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Transcript
Living Shipwrecks: Science Under the Sea 1. UNDERSTANDING LIFE IN THE SEA We are land animals. It is hard for us to begin to understand what it is like to live in the sea. Sea creatures have to face all sorts of problems, quite strange to us. Even those familiar seashore plants and animals such as crabs, snails and seaweed have to put up with salty water, the tide going in and out, sun and wind, crashing waves, not to mention us poking them about! Under the sea the main factors that decide what lives where are: depth and light, currents, food, competition and the type of seabed. Depth and Light Sunlight, shining down on the sea, is absorbed by the seawater as it goes down. In shallow water there is plenty of light but as you go deeper it gets dimmer and dimmer. A diver exploring a wreck in deep water would have to take a torch. Why is sunlight so important? Seaweeds, like all plants, need sunlight to grow. They get their energy from the sun. So… You only find seaweed growing in shallow water. Animals, such as sea snails, that eat seaweed have to live where their food is. So… You find plant-eating animals (herbivores) only in shallow water. Animals that need to see their prey must live where there is plenty of light. So…You find some predators only in shallow water. Animals that use their eyes to avoid being caught and eaten by a predator must live where there is enough light. So… You find some prey only in shallow water. ? Why is the sea blue? Sunlight contains all the colours of the rainbow: red, orange, yellow, green, blue, indigo and violet. Seawater absorbs all the colours to a different degree. Red colour is absorbed quickly, so can only travel to a very shallow depth. Blue can travel to depths. This is why animals living in shallow water use many different colours to defend themselves or attract a mate. Colour becomes less important as you go deeper; fish use variations of lightness, darkness and brightness, instead. Blue colour is reflected in all directions, making the sea look blue. The brighter the sunlight, the bluer the sea looks. Particles, suspended in the water, can also reflect light, altering the blueness – that is why the sea looks turquoise when the cliffs and the beach are made of chalk or clay. Currents - Rivers in the Ocean The sea does not stay still, like a pond. It is constantly moving. On the surface waves are formed by wind blowing over the surface of the water. The water moves beneath the surface, too. These water movements are called currents. they are often mapped on charts to help sailors work out where they are and plan their voyages. The rise and fall of the tides cause horizontal currents. The wind also creates horizontal currents. Water may also move up and down when salty water meets less salty water. Why are currents so important? Many creatures in the sea feed on microscopic plants and animals in the seawater called plankton. Currents bring them a fresh supply of plankton. So… animals that feed on plankton live where there are currents. Many creatures in the sea release eggs and sperm into the seawater. The fertilised eggs form microscopic larvae, which are swept away in the current to settle and grow somewhere else. So… animals that produce larvae and need to find space for the larvae to settle, live where there are currents. Food Understanding Marine Food Webs From the microscopic plankton to the largest whales, all the plants and animals in the sea depend on each other. They are all important links in marine food chains and form a pyramid of life. Energy is passed from link to link. Plants trap the sun’s energy, herbivores (plant-eaters) feed on marine plants, small animals prey on the herbivores, larger predators hunt the smaller ones and so on, up to the top predators (sharks, dolphins and, of course, humans). Long food chains are formed, making up a complicated food web. Energy is transferred from level to level. These are known as trophic levels. Energy is lost each time it is transferred from trophic level to trophic level. The upper trophic levels are very much limited by the availability of energy. Animals use energy up as they swim, feed, hide, fight...and just exist. Therefore, because energy is lost along the way, many small creatures are required to support the larger animals further up the pyramid. As a result there are far fewer animals at the higher levels – being a top predator is hard work so the ocean