Did you know on November 3rd we celebrate some remarkable creatures: jellyfish!
Often disliked because of their stinging tentacles, jellyfish are some of the most fascinating creatures in the ocean, and they play an important role in the marine ecosystem. They are also a common sight in UK waters, and their presence has been increasing in recent years.
Key facts about jellyfish:
Jellyfish are gelatinous invertebrates (animals with no backbones) that belong to the phylum Cnidaria.
They have a bell-shaped body and tentacles that are armed with stinging cells.
Jellyfish can range in size from a few millimeters to over two meters in diameter.
Some jellyfish species are bioluminescent, meaning they can produce their own light.
Jellyfish are found in all oceans and at all depths.
They have a complex life cycle that involves two distinct stages:
polyp: polyps live on the seabed and reproduce asexually by budding off new polyps.
medusa: they reproduce sexually by producing eggs which develop into larvae that will settle to the seabed and become polyps.
They have been around since the Cambrian Period more than 500 millions years ago.
Why are they important for the marine ecosystem?
Jellyfish provide shelter and protection under their tentacles for young fish.
Jellyfish also help young fish to feed on small organisms found on them or on prey that jellyfish kill on their travels.
By providing food and shelter, jellyfish help to increase populations of fish species, such as whiting in the North Sea, and other commercially-important species.
Jellyfish are an essential part of many food chains, being preyed upon by lion's mane jellyfish, sunfish, spadefish, crabs, other large crustaceans, seabirds and marine turtles.
Jellyfish continue to sustain marine species even after death, as deep-sea creatures like hagfish feast on their remains.
Jellyfish help with nutrient cycling in the ocean by transporting nutrients, such as nitrogen and phosphorous, through the sea.
Nutrients released by jellyfish through feeding or excretion are a great source for other organisms, such as phytoplankton.
Jellyfish can play a role in water quality by filtering out plankton and other small organisms.
Presence of jellyfish in the UK:
There are thousands of jellyfish species around the world but only 6 jellyfish species and 2 jellyfish-like hydrozoan species have been frequently reported in UK waters:
Barrel jellyfish (Rhizostoma pulmo)
Blue jellyfish (Cyanea lamarckii)
Moon jellyfish (Aurelia aurita)
Compass jellyfish (Chrysaora hysoscella)
Lion's mane jellyfish (Cyanea capillata)
Mauve stinger jellyfish (Pelagica nocticula)
Portuguese man o' war (Physalia physalis) - a floating colony of hydrozoans
By-the-wind-sailor (Velella velella) - a floating colony of hydrozoans
Learn some fun facts about them here.
Jellyfish can be found all around the UK coast, but they are most common in the warmer waters of the south and west. They are also found in estuaries and rivers.
Is the presence of jellyfish in UK waters a sign of climate change?
There is strong evidence to suggest that the presence of jellyfish in UK waters is a sign of climate change. Warmer sea temperatures and ocean acidification are both known to favour jellyfish growth and reproduction (Purcell et al., 2007; Attrill et al., 2007; Enrique-Navarro et al., 2021).
Climate change is not the only factor that can affect jellyfish populations. Other factors, such as pollution and overfishing, can also play a role. However, climate change is likely to be the most significant factor affecting jellyfish populations in the long term.
As mentioned, jellyfish play an important role in the marine ecosystem. They are a food source for many marine animals, and they help to control the populations of other organisms. However, increasing jellyfish populations can have negative impacts on marine ecosystems and human communities. For example, jellyfish blooms can disrupt fisheries, damage fishing gear, and pose a risk to human health.
As climate change continues to warm the oceans, we can expect to see more jellyfish blooms in UK waters. It is important to understand the causes and impacts of jellyfish blooms so that we can develop effective management strategies.
The upcoming COP28, the 28th United Nations Climate Change Conference, which will be held in Dubai from November 30 to December 12, 2023, is a critical opportunity for world leaders to come together and take action to reduce greenhouse gas emissions and limit global warming. By addressing the root cause of climate change, we can help to mitigate the impacts of jellyfish population increases and protect the marine environment.
Conclusion:
Jellyfish are an important part of the marine ecosystem, but their increasing presence in UK waters is a cause for concern. Climate change is likely to play a role in this increase, and it is important to understand how this will affect jellyfish populations and the wider marine environment, and to prevent deleterious impacts of jellyfish blooms.
Conservation actions start now and you can help the Marine Conservation Society, a leading voice in the UK for jellyfish conservation, by reporting your jellyfish sighting. Learn to identify jellyfish and become a citizen scientist.
Happy World Jellyfish Day!
BEES