Author: Eve Grayson

Cnidarians… a little bit of history

Simple pioneering creatures

Soft corals: Dead-man’s fingers (Alcyonium digitatum). Photo Credit: Linda Pitkin/2020VISION

Cnidarians sound like complicated marine creatures, but in actual fact, they’re quite simple. Simple in terms of their body structure anyway. They have no proper organs to speak of, but a very basic nerve network, and with no anus to get rid of waste, their mouth doubles up as both! They may not appear to be pioneering, but the development of cnidarians marked a turning point in our evolution history, making them possibly the most important creatures to populate our earth.

What are cnidarians?

There are over 11,000 species of cnidarians, mostly of which are carnivorous living in the marine environment. They can occur in the form of either a polyp (anchored to the sea bed) or a medusa (free-swimming), with some spending their lifecycles alternating between the two. A distinguishing feature is their stinging cells, called cnidae, which contain a capsule that can be discharged in defence or to capture prey. These extraordinary weapons can come in a variety of forms, but are usually are a harpoon like structure attached to a coiled thread that shoots out under water pressure when the cell is triggered by touch or chemical stimulus.

There are three classes of cnidaria we find here in Wales:

A group of plumose anemones (Metridium senile) feeding on a moon jellyfish (Aurilia aurita), which they have captured. Photo credit: Alexander Mustard/2020VISION

Anthozoa (anemones and soft corals)

These are unique in the sense that they don’t have a medusa phase, and live their entire life as a polyp. Their name translates to ‘flower animals’, which is very describes these creatures beautifully. They include sea fans and sea pens.

Hydrozoa (marine hydroids, Portuguese man-o-war, Obelia)

Oaten pipes hydroid (Tubularia indivisa) Photo Credit: Linda Pitkin/2020VISION

Most of these live in colonies and their life cycle includes both polyp and medusa phase.

Scyphozoa (jellyfish)

Spend most of their life-cycle in the medusa phase, which is what we typically think of as a jellyfish; a large floating predator.

Compass jellyfish. Photo Credit: Paul Naylor

Cnidarian Evolution

Before cnidarians, sponges were the only living animals on planet earth. However, around 630 million years ago, the first cnidarians appeared, set to be possibly the most pivotal moment during evolution. Cnidarians were the first animals to have a mouth attached to a stomach that could digest food, an incredible invention that would spread across the animal kingdom. Their radical developments don’t stop there either. They also created movement. Cnidarians have two sets of muscles meaning they can bend in any direction, and along with a network of nerves that send electrical impulses to the muscles, they were the first animal to be able to generate movement. It may not have looked like much to us now, perhaps a very subtle stirring or swaying, but this was ground-breaking in the sense that all creatures that have evolved to soar, swim or crawl today rely on this ancient inheritance from cnidarians.

Sea fans. Photo Credit: Paul Naylor

It was originally thought that hydrozoa were the most primitive of cnidaria, yet new evidence suggests that anthozoa were among the first to develop. What we are certain of is that humans, along with many other animals have so much to thank those first cnidarians for, with many later species trialling different methods of reproduction, feeding and sensing .

So the next time you see a jellyfish pulsating by, or a swaying anemone in a rockpool, take a little minute to think “you’re an ancestor of mine”.

Seagrass: Meadows of the Sea


Seagrass meadows (or beds) are a vital part of our marine environment and provide a wealth of ecosystem services, from capturing carbon to providing vital species habitat. But we’ve lost over 90% of our seagrass meadows in the UK since 1920 and the fragmented bits that are left of these unique underwater environments is threatened.

Seagrass Bed . Photo credit: Paul Naylor

What is a seagrass meadow?

Seagrass is the only flowering plant that lives and pollinates in the seawater. It inhabits shallow waters (typically up to about 4 metres in depth) near to the coast and relies on high levels of sunlight in order to photosynthesise. Plants grow in large groups, similar in appearance to terrestrial meadows. In Wales, we have 4 species of seagrass;  two zostera species which are considered ‘true’ seagrass, otherwise known as eelgrass, and two species of tasselweeds, which grow in brackish waters.

Lungs of the sea

Although seagrass meadows take up just 0.1% of the seafloor, they are responsible for storing 11% of the annual ocean carbon storage globally, at a rate 35 times faster than that within tropical rain forests. One square metre can produce 10 litres of oxygen daily, hence the nickname “lungs of the sea”.

Short snouted seahorse. Photo credit:Paul Naylor.

