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Why Is Seagrass So Important To Our Planet?

Seagrass and the species that live amongst them are surprising allies against a warming climate”

Sir David Attenborough, Blue Planet II

Coral reefs are the shining celebrities of the marine ecosystems, with mangroves following not too far behind. Yet, the less famous seagrass meadows are just as important due to the benefits they provide marine life and maritime nations globally.

Seagrasses are marine flowering plants. They differ from seaweeds and form large and dense beautiful meadows under the sea. Look into one of these meadows and you’ll find that much like the rainforests you see on programs like “Planet Earth (BBC)”, there is a wealth of colourful life, ranging all different shapes and sizes. If you are an admirer of green turtles, dugongs, and seahorses, then you should also be an admirer of seagrass…

But what if I told you, they do not just support marine animals…

They support humans too! [1]

This blog aims to inform you on the astounding benefits that seagrasses provide globally, ranging from carbon storage to fisheries, to fighting poverty and to helping biodiversity.

Biodiversity: Food and Habitat

Seagrass and turtle

Seagrass meadows host multiple species ranging from tiny epiphytes (plants that grow on other plants), invertebrates and fishes to large mega herbivores such as green turtles and dugongs.

In fact, these beautiful but endangered green turtles [2] feed upon seagrass all around the globe!

But wait… it’s not just the turtles that benefit from the seagrass, the seagrass benefits from the turtles too!

By grazing upon new growth of seagrass tissue, green turtles are actually able to help provide seagrass with greater resilience to impacts from humans such as eutrophication [3]. Eutrophication, a process which occurs when the environment becomes enriched with nutrients [4]. It can be deadly!

British Isles

In the British Isles, the intelligent and beautiful cuttlefish are known to lay their eggs in seagrass meadows, where they attach their eggs (called “seagrapes”) to the base of the seagrass leaves. During the summer, you might even spot the juvenile cuttlefish hiding amongst the seagrass leaves.

Furthermore, the two species of sea horse in the British Isles: the spiny seahorse and the short-snout seahorse, are also known to forage in seagrass meadows, where tiny shrimp that reside in seagrass meadows are the perfect meal for these majestic creatures and their small mouths.

Other notable species include: Plaice, Pollack, Snakelocks anemones and herring.

Find out more here!

Biodiversity: Fish Nurseries

Seagrasses provide shelter much like a nursery for young juvenile fish that are both commercially and recreationally recognised species [5]. The blades of the grass provide the fish with protection from predators and an increased availability of food. This food can be in the form of small crustaceans that dwell on the seafloor and consume dead seagrass.

Yes, that’s right, the fish you have with your fish and chips you eat on the coast… may have grown up in a seagrass meadow! [6]

Seagrass and Fisheries

Hundreds of millions of human beings across planet earth consume seafood through enjoyment and or necessity.

Current fishery stocks declining do not align with requirements of the planet. It is expected by the year of 2050, the human population will require an additional 75 million tons of protein from fish and aquatic invertebrates [7], which is an increase of 50% from current supply!

Whilst a significant proportion of efforts towards securing sustainable fisheries through policies and regulations target the act of fishing, the vital habitats that many fisheries depend on need to also be considered and protected [8].

“The plants are important fish nurseries and key fishing grounds. Losing them puts the livelihoods of hundreds of millions of people at risk too and exposes them to increasing levels of poverty.”

- Dr Richard Unsworth, Swansea University

Small Scale fisheries and Poverty Alleviation

Notably, since seagrass meadows are shallow coastal habitats, they offer a potentially exploitable fishing ground. In a recent study by Dr Richard Unsworth, Swansea University, it was found of the 10 most landed small-scale fisheries from 13 locations across the tropics/subtropics, roughly 79% have been associated with seagrass [9].

These small-scale fisheries provide the major protein source for millions of people in the tropic/subtropic developing regions, displaying significant evidence that seagrass contributes greatly to food security in such areas.

In essence, seagrass provides easy access for fishing at a low cost, which is beneficial for poorer fishers using only lines and canoes. 

Major Offshore Industrial Fisheries

The nursery habitat that seagrass provides is utilised by 21.5% of the landings from species recorded on the Food and Agriculture Organisation (FAO) “Top 25 most landed species” list. The most landed species on the planet, the Alaska Pollock is included on this list.

