The Botanical Ocean: Seaweeds and their Ecology

Elyssa Quinton

Summer is all around us in the UK; the flowers are in full bloom, the sun is out and we are heading to the beach at every opportunity we can find! This is the perfect season to learn about a group of marine organisms that frequently get overlooked whilst visiting our shores; but they are simply fascinating: seaweeds. They are key in maintaining a happy marine ecosystem, they have a very interesting biology, and are also under threat. Continue reading and check out our youtube video to find out more….

When the tide is low, a whole array of seaweed can be found. Photo: Toby Russell @trfilmphoto

When the tide is low, a whole array of seaweed can be found. Photo: Toby Russell @trfilmphoto

What is a seaweed?

So a seaweed is an algae, and algae are split into two groups: micro-algae (phytoplankton) and macro-algae (seaweed). All algae contain chlorophyll, the green pigment that land plants also have. Chlorophyll uses sunlight to make food for plants in a process called photosynthesis. Unlike land plants, seaweeds lack true stems, roots, leaves and vascular tissue (tissues that conduct water, sap and nutrients). Instead of roots, seaweeds attach their fibrous structures to the sea bottom or other solid structures using root-like ‘holdfasts’. However these holdfasts do not extract nutrients as the roots of plants do. Seaweeds absorb their nutrients from the water column via their blades (the seaweeds ‘leaves’). With all these yummy nutrients, seaweed can then grow and reproduce to form dense aggregations, such as:

  • Underwater kelp forests

  • Free-floating gulfweed (Sargassum) mats in the Sargasso Sea

  • And a wide variety of species you find along the UK rocky shore such as toothed wrack (Fucus serratus)

Toothed wrack ( Fucus serratus ), a common brown seaweed found on British rocky shores. Photo: Toby Russell @trfilmphoto

Toothed wrack (Fucus serratus), a common brown seaweed found on British rocky shores. Photo: Toby Russell @trfilmphoto

There are many types of seaweed…

You may have realised from your trips to the seaside that seaweeds come in three different colours; red, brown and green. Green (Chlorophyta) tend to be found mostly at the top of the shore, for example sea lettuce (Ulva spp.). Brown algae (Phaeophyta) include kelp and wracks (Fucus spp.), are more commonly found in colder zones, and are absent from tropical waters. Red algae (Rhodophyta) include coralline algae, laver (Porphyra spp.) and Irish moss (Chondrus crispus), which carpet the lower half of the rocky shore which is exposed at low tide along the coasts of the Atlantic. Each species is adapted specifically to where they are found and what conditions they are subject to. But ALL seaweeds are only found at depths of 50m or less. 

Ulva  spp., a common green seaweed found along the british shore. It’s also called Sea Lettuce and is edible! Photo: Toby Russell @trfilmphoto

Ulva spp., a common green seaweed found along the british shore. It’s also called Sea Lettuce and is edible! Photo: Toby Russell @trfilmphoto

Oxygen Production

Seaweeds get their food through the process of photosynthesis, which uses energy from the sun to convert carbon dioxide into organic molecules, and produces the by-product oxygen. Algae produce an estimated 30-50% of the net global oxygen available to humans and other terrestrial life. Although they are not as complex as plants, they play the same role in the ecosystem as primary producers. They are at the base of the food chain, and the existence of nearly all marine life (whales, seals, fish, turtles, shrimps, lobsters, clams, octopuses, worms etc.. the list goes on) depends upon seaweeds and phytoplankton. It’s estimated that 2-10% of global primary production is a result of seaweeds, which may not sound like a lot, but it’s pretty impressive when seaweeds inhabit such a small area!

Algae (including seaweeds) produce 30-50% of the worlds oxygen production and sustain a whole ecosystem of life. Photo: Toby Russell @trfilmphoto

Algae (including seaweeds) produce 30-50% of the worlds oxygen production and sustain a whole ecosystem of life. Photo: Toby Russell @trfilmphoto

Why are they so important?

Seaweeds create structure and habitat that provides shelter and food for thousands of marine creatures, such as fish, sea urchins and crustaceans. They also support commercial fisheries, are used in foods, cosmetics and medicines, and protect our coasts by reducing wave action and storm surges. It’s important for us to monitor them so we can understand and manage these vital resources sustainably. For example The Big Seaweed Search is a citizen science project in the British Isles which enables members of the public to complete a survey on 14 seaweed species found in the UK. So make sure to check out their website and get involved!

Threats

Along with all other marine organisms, all seaweeds are under threat from….

  1. Sea temperature rise 

  2. Ocean acidification 

  3. Non-native species 

Case Study: Underwater forests, a fragile ecosystem

Kelps are among the largest algae; some species exceed 33 meters in length, and grow faster than tropical bamboo e.g. the giant kelp in Monterey Bay has been recorded to grow 10-12 inches per day! Kelp is held upright in the water column by gas-filled bladders at the base of each leaf-like blade. Kelp forests sustain a whole ecosystem just like rainforests do, but once the ecosystem is altered slightly there can be detrimental effects. This happened in California in the 1820s when sea otters (a keystone species) were hunted to near extinction. Their prey’s - sea urchins (the vacuum cleaners of the ocean floor) - population was then able to explode and take over. The sea urchins feasted endlessly on the holdfasts of the kelp once their only predator was removed, creating underwater barrens devoid of the abundant life once found in the kelp forests. These urchin barrens contain very low biodiversity, but due to the ban of sea otter hunting in 1911 sea otters are slowly making a comeback in California. Yipee!

New seaweed discoveries

Here are some exciting new discoveries about seaweeds….

From superfood to super-conductor 

American Chemical Society. "Seaweed: From superfood to superconductor." ScienceDaily. ScienceDaily, 5 April 2017

Researchers have made a seaweed-derived material to help boost the performance of superconductors, lithium-ion batteries and fuel cells. Testing showed that the seaweed-derived material had considerably more of a power output than the capacity of traditional graphite anodes for lithium-ion batteries. This for example could help double the range of electric cars using a completely carbon free material!

Seaweed helps trap carbon dioxide in sediment

Florida State University. "Seaweed helps trap carbon dioxide in sediment." ScienceDaily. ScienceDaily, 3 June 2019

‘Blue carbon’ is the term used when carbon is captured in marine systems, both through photosynthesis and then by trapping it in the seafloor. This study confirmed that seaweeds are just as important as seagrasses and mangroves is capturing and storing carbon dioxide, ultimately helping to stabilise the global climate system. The team found that about 8.75 grams of carbon are trapped per square meter of sediment each year by macroalgae!

Hopefully I have shown you there is a lot more to seaweeds that meets the eye… So next time you visit a rocky shore, take a second to stop and appreciate the ecosystem services seaweeds provide.


If you want to find out more, watch short this video where Elyssa take you through some fun facts about seaweeds found on the UK rocky shores.

If you’ve enjoyed reading this article, look out for more articles from Elyssa and follow her here @elyssa.quinton

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