There has been a marked increase in recent years in what are commonly called "red tides." These can occur when microscopic algae increase in abundance until their pigments discolor the water, making it red, brown, or even green. Not all red tides are toxic or dangerous, and conversely, the water can be quite clear yet still be very dangerous due to the presence of small numbers of highly toxic organisms. Their toxins enter the food chain and concentrate in fish and shellfish, where they cause various types of poisoning to people who eat them. Red tides are thus more accurately called harmful algal blooms (HABs).
Although not always red or even visible to the naked eye, each year HABs make thousands sick and even cause death. Fishing and aquaculture industries, as well as tourism, can lose hundreds of millions of dollars because of killed fish, toxic shellfish, and closed or unsightly beaches.
Don Anderson, a senior scientist at the Woods Hole Oceanographic Institution and an expert on HABs, explains the basic biology and ecology of HABs. He highlights the organisms responsible, what kinds of toxins they produce, and what possible measures can be taken to control them.
What has caused the apparent increase in HABs over the past 30 years is hotly debated among scientists, and even more controversial are proposals on how best to control HABs. Many scientists are concerned that climate changes and increased pollution levels will only make the problem worse, thereby damaging coastal areas that are important as food sources and for trade and tourism. Others argue that the problem has not expanded in size, but rather that we are better at detecting toxic or harmful blooms than in the past.
