MarBiolNekton_Oct_13 - Nekton Nekton The Swimmers Nekton...

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Unformatted text preview: Nekton Nekton The Swimmers Nekton While plankton are animals or plants that cannot swim against a horizontal current, nekton are larger, stronger swimming animals that are able to move against currents. While plankton usually occupy lower trophic levels in marine food webs, nekton are herbivores or predators that occupy higher levels ranging up to the top of oceanic food webs. Review: What is a Review: What is a trophic level? • A food chain has different • • • • trophic levels The first level is occupied by photosynthetic organisms. These are the “primary producers” Herbivores are the second level, and they eat the “primary producers” The third level would be predators which eat the herbivores. There may be more trophic levels in a food chain, and an “apex predator” such as a white shark would be in the top trophic level. Fish Fish were the earliest vertebrates. There are three living classes: Jawless and cartilaginous (agnathans). Cartilaginous but with a jaw (chondrichthyes) Bony (osteichthyes) Gills Gills – Fish oxygenate their blood (and remove CO2) by pumping blood through their gills. Gills also used to take in or release salts Jawless Fish (most primitive class) Examples: Mouths are jawless, boneless holes with a mouth Hagfish & Lamprey adapted for sucking. Hagfish are prominent in deep water , secrete a lot of slime, are scavengers. Lampreys are external parasites on live fish. Hagfish have about 70­100 slime Hagfish have about 70­100 slime glands for producing the mucous Hagfish mucous/slime Hagfish mucous/slime • They produce it as a defense against predators. To get rid of it they tie themselves in a knot and move the knot along the length of their body Cartilaginous (have cartilage, no bones) Fish With jaws Sharks, Rays, Ratfish Lay eggs (some incubate eggs within body) Do not have gas bladders (to help with buoyancy) so they must move continuously to keep from sinking. Tiny pointed scales, and teeth are essentially exaggerated scales. Sharks, Skates & Rays excrete Sharks, Skates & Rays excrete urea Animals that lay eggs excrete urea because it is non toxic. This allows waste products to build up in the egg as the animal develops. If ammonia were excreted, it could build up to toxic levels in the egg. Shown is a skate egg case. Some sharks are plankton feeders (whale shark, basking shark) Some small sharks, such as Cookie Cutter Sharks, feed by taking a bite out of larger prey, such as a whale. Many sharks are predators and occupy top trophic level Whale shark, Largest fish Whale shark, Largest fish • Up to 20 m long, eat crustaceans, fish, squid Some sharks have a heterocercal tail (upper lobe is larger than lower, and spine goes into upper tail) which pushes the snout down as they swim. Pectoral (front) fins provide lift and balance the tail motion. Sharks can sense electronic fields with the Ampullae of Lorenzi scattered on head. They can use them to detect fish hidden in the sediment, such as flounder. There are freshwater sharks in lake Nicaragua in Central America Ampullae of Lorenzini Ampullae of Lorenzini Note the pores from Ampullae on Note the pores from Ampullae on ventral side of Hammerhead • Used to detect electrical fields of prey. Head is wide to distribute electronic field sensing capabilities, plus it spreads out nostrils to allow better sense of direction of where a smell comes from The electronic senses of sharks are The electronic senses of sharks are phenomenal! • They can detect 10 billionths of a volt at 1 cm • Or the output of a 1.5 volt (AA) battery at 1500 km distance Sharks set up their own Sharks set up their own electromagnetic field to detect prey and direction relative to earth’s magnetic fields Sharks (and bony fish too) sense Sharks (and bony fish too) sense vibrations in the water with a lateral line system • This is a line of sensitive cells which helps them to locate prey Sharks hunt using smell (taste) and Sharks hunt using smell (taste) and hearing • Vision and the lateral line become more important as the • shark gets closer to the prey When close (< 1 m) to the prey, sharks then use electroreception to locate the electrical field of the prey and home in on it. Unlike bony fishes which pump water over Unlike bony fishes which pump water over their gills, sharks pass water by opening their mouth and swimming forward • Thus sharks