food web forms a pyramid of life with millions at the bottom and only a few at the top. Trapping the Sun The sun's energy is first trapped by plants – not just seaweeds but the seawater is also full of tiny plants (phytoplankton). You need a microscope to see them but they are the base of our pyramid. We call these plants producers. We refer to the amount of the sun’s energy harnessed by marine plants, as productivity. Because sunlight can only penetrate seawater to a limited depth, the areas of highest productivity are the surface layers of oceans and shallow waters around our coast. Tiny Drifters The phytoplankton share their microscopic world with tiny animals (zooplankton). That crystal clear seawater is teeming with zooplankton; many are the young (larvae) of creatures like crabs, barnacles and starfish. They feed on phytoplankton. Sieving the Sea Many marine animals, such as soft corals, sea squirts and sponges, sieve plankton from the passing seawater. We call them filter-feeders. They are consumers and the next trophic level of our pyramid. Hungry Browsers Filter-feeding animals, anchored to the rocks, provide endless low energy snacks for fish such as wrasse, whose sticking-out teeth are specially designed to nibble at the animal growth on the rocky reefs. Other animals, such as sea urchins and starfish, also prey on filter-feeders. Predators and prey The energy is starting to build up now, enough to sustain larger fish and shellfish, such as the lobster. These are predators hunting for their prey. The Hunters There are fewer animals at the 'top' of our pyramid but they are large and must hunt to get their share of the sun's energy, originally trapped by tiny plants. A good-sized fish for lunch will provide the bottle-nosed dolphin with the energy it needs to search for its next meal. It is a top predator. Scavengers, such as crabs, prawns and some snails have an important role to play in the ocean food web. Like vultures on land, they clean up dead matter. ? Where do you think people fit into the marine pyramid of life? So… animals are found where their food is. Competition Marine animals compete for space and food. The more competition there is for food, the less chance there is of getting your share. Different types of animals therefore have special design features – we call it adaptation – to live and succeed in a particular place (niche). This adaptation might give them an edge over competitors. They might be camouflaged to sneak up on their prey or to prevent a predator spotting them. They might be specially adapted to burrow. If other conditions (light, currents etc.) do not suit, another type of animal will occupy the niche. If animals are adapted to live in particularly difficult conditions, they have less competition to worry about! So… animals are found where they are adapted to live and can compete successfully for food. The Seabed Non-divers often make the mistake of thinking the seabed is a flat, sandy desert. In fact, it is like a landscape under the sea – a seascape. There are rocky reefs with overhangs, caves and crevices – plenty of hiding places for sea-dwellers; sandy plains – perfect for burrowing; coarse gravely areas; rocks and boulders. And… there are shipwrecks! All these provide a physical environment (habitat) – ‘a home’ for communities of marine life. We have all these marine habitats off the Dorset Coast. So… seaweeds, and animals such as barnacles, sponges, soft corals and sea firs, which are stuck to the rock, are found on reefs, rocks and wrecks. So… animals, such as lobsters and crabs that need safe hiding places are found in cracks, crevices and caves. So… animals, such as sea squirts and fan worms, which like shady places, are found under rocky overhangs. So… burrowing animals are found in soft sand or gravel. Finding a Home Different types of marine animals have different strategies to make sure their young have a chance of surviving and spreading to other similar habitats in the sea. Some fish, like the Cuckoo Wrasse, guard their eggs until they hatch – in wrasse, it is the male who plays nursemaid! Most marine creatures, however, release eggs and sperm (spawn) into the sea. Huge numbers of larvae are swept away. These are the plankton – microscopic larvae of crabs, lobsters, starfish, mussels, sea squirts and many more marine animals. Perhaps better not to think about it next time you are sea bathing and swallow a mouthful of ‘clear’ seawater! Often these larvae bear no resemblance to the adult. They drift with the currents and most get eaten, but… and here’s the strategy… a few make it and settle down in a suitable place and change into adults. So… so long as there are communities of these animals fairly nearby and currents to transport their larvae, a suitable new habitat will be colonised. A shipwreck might provide such a habitat. 