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The Seashore

Questions and answers

Here are some answers to general queries and facts

Stephen Mundy of Oxfordshire has asked multiple questions: 1)What is the origin of the name of the mollusc Crepidula fornicata (the slipper limpet)? 2) Are there high and low tides at the North and South Poles (or at least on the coast around them)? 3)Am I related to Dale Winton?

1) The answer to your first question is as you suggest, related to the characteristics of the animal (although not perhaps in the way you might imagine). You are obviously a big fan of Crepidula fornicata, for the more general reader, here is a bit of basic information: Crepidula fornicata is a mollusc of the family Calyptridaeidae (the same family as cowries). It is an introduced species (to the UK) and was first found in Essex around 1890. It's a pest of oyster beds because the animals settle and grow on oysters and smother them by sitting on them and silting them up with poo (to use a technical term) and debris. It was first found in Milford Haven in 1953 and was very common in some areas by the 1960s. It has the curious habit of living in chains of animals one on top of another up to about 12 individuals. The bigger, older ones at the bottom are females and the smaller, younger ones at the top are males. As they grow the males turn into females (this is called protandric hermaphrodity and is quite common in the liberated world of invertebrates). The boys on top of the chain copulate with the girls beneath and fertilization is internal. The females lay the eggs in little capsules near or even attached to themselves. There is a planktonic larval stage and the baby Crepidula settle either on an existing chain or on a rock. They feed on detritus and plankton which they trap on a mucous net in their mantle cavity. Now you might expect given their to say the least, exciting and unusual sexual proclivities, that the name fornicata derives from them. Until that is you find out who named them. This was the famous Swedish scientist who invented the method we still use for naming and classifying organisms. Carl von Linne was our man (known usually as Linnaeus, a Latinised form of his name). Linnaeus was a) Swedish and extremely polite, b) son of a curate, c) easily shocked, so he would not have named it fornicata after its reproductive habits. In fact, Crepidula comes from the Latin Crepitaculum meaning a rattle (like a rattle snakes rattle). The chains of animals resemble this shape. Fornicata comes from the Latin fornicatus meaning vaulted, concave on the inside and convex on the outside (the shells are shaped thus).

2) There are high and low tides at the poles but there is no coast at the North Pole. The tides around UK coasts follow a semidinurnal pattern (roughly 2 high and 2 low tides a day). At the poles the tilt of the earth on its axis means that only one tidal bulge is passed through as the earth rotates so there is a diurnal cycle (roughly 1 high and one low tide a day).

3) Only in the sense that we are all brothers and sisters in the vast comity that is the cosmos, we are stardust we are golden and we are big fans of Supermarket Sweep.

Mrs Boot of Nuneaton asks: Very few animals seem to walk sideways. Why does the crab do this? What possible advantage can it confer?

Crabs have lots of legs (10) all the same length and all packed into a small space along either side of the carapace. Spiders have lots of legs all different lengths all packed into a small space. Because they are different lengths spider's legs can slide underneath one another and they can make forward motion. Crab's legs can't slide underneath each other so they have to articulate sideways. "Why have so many legs then?" I hear you ask Mrs Boot. Well, another thing about crabs is that they live in a precarious environment where movements of pebbles and stones and attacks by predatory fish could easily cause them to lose limbs. So it's probably an advantage to to have a few spares because at any one time you may be a couple short. Crabs can regrow their limbs if they lose them (this process is called autonomy and shows us that genetic engineering of body parts is not necessarily a new idea).

Felicia of Huddersfield asks for advice on whether or not to do a PhD in marine ecology

This sort of question is probably better addressed to your Careers Officer, Parents, Friends etc. My advice would be do it if you are interested because you'll probably enjoy it greatly but don't expect to make much money if you make it your career.

Earnst Haythornwaite (who sounds like a nom de plume) asks: How did the research go on eradicating the invasive Japanese seaweed Sargassum muticum? How come it's still there when some fine scientific minds devoted themselves to the problem?

Well Earnst, you are correct a lot of thought was given to the seaweed Sargassum muticum. A lot of knowledge concerning the biology and ecology of the species was gained. You can access some of it on this very website by reading some of the Dale Fort Diary sections. Even fine scientific minds find it difficult to achieve the impossible and the eradication of Sargassum was probably just that. They did show how it could be controlled and what the likely impacts of any controlling measures might be.

J. Adams of Bath asks: What happened to Dave the Tent?

You are obviously a previous visitor to Dale Fort where Dave was for many years a not all that skilful handyman. He made up for this by virtue of his wealth of astonishing tales gleaned from a life-time at sea and his riotously cantankerous personality. Sadly he passed away in 1997 aged 69 and given his massive intake of alcohol and tobacco that was a pretty good age. He is much missed.

Chris of Barnes asks: What is the world's biggest seaweed, what is the biggest seaweed in Pembrokeshire? Who is the World's most useless man?

The biggest seaweed in the world is the giant kelp that grows off the coast of California (also known as bull kelp or Macrocystis pyrifera. It can reach 50m long and have a holdfast (the bit it sticks to the rocks with) 1m in diameter. Its fronds have been measured growing at some 45cm a day....You could almost see it growing, this is the fastest growth of any plant (if you count seaweeds as plants). The biggest one in Pembrokeshire is probably Saccorhiza polyschides another kelp that can reach 4m or so in length. Laminaria saccharina (sugar kelp) might also reach this sort of length. Sargassum muticum given calm conditions can also grow very long, 6m is the longest I've ever seen but not in Pembrokeshire. (You can read all about this recent introduction to Pembrokeshire in the Dale Fort Diary section of this site).

There is some dispute as to who is the World's most useless man. Most people think it's Keith Seed of Watford.

Geoff of Devon asks: Which is the biggest crab?

