Plankton's Fight: Understanding Pollution's Impact On Tiny Creatures

Plankton are the main primary producers in aquatic ecosystems, and their productivity is controlled by a number of environmental factors, many of which are influenced by human activities. Plankton are a pivotal trophic level impacted by pollution in the marine environment. They are sensitive to various environmental pollutants, including sewage, industrial waste, and mining effluents. Pollution affects plankton communities at different levels, including abundance, growth strategies, dominance, and succession patterns.

Plankton are also affected by microplastics, which can be ingested by zooplankton and have toxic chemicals attached to them. Climate change, such as increasing ocean temperatures, also impacts plankton, as some species prefer cold water and are relocating to patches of cooler water. Additionally, phytoplankton may be affected by organic contaminants, which can be transformed into less toxic chemicals through a process called biotransformation.

The impact of ocean warming

Plankton are incredibly important to the ocean ecosystem, and very sensitive to changes in their environment, including in the temperature, salinity, pH level, and nutrient concentration of the water. As the oceans warm due to climate change, the impact on plankton can be significant.

One of the main effects of ocean warming on plankton is the reduction in nutrient supply from the deep ocean. As temperatures rise, ocean currents and stability of the upper ocean are altered, resulting in decreased upwelling of nutrient-rich water from the depths. This, in turn, leads to a decrease in the number of phytoplankton, which rely on these nutrients for growth. Phytoplankton are microscopic plant-like organisms that play a crucial role in the marine food web and the Earth's carbon cycle. They are the primary producers in the ocean, taking in carbon dioxide and releasing oxygen through photosynthesis. With fewer phytoplankton, the ability of the oceans to absorb carbon dioxide is reduced, leading to increased carbon dioxide levels in the atmosphere and further contributing to climate change.

In addition, rising ocean temperatures can also impact the composition, distribution, and biomass of plankton communities. Some species may migrate towards higher latitudes or deeper waters in search of more favourable conditions. For example, both phytoplankton and zooplankton communities have been found to migrate poleward as a result of global warming. The increase in temperature can also lead to temporal shifts in the onset of regular annual blooms, their composition, duration, and amplitude, as well as mismatches in timing between trophic levels.

Moreover, ocean warming can influence the frequency and magnitude of plankton blooms. Warmer water temperatures, combined with increased nutrient runoff from land, can create favourable conditions for large phytoplankton blooms. While these blooms can be beneficial for marine life and fisheries, certain types of phytoplankton, such as harmful algal blooms, can have toxic effects on other organisms and the environment.

The effect of ocean acidification and changes in seawater chemistry

Ocean acidification is the process by which the ocean's pH decreases as it absorbs excess carbon dioxide from the atmosphere. This occurs when carbon dioxide molecules react with water molecules to form carbonic acid, which releases hydrogen ions and lowers the pH of the water. This has a significant impact on marine life, particularly those that rely on calcium carbonate to build their shells and skeletons, such as corals, oysters, mussels, and starfish. As the ocean becomes more acidic, these organisms struggle to build and maintain their shells, which can have a ripple effect on the entire marine food web.

Ocean acidification also affects phytoplankton, which are microscopic plants that form the base of the marine food web. Phytoplankton are essential for carbon fixation and sequestration, and their productivity is influenced by a variety of environmental factors, including light availability, temperature, and nutrient concentrations. Ocean acidification can impact the growth and photosynthesis of phytoplankton, with some species benefiting from increased carbon dioxide availability while others are harmed by the drop in pH.

In addition to ocean acidification, seawater chemistry can also be altered by changes in nutrient availability, such as nitrogen and phosphorus, which can affect phytoplankton communities. Increased nutrient supply can support the occurrence of harmful algal blooms, which are often formed by dinoflagellates.

The effects of ocean acidification and changes in seawater chemistry on phytoplankton communities are complex and can vary depending on the species and environmental conditions. Some phytoplankton species may be able to adapt to more acidic conditions, while others may struggle to survive. Overall, ocean acidification is expected to have significant impacts on marine ecosystems and food webs, with potential consequences for fisheries, aquaculture, and human food security.