Aside from this, seagrass provides a host of other ecosystem services. Through trapping sediments within their roots, they help to stabilise the seafloor, improve water clarity and reduce erosion, whilst also acting as a buffer against stormy seas. Furthermore, seagrass improves water quality through absorbing excess nutrients within run-off; yet in nutrient poor areas, seagrass can act as a pump, taking up nutrients from the soil and releasing into the sea. Seagrass beds are host to a wealth of wildlife too, providing food, protection for predation, allowing for rich marine biodiversity. Thousands of species depend on seagrass meadows. Small fish, cuttlefish, shellfish and rays use seagrass meadows as nurseries, whilst other species including pipefish, and the UK’s two species of seahorses (long snouted/ spiny and short snouted) may call it home.

Threats to seagrass beds

Spotted gobies amongst Eelgrass. Photo credit: Paul Naylor

A colourful nudibranch (Facelina auriculata) searching for its food of small hydroids by climbing on a blade of seagrass (eelgrass: Zostera marina) meadow. Photo Credit: Alexander Mustard/ 2020 VISION

Seagrass is vulnerable to physical disturbance, so stormy weather can cause damage, but this is part of the natural life-cycle which ensures the habitat stays healthy and productive.

Pollution and nutrient rich run-off from fertilisers boost seaweeds and algal blooms, blocking sunlight and therefore disrupting photosynthesis within seagrass plants. Boats leave scars and damage plants, whilst also increasing erosion and fragmenting the habitat. Disease is another significant threat. During the 1930’s a wasting disease caused catastrophic loss of seagrass habitat throughout the UK’s coastal waters and beyond. It was so severe that it led to the extinction of a sea snail that specialised in living on an Eelgrass. The disease caused brown spots to develop on the leaves, reducing ability to photosynthesise. Seagrass meadows that are healthy are resistant to disease, yet direct and indirect human pressure means that seagrass meadows have been pushed beyond their coping mechanisms. This has been attributed to the huge loss we’ve seen over the last century.

Seagrass recovery

The world is beginning to wake up to the ecosystem services seagrass beds provide and they are often likened to canary birds, indicating the state of overall health of the marine environment. Various projects around the UK are successfully replanting and restoring seagrass meadows. In North Wales, the seagrass beds of Porthdinllaen are being closely monitored, whilst in South Wales at Dale Bay, a restoration project has enabled the planting of 2 acres of new seagrass meadow.

During the Covid-19 lockdown, it was reported that the seagrass beds at Studland Bay, Dorset, had started to repair itself due to a reduction in the number of boats and people in the area, allowing for the spiny seahorse to take advantage. There had been no sightings within the last 2 years of the creature, but on a recent dive, 16 were recorded; the largest daily recording since 2008.

A female spiny seahorse (Hippocampus guttulatus) shelters is a meadow of common eelgrass (Zostera marina). Photo credit: Alexander Mustart/ 2020VISION

So there is hope for seagrass yet, with some seagrass species demonstrating that recovery can be rapid, but in order to have long-term results, there has to be a concerted effort to reduce the human pressures on the habitat.

For more information, take a look at Project Seagrass.


Shifting Seasons of the Sea

Autumn’s Arrived, or at least it feels like it anyway

If you have been observing recent seasonal changes on the land that signal the end of the summer and of autumn’s arrival, you might be, like me, surprised that it feels a little early. Leaves of sycamore are turning that beautiful bronze colour, falling and scattering on the ground, flocks of migratory birds are gathering to begin their long journey south to warmer grounds and swathes of rowan berries are beginning to turn crimson. With still a week and a half of August left, this feels a bit premature, especially as there’s barely been a chance to pick a blackberry before they’ve gone over and turned into mush!

But shifting seasons is a reality and directly linked to climate change, and it goes much deeper than what we observe on our daily walks or drive to the shops. Changes in the timing of natural events such as the warming of the soil in spring or songbird migration can have harmful effects on ecosystems. Different species respond to different environmental cues, therefore resulting in species that rely on one another becoming out of sync. So for me it might mean an earlier and smaller blackberry crumble, but this shift is a much greater issue for plants and animals.

Sea-sonal Changes

Similar to that of the land, the marine biome experiences seasonal changes that are a critical driving force for natural events. Sea temperature, sunlight and ocean currents all play a triggering role. Plants grow and animals spawn, reflecting what’s happening on land, only sea temperatures lag about a month behind that of the atmosphere. The migration of leatherback turtles, which come from tropical waters to the Irish Sea in the summer and autumn months to feed on jellyfish and the growth of seasonal seaweeds, which provide important habitats for marine wildlife; these are just two examples of seasonal occurrences in the waters surrounding Wales.