Probably the spider crab (which is really sublittoral but you might find it on exceptionally low tides)

Ali G of Berkshire asks: Which is da 'ardest crab?

The hardest looking crab with the best name is Xantho incisus but the velvet swimming crab is breathtakingly aggressive at times (especially after a few beers) (Bo selector)

Alan C of Normandy asks: What is the longest seaweed?

On British coasts Sargassum muticum would have to be a contender, it can reach over 5 metres. The giant kelps of the South Atlantic can be much bigger than this (20m+). (They are of course sublittoral).

D. Emerson of Lincoln asks: How high does the tide go?

In British waters the Bristol Channel has the biggest tidal range of about 20metres

F. Bunker of Wales asks: Are anemones poisonous?

Some folks say that Anemonia viridis (the snakelocks anemone) can sting humans but you probably have to be especially sensitive, I've never been stung by one. I know someone who by way of an experiment licked Actinia equina (the beadlet anemone) and he said it hurt like hell. (Of course you have to be completely mad to do this, it's not recommended).

Bethan Cox of Worcester asks: What's Dogger Bank Itch and is it contagious?

There's a Bryozoan called Alcyonidium which produces chemicals that irritate your hands if you handle them. You get a lot of it washed up on the North Sea coast from time to time. North Sea Fishermen coined the term Dogger Bank Itch, so as long as you avoid handling it or them, you should be OK

Mary Kate of Mabesgate asks: Why aren't there any insects in the sea?

Good question. They've colonised virtually everywhere else why not the sea? I don't know the answer to this but there are a couple of insect like creatures on the seashore. Petrobius a bristle tail that looks like a terrestrial silver fish and Anurida maritima a little spring tail often found trapped in the surface tension on the surface of rockpools.

Jonathan of St Ishmaels asks: How many pairs of data do I need to use Spearman's Rank Correlation Coeficient?

Minimum 6 but you'd be well advised to get at least 8 if you want to stand a chance of rejecting your null hypothesis at 5% significance.

John AT of Dorset asks: How can I work out the height of the tide?

Your best bet is to buy a set of tide tables for the area you are interested in and use the reduction tables at the back of the book. Alternatively you can apply the rule of twelfths. If you know the total range of the tide you can divide it up into twelve parts and assume that one twelfth of the total will come in in the first hour after low tide. Two twelfths will come in in the second hour, three twelfths will come in in the third hour. The fourth hour will also see three twelfths come in the fifth two twelfths and the sixth hour one twelfth.

Assum of Leicester asks: I go to the Isles of Scilly each year for my holidays. The water seems to be getting warmer as the years go by. This may be why there are more and more of those little stinging fish which make my feet swell and hurt terribly (I now wear sandles when I bathe). What really worries me is whether more dangerous warm water species may soon be roving inshore British waters. Am I in danger of being eaten by sharks or perhaps gulped down by some gargantuan killer whale?

This is an interesting if rather general question (or set of questions). I would be surprised if your tootsies can remember the temperature from one year to the next. Also your perception of sea depends on several factors besides the actual temperature (general physical health, amount of blubber, time since last meal, air temperature, wind chill etc). Sea temperature recording devices are in place at several sites around Britain and they seem not to indicate any large upward trend. It does however take a long time to change anything about the sea due to its massive volume and the high specific heat capacity of water. Small changes might therefore be very significant. The temperature of the Sea this morning (10 am 20.12.01) was 11.1 degrees Celsius off the west coast of Ireland and 11.3 degrees Celsius off the east coast. There are big technical difficulties in monitoring ecosystems by measuring physical (abiotic) factors. Your query relates really to the use of organisms as indicators of change in the physical environment. This idea is used in freshwater ecology for instance where certain species are characteristic of organic pollution. Lichens are well known as indicators of sulphur dioxide pollution in the atmosphere. The little fish you speak of are almost certainly weever fish and you are wise to bathe in sandles (I'd recommend a swimming costume as well). Weever fish live buried in sand in the shallow waters around the whole of the British coast. Some years ago a student of mine was paddling and was stung by one. She was in agony for several hours. There is not a lot that can be done about this. It is said that if you put the affected part in water as hot as you can stand it helps to denature the poison and hasten relief. Weever fish are more common in the south west so maybe an increase in water temperature would favour them leading to an increase in population size. Around Dale we have seen an increase in the population of another warm water species- the toothed top-shell (Ocilinus lineatus). It is not possible to state that this seashore snail's increase is related to warming because populations often fluctuate for reasons that may be unclear. We also now have resident little egrets, these birds were unusual summer visitors from southern Europe until recent years. We occasionally see sun-fish around our coasts, these may become more common if the water does warm up. Some climate models predict a reversal or change in flow of North Atlantic Drift (the warm Atlantic current that moderates the climate of the west coast of Britain) if this happens the sea temperature could go down and you might have to start worrying about rampant polar bears.

With regard to your shark fears. This is probably the least of your worries. You have a much better chance of winning the National Lottery than of being eaten by a shark in British waters. I think there has been but one (dubious) record of a shark biting a human in the whole of recorded history. As you approach the equator and the water warms up shark attacks increase proportionately. This may due to there being a lot more people available in warm tropical waters or maybe warmer water leads to hungrier sharks or both.

Killer whales are not seen very often in British waters but they do live in them. Our ex-lifeboat was passed by a pod of 6 killer whales in Ramsey Sound (north of Dale Fort) a few years ago. An absolutely spectacular, never to be forgotten sight. I don't recall any reports of them eating humans but I do believe they are very fond of seals.

I hope this allays your fears and could you please make your query a bit more specific next time?

Keith of Watford asks: Could you tell me the Latin name of the Manx shearwater?

Curiously enough it's Puffinus puffinus. (The Latin name for the puffin is Fratercula arctica)


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