Natural Algal Phenomena
Below are some examples of common algal phenomena observed in the natural world. These examples are intended to serve as the foundation for your experimentation. Click one of the buttons below, read through a description of the dynamics at play during the event, and think about how you could model this phenomenon. What questions about the could you ask and answer using our products?
You may have watched (and been disturbed by) Albert Hitchcock's The Birds, but did you know that Hitchcock's inspiration for this flick came from a real life event? Seabirds who had ingested shellfish with dangerous amounts of domoic acid (a neurotoxin produced by the diatom Pseudo-nitzschia) developed Amnesiac Shellfish Poisoning and attacked the coastal Californian town of Monterey Bay in 1961. But where did this toxin originate? To decipher this mystery we must examine the dynamics of phytoplankton blooms.
(Left) Algal bloom in Lake Erie off the coast of Toledo, courtesy of NASA/USGS Landsat-8. (Right) Offshore bloom of Emiliana huxleyi in the Barents Sea, courtesy of the MODIS sensor on NASA's Aqua earth-observing satellite.
Phytoplankton biomass in regions of the ocean varies based on the concentration of nutrients in their region. In certain coastal regions the rotation of the planet combined with coastal winds pushes the top layer of water offshore, bringing nutrient-rich water from the deep ocean in so-called upwelling events. This physical forcing gives rise to high phytoplankton biomass on the coast, but similar forcings are not present in the open ocean. Consequentially, the biomass of pelagic (open ocean) phytoplankton is not as high` as it is on the coastline. In many cases only one nutrient is termed "limiting," because while there may be enough of other nutrients to sustain growth, only one need to be deficient in order to suppress it. Regardless of the normal or average phytoplankton biomass in a region, that most of the concentration can be explained by the limits of the most depleted nutrient raises many questions. Chief among them: what happens when nutrients are suddenly dumped into a nutrient limited environment? Sudden spikes of the limiting nutrient into an environment gives it additional carrying capacity, which leads to a rapid increase in phytoplankton biomass. This now abundant assemblages can cloud the water column to such a degree that these events are called "blooms." Although blooms come in many different colors, they are also colloquially known as "red tides."
Some blooms are seasonal, whilst others can be attributed to abnormal fluctuations in the carrying capacity of the region. There are seasonal upwelling zones on certain coasts across the planet and a moderate band of upwelling is present at the equator. Trade winds blow Saharan dust into iron-limited Atlantic Ocean regions, and swirling kilometers-wide eddies of nutrient-rich surface water can be pushed offshore into oligotrophic waters. One of the largest global biomass increases in the ocean comes in the spring, when large blooms occur in the open ocean which can often be seen from space. The ocean has layers of water with different temperatures, salinities and pressures, which can create a cake-like organization of water slices that do not interact because of those differences. Sitting atop the cake is the mixed layer, which as the name suggests is mixed homogenously by passing storms. The mixed layer is present mainly because of the sunlight that warms it, separating it from the colder and denser layers of the ocean. During winter when heating is minimal, the mixed layer increases in size and interacts more with the colder, nutrient-rich water below it. During winter conditions are not conducive to a bloom, but as spring comes and the water column warms, the mixed layer becomes smaller. This gives phytoplankton more daily sunlight, which when combined with the nutrients that have been pooling throughout winter cause normally sparse regions to bloom in magnificent blooms of life. All of these events and more are seasonal cycles dictated by natural processes, but human activities can also have effects. Some are scientific, like the IRONEX and later iron fertilization experiments, which studied the effects of artificial iron seeding in iron-limited pelagic regions. Others are more systemic and long-lasting pollution, like river runoff carrying agricultural fertilizers into the ocean. These events can cause eutrophication (nutrient levels that are abnormally high), which can lead to dead zones, both of which will be explored in later sections.