In the Mediterranean, seagrass associated fish species were estimated to contribute up to 40% of the value of commercial fisheries landing [10]. It was also estimated that seagrass beds annually directly contributed 4% to the total of commercial landings (€58–91 million). Seagrass beds managed all of this despite only covering 2% of the seafloor in the area.

However, much of the industrial scale fishing activity is located offshore with lots of catch exported, resulting in a disconnect between the consumers (such as you and me) and the supply chain and habitats. This may result in seagrass meadows not being appreciated in the world of offshore fisheries. 

Wait a minute, hold up…

Let’s just wrap our heads around how many fish species utilise seagrass?

According to Unsworth et al., 2018 [11]

Et al meaning “and others’

  • 746 species in the IndoPacific
  • 486 species in Australasia
  • 222 species in the North East Pacific
  • 313 species in the Caribbean
  • 297 species in the North Atlantic

Carbon Sequestration

Seagrass occupies a small area of the ocean, but it packs a hefty punch.

Despite occupying less than 0.2% of the area of the world’s oceans, seagrass is responsible for storing up to 11% of the yearly estimated organic carbon buried in the oceans [12]. Seagrass is capable of storing carbon at a greater rate than tropical forests!

Yes, that’s right! Seagrass is key in the fight against climate change [13].

Sediment Stabilisation

Another fascinating service seagrass provides humans is coastal protection.

The presence of a seagrass meadow can reduce the force of incoming waves before reaching the beach, which lowers beach erosion rates [14].

Who would’ve thought this plant would be able to protect our coasts against storm induced wave action?

Furthermore, seagrass beds can reduce sediment resuspension up to three-fold when compared to an unvegetated bottom [15]. This stabilisation of sediments helps coastal habitats and allows an area for mangroves to grow on.

Reduces exposure to Pathogens

Studies have shown up to a 50% reduction in the relative abundance of bacterial pathogens that could potentially harm humans and marine organisms when seagrass meadows were present [16].

Corals have also been shown to display lower levels of diseases associated with bleaching when seagrasses were present nearby.

That’s right, seagrass is keeping our waters nice and healthy! 

To Summarise

Reading this, so far you have seen how wondrous and helpful seagrass can be towards our planet and its people by providing the following:

  1. Food and habitat for marine organisms
  2. Nurseries for fish
  3. Carbon sequestration
  4. Poverty alleviation
  5. Sediment Stabilisation
  6. Reducing exposure to pathogens

…and yet we are only scratching the surface.

Despite seagrass being a marine powerhouse, it is not invincible, and it is facing horrific threats, many of which are human induced.

The loss of seagrass will have detrimental impacts to marine ecosystems and human lives across the planet.

Stay tuned for next time when we find out why seagrass is endangered.

 

Written by Callum Hobbs - Marine Habitats Advisor, MSc Marine Environmental Management.

 

References 

[1] https://conbio.onlinelibrary.wiley.com/doi/pdf/10.1111/conl.12566

[2] https://www.iucnredlist.org/species/4615/11037468

[3] https://besjournals.onlinelibrary.wiley.com/doi/10.1111/j.1365-2745.2011.01900.x

[4] https://oceanservice.noaa.gov/facts/eutrophication.html

[5] https://www.sciencedirect.com/science/article/pii/0304377084900792

[6] https://www.sciencedirect.com/science/article/pii/S235198941400050X

[7] https://academic.oup.com/icesjms/article/68/6/1343/704758

[8] https://theconversation.com/for-the-love-of-cod-lets-save-our-disappearing-seagrass-33196

[9] https://conbio.onlinelibrary.wiley.com/doi/pdf/10.1111/conl.12566 

[10] https://conbio.onlinelibrary.wiley.com/doi/abs/10.1111/cobi.12436

[11] https://conbio.onlinelibrary.wiley.com/doi/pdf/10.1111/conl.12566

[12] http://game-csic.com/site/wp-content/uploads/2016/08/Fourqurean-et-al-2012.pdf

[13] https://www.projectseagrass.org/why-seagrass

[14] https://journals.plos.org/plosone/article/file?id=10.1371/journal.pone.0062413&type=printable 

[15] https://www.researchgate.net/publication/223719945_Sediment_Retention_by_a_Mediterranean_Posidonia_oceanica_Meadow_The_Balance_between_Deposition_and_Resuspension

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