must constantly move! How do they sleep? • The nerves that control body movement are located in their spinal cord, not their brain. A shark can theoretically sleep but keep swimming. More research is needed to understand, however. Sharks hunt using smell (taste) and Sharks hunt using smell (taste) and hearing • Vision and the lateral line become more important as the • shark gets closer to the prey When close (< 1 m) to the prey, sharks then use electroreception to locate the electrical field of the prey and home in on it. Locations of unprovoked Shark Locations of unprovoked Shark Attacks • 1580­2005. USA has the most Since 1952, only 81 recorded shark Since 1952, only 81 recorded shark attacks in California • You are 30X more likely to die from a lightning strike than a shark. Of course if you are a surfer, the odds are more likely for a shark attack. Here is an Average per year death chart of the following animals , notice where sharks come in. Deer ( Vehicular collision ) ­ 130 Death Dogs ­ 18 Deaths Snakes ­ 15 Deaths Mountain Lions ­ 0.6 Deaths Sharks ­ 0.4 Deaths or you are over 1100 times more likely to die in a bicycle accident then in a shark attack. Your odds of a Drowning Death ­ 1 in 3 million Your odds of a Shark Attack Death ­ 1 in 265 million Only about 18% of shark attacks Only about 18% of shark attacks are fatal • Surfers Zac Golebiowski & Bethany Hamilton. Lost a leg and arm to sharks Still Surfing! Still Surfing! Sharks have color vision and very Sharks have color vision and very sensitive eyes. • The eye has a mirror • like layer (Tapetum lucidum) in the back of the eye which doubles the eye’s sensitivity The nictitating membrane can close like an eyelid for protection when killing prey Great White Shark is an Apex Great White Shark is an Apex Predator The skin of sharks is covered with very hard The skin of sharks is covered with very hard dermal denticles (skin teeth) which reduce drag. Speedo lzc swim suit does the same • Running your hand from front to back skin feels smooth but rough if done other way. Riblets are ridges separated by grooves. As water flows over these, they prevent the formation of eddies which would produce drag. New suit based on shark skin New suit based on shark skin denticles gives basically a 6 meter head start in a 200 m race. Your inner shark Your inner shark • Gill arches: jaws in fish evolved from the gill arches (used to support the gills) The developing human embryo The developing human embryo also has gill arches in early stages • First arch becomes the jaw (upper & lower) plus the • • • malleus &incus ear bones Second arch forms the stapes (3rd ear bone) plus a tiny throat bone and muscles that control facial expression Third arch forms muscles & nerves in throat for swallowing Forth arch forms larynx Skates and Rays live mostly on the bottom and eat benthic organisms. Steve Irwin was killed while Steve Irwin was killed while swimming above a Stingray • The Stingray raised it’s tail and it punctured his heart. Barb has poison Barb has poison • Treatment for stings includes application of near­scalding water, which helps ease pain by denaturing the complex venom protein, and antibiotics. Immediate injection of a local anesthetic in and around the wound is very helpful, as is the use of opiates such as intramuscular pethidine Farallon Islands Farallon Islands • In the fall, thousands of marine mammals congregate on this rocky promontory to breed and calve their young. This event attracts the largest White Sharks in the world to South East Farallon Island (SEFI), where they feed on Elephant Seals before their long trans­Pacific migration. Is this for real? Is this for real? • There are few dangerous sharks in the Bay San Francisco Bay Sharks San Francisco Bay Sharks • Leopard Shark (2­3 ft long) Others Others • • • Sevengill, Spiny Dogfish Soupfin Great White Sharks are Great White Sharks are endangered and populations of most all sharks have been dropping worldwide • This is partly because of cutting fins off for shark fin soup & overfishing • Peter Klimley of the Bodega Marine Lab studies shark populations and behavior In many places, sharks are captured and In many places, sharks are captured and fins cut off then the live shark is tossed back into the water Sharks don’t just live in coastal Sharks don’t just live in coastal areas. This shows movements of tagged salmon sharks • Apparently migrate to give birth in Warmer waters Because of over harvesting, shark