The influence of microplastics

Microplastics are a new class of environmental pollutants that are accumulating in the environment at an uncontrollable rate, threatening aquatic organisms. Plankton are the basis of food webs and play a significant role in the material circulation and energy flow of aquatic ecosystems. They are also sensitive to various environmental pollutants.

Microplastics can affect plankton on different scales, from individual to community level. However, few studies have been carried out on the impacts of microplastics on plankton from a microcosmic perspective, such as genomics and proteomics, and from a macroscopic aspect, such as population and community responses.

Microplastics can affect plankton in the following ways:

• Microplastics can interfere with the delicate food web and consequently may even affect element cycling.
• Microplastics can be mistaken for prey by plankton, which can lead to a buildup of phytoplankton at the ocean's surface. This excess organic matter, when it dies, consumes oxygen as it rots, exacerbating deoxygenation driven by climate change.
• Microplastics can alter microbial communities in aquatic sediments, changing their species composition and altering their nitrogen cycling activity. This could magnify the ecological consequences of already occurring human changes to natural nutrient cycling, possibly intensifying harmful aquatic algal blooms caused by synthetic fertiliser runoff.
• Microplastics can affect the feeding behaviour, reproduction, and survival of plankton.
• Microplastics can reduce the growth, lifespan, reproduction and fertility of plankton.
• Microplastics can alter how feces and other organic particles form, sink and break down in the ocean, potentially slowing and disrupting ocean carbon storage.
• Microplastics can impact the settlement of barnacle larvae.
• Microplastics can release toxic leachates that interfere with development and survival.
• Microplastics can act as vectors for toxic chemicals that adsorb to the plastic surface, as well as potentially transporting invasive species long distances.

The consequences of eutrophication

Eutrophication is a leading cause of impairment of many freshwater and coastal marine ecosystems in the world. It is characterized by excessive plant and algal growth due to the increased availability of one or more limiting growth factors needed for photosynthesis, such as sunlight, carbon dioxide, and nutrient fertilizers. Eutrophication occurs naturally over centuries as lakes age and are filled in with sediments, but human activities have accelerated the rate and extent of eutrophication through both point-source discharges and non-point loadings of limiting nutrients, such as nitrogen and phosphorus, into aquatic ecosystems.

Eutrophication has several consequences, including:

• Increased biomass of phytoplankton resulting in algal blooms
• Dissolved oxygen depletion or hypoxia
• Eutrophication-driven acidification
• Species biodiversity decreases and the dominant biota changes
• Increased blooms of gelatinous zooplankton
• Toxic or inedible phytoplankton species (harmful algal blooms)
• Human health impacts
• Impact on recreation and tourism
• Aesthetic impacts
• Economic impacts

The effect of pollutants

Pollution is a pressing issue for plankton, as it can affect their abundance, growth strategies, dominance, and succession patterns. Even if there are no direct changes in plankton communities, pollutants can accumulate in plankton and be passed on to other trophic levels, resulting in biomagnification.

Climate change

Climate change is a significant threat to plankton. Phytoplankton are the main primary producers in aquatic ecosystems, and their productivity is controlled by a number of environmental factors, many of which are influenced by human activities. For example, phytoplankton productivity is highly dependent on light availability, but excessive visible and UV radiation can impair productivity.

Increasing temperatures can also cause deoxygenation, especially in coastal and estuarine ecosystems, which can turn into "dead zones" for most marine organisms. Warmer temperatures can also favour blooms of toxic phytoplankton.

Ocean acidification

Increasing atmospheric CO2 concentrations can also negatively impact phytoplankton. Ocean acidification due to increased atmospheric CO2 concentrations changes seawater chemistry, reducing calcification in phytoplankton, macroalgae, and many zoological taxa.

Nutrient pollution

Nutrient pollution, such as from agricultural runoff, can also impact plankton communities. While phytoplankton may benefit from increased nutrient availability, it can also lead to harmful algal blooms, which can be toxic to other marine organisms.

Microplastics

Microplastics are a new class of environmental pollutants that can accumulate in the environment and threaten aquatic organisms, including plankton. Microplastics can directly harm plankton by blocking sunlight, which is necessary for photosynthesis, and can also introduce toxic chemicals into plankton, which can then be passed up the food chain.

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