Tiny but mighty: The ocean’s most important producers

The ocean’s smallest organisms have the biggest impacts.

What are Phytoplankton?

Phytoplankton are a type of microscopic marine organism. As primary producers, these organisms create their own energy through photosynthesis, a process in which carbon dioxide and sunlight are converted into glucose and oxygen. To trap the light needed for photosynthesis, phytoplankton use chlorophyll, a type of pigment found in many autotrophic producers.

These plankton can be split into two main classes: dinoflagellates and diatoms. Diatoms have shells made of silica while dinoflagellates have flagella which they use for movement. These groups amass many different physical forms; they are a diverse batch of organisms.

What is Ocean Productivity?

In Earth’s oceans, primary productivity refers to the rate at which autotrophs convert carbon dioxide to organic material. Primary production commonly occurs through photosynthesis, and phytoplankton control most photosynthetic processes in the marine biosphere. Increased levels of productivity directly contribute to a decrease in atmospheric carbon dioxide. Excess carbon dioxide is one of the largest constituents in the current climate crisis; atmospheric carbon leads to rising temperatures and marine carbon leads to ocean acidification. Phytoplankton are crucial to keeping excess levels of carbon dioxide, and therefore carbon, at bay.

Phytoplankton are important in the promotion of marine diversity. These small organisms allow beautiful, extensive reefs to flourish in otherwise barren areas of the ocean. This phenomenon is known as the Island Mass Effect (IME). Coastal upwelling brings nutrient-rich water to the surface; this increases food availability for the phytoplankton. As a result, productivity increases and promotes community diversity.

We can measure the productivity levels of phytoplankton to determine the extent of their impacts on certain ecosystems. Phytoplankton can be collected from upper water regions through bottling. This sampling method is as elementary as it sounds; a container is used to collect a sample of water, then phytoplankton species can be quantified from this sample through select identification methods.

Rates of production can be determined though mapped satellite data and the measurement of certain carbon isotopes found in the areas these phytoplankton occupy. The mapped data displays differing concentrations of the photosynthetic pigment, chlorophyll. This data shows areas which should have higher levels of production, as higher concentrations of chlorophyll point to higher concentrations of phytoplankton.

It is important to understand the impacts phytoplankton have on their marine communities. By identifying areas with higher rates of diversity due to higher primary production from phytoplankton, efforts to preserve ideal water temperatures can be implemented.

Production can also be measured through a phytoplankton’s rate of photosynthesis. Carbon tracers are commonly used to follow the path of an isotope from its reactants to its products. An isotope is a variation of an element; it has the same atomic number as its periodic table counterpart, but the isotope could have different physical properties. In this instance, we can use carbon-14, an isotope of carbon, as a tracer. The carbon-14 will be separated from pools of dissolved inorganic carbon. The resulting carbon can be compared to the total carbon dioxide content, which can allow for the determination of the rate of photosynthesis.

Phytoplankton in Action

Phytoplankton serve as the base of marine food webs; they dominate the ocean’s biogeochemical cycles. These organisms control the trophic structure of their ecosystems. A greater concentration of phytoplankton will result in a rise in production, leading to an increase in species diversity for a given area. Elevated levels of phytoplankton can support groups with larger biomasses; organisms ranging in size from krill to whales thrive because of these planktonic communities.

Marine phytoplankton produce around half of the world’s supply of oxygen. They occupy the first hundred meters of the ocean in order to obtain light needed for their biological processes. They are consumed by zooplankton, which serve as an energy source for smaller fish. These fish are food for larger fish, and then larger predators, like dolphins and sharks. Decaying phytoplankton release the nutrients they have consumed and sequestered; these nutrients are recycled and used by other phytoplankton to keep their oceanic life cycle in motion.

Bad News for Phytoplankton

Earth’s ocean temperatures have been increasing in conjunction with anthropogenic climate change. Increasing temperatures impact a variety of oceanic constituents: sea ice coverage, water temperatures, winds, ocean currents, and circulation patterns. Disruptions on these components would result in a change of the stratification of the water. Phytoplankton tend to occupy shallow water in order to obtain sunlight needed for photosynthesis. Nutrients from surface waters may sink, and in turn, surface marine ecosystems will experience great losses in diversity.

Since phytoplankton control the marine biosphere, they play an important role in our lives on land. Fisheries and shellfish hatcheries rely on phytoplankton to control excess carbon levels in ocean waters. Carbon can raise the pH of marine water, leading to a phenomenon called ocean acidification. Ocean acidification can prevent shellfish larvae from forming their protective shells, leading to massive deaths and failure to reach maturity. This impacts overall shellfish diversity and hatchery harvesting; phytoplankton productivity is linked to our economy.

Phytoplankton play a huge role in the ocean’s overall carbon sink, which is a type of reservoir that serves to absorb and hold atmospheric and marine carbon. Carbon dioxide is a greenhouse gas which directly contributes to the warming of Earth’s atmosphere. By sequestering excess carbon, these small organisms can help lessen the rate at which the Earth is heating. They prove to be of great importance for all of Earth’s organisms and biological processes.

Protecting Our Producers

It is easy to see how a loss in the diversity and sheer number of phytoplankton communities would be detrimental to our own ecosystem. Currently, research mapping the effects of changing temperatures on marine phytoplankton communities is underway. These studies will help researchers improve their understanding of species survival. With this increased knowledge of the innerworkings of plankton adaptation, methods of protection can begin to be implemented to help save these producers.

In the meantime, choosing sustainable methods in performing daily activities can best support both the marine and terrestrial biosphere.

References: Gove, J. M., McManus, et al., (2016). Near-island biological hotspots in barren ocean basins. Nature Communications, 7(1), 1–7., Sigman, D. M. & Hain, M. P. (2012) The Biological Productivity of the Ocean. Nature Education Knowledge, 3(10),21., Thomas, M. K., Kremer, C. T., et al. (2012) A Global pattern of thermal adaptation in marine phytoplankton. Science, 338, 1085.