• Harriet

Sharks and Ocean Forests

Updated: Apr 8

This years UN World Wildlife Day theme was ‘Forests and Livelihoods: Sustaining People and Planet’. Naturally we made it ocean and our focus was forests of the sea - that’s kelp and seagrass! We had so much fun researching these underwater plant-playgrounds that we couldn’t resist passing on that joy to you.

We hear you... "Plants? That’s not why we came here!”. Maybe these seaweed statistics will intrigue you, and we promise we'll get back to sharks just a little further down!

  • Kelp forests are among the most biologically productive habitats in the ocean.

  • They provide food, shelter and nursery grounds for a vast range of species including sharks.

  • Their photosynthesis results in vast amounts of carbon sequestration and oxygen saturated waters.

  • They cover 25% of the worlds coastlines.

  • Some species can grow up to 30cm a day.

  • Kelp forests reduce eutrophication and acidification in their local area.

  • They increase water clarity, in turn increasing phytoplankton diversity and mass.

Darwin quote earlier went on to state...

“If in any country a [terrestrial] forest was destroyed, I do not believe as many species of animals would perish as would here from the destruction of kelp.” - Charles Darwin 1839 in Voyages

Great whites revealed to the world that they were not bothered by kelp in a study published in 2019. Until then, it was widely believed that kelp forests were safe spaces for seals to hide from the predation of sharks - spoiler alert, they’re not. Barriers designed to mitigate shark-human interactions were even created to resemble kelp forests in the hope of deterring sharks from beaches. It turns out that a hungry great white cannot be dissuade by kelp. (Who’d have thought?!) The authors attached cameras and trackers to sharks in South Africa. The trackers revealed all sharks actively swam through dense kelp forests and the cameras showed cape fur seals displaying predator evasion behaviour. Make of that what you will but our conclusion is, seals aren’t safe in seaweed.

Swell sharks and pyjama sharks both use kelp to anchor their egg cases, providing protection during this vulnerable stage of life. The kelp forests also provide ample hunting and hiding grounds for the adult sharks. Broadnose sevengill sharks display clear seasonal aggregation in the kelp forests of South Africa during the summer months. One of the reasons they habituate the forests is due to the abundance of their prey, catsharks. In Australia, you are more likely to encounter a reef shark if you are within 2km of a seagrass meadow, and tiger sharks actually show a preference towards shallow seagrass habitats as this is where their prey is most abundant.

In conclusion, many sharks use many marine forests for many different reasons. Protection for kelp forests and seagrass meadows is protection for sharks.

Forests sustain people, and the underwater world is no different.

Kelp forests are of immense ecological, social and economic importance. These forests are always coastal due to the requirements they need to grow. As such, coastal livelihoods have previously thrived on its industrialisation, farming and harvesting. Many commercially viable fish stocks reside in these underwater forests, proving they are just as important for people as they are the ocean. In South Africa alone, kelp forests support at least 39 different species that are of economic value, and marine tourism is greatly enhanced by these thriving and biodiverse ecosystems.

Potential products that can be attained from farming kelp, seagrass and seaweed include fertilisers, ingredients for ice cream, lipstick, paint, cement, and toothpaste, a source of alginate, and food for human and animal consumption.

Kelp forests and coastal seagrass meadows act as a buffer dissipating wave energy, providing protection to low-lying coastal communities and mitigating damage caused by storms. Coastal protection from erosion and flooding is also a significant benefit of keeping these habitats thriving. However, we must ensure that they are not being damaged via boat entanglement and anchoring, coastal pollution and destructive fishing practices, as they have been previously.

A fascinating five year study published in 2018 showed fishermen of the Sapeken Islands, Indonesia catching protected sharks and other fish illegally. They were doing so via incredibly destructive methods including using fish bombs, potassium poison, and trawling. The authors write "there has been a change in the life and mindset of the people in the Sapeken Islands... these changes were generally driven by at least four main things.” One of these was the improved cultivation of seaweed, seaweed products and subsequent contributions to community development. The islanders improved efficiency and maximised seagrass yields using simple farming techniques. Providing shark fishermen with a tangible alternative income can be a game changer for oceans, and in this situation seagrass was part of the solution!

Bioplastic polymers derived from microorganisms that feed on seaweed have been produced, claiming zero toxic waste and the ability to be recycled into organic waste. Other biodegradable and even edible bioplastics have been created using seaweed. Seagrass has also been shown to tackle oceanic plastic pollution a different way... When blades of the seagrass break off, their fibers form clumps called Neptune balls. These balls have the natural ability to trap small fragments of plastic, these balls then wash ashore during storms. - just waiting for a friendly beach cleaner to come along and pick them up!

Neptune balls, resembling plastic speckled kiwi fruits!

Seagrass meadows store 18% of all oceanic carbon, and can sequester 35 times more carbon than rainforests. Increasing sea temperatures effects the shape of coastlines, increases coastal erosion and is the diminishing Arctic ice is already impacting indigenous people. The European Commission has previously stated that "habitat loss and degradation, pollution, overexploitation of fish stocks, climate change and natural hazards affect the coastal ecosystems”.

All of these can be mitigated to some extent with the propagation and protection of kelp and seagrass forests. Sharks will thrive, and so will humans - let’s hear it for our underwater forests!

If you liked this, you might also like these:


Recent Posts

See All