By 2081-2100, almost forty percent of the phytoplankton and zooplankton assemblages of the subpolar seas will be replaced by poleward shifting plankton species
Ocean Matters podcast hosted by the oceanographer and physicist, Helen Czersk
Seawater may seem like an empty substance to the naked eye. But under a microscope, saltwater would look populated by an array of microscopic plants; bacteria, viruses, and animals. One single teaspoon of seawater can contain more than fifty million viruses. Five million bacteria, 100,000 archaea, and 50,000 eukaryotic microbes; making up ninety percent of all the living biomass in the marine ecosystems. This covers seventy percent of the globe’s surface (Seymour, 2014).
«You can look at a patch of ocean and think there’s just not much happening there. That it’s just a bunch of water. But when you look under a microscope; the diversity of things in that little bit of water is huge. There are so many different life forms. Different shapes and colors and sizes. Modes of existing in that patch of water. For instance, you can spend hours looking at all of these different life forms under a microscope». Explains Dr. Jill Schwarz on the podcast, Ocean Matters, hosted by the oceanographer and physicist, Helen Czerski. Schwarz is a lecturer in marine remote sensing. At the School of Biological and Marine Sciences at the University of Plymouth, UK.
German zoologist, Victor Hensen
This miscellaneous group of microscopical beings is what the German zoologist, Victor Hensen, named plankton in 1887. From the Greek word πλαγκτός (planktons) which means errant. It lay the basis for biological oceanography and planktology. Moreover, these tiny floating microorganisms are in the sea and the ocean’s surface. For instance, they play a key role in the marine ecosystems and the global climate. They are actors in the carbon cycle and oxygen production. As a consequence, the consequences of climate change impacts every ecosystem and species. It also affects plankton; and thus, could impact the regulation of plankton-mediated ecosystem services.
What are the plankton, and what is their role? the basis for biological oceanography and planktology
The world of plankton contains a heterogeneous group of microscopic organisms. Archaea, algae, bacteria, protozoa, crustaceans, mollusks, and coelenterates. Their characteristically morphological and physiological peculiarities drive from their adaptation to their particular living conditions.
In terms of size, these living organisms; unable to control their movement against the currents; transported by the ocean and seas’ wave motion. There are macroplankton, mesoplankton, and microplankton, otherwise called net plankton. The macroplanktons are organisms visible to the naked eye. Jellyfish, crustaceans, and sargassum. Size-wise the mesoplankton like cladocera, chaetognaths, ostracoda, pteropods, and tunicata; range from one to five millimeters. The latter group includes beings like the rotifers; whose size ranges between zero-point-zero-five and one millimeter (zero-point-zero-zero-two and zero-point-zero-zero-four inch).
The seawater food pyramids positive effect on ocean ecosystems
In addition, the division of plankton is: phytoplankton, zooplankton, mycoplankton, bacterioplankton, and virioplankton; based on their functional and trophic characteristics.
«Plankton is the largest catch-all-term for the things that drift in the ocean. The stuff that can’t propel itself. However, it is alive. It describes different life forms, from viruses and bacteria. Extremely small, to phytoplankton. Then there is zooplankton, and small animals. Things like jellyfish that also can’t swim against currents», says Dr. Jill Schwarz. «The phytoplankton start at a micron, so a 1,000th of a millimeter. Go up to as much as a millimeter», explains Dr. Schwarz. «Then there is zooplankton, about the same at the starting points. In addition, some can be very small, and then they go into the millimeters and larger. So often, zooplankton is visible to the naked eye».
Its name derives from the Greek word φυτόν (phytón), meaning plant. It lives near the water surface where there is sufficient sunlight to support photosynthesis. They are autotrophic prokaryotic or eukaryotic algae; for instance, cyanobacteria, coccolithophores, diatoms, and dinoflagellates. Bacteria and archaea belong to the bacterioplankton group, while fungi and fungus-like organisms belong to the Mycoplankton group. The virioplanktons are viruses, while small protozoans and metazoans; such as small crustaceans and other sea animals; belong to the zooplankton group named after the Greek word ζῷον (zoon), meaning animal. However, in marine ecosystems, plankton is a crucial food source to large groups of aquatic organisms. Including fish, whales and marine mollusks like the bivalves.
