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2267
Rubric: Live and Learn
Section: Biology
Sea Urchins: Green and Black, Round and Flat, Delicious and Deadly

Sea Urchins: Green and Black, Round and Flat, Delicious and Deadly

The first feeling one gets when seeing a sea urchin is bewilderment: is it an animal at all?! Indeed, its appearance evokes the images of unusual toys made by Nature just for fun. The spherical shape, the rigid shell constructed out of oddly-shaped plates, straight rows of hinged spines… The impression is intensified by the sea urchin’s immobility. Even the movement of its spines seems to be actuated by a hidden engine, with a weakened spring or nearly dead battery. By the way, when getting better acquainted with the object under a binocular magnifier, one can notice some moving pipes, suckers, tweezers… Hydraulics at work! In short, it is just a prickly, absolutely noiseless, mechanical toy...

The feeling that you are watching a curiously made thing and not a living being does not disappear after dissecting the latter: the inner space, which you can observe after the transparent cavity liquid — neither blood nor lymph — has flown out, is filled with radial yellow-orange segments, resembling tightly packed plastic containers. No plasticity whatsoever, the triumph of radiality!

In the center of the bottom surface of the shell one can notice quite an intricate device. It is the mouth organ of the sea urchin, which is called Aristotle’s lantern. Inside the inner mechanics one can discern some green-grey interlacements of soft wide pipes, which is nothing less than its digestive system.

And at this moment the real nature of the sea urchin is beginning to emerge: the pipes contain not fuel but remnants of algae, its basic food. Some species of sea urchins demonstrate a more sophisticated menu: sponges, bryozoans, and colonial sea squirts. Sea urchins also eat detritus, which contains microscopic algae and microorganisms.

This is what I remember of my first encounter with these unique animals, though with time sea urchins became for me just common sea inhabitants.

There’s no ocean without sea urchins!

Sea urchins are an indispensable element of underwater stony landscapes of many seas, including those of Russia. They are widespread not only in the cold waters of the Arctic and Antarctica but also in the tropical areas of the World Ocean. There are about 940 different species of these animals, which live exclusively in the marine environment.

Some species, inhabitants of shallow bays, settle right behind the waterline. Sometimes they even dry up at ebbs, and only the rock cracks and stone cavities that they themselves have made can save them from complete desiccation. In the deep, the rays of bathyscaphe searchlights spot other species of more deepwater sea urchins, not all of which have been studied yet.

Some representatives of the sea urchin “family” hide in underwater dunes, which cover them from the eyes of inexperienced divers. The flat or heart-like shape of the shell helps them to bury themselves in the sand fast and easy. On the northeastern shelf of Sakhalin, the so-called sand dollars carpet the bottom in certain places, thus hindering the mass settlement of other animals. Adult sand dollars hardly have any serious enemies and obviously are not a delicacy for other sea inhabitants, taking into consideration scarce amount of nutrients inside the beautiful calcareous shell.

Round sea urchins, or sea eggs, on the contrary, have a fine and less durable skeleton and well-developed internal organs, especially sex glands. Owing to this they are the favorite food of many pinnipeds, crustaceans, fishes and sea birds. The grey sea urchin, whose spines are not so dangerous as those of the black sea urchin, prefers to hide from the eyes of predators by pinning on it pieces of algae and other things it finds on the bottom. In the autumn, in the bays of the Sea of Japan, one can see how it uses, for mimicry, the Mongolian oak leaves, brought with the wind and drowned — in fact, these sea urchins behave like hedgehogs. By the way, in Russia sea urchins are called “sea hedgehogs”.