Plankton shifting polewards

Minke whale’s are the smallest of the baleen whales, and feed on plankton using their mouths as filter feeders. Photo Credit: Eleanor Stone

But perhaps one of the most important events is the blooming of plankton. Acquiring its name from the Greek work ‘planktos’, meaning wanderer, plankton forms the basis of many marine food chains. Plankton blooms when water temperature, salinity and nutrient availability in the correct amounts are all favourable, and these conditions vary for each species. Phytoplankton are microscopic plants, and zooplankton are microscopic animals which feed on phytoplankton. From jellyfish to baleen whales, a great number of marine animals depend on plankton for food.

Lion’s mane jellyfish (Cyanea capillata) feed on zooplankton along with fish and other jellyfish. Photo Credit: Alexander Mustard

Yet, a recent study on zooplankton published in the journal Nature shows that this microscopic but vital fodder is shifting pole wards in response to climate change and an increase in ocean temperature. In fact, it’s found to have moved a whopping 602 Km on average since pre-industrial times. Apart from being greatly concerning for the marine species that rely on zooplankton, this study demonstrates that marine ecosystems have now entered the “Anthropocene”.

Photographs of plankton taken through a microscope. The far left is a zooplankton species, with the right hand two being phytoplankton. Photo credit: Allan Rowat

Why only talk about one study? Being at the bottom of the food chain within the world’s largest ecosystem, and the basis for all marine life that lies above it, the movement of plankton is highly indicative of what’s happening to other marine species too. Therefore, this study demonstrates the shifting of plankton is just the tip of the iceberg.

So the next time you see a berry ripen on a tree early, or you’re wondering why where did the last frost of the winter go, take a moment to ponder the sea, and what the seasons are doing beneath the surface of the ocean.

Emperor’s of the Deep

During the summer of 1975, something happened which was to alter our perspective on sharks. The film ‘Jaws’ was released. The notion of a huge great white shark terrorising the shores and brutally attacking

Thornback Ray. Photo: Paul Naylor

unsuspecting beach dwellers as they went for a casual paddle was enough to send us humans into a terrified frenzy, and ever since, we’ve feared this beautiful creatures of the deep. It hasn’t helped that the film was so popular, with subsequent filmmakers copying the idea, and fuelling our anxiety.

But are we right to be scared? Yes attacks can occur, but in 2018, there were just 4 deaths worldwide that were attributed to sharks. In that same year, over 100 million sharks died due to humans. Now who should be scared of who?

Evidence that the sharks are there is in the form of egg cases washed up on the shore. These belong to skates and rays.

There are over 500 species of shark worldwide, and together they inhabit a diverse range of niches and marine habitats, which they have adapted to over the last 450 million years they’ve been around. They are incredibly resilient fish, which have withstood 5 mass extinctions, and many species of shark are apex predators, meaning they’re within the top trophic level of the food chain. This may be another reason why they’re feared so much, but without sharks, the health, diversity and entire function of an ecosystem will disintegrate.

At least 21 species of shark live in British waters all year round, with other shark species visiting seasonally too. Unfortunately, 50% of our shark residents are considered to be threatened or near threatened species, and one that is critically endangered is the angel shark, which is not a particularly sought after fish, but has had a history of being caught as by-catch.

The basking shark, the second largest fish in the world, was once regularly seen around the coast of Wales during the summer months. It feeds on zooplankton with its large filter feeding mouth. It looks like it could

Basking Shark
Photo Credit: JP Trenque

swallow a human whole, but it can’t and won’t. Sadly, they are now rarely seen, and although protected in the UK, still many threats remain to this gentle giant.

Only a few sharks in the world are potentially dangerous to humans, and the closest we’ve come to having any of them near was when a white shark (also known as a great white) was captured in 1977, 168 miles off the coast of Cornwall.

If you want to learn more, a new book by William McKeever, ‘Emperor’s of the Deep’ focuses on four shark species (mako, tiger, hammerhead and great white) and argues the importance of caring and embracing our wonderful sharks. We need to protect them, as without them, our oceans will be considerably compromised.

For more information on sharks or identification sheets, visit the Shark Trust or Angel Shark project Wales.

A Tern of Events

Renowned for being home to over 3000 pairs of Arctic terns every year during the breeding season, the Skerries provides an extremely important habitat for ground nesting sea birds, including terns, puffins and gulls. The group of small islets are located about 3 km off the north-west coast of Anglesey. Their rough, rocky terrain combined with sparse vegetation makes them inhospitable to humans. Yet for nesting sea birds, they provide the space and conditions to host thousands of broody pairs.