The circumstances surrounding bloom formation in the ocean depends on a variety of factors, and all blooms are by no means the same. The dynamics at play are dependent on the location of the bloom, which particular environmental variable changes, and the species present. Regardless of formation dynamics, most blooms in the marine environment consist of large phytoplankton like diatoms or dinoflagellates. Even in nutrient-limited pelagic regions (oligotrophic or low-productivity, low nutrient regions) where small phytoplankton like cyanobacteria typically dominate, this phenomenon still occurs. This has to do with differential grazing rates on different sizes of phytoplankton. When nutrients are spiked into a region, phytoplankton of all sizes begin reproducing at higher rates. This is true for their predators as well, however as size increases from the smaller unicellular zooplankton that graze cyanobacteria to the larger and more complex multicellular zooplankton graze on diatom and dinoflagellate-type size classes, reproduction time increases. Copepods, shrimp, salps, krill and other large grazers have complex life cycles, and cannot as rapidly increase their biomass in response to a bloom of their prey as the grazers of smaller, unicellular phytoplankton can. So when bloom-forming pressures are exerted, smaller phytoplankton's rapid biomass rise is checked by their grazers while the larger phytoplankton are more free to take advantage of the situation.
So if the larger phytoplankton are typically blooming in the marine environment, which species or genera are the usual suspects? Diatoms, dinoflagellates and other eukaryotic phytoplankton like cryptophytes mostly, though there are some larger colonial cyanobacteria that can form blooms. The types of blooms spoken of normally typically carry with them some kind of environment-altering characteristic that makes the public aware of their presence, either wonderous or harmful. In San Diego, dinoflagellates named Lingulodinium polyedra bloom right offshore in huge numbers. In 2020 this species recorded historically high abundances (over 9 million cells per liter), mostly due to the equally historic high sea surface temperature and their ability to migrate to deeper waters at night for access to nutrients and up to the surface during the day to photosynthesize. These phytoplankton are bioluminescent, they can glow in the dark when disturbed. Even during a pandemic, San Diegans flocked to the beaches at night to safely watch glowing waves crash into the surf. The species of diatom that caused seabirds to behave erratically in Northern California (and spawn a Hitchcock movie) secreted toxins that were filtered out of the water by bivalves and concentrated in their tissues, which when eaten caused neurological damage and avian psychosis. These types of bloom are termed Harmful Algal Blooms, because they present a danger to the surrounding ecosystem. Even the beautiful dinoflagellates in San Diego died eventually, causing heterotrophic microbes in the area to burn up all the oxygen while consuming this massive biomass input. The resultant dead zone killed fish and other sea life throughout the area. Blooms with effects that are a hindrance but not immediately threatening the ecosystem are termed Noxious Algal Blooms. While most blooms are not at all harmful and indeed promote growth throughout their regional food web, it is important to highlight deleterious effects (both natural and man-made) that blooms can have on fisheries other regions.
When an algal bloom occurs, a larger-than-normal amount of biomass is created due to the additional photosynthesis being carried out in the environment. But the nutrients that sustain the bloom are eventually depleted, which poses an interesting question. What happens to all of that extra biomass? How does the environment deal with degrading and recycling all of that growth? Are there any detrimental effects of abnormally high growth over short time scales?
Photosynthesis requires inputs of water, carbon dioxide, and light energy, producing oxygen and glucose. When algae bloom, they take up more carbon dioxide and produce more oxygen than would be regionally standard for that time of the year. But that is only one half of the story. Suspended in the plankton with algae are heterotrophs, microbes that do not photosynthesize and instead consume organic sources of carbon for energy. In the simple equation outlined above, these organisms would take the glucose from phytoplankton and respire it, using oxygen to convert it back into carbon dioxide. In this way both sides of the equation are continuously explaining the cycle of microbial growth and death.
When the organisms on one side of the equation experience rapid growth, it must be balanced on the other side. We can see the effects of blooms like the one in La Jolla during 2020 through measurements of dissolved oxygen in the region. Measurements from the Smith Lab at Scripps Institution of Oceanography's SOAR (Scripps Ocean Acidification Real-Time) program show that during the period of the bloom, oxygen concentrations increased substantially due to the the rapid increase in primary production. After nutrients were depleted and the bloom died, heterotrophic life began to consume the dead assemblage. As they ate they respired, consuming oxygen until regional levels were below that capable of sustaining fish and animal life. Animals across San Diego began washing up on shore, dead of hypoxia (low oxygen).
What had happened was the formation of a "dead zone" or body of water with oxygen levels too low to sustain heterotrophic life. Decreases in oxygen concentration like this are usually due to the respiration of microbial life and can be used as an indicator for which areas in the open ocean have recently bloomed. The scenario described above was temporary, the dead zone eventually disappeared when all the organic material had been degraded and the region re-stabilized.