In the tropics, some species of sea urchins serve as a house for other sea animals — sea anemones and soft corals; some carry a certain species of shrimps in between their spines. The activity of tropical sea urchins increases at night when they get out of their hideouts. The time of day is of no importance only for diadems, well armed with long spines, and for some venomous species that have no natural enemies to be afraid of, save divers…

Sea long-livers

Many pages of journals and monographs are dedicated to sea urchins. Their contribution to embryology is especially great, since they can live and breed relatively easily in a comparatively small amount of sea water. It takes only a few weeks to see, under a microscope, all the changes that happen to the egg: from fertilization through cell division to a small sea urchin. This recognized classical object for embryological research is also used for testing the environment quality and for studying how different substances influence biological systems since the effect of negative factors is seen immediately in the violation of breeding and development of the animals.

Scientists from the University of Oregon have recently published an interesting fact of sea urchins’ life. It turned out that red sea urchins, which inhabit the Pacific coast of the USA and which are of commercial interest, are likely to live much longer than they were believed to.

The age of sea urchins is determined by counting the rings on cleared sections of shell plates. The method is quite precise for the regions where sea depths exhibit well-pronounced seasonal fluctuations. Principally, sea urchins grow throughout their life, but the growth is fading, so it is extremely difficult sometimes to identify the yearly layers of growth.

Usually red sea urchins live about fifteen years. American scientists studied very large individuals and found out that urchins actually grow quite slowly and that some individuals show the record longevity — more than 200 years! — without a sign of senility. Obviously, such a sensational statement needs an independent study of the real age of sea urchins by other scientific groups and with other methods. Anyway, we have every reason to believe that sea urchins can enrich not only embryology but also gerontology — study of organism aging — which is so crucial for us.

Caution: Sea urchins!

It is a well-known fact that some sea inhabitants can represent a serious danger for human beings: some creatures behave very aggressively; others can poison you if you eat them. As for the sea urchins, everybody knows that their spines can puncture the skin. However, few people are aware that some venomous short-spine sea urchins, very beautiful in appearance, can be much more dangerous than, say, diadems, which have long spines and look like a pin-cushion for very long pins. Venom can be found not only in the spines of such sea urchins but it can also ooze from special mobile “tweezers” thrusting out of the shell.

As a rule, if it is the “tweezers” that are venomous, the spines are harmless; and vice versa. The venom is a complex substance of protein nature. Its action has not been studied well. Besides reddening and loss of skin sensibility, you can feel nausea, heavy breathing and muscular weakness. When attacked by several sea urchins, a person can experience a severe pain, giddiness, paralysis of the lips and of the tongue, and even delirium.

The venom of sea urchins is hardly ever lethal, though it is known that a Japanese pearl-diver drowned having lost conscience when struck by sea urchins. Several cases of survivable poisoning which happened because of eating sea urchin roe have also been described.

After the spines have been removed, the skin affected by non-venomous sea urchins heals up in two to four days, if a secondary infection does not penetrate the wound. The flinders of the spines may stay in the skin and be “encapsulated” inside, causing slight disturbance for a few months. It has been observed that the flinders of terrifyingly long spines of the tropical diadems dissolve in the body better in comparison with pieces of relatively small spines of grey or black sea urchins.

Non-aggressive towards humans and quite slow, sea urchins can nevertheless injure skin, provoke dermatosis and, as a result, spoil vacation for a diver who finds himself at the mercy of waves near coastal rocks. The numerous bruises from the rocks may be aggravated by holes left by dozens of spines, cuts from sea acorn shells and oysters… But we shouldn’t blame underwater inhabitants for our misfortunes: after all, it’s their world, where we are but unexpected guests.

Sea urchin roe

In the old times, on different continents, people who inhabited the coast were eating sea urchins; this now tradition is alive only in a few countries. This food, unusual for Russians, is now mainly consumed by the rich Japanese. Seventeen countries export sea urchins to Japan. The main exporters are the USA, Chile, Peru, China, Canada, South Korea, North Korea, and Russia. The world’s catch of the eighteen food species of sea urchins totals about 117 thousand tons per year.

The very body structure of the sea urchin does not suggest a lot of muscular mass or fat storage. The only edible part of the sea urchin’s body is lobules of the developed sex glands of males and females, which, by the way, cannot be distinguished without our breaking the shell. That’s why the everyday and commercial name of the product — sea urchin roe — is not exactly correct.