2. SHIPWRECKS AS HABITATS Artificial Reefs When a ship sinks, it is a disaster for the sailors and passengers on board and the owners of the ship and its cargos. Every cloud has a silver lining, though. It is great news for sea life! A wreck, like other man-made structures in the sea – sea walls, groynes and piers - creates an artificial reef with all the different habitats found on a real, rocky reef: a hard surface to cling on to, shady overhangs and lots of hiding places. Marine life is quick to colonise any suitable man-made structure, as any boatowner will know! We have many such structures in Dorset… The piles of Swanage Pier are an underwater photographer’s paradise. Shaded by the pier itself, they are colonised by the invertebrate animals you would normally have to dive to some depth to see. They are covered with sponges, plumose anemones, dead man’s fingers, fan-worms and much, much more. The breakwater around Portland Harbour provides a habitat for several rarities because the currents and wave action are weak, allowing silt to build up. Rarities include the shy Black-faced Blenny. Artificial reefs are being placed under the sea in various parts of the world to attract fish. In Poole Bay in Dorset, in 1989, an experimental artificial reef was laid on the seabed by Southampton University to study colonisation by marine life. The reef was made from blocks of coal ash and cement. The growth of animals on the reef was monitored. Within an hour, small shoaling fish, such as Pout and Pollock, were attracted – in hope of finding a meal sheltering there, or perhaps the ‘reef’ was a welcome hiding place, or just curiosity, who knows? Wrasse, which are typical territorial fish of inshore rocky reefs, arrived within the first month and lobsters and crabs soon began to move in. The surfaces of the blocks were first colonised by tube worms and sea squirts and after 3 months, small red seaweeds were growing on the tops of the blocks. Now it is covered with a dense growth of plant-like animals – hydroids, bryozoans and sea squirts. 90 different types of plants and animals have been recorded on and around the ‘reef’. Poole Bay is a perfect place for an artificial reef because the seabed is soft and sandy so hard reef is in short supply, but there are natural, rocky reefs within a few miles. So… the currents bring a constant supply of larvae of reef-dwelling animals just looking for a home. ? What can we make artificial reefs out of next? Marine Scientists at Southampton University are currently researching the use of old car tyres to build reefs… and there are plenty of them around! So… what about Dorset’s wrecks? Just like the natural habitats under the sea, what lives on, in and around wrecks depends on the depth and the amount of light, currents, food, competition and the surrounding seabed. It also depends on the material the ship was built from and how long it has lain on the seabed. Marine Life on and Around Wrecks In this section are listed some of the plants and animals that are found on and around wrecks. For each is given some information on where it likes to live. All plants and animals have a Latin name as well as their local common name. This is so that there is no confusion when it occurs in different countries. Scientists always use the Latin name to describe a type of plant or animal. The Latin name is always written in italics, or underlined. The first word is like your surname and is the generic or name of the genus. It begins with a capital letter. The second word, the specific or name of the species, is like your Christian name. It is all written in lower case. Fish Pouting (Trisopterus luscus) – Common, shallow water, shoaling fish, often found around wrecks more than 10m. deep. Pollack (Pollachius pollachius) – Common, shallow water shoaling fish, often found around wrecks more than 10m. deep. Tompot Blenny (Blennius gattorugine) – In kelp forests, small holes and crevices in reefs down to a depth of 35m. Omnivorous - feeds on sea firs, molluscs, shrimps, worms and seaweed. Conger Eel (Conger conger) – Hides in large holes in rocks and wrecks during