LONG hours of sunshine in the spring months have not only seen my garden plants bloom in South West England like they have never bloomed before and now, in summer with bees and butterflies harvesting nectar from lavender and lilac beds. Moreover, such warmer conditions have seen phenomenal blooms of marine algae in the North Atlantic Ocean much to the delight of British and French fishermen. These marine blooms are composed of phytoplankton or microalgae, which are not dissimilar to most terrestrial plants for both contain chlorophyll and need sunlight to survive. Through photosynthesis they convert carbon dioxide, via sunlight, and then release oxygen into the seas.
Microscopic as they are, plankton in vast numbers are essential parts of the oceanic food chain as readily available sustenance for zooplankton, krill, jellyfish, shrimp, and even many species of whale. The very word ‘plankton’ is derived from the Greek word ‘plagktos’, meaning wandering or floating for, indeed, they drift in ocean currents, requiring inorganic nutrients such as nitrates, phosphates and sulphur to convert into proteins, fats, and carbohydrates.
Types of phytoplankton
The two most common types are diatoms and dinoflagellates. The former are single celled algae of over 100,000 species and viewed under a microscope look like designer buttons! These minuscule diatoms create between 50 and 80 per cent of all organic materials in our oceans. With an outer shell, thought to be composed of calcium carbonate, which is rigid, they can grow to up to a couple of metres and weigh up to a tonne.
Relying on ocean currents for transport, in North Atlantic waters they capitalise on the warm North Atlantic or Gulf Stream Drift to move to Western European seas. Not only do they sustain fish with food and us as apex predators but create diatomaceous earth derived from their skeletons, which upon their deaths sink to the seabed. This material is used in the brewing industry to clarify beer!
Dinoflagellates are constantly on the move generating their own energy and whip their tails or flagella effectively for propulsion over short distances. Most phytoplankton species are found in the upper layers of oceans. This summer, in the Western Approaches to the English Channel, huge phytoplankton blooms had developed in June. Marine Biologists at the University of Plymouth have ascribed this feature to the hottest May month ever recorded in Europe. This exceptionally warm weather caused a stratification of saltwater temperatures thus allowing plankton to float very near the surface to catch sunlight and thrive. Over the last 60 years, researchers have observed a massive shift of warmer water species of plankton spreading northwards, indirectly related to climate change.
Zooplankton or animal plankton
These species essentially feed on other plankton form and range in size from tiny copepods of under one millimetre long to the size of jellyfish. Copepods look like transparent noodles yet, in a bloom, weigh more than any other species of animal on Earth. They feed on phytoplankton blooms and quickly breed to create huge blooms of their own, constituting 70 per cent of the total zooplankton species.
Only a few millimetres long, they have small beating legs to sweep phytoplankton towards their heads where they are trapped in leg-baskets. On moonlit nights, they swim upwards from the deeper ocean to graze on the phytoplankton blooms.
These are a form of animal plankton composed of larvae and very small pelagic fish eggs, which spend their earliest lives amongst phytoplankton. They spend the summer months in colder waters and for the rest of a year in tropical and subtropical seas hunting for food. In the main they are herbivorous but as they mature they may become large fish in open waters or else settle for life on the seabed.
Not all is good news
Whilst plankton blooms may excite fishermen and their incomes, these blooms can be nuisances when tidal movements sweep into river estuaries and allow further blooming to occur. This can lead to the eutrophication of river species of fish. Such algae blooms thrive on an excess of nutrients as rivers discharge their load into the sea.
The main nutrients come from nitrate and phosphorous compounds from farms, sewage, and fossil fuel burning. In regions of heavy rainfall fertilisers and pesticides are leached out from the soil into rivers. Such inputs into the sea we have seen affecting offshore coral reef polyp-growth in both Sabah and Sarawak. Healthy plankton affects the whole marine ecosystem and is vital to the food chain. Let’s not dismiss these small ocean dwellers because of their minute size for plankton creates almost 50 per cent of the oxygen we breathe as well as fish food for our stomachs!
Climate change effects
As global warming has gradually increased so has the frequency and intensity of typhoons, hurricanes, and tropical cyclones related directly to increases in ocean temperatures. This has resulted in a 40 per cent loss in phytoplankton mass over the last 70 years. Plankton survives better in cooler oceanic areas and when other areas become too warm, the sea algae and its marine grazers follow a migration pattern. This will, in turn, affect local fishermen in catches and economies.
Without phytoplankton, more carbon dioxide will remain in the atmosphere and our climate will forever become warmer for both the realms of our atmosphere and our oceans are interlinked. As atmospheric gases have been absorbed in the glacial and periglacial areas of our world, these gases are now rapidly being released, with ever present thawing, so plankton will become an even more important trap of these gases. When plankton dies it sinks along with its carbon dioxide stores to the ocean bed, thus ‘locking up’ these gases for millions of years.
Not all forms of plankton are beneficial to marine and human life for there are toxic species which can breed cholera and destroy marine life. Such algal blooms, known as ‘red tides’ have, over the years, caused fisheries to collapse along both the Atlantic and Pacific coastlines.
Whilst the frequency and intensity of tropical and subtropical storms cause huge amounts of damage and loss of human lives, they do, in fact, stimulate plankton growth by churning up oceanic waters and thereby lifting valuable compounds to the surface. Such compounds of iron, nitrates, and phosphates are vital to plankton growth.
Many nations in our world rely on fish as their major source of protein and thus healthy plankton at the bottom of this food chain is vital for our sustenance. We are in the new geological era of the Anthropocene and our prayers for the oceans rid of floating plastic and a cleaner atmosphere can only be answered when all nations ‘bite the bullet’ to ensure pledges are converted into realities.
The simple answer lies in the adage, ‘Actions speak louder than words!’ Climate change, whilst stimulating plankton growth in some areas of our oceans, has seen a depletion of plankton in other areas. Traditional local fisheries are seeing, more and more of their vessels travelling to ever far flung parts of the oceans, for where plankton blooms so the fish are more plentiful.