Taken from the shingle ridge at Cemlyn, looking towards the colony ‘dreading’


Over the past few years, the Skerries (managed by the RSPB) have been in the news due to the success of increasing pairs of roseate terns, which are the UK and Europe’s rarest seabird. Roseate terns like to nest in amongst other terns, and the Skerries allows them to do just this, nestling in amongst the Arctic terns, along with over 300 pairs of nesting common terns too. Sadly, this year the news is not that of success, but a failure of the entire tern colony.

Wardens, who spend the season observing the colony, stepping in if anything looks untoward or like it might be detrimental to the success of the colony, typically look after the reserve over the Spring and Summer months However, this year was different. With Covid-19 restrictions and furloughed staff, the RSPB were unable to position wardens on the islands, which seems to have been critical.

An Arctic tern. Photo credit: Gillian Day

A pair of peregrine falcons nested on the Skerries, which was most likely to have been the cause of the desertion, and could have been mitigated against had wardens been present. This unfortunate event highlights just how important it is to have people on the ground looking after these birds. It is crucial that tern colonies are wardened as loss of habitat and disturbance by people has made it much more challenging for terns to breed.

The colony island at Cemlyn on a calm day


Yet all is not lost for this year! Terns are adaptable birds, and have the ability to move and re-colonise swiftly. Luckily for Cemlyn, our reserve situated on the north-west coast of Anglesey, not so far from the Skerries, we have welcomed many more Arctic and common terns to the colony. Many of these have settled quickly, got down to business, and are already incubating eggs after being there just a week or two. We believe we’ve inherited at least another 1500 terns, making it the most successful year for common and Arctic terns recorded at Cemlyn. Where they’ve found space amongst the 2000 pairs of breeding Sandwich terns, 130 breeding pairs of common and Arctic terns that were already there, not to mention the nesting black headed gulls, we will never know! But Cemlyn is a noisier and more hectic than we’ve seen it in recent years, and it’s a marvel to watch! Then again, it’s been lucky enough to continue to be wardened throughout Covid-19.

What happened to the rest of the terns that deserted the Skerries? We’ve yet to find out. Some will have gone to other colonies, and in time we will know more. For now, we are keeping everything crossed for the success of the Cemlyn colony, and we hope to see more returning in years to come!

In these unprecedented times, our Cemlyn terns are in need of help. To find out more information about the Cemlyn appeal, please visit our Cemlyn Appeal.

For more information on the conservation of the roseate tern, check out the Roseate Tern Life Project.

Tracks in the Sand

A bare foot wander on the beach leaves you feeling refreshed and at this time of year, having warmed up a little bit, the trek is not too arduous. Look around you.


You may not realise it, but even on vast sandy beaches where the presence of living creatures may not be so obvious you’re actually surrounded by wildlife.


Sand provides a perfect medium for looking for tracks and signs; you need only to look along the beach at low tide and you’ll see patterns left behind by the creatures that form them. Creatures of the sandy shore simply burrow to protect themselves from the range of environmental conditions they are exposed to once uncovered by the tide.

One of the most well-known signs is that of lugworms, which live in U-shaped burrows in the sand. At the opening end you’ll notice a small round depression in the sand where the lugworm swallows some of the sand, cleaning it of its organic matter. At the tail end you’ll see a more obvious pile of coiled sand (I will leave it to your imagination what these casts actually are!).

Lugworm poo and hole Photo Credit: Julie Hatcher

Sand mason Photo Credit: Nigel Phillips

A somewhat more beautiful sign of the presence of a worm is that of the sand mason worm; large particles of sand bound together to form a delicate tube topped with hair-like protrusions created by finer sand. When the tide is in, its gills and tentacles extend out of the tube for feeding and respiration, but when the tide is out it retreats to safety.

It’s not just worms that leave us evidence; the elongated blade-like shells of a razor shell are often seen empty on the beach, but look for keyhole shaped holes in the sand at low tide to spot where these creatures actually reside. Empty shells all along the seashore provide evidence of the wealth of shelled creatures living in our seas. Look carefully, particularly along the water line, as the tide comes in and you may see their tubes emerging for feeding as the water inundates them.

Sea potato shell (also known as a test) Photo Credit: Paul Naylor

You might be lucky enough to find the fragile empty shells of creatures such as the sea potato. When alive they burrow in the sand, often near or below the low water mark. It is a weird and wonderful creature, which burrows up to 8” deep and retains contact with the surface by way of a narrow funnel.



Often, after big storms have churned up the sand, you’ll find hundreds of sea potatoes and other burrowing creatures washed up on the beach.


The clues are written in the sand and there is nothing better than spending a couple of hours unravelling some of the mysteries of our coasts. It’s very easy to get carried away whilst thus engaged so, as I always say, please do keep your eye on the tide!