the day from shallow to very deep water. Has a very large mouth and strong jaws. A top predator, feeding on fish and shellfish – anything that moves – at night! Can inflict a serious bite. Brill (Scophthalmus rhombus) and Plaice (Pleuronectes platessa) – Flat fish, adapted to live on sandy seabed to about 100m depth. They feed on small shrimps and fish on the surface of the sand. Ballan Wrasse (Labrus bergylta) – Among rocks and seaweeds down to 20m. They scrape barnacles and mussels from rocks and wrecks with their teeth. Sea Squirts Star ascidian (Botryllus schlosseri) – a colony of tiny, jelly-like animals, forming a smooth mat showing star patterns on weed, rocks and wrecks from the shore down to 20m. depth. Lightbulb sea squirt (Clavelina lepadiformis) – Transparent, jelly-like, stalked creatures, resembling light bulbs. On rocks and wrecks, where there are strong currents, from 5 to 20m. depth. Feeds on tiny particles of food, suspended in the water. Starfish Brittle star (Ophiothrix fragilis) – Has a central disc and long, thin arms. From 10 m. to 150m. depth. They can form a thick carpet on the seabed (up to 10,000 sq. m.). They feed on plankton and occasionally scavenge dead material. Shellfish (crustaceans) Lobster (Homarus gammarus) – Lives in holes and gullies in reefs and wrecks, where there are strong currents, from 5m. to deep water. They come out at night and are scavengers, feeding on dead animals. Edible Crab (Cancer pagurus) – They hide under rocky ledges and in wrecks, where there are strong currents, from 5m. to deep water. They feed on other crabs, molluscs and sometimes scavenge. Barnacle (Balanus crenatus) – On any hard surface in fairly still water. They catch plankton with their legs, which protrude from their hard shells. Molluscs Shipworm (Teredo navalis) – Not a worm but a mollusc with a small, hinged shell (bivalve) and a long body in a tube. They bore into any wood, under the sea – piers, bridges, ships and wrecks – and feed on tiny bits of wood and plankton. Grey Sea Slug (Aeolidia papillosa) – On rocks and wrecks from the shore to 30m. depth. Feeds on sea anemones. Mussel (Mytilus edulis) – Clings to rock and wrecks between 5 and 10m. depth. Feeds on tiny particles of food, suspended in the water. Worms Candy stripe flat worm (Prosthecereus vittatis) – Lives on clumps of light bulb sea squirts and beds of mussels. Peacock worm (Sabella penicillus) – This worm creates a tube from mud to live in. It occurs at all depths, attached to rock, wrecks, mooring chains in muddy areas. Soft Corals, Cup Corals and Sea Fans Dead man’s fingers (Alcyonium digitatum) – Aptly named, finger-like mass of tiny polyps with tiny, stinging tentacles. They are attached to rocks and wrecks from 5m. to 50m. depth where there are very strong currents. Devonshire cup-coral (Caryophyllia smithii) – On rocks, boulders and wrecks at all depths below 5m. Very rarely found east of Portland. Pink Sea Fan (Eunicella verrucosa) – Attached to rocks, boulders and wrecks, where there are strong currents, below 20m. depth. Very rarely found east of Portland. Anemones Plumose Anemone (Metridium senile) – A large, fluffy anemone often found attached to wrecks from 5m. depth to deep water, where currents are strong. Sea Firs Sea firs – Branching, plant-like animals – like tiny anemones on stalks, forming dense, bushy mats from below 10m. depth, where there are strong currents. Sponges Many different types of encrusting sponges (animals) cover any hard surface, from 5m. to deep water, where the currents are strong. Seaweeds Kelp (Laminaria hyperborea) – This is a heavy plant that needs something hard to attach to. It grows in a dense forest in shallow water (5 – 15m.) where there is plenty of light. Many smaller, red seaweeds attach to kelp plants for support (epiphytes). Dorset Wrecks Factfile The Royal Adelaide Type of vessel: Iron sailing ship ?… Length overall: 235 feet ( metres) Weight: 1500 tons Date sunk: 25 November 1872 Position: Chart Reference 50 34.65N; 02 28.50W. Map Reference SY664 755. ? Can you find out what these mean? Description of location: Approximately 100 metres (depending on the tide) off Chesil Beach, south west of Weymouth. Seabed: At the bottom of steep, terraced shingle seabed, where it levels off. It is an underwater desert. Towards Portland, there are kelp-covered rocks. Depth and visibility: 10m. Visibility up to 13m Physical factors: Scoured by shingle in winter seas. Type of dive: Dive from the beach using SCUBA or snorkelling. Access: Swim out from Chesil Beach. Impossible if wind is from the south and more than a Force 3-4. Currents: Strong, running parallel to the beach. Speciality: Trigger Fish, which have been recorded by divers during the last few years in the summer months. Were they there before but were just not recorded? Earl of Abergavenny Type of vessel: Sailing ship, timber clad with copper. ?