Have you ever heard of a red tide?
This phenomenon is one type of algal bloom that can result in fish kills.
Harmful algal blooms (HABs) are caused when photosynthetic microscopic algae, or phytoplankton, grow uncontrollably within an aquatic ecosystem.
These blooms pose a threat to marine habitats but they can also cause harm to humans.
Some research shows that HABs are capable of producing toxins that can bioaccumulate as they move up the food chain.
HABs occur when nutrients – like nitrogen and phosphorus – find its way into natural water courses and the sea from agricultural activities, industrial processes or even the use of excessive fertilisers in our home gardens.
Upwelling (a process in which deep, cold water rises toward the surface) from deep ocean water can also increase the nutrient levels at the surface and cause blooms.
But the physical chemistry of water has to be ideal for these overgrowth events to occur.
Warm temperatures and slow water movement, as is often the case during the dry season or a drought, are ideal.
Climate change can also worsen both the frequency and severity of HAB events globally which can result in a higher occurrence of toxin-producing algae.
Ecological Impacts and Human Health Concerns:
HABs are considered a “one health” issue globally because it has the potential to affect an entire ecosystem (including aquatic animals and human health).
Of particular concern are the toxins produced by the cells of microalgae:
- Cyanobacteria are a type of gram-negative bacteria which is often mistaken for green algae. When these bacteria die or there is a cell lysis (cellular disruption), they can produce a highly potent toxin known as cyanotoxin. In some rare cases, these toxins can be secreted extracellularly into the water whilst the cyanobacteria is still alive.
- Dinoflagellates and Diatoms are forms of microalgae responsible for the algal blooms found in marine and brackish water.
Climatic conditions working in harmony with the pigments of these algal cells can give rise to a brick red (or some variance of it) appearance at the water surface.
Of even greater concern are the toxic benthic (at the bottom of the water) dinoflagellates which can fix itself onto macroalgae particularly in coral reefs.
Reef fish – like commercial species of barracuda and grouper – then graze on these toxins.
Humans are normally exposed to these toxins by physical contact (swallowing contaminated water or eating contaminated food) and even breathing.
But on rare occasions, some people may experience health crises by breathing-in the toxins found in mist, sea spray or consuming water droplets from contaminated water.
Symptoms can range from skin irritation to respiratory problems and other extreme ailments.
Ecological damage occurs when:
- Fish and other aquatic organisms come into contact with these toxins
- Blooms become so dense that they block out all sunlight needed by other primary producers.
- The blooms die and oxygen demand for their decomposition is so high. So, the available dissolved oxygen in the water required to sustain the life of other organisms becomes dangerously low.
HABs in the Caribbean:
The presence and impact of HABs in Latin America and the Caribbean have been well documented over the past 50 years.
In Latin America and the Caribbean, prevalent species of algae which causes HABs include:
- Gambierdiscus spp
- Margalefidinium polykrikoides (a dinoflagellate) has become more common, often resulting in mass mortalities of fish and invertebrates
International organisations like the UNESCO Intergovernmental Oceanographic Commission have conducted several research studies on HABs events in the region.
These studies have largely focused on increasing awareness of toxic species, detecting new toxins, examining the geographical expansion of the known species, and their impact holistically.
However, the impact of HAB events on the economy and marine ecosystems within the region has not been sufficiently studied.
Mitigation Practices and Policies:
Given nitrogen and phosphorus are the main contributing nutrients to HABs, the prevention of these events are centered around controlling the release of these nutrients into waterways.
In Trinidad and Tobago, the Institute of Marine Affairs (IMA) has been continuously monitoring water quality across the country.
These monitoring exercises have been carried out by the Institute’s Environmental Quality Programme.
HABs can also be mitigated when:
- Industrial and municipal bodies reduce their output of nutrients.
- Community-based programs are implemented to manage practices that reduce nutrient loading to streams and rivers. These practices can be as simple as ensuring fertiliser and livestock waste are diverted away from major watercourses and treated appropriately.
Algae – whether phytoplankton or seaweed – are a valuable resource for the oceans and humans.
It is estimated that algae are responsible for producing half of the oxygen needed to sustain life on earth.
However, care must be taken to avoid proliferation of these organisms in an unsustainable way.
Human activities can be positively influenced to prevent HABs from occurring and manage their negative effects.
Education, policy reform and policy implementation are all tools which can be used to positively influence human activities with the aim of reducing nutrient outputs into water courses.