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What’s up with the algae, and why should we care? | Mollie Allerton

Algae are like plants, they need the right amount of light and nutrients to grow and they take

up carbon dioxide to photosynthesise and produce oxygen. Phytoplankton are micro-algae

and form the basis of marine food webs, either directly or indirectly providing food for a lot

of life in the ocean. Phytoplankton are pretty important - phytoplankton photosynthesis

provides 50% of the world’s oxygen- that’s every other breath that you take!

Diatoms are a common type of phytoplankton and are amazingly diverse! Image by Carolina Biological Supply Company.

The core of my project is monitoring changes in phytoplankton communities in response to

changes in water quality, and translating this into policy changes which will aim to better

manage and monitor our coastal ecosystems.

Water quality can be impacted by a wide range of factors. I am investigating how nutrient

enrichment (specifically of nitrogen and phosphorous), and subsequent eutrophication, impacts water quality and phytoplankton. Eutrophication happens when waters are enriched with nutrients, allowing increased growth of phytoplankton which might have previously been regulated by limited nutrient concentrations. Nutrients can come from point sources, such as industrial wastewater which are directly discharged into water. Point sources are easily identifiable sources of nutrient pollution which makes them easier to manage and regulate. Diffuse sources, on the other hand, are less manageable. Diffuse sources mainly refer to the runoff from agricultural land. When it rains, nutrients are washed off into rivers and into coastal waters which leads to the undesirable effects of eutrophication.

Research in action: Samples can be taken from an instrument called a CTD to test for dissolved oxygen concentrations in the water column. Depleted oxygen concentrations can occur as a result of eutrophication [left image]. The instruments pictured on the right are called Cefas SmartBuoys. The SmartBuoys collect data on (amongst other things) nutrient concentrations and phytoplankton samples, to help track changes in water quality and phytoplankton communities.

What exactly are those effects? Eutrophication causes increased phytoplankton biomass,

which means blooms of algae. This is undesirable because:

a) Algal blooms covering the surface of the water prevent light making its way down

into the water column and can limit the growth of other life

b) Some types of algae can be harmful, which is problematic for those feeding on the

algae, but this can also be harmful to us if we were to eat anything contaminated with

the toxins, like shellfish. Toxins from harmful algal blooms can also be airborne!

c) When phytoplankton die, oxygen is used up as they decompose. In areas where there

have been large algal blooms, oxygen depletion can occur in the water column,

meaning nothing is able to live there.

There are efforts to manage and regulate the nutrient enrichment and subsequent eutrophication of our coastal waters. This is positive. Reduced nutrient enrichment is likely to

result in fewer eutrophication events. However, phosphorous has been much more effectively

managed than nitrogen, resulting in an increase in the ratio of nitrogen (N) to phosphorous (P) that is entering our coastal waters, and has resulted in an imbalance in nutrients concentrations. This might not seem like a big issue but a change in N:P has implications for phytoplankton. Different species are likely to react differently to the change, and so there is also the potential for a shift in the community composition of phytoplankton as a result of the imbalance. Changes in the species making up coastal phytoplankton communities could impact the entire food web as variations in phytoplankton species can mean changes in the food sources and nutritional quality for grazers, and this includes fish that we eat.

Keeping phytoplankton communities healthy and balanced is important for us and is something we should definitely be concerned about; they provide us with the essentials – air and food! When we think of clean and healthy oceans, we should be considering everything, especially down to the microalgae.


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