… Length overall: 176 feet 11 inches ( metres) Weight: 1200 tons Date sunk: 5 February 1805 Position: Chart Reference 50 36.15N; 02 24.95W. ? Can you find out what this means? Description of location: 1 1/2 miles south east of Weymouth Harbour entrance. Seabed: Mud. Weymouth Bay mainly sand and mud. Depth and visibility: 18m. Visibility good but divers can easily stir up the mud. Physical factors: The wreck is fairly well buried in mud. Sheltered from west and south-west winds. Type of dive: SCUBA. Access: Boat dive from Weymouth or Portland Harbour. Currents: Mostly weak. Avalanche Type of vessel: Iron sailing ship with timber decking ?… Length overall: 214 feet ( metres) Weight: 1210 tons Date sunk: 11 September 1877 Position: Chart Reference 50 26.56N; 02 50.65W. ? Can you find out what this means? Description of location: West of Portland Bill Seabed: Silt, sand and broken shale Depth: 52 metres. Physical factors to consider: Depth Type of dive: SCUBA. Access: Boat dive from Weymouth or Portland Harbour. Currents: Mostly weak. The Halsewell Type of vessel: Timber sailing ship ?… Length overall: 139 feet 7 inches ( metres) Weight: 785 tons Date sunk: 6 January 1786 Position: Chart Reference 50 34.10N; 02 01.75W. ? Can you find out what this means? Description of location: Off Seacombe cliffs, near Winspit, west of Swanage Seabed: High rocks near the cliff. Gravel and sand patches with areas of bedrock showing. Depth: Less than 10 metres Physical factors to consider: At the base of the cliff – waves and swell. Type of dive: SCUBA. Access: Boat dive from Swanage Currents: Weak. 3. THE MARINE SCIENTIST A New Science The modern study of marine science began with the voyage of The Challenger (1872) and was furthered by the curiosity of Victorian naturalists, so marine science didn't really exist earlier than that. The sea - still a mystery Only in the last century have people been able to explore under the sea – either SCUBA diving (using self contained underwater breathing apparatus), and in submersibles. We know more about space than the deepest parts of the ocean. Marine scientists have to face a whole different set of problems to scientists studying the land. Just think about why surveying the sea is "a different kettle of fish". What are the problems a research diver has to face? Weather (rough sea) Tides and currents Cold Air Bulky equipment Depth (a diver can only spend a limited time at depth) Boat transport Communicating underwater Limited vision Sea sickness And more…. A simple task on land can become difficult once you are underwater. ? How would you make field notes? ? How would you collect a water sample from exactly 20 metres depth? Can you design a piece of equipment to do this? ? How would you collect a sample of sediment from the seabed? Can you design a piece of equipment, which can be operated from a boat, to carry out this task? Preparing to Dive Equipment the marine scientist might need to survey a wreck: A buddy to dive with – YOU NEVER DIVE ALONE A warm dry or wet suit – the deeper you go, the colder it is SCUBA (self-contained underwater breathing apparatus) Mask and fins A buoyancy device – a life-jacket, which can be inflated underwater to help the diver go up and down and maintain any depth in the water A weight belt – a diver has to have weights to compensate for the air in his / her tank and suit A slate and pencil for writing notes An underwater torch An underwater camera/video camera Sample pots to collect specimens to identify An underwater compass A tape measure A quadrat – a 1 metre or ½ metre square frame, used to work out how much seaweed or how many animals there are. Before the survey, the marine scientist would find out as much as s/he could about the wreck. S/he would study plans and charts. If the location is not well documented, s/he might map the seabed using side scan sonar. This is a form of echo sounding, operated from a boat. It produces a ‘picture’ of the seabed, showing the hard and soft areas. A large wreck can be seen on a soft seabed. After the survey s/he will complete a