystems likely play a role in their growing frequency and intensity.
Lasley-Rasher and her team call for additional studies on animals that consume such blooms, to better determine their impact on not only these grazing species but also on those that feast on them up the food chain.