Harmful algal blooms, like this red tide washing over a Florida beach, are increasing in frequency and duration. Efforts at prevention, mitigation, and early warning are ramping up around the world. Credit:

World - Harmful Algal Blooms: No Good, Just the Bad and the Ugly

Natural and human factors are leading to larger, more frequent, and longer-lasting algal blooms. Recent research is increasingly revealing the scope of the problem and informing potential responses.

With the annual emergence of summer heat, happy vacationers and weekenders are often eager to cool off at nearby lakes and beaches. More and more, however, they are having to cancel their plans, or at least stay out of the water, as reports come in from all over the United States and elsewhere warning of unwelcome summer visitors: algal blooms.

Among numerous recent examples, the Missouri Department of Natural Resources (MoDNR) notified the city of Sedalia on 13 June of a potentially hazardous algal bloom in nearby Springfork Lake. City officials had previously discontinued using water from the lake for drinking, and in response to MoDNR’s notice, they temporarily closed the lake to public recreation. The same day, the Florida Department of Health in Orange County cautioned Orlando area residents not to drink from or swim, wade, or boat in waters with visible algal blooms in two of the city’s lakes. Shortly before those instances, similar warnings were issued for Red Bud Isle near Austin, Texas, and for Minnesota’s Lake Hiawatha and Lake Harriet. And in mid-July, residents were advised about possible blooms in Lake Micmac near Halifax, N. S.

It is becoming increasingly crucial that we establish harmful algal bloom (HAB) early-warning systems and response strategies to help safeguard communities today as well as future generations.

Not all algae are hazardous—as a group, algae are, after all, nearly ubiquitous inhabitants of marine and freshwater environments. Yet some species produce compounds toxic to humans and wildlife, and at high enough concentrations, even species that are typically harmless can become harmful.

Harmful algal blooms (HABs) appear to have escalated globally in recent decades. In South Korea, for example, HABs typically lasted less than a week in the 1980s, but since 1995, they have often lasted more than a month [Park et al., 2013]. HABs are also becoming more frequent and are occurring over larger areas, as in the coastal waters of the northern Beibu Gulf, China, where HABs have expanded from covering tens of square kilometers in the late 20th century to hundreds more recently [Xu et al., 2019]. In south Texas, where I live and conduct environmental research, HABs also are emerging more often along the Texas coast.

With their growing frequency, duration, size, and impact over the past 30–40 years, doing nothing to control them is not an option; rather, it is becoming increasingly crucial that we establish HAB early-warning systems and response strategies to help safeguard communities today as well as future generations.

The ABCs of HABs

HABs come in different varieties—and colors—and occur in both marine and freshwater settings. Red and brown tides, aptly named for the hues they contribute to coastal waters, are caused by certain algae species—such as Karenia brevis and Aureoumbra lagunensis along the gulf coastlines of Florida and Texas. Meanwhile, blooms of blue-green algae (which are actually cyanobacteria rather than algae) commonly occur in freshwater and saltwater settings. The common thread is that they are toxic to aquatic life as well as to people.

Respiratory and digestive symptoms and illnesses, sometimes severe, caused by airborne and waterborne toxins emitted during some HAB episodes are the most common impacts on human health. HABs have several negative effects on aquatic ecosystems. Microbial breakdown of large quantities of dead algae can cause hypoxia (low oxygen levels) or anoxia (depleted oxygen levels) in the surrounding water. And excessive algal growth can increase levels of toxic compounds and decrease water clarity. As a result, nearby fauna, including seabirds, fish, marine mammals, and sea turtles, can be poisoned or may alter their feeding behavior, which can sometimes prove fatal [Mateus et al., 2019].

Harmful algal blooms have afflicted coastal communities for centuries. Alaska first recorded issues with shellfish poisoning associated with algal blooms in the late 1700s [Anderson et al., 2019]. Not surprisingly, HABs are a major threat to today’s shellfish industry as well. In Europe, for example, persistent closures in shellfish-producing regions have resulted in annual costs exceeding $850 million [Mateus et al., 2019]. In addition to commercial fisheries, the aquaculture (fish and aquatic plant farming), tourism, restaurant, and lodging industries also have suffered income losses due to recurring HAB events.

Factors Favoring Harmful Algal Blooms

Increasing populations, expanding agricultural activities, and industrial growth all have magnified nutrient inputs into coastal waters, further feeding HAB events.

Natural factors affect the development of HABs. The circulation of surface currents can promote algal growth by transporting nutrients (e.g., nitrogen, phosphorus, and iron) and algae to certain regions. Also, as phytoplankton and other plants near the surface die and settle through the water column, bacteria degrade them, releasing nutrients into the deep water. Coastal upwelling, the upward flow of deep, nutrient-rich water to the ocean surface, similarly can spur the formation of HABs in coastal areas like those in California, Portugal, and Angola, as can rivers that deliver nutrients from the land to the ocean.

Read more.