log of the dive, identify any specimens and write up the results. Speaking the Same Language Ecology is the science of plants and animals in their environment. Marine scientists use ecological terms. To carry out a scientific survey, you need to use these terms. Here is a list of some of the terms scientists use. Many of the words originate from Greek or Latin. If you wish to carry out the virtual dive activity included in the Teachers Centre (Diving with a Purpose) (***LINK***) you will need to use these terms … just to make sure we are speaking the same language! Organism – A living plant or animal Adaptation – A feature or features that make an organism able to succeed. Benthic – Plants and animals that live on the bottom of the ocean are called benthic organisms. They are not free-floating like pelagic (***LINK**) organisms are. Carnivore - An animal that eats meat (other animals). Consumer - Any organism, which must eat other organisms (living or dead) to get its energy. Dispersal - Spread of a species to a new location. In many organisms, this happens at a particular stage in the life cycle, and is often crucial to the survival of the species. Organisms may disperse as spores, eggs, larvae, or adults. Ecosystem - All the organisms in a particular region and the environment in which they live. The elements of an ecosystem interact with each other in some way, and so depend on each other either directly or indirectly. Environment - The place in which a plant or animal lives, and the circumstances under which it lives. Epiphyte - A plant, which grows upon another plant. The epiphyte does not "eat" the plant on which it grows, but merely uses the plant for structural support Food chain / food web - All the interactions of predators and prey within an ecosystem, describing how energy passes from one organism to another. Habitat - The place and conditions in which an organism lives. Herbivore - An animal that eats plants. Kelp forest - Marine ecosystem dominated by large kelps. These forests are restricted to cold and temperate waters, and are most common along the western coasts of continents. Marine - Refers to the ocean. Niche - The portion of the environment, which a species occupies. A niche is defined in terms of the conditions under which an organism can survive, and may be affected by the presence of other competing organisms. Nocturnal - Active only at night. Nutrient - Any element or simple compound necessary for the health and survival of an organism. This includes air and water, as well as food. Omnivore – An animal that will eat anything – plants or other animals. Pelagic - Pelagic organisms swim through the ocean, and may rise to the surface, or sink to the bottom. They are not confined to live on the bottom as benthic (***LINK***) organisms do. Photic zone - Region of the ocean through which light penetrates, and the place where marine plant organisms live. Phytoplankton - Tiny, free-floating plants living in water. Plankton - Tiny, free-floating organisms of the ocean or other aquatic systems. They may be phytoplankton or zooplankton. Predator - Organism which hunts and eats other organisms. This includes both carnivores, which eat animals, and herbivores, which eat plants. Prey - Organism hunted and eaten by a predator. Producer - Any organism which brings energy into an ecosystem from the sun. Most plants and many single celled creatures are producers. Scavenger – An animal that eats dead animals Sedentary - Not moving. Many organisms, both plants and animals, spend the majority of their lives in one place. Species – A group of individual organisms with common characteristics. Zooplankton - Tiny, free-floating animals in the sea. Unlike phytoplankton, zooplankton cannot produce their own food, and so are consumers. Find Out More… If you want to discover more about marine science there are lots of books and other websites to help you. Check out some of these… Web Sites Marine Conservation Society: http://www.mcsuk.org British Marine Life Study Society: http://ourworld.compuserve.com/homepage/BMLSS/ Southampton Oceanography Centre (Artificial Reef Project): http://soc.soton.ac.uk Marine Biology Web: http://life.bio.sunysb.edu/marinebio/mbweb.html Books Guide to Inshore Marine Life, David Erwin and Bernard Picton (Marine Conservation Society) A Discovery Guide ‘Underwater World’, Dr. Richard Pagett (Salamander Books Ltd.) Junior Nature Guides ‘Saltwater Life’, Leslie Jackman (Dragon’s World Children’s Books)