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Tank Tuesdays 2

The Snakelocks Anemone

With serpentine tentacles like Medusa’s weave* it’s easy to see how the snakelocks anemone Anemonia viridis got it’s name. Like a gorgonian perm this cnidarian** wafts its tentacles about to catch pieces of food, passing them back to it’s body to digest. This is exactly what our anemone here at ARC Marine’s Brixham lab does: sit around, chill (average water temperature at a balmy 15°c) and eat. Nothing out of the ordinary then; except for where our anemone has made itself at home. Our snakelocks anemone was originally introduced to our native UK tank on a rock. It then made its way over to the top of a Reef Cube where it stayed for about six months, before moving to the interior of another. That was back in 2017 and it’s been inside the Reef Cube ever since! Comfortable and secure in it’s home, it’s tentacles float out of the openings of the cube to collect food. We feed the anemone tiny mysis shrimp and when a tentacle finds one it quickly curls up and takes it back in to the cube to be eaten. It’s easy to be mesmerised watching the tentacles move in the invisible currents. On a more serious note though; A.viridis is an excellent demonstration species which is why we’ve dedicated a whole article to our special anemone. It even forms a habitat of it’s own! So within our artificial habitat, we have a species that provides habitat for other species (win). We’ve even demonstrated this by giving the anemone a new house mate; the Leach’s spider crab.

ARC Marine Tank Tuesdays Snakelocks anemone 1
Figure 1: The snakelocks anemone Anemonia viridis

In an ecosystem, species frequently have ‘jobs’ that they perform which benefit the ecosystem as a whole (though, like people; some species do more than others). For example, some animals are scavengers; acting as the clean-up crew of the ocean by consuming detritus and the long dead. Some animals, like A.viridis, work as host organisms; effectively acting like a house and a landlord simultaneously. Anemones in general, often have these associations with species that live closely with them, in what are known as symbiotic relationships. A famous example is the clown fish which lives in it’s own anemone host (think Finding Nemo). By being a host to lodgers the anemone helps to increase the survival of its tenants and to increase the diversity of an ecosystem. In the case of the snakelocks anemone a number of species house themselves within the embrace of it’s tentacles. For the most part this is of no benefit to the anemone so can be described as a commensal relationship, where one species benefits and the other is unaffected. Bucchichi’s goby is a fish species that hides in the anemone to avoid predators. In the Mediterranean, a shrimp Periclimenes aegylious hides within the anemone, eats any food the anemone drops and sometimes even nips off tips of the anemone’s tentacles for a snack; taking the relationship a step towards parasitism.

The leach’s spider crab is a strange looking crab with fat boxing glove claws. According to the scientific literature it’s supposed to have a similar commensal relationship with the anemone, except it doesn’t try to eat it’s tentacles. We were pleased to notice that we’d misidentified a crab in another tank and that we were actually in possession of a Leach’s spider crab, while we were researching this article. So, we thought that our snakelocks here at ARC Marine looked a little lonely and that we should buddy it up with it’s very own house mate. On 24/11/18 we introduced the two. Our crab seemed hesitant at first probing with it’s claws at the anemone. It wasn’t long though before the crab made it’s moves to snuggle up to the snakelocks. At first these attempts were quite comical with the crab backing in to the bulk of the anemone and being rejected. After a couple of days though it found it’s way inside and now the anemone and crab happily share their Reef Cube.

ARC Marine Tank Tuesdays Snakelocks anemone 2

Figure 2: The spider crab’s first attempts at gaining entry to the Reef Cube were awkward and unsuccessful

So what’s the point? Well, A.viridis is just one of the species that we would expect and like to see colonising the Reef Cubes when they’re deployed around the UK’s coast. The snake locks anemone is commonly found around the United Kingdom and is indicative of shallow rocky regions. If you want to find one have a look around in shallow water pools, they will often be attached to bare rocks or among seaweed. They don’t like to live in deeper water and are found most of the time living above the 10-12m zone. As the concrete used in Reef Cubes is similar in texture and density to rock, and will be placed on the seafloor; we hope that a similar community to a natural rocky reef would develop on them. So a successful colonisation by rocky reef animals is exactly what we want, and it’s what we see here with the snakelocks anemone in our tank. The anemone chose to move in to our Reef Cube and now the Leach’s crab along side it. Which means that our materials and design have successfully emulated the natural habitat that these species would be happy with and facilitated a natural symbiotic relationship between the crab and the anemone!

ARC Marine Tank Tuesdays Snakelocks anemone 3

Figure 3: Now the spider crab is safely sheltered by the snakelocks’ tentacles

To top it off, the anemone actually lives inside the cube; occupying the hollow interior space. We designed the Reef Cube with this spherical space, for the exact purpose of giving animals extra shelter; so it’s very reassuring for us to see the anemone and spider-crab choosing to shelter inside. This interior space is interesting because is it’s own little micro-environment. In some ways it could be similar to the crags and ledges of a rocky outcrop. With more complex structures though multiple Reef Cubes will be connected together and the spaces will be linked. The result would then be a system of underwater tunnels and caves!

It’s very exciting because these species could be pieces of the puzzle in the diverse ecosystems that we hope to create with our reefs. A.viridis in particular could be an important piece. Besides it’s role as as a host, to animals like the spider crab; A.viridis acts as a link from the lower levels of food webs to the higher levels. The anemone feeds on amphipods***, organic detritus and parasitic worms and is then eaten by octopus, starfish, turtles, certain crabs and fish. The anemone even alters the local water chemistry for the better by releasing oxygen and absorbing carbon dioxide. In another symbiotic relationship it hosts algae, just like coral; which photosynthesise light, producing an additional food source for the anemone. Not to mention that this species is important to humans too. It’s used in labs worldwide as a model species for resilience to heat stress in cnidarians, giving us an idea of the coral bleaching process and the genetic pathways involved. The venom in it’s tentacles is harvested for effective anti-cancer treatments, blocking growth signals from tumours, to feed the cancers growth with blood supply. It really is a giver.

What one can discover with a little research is quite amazing. What might seem like just an anemone to many actually has been researched in hundreds of papers on a wide range of subjects. Here at our lab we’re thrilled to have A.viridis in our tanks. We hope to create habitats for a multitude of species like it and in so doing, engineer rich and diverse ecosystems. Who’d have thought a simple anemone could do so much.

Trickier terms

*For those unaware of Greek mythology: Medusa was a gorgon; a female monster with snakes for hair that could turn you to stone with a glare. Interestingly scientists frequently associate cnidarians with gorgons. What we would call a jellyfish, is the medusa stage of a medusozoan cnidarian. Sea-fans, which are closely related to corals are called gorgonians.

**For those unaware of cnidarians: hydroids, jellyfish, anemones, corals.

***Amphipods for the most part are small crustaceans, a common example being the ‘sea flea’.

By Sam Hickling and Jamie Matthews

Tank Tuesdays is a series of mini articles describing the marine life here at ARC Marine’s aquaria; and their interactions with our artificial habitats.