The sea urchin has five such reproductive lobules, resembling in shape sections of a tangerine. By the beginning of spawning, the volume of sex glands is about 6—20 % of the total weight. The roe color varies greatly and depends on the sex, maturity, nutrition, species, season of harvesting, storage, and other factors. Depending on the color of the product, experts distinguish a great variety of its kinds. The bright yellow or orange indicates that the roe is fresh and of good quality. The raw product is used for cooking certain dishes, like sushi, and can be preserved in alcohol for further processing.

Sea urchins with Russian citizenship

In the northern Pacific, there live quite a number of species of edible sea urchins, but only eleven of them are considered commercial. The Russian zone shelters three kinds of round sea urchins (i. e. sea eggs) Strongylocentrotus, which have different commercial value and are harvested in different amounts. Some species of sand dollars — perfectly inedible — are harvested because of their unique biologically active substances that improve vision. Research in this field is being conducted by scientists from the Pacific Ocean Institute of Bioorganic Chemistry in Vladivostok, while researchers from the Russian Pacific Federal Fisheries Research Institute study the medical and biological characteristics of the sea urchin roe and make various preventive medical preparations out of it.

The black sea urchin (Strongylocentrotus nudus) is a mass and commercial species. It owes its name to the almost black or dark purple color of the covers. It has rather long, about 3 cm, strong spines, which hinders its harvesting, storage and shipping. It lives at depths of up to 200 m, colonies of commercial value are situated at a depth of 10—15 m. It is collected by divers, with the help of special claws. The harvesting volume amounts to several dozen tons per year.

Lately the deep-water pale-yellow sea urchin (Strongylocentrotus pallidus) has begun gaining certain commercial importance. It inhabits the Russian coast from the southern border of the Primorskiy Kray to the Tatarskiy Strait. In Canada it is sometimes called the white sea urchin. The inconsistency in naming is not accidental: the color of individuals of the species varies greatly and depends on the region, depth and harvesting season. In Canada it is indeed whitish, though its color can be better defined as grey and green and crimson, in decreasing proportions. The taxonomy of the species remains to be amended — it is not improbable that today the group includes animals of different taxonomic attribution. The spines of the pale sea urchin are thin and short. We can catch it in large amounts when sweeping the coastline on silted or sandy grounds at a depth from 80 to 1500 m. It also can be caught with the help of special traps. However, there are no official data that the pale sea urchin is delivered to Japan on a commercial scale, and earlier attempts to export it were not successful.

The most valuable species of the sea urchin is the grey sea urchin (Strongylocentrotus intermedius). It lives in the Far East of Russia at the coasts of Primorye, South Sakhalin, the Kuril Islands, near northern Japanese islands and the Korean Peninsula. The name and color of the species do not match either. Its color can be almost anything but grey: greenish-brown, purple-brown, greenish-violet, or brown-reddish.

The grey one is the best

The shell diameter of the grey sea urchin reaches 8 cm, and its weight 160 g. Puberty comes in the third year of life; the animal lives for about 7—10 years. As a rule, a large number of grey sea urchins are encountered at depths of no more than 40 m. They feed mainly on the algae found on the rock and pebble grounds, preferring laminaria; however, they do not mind eating dead sea animals either.

In our temperate waters characterized by significant seasonal fluctuations of water temperature at shallow depths seasonality in the sex glands development of sea urchins is also perfectly pronounced, which is taken into consideration at harvesting. For example, on the Kuril Islands, the harvest season is longer than at the shores of Primorye. In winter there is not much roe, so it is collected mostly in summer months. However, directly before spawning and during it, the glands get “squashy”; so it’s next to impossible to collect the product. After the spawning the gland is not big enough yet.