As a consequence, phytoplankton contributes to the global oxygen production and life on Earth. By absorbing energy from sunlight to produce the chemical energy they need. In addition, through the process of photosynthesis, the phytoplankton release oxygen into the water. Delivering a sizable portion of the world’s oxygen. The death and consumption of plankton sets in motion a set of processes known as the biological carbon pump. To conclude, this takes and sinks carbon from the water surface into the deep ocean. In other words, making the seas and oceans the most significant carbon sink on the planet.
Why is plankton important to our climate?
In September 2021, a study authored by a group of researchers from the Institute of Biogeochemistry and Pollutant Dynamics; and the Department of Environmental Systems Science of the ETH Zürich; published in the British scientific journal Nature Communications. In other words, for this study, the scientists focused on the restructuring of marine plankton assemblages; and the migration happening under the ongoing anthropogenic global warming.
To do that, they used an ensemble of species distribution models. As a result, a total of 336 phytoplankton and 524 zooplankton species. Thus, through these models, the researchers determined the plankton species’ present and future habitat suitability patterns.
Based on their new global dataset, plankton will move to cooler waters to survive. For instance, they will be heading polewards to seek out new suitable habitats, replacing species adapted to cooler waters. The shift of the species’ distribution will be at a median speed of thirty-five km/decade; under a high emission scenario for the end of the current century.
Under warming marine temperatures, there will be an increase in plankton species richness across many regions. Warmer water temperatures tend to promote greater diversity. With phytoplankton species richness that will rise by more than sixteen percent over most areas; aside from the Arctic Ocean.
The changing state of the world’s marine ecosystems consequences for the marine food webs
By 2081-2100 in the subpolar seas; at latitudes projected that global migrations will affect; the number of zooplankton species could rise by up to forty percent. Almost forty percent of the phytoplankton and zooplankton assemblages of the subpolar seas; poleward shifting plankton species will replace them. In this scenario, the quality of the habitats would increase for the smaller organisms. In addition, while decreasing for the larger ones, which would lead to smaller species replacing larger ones.
Therefore, the climate crisis threatens the contribution of the global plankton communities to the ecosystem services. Such as biological carbon sequestration. To conclude, given that the transfer of carbon to the deep ocean would decrease under such conditions.
How are humans affecting plankton communities?
The climate crisis is not the sole anthropogenic phenomenon threatening the plankton communities. After that, ocean pollution has a role as well. Marine pollution may arise from different sources that can affect these species.
With an annual average input of one-point-three million tons; the hydrocarbon inputs to the ocean amount to between 470,000 and eight-point-seven million tons each year. (NRC, 2003).
To conduct an assessment of the effect of oil spills on the dynamics of the microbial plankton communities; a team of researchers from the Centro de Investigación Mariña; Universidade de Vigo and the Instituto de Investigacións Mariñas CSIC; conducted four experiments in the Ría de Vigo during the main characteristic periods of the seasonal cycle.
The samples collected from the experiment were then analyzed using an NPZD model (Nutrients-Phytoplankton-Zooplankton-Detritus; in which the approach was to keep as many model parameters constant as possible. The data they collected allowed them, for instance, to discard the hypothesis of the indirect effects of oil spills on microbial plankton. Under experimental conditions close to natural (González et al., 2022).
How is the climate crisis impacting the plankton?
Marine plastic pollution and microplastics have an adverse impact on the uptake; and the long-term storage of carbon dioxide in the oceans. Such can be seen by their effects on plankton. In conclusion, revealed in a study conducted by researchers from the Ryan Institute at NUI Galway; the UCC, and the Villefranche Sur Mer Laboratory (Wieczorek et al.19).
«Salps play a relevant role in the carbon dioxide uptake and transport down to the seafloor. In our recent study, we found that microplastic ingestion by these little creatures; this may disrupt this natural mechanism of removing the greenhouse gas from our atmosphere. Thus we found that if salps ingest microplastics, they incorporate them into their fecal pellets. Plastics have very low densities and cause the fecal pellets to sink at a slower rate. This means that they stay at the sea surface for longer. Here they’re available for breakdown by bacteria and other organisms; in conclusion, the carbon within the fecal pellets may be respired and released back to the atmosphere as carbon dioxide». Explains the pelagic marine ecologist and lead author of the study, Alina Wieczorek, from the Ryan Institute of the NUI Galway, in a video-presentation of the study released by the aforementioned university.
Alina Madita Wieczorek
Pelagic marine biologist and a post-doctoral researcher at the Marine Institute in Galway.