By Nigel Jaffe
Picture this: On beaches from Norway to Cancún, fish wash up in the millions. Huge groups of birds and marine animals go the way of the fish, bringing the coastal seafood industry to a halt. Shellfish populations, riddled with deadly biotoxins, become dangerous for humans to eat. People enjoying a day at the beach develop potentially serious respiratory problems, while the water around them turns a menacing shade of red, the hallmark of a destructive phenomenon that has been reported in every coastal state in the U.S.
The question of what could be responsible for such havoc is one of global significance. The answer is everywhere; it is microscopic, yet at the same time, can be seen from space. We know it as the loose collection of aquatic, plant-like organisms called algae. The members of that diverse group fall into a huge range of size and complexity: the smallest algae are simple, unicellular specks that we wouldn’t even notice in water at normal concentrations, while in the largest species, such as giant kelp, individual specimens may reach 150 feet in length.
The deadliest algae are often the smallest, and their danger comes in numbers. When conditions are right, populations of algae skyrocket, reaching such densities that entire bodies of water turn shades of red and brown in an effect known colloquially as “red/brown tide.” It is that excessive growth that creates so-called “harmful algal blooms” (HABs), a term that scientists use to describe algae populations that have reached dangerous levels of growth.
Though algae are harmless at normal concentrations, HABs can create serious large-scale problems for ecosystems around the world. Some HABs produce toxins that kill fish, birds, and mammals while indirectly causing illness (and in some cases death) in humans. Other HABs are nontoxic, but grow to such numbers that their eventual decay saps so much oxygen from the surrounding water as to make it unlivable for marine life. Still other HABs may block sunlight from penetrating the water’s surface, thereby stifling plant growth beneath the waves and destroying fragile food chains. Meanwhile, the foul-smelling dead algae pile up on shores in huge quantities, making life difficult for beachgoers everywhere.
Oceanographers at the U.S. National Oceanic and Atmospheric Administration (NOAA) have been successful in harnessing satellite imaging and buoy data to track and forecast HABs in the Gulf of Mexico, but blooms of algae are hardly limited to that region. Indeed, HABs are a risk in all coastal areas of the United States as well as the Great Lakes. The ways that different factors contribute to HABs are not entirely understood, but what scientists do know is that they often occur after large quantities of nutrients are released into the waterways. This is especially likely after severe storms and natural disasters, when flooding causes rivers to swell and move nutrient-rich soil downstream. Larger HABs are harder to trace to clear causes, and generally occur when a series of different factors—such as water temperature, currents, and even wind—combine in the right way.
The increased frequency of HABs in recent years can be traced back to the widespread disruption of natural processes and ecosystems by human infrastructure. Scientists continue to look for causes and study ways to fight them, but the massive scale at which these phenomena operate makes it difficult to address them in an effective manner. HABs are just one example of the ways in which our society’s impact on the environment can come back to bite us.