The harvesting of the grey sea urchin in the Russian Far East has been carried on long since. In the Soviet times, the cans named “Sea Urchin Roe” were sold in small quantities in Russia — in Vladivostok and some other towns. The small cans were expensive, and their salty contents could hardly be called a delicacy; they might have been a rejected consignment. The product exported to Japan was much more decent, but not many Soviet citizens were lucky to visit the country at that time, and even fewer dared to spend their money on the exotic food. No wonder, not any Japanese could afford the delicacy.

Rumors and translated literature made it known to Russians that regular eating of roe from only two sea urchins a day could strengthen health and prolong life. In the 1970s—80s, near Vladivostok, divers without a scuba were able to harvest a couple of hundreds of sea urchins. However, not many people fancied the useful product at the moment, while now you are extremely lucky if you manage to bump into a small colony of grey sea urchins near tourist spots, even diving with a scuba.

The sea urchin dumping

In our days only the official yearly harvest of the grey sea urchin in Primorye amounts up to 580—1.100 tons, and it is exported entirely to Japan.

Sea urchins are delivered to Japan fresh. Individuals good for trade weigh 65—75 g and have the shell diameter not less than 4.5 cm. They are caught by divers from boats. For harvesting divers often use small 20 ton Japanese schooners (as a rule confiscated), which carry twelve members of the crew, twelve divers and a representative of the company. If harvesting is conducted with the purpose of studying the control catch, a researcher is also present. In harvesting zones, there are 15—35 catching ships and about a dozen transporting ones. The quota for the sea urchin harvest is about 1000 tons, but in reality much more is caught.

Harvesters dive from the boats and collect sea urchins into a gauze bag called pitomza. A diver has about a dozen of such bags, each holding up to 80 kg of sea urchins. The diver is paid a certain percentage of the harvest cost. Some companies hire poorly trained people, and, as a result, accidents might happen. Once a poacher schooner trying to escape from inspection first forgot and then lost a diver under water. The unfortunate fellow was lucky to find in the open sea an anchored buoy of the fishing net, on which he spent more than twenty hours before Japanese fishermen found him. What’s even more astounding is that the brave diver continues to work!

In Japan the price of a kilogram of pure sea urchin roe can reach $ 220 in the holiday season. The sea delicacy is not cheap in Russia either: in an expensive Korean restaurant in Vladivostok you would have to pay a thousand rubles for a sea urchin appetizer (about $ 35 for a small dish).

The usual purchase price for 1 kg of fresh sea urchin (with shells and cavity liquid) is $ 10—14, though it varies from year to year. Last year saw a slump of the purchase price to $ 2, most likely because of the large volume of delivery. The Japanese fishing community sent a protest to their government demanding to ban the sea urchin export from Russia and to stabilize the situation of the national seafood market.

The national organizations and trade companies in the Russian Far East should work out a more profitable strategy to provide measures for the recovery of sea urchins resources while keeping their harvesting economically attractive, taking into consideration the foreign market. Indeed, so far the sea urchin is a mass species and is not so vulnerable as, for instance, the sturgeon. However, when continuously and abundantly caught, even mass species can rapidly be replaced by their not valuable relatives, especially if this process is accompanied by a change of environment.

Banning harvesting without reliable protection can only raise the prices without eliminating poaching. There are two ways of decreasing the risk of disappearance of the most valuable species: first, their cultivation and, second, creation of cheap artificial analogues of those biochemical components that make the animal unique. Then much more people could make use of the admirable “underwater pharmacy” without crippling the sea inhabitants.

From the editor: Having read the article, one can’t help thinking that if the healthy and wise Japanese enjoy the sea urchin roe so much, there must be something in it. Maybe our sea urchin harvesters should turn their eye to the domestic market, aiming at the huge Russian canap? After all, roe, even that of sea urchins, perfectly matches our mentality, unlike, say, frog legs. On the other hand, in the end it is sea urchins who will pay for it, and they are an exhaustible resource. But this may be of interest only for the scientists, while all the rest have something to put into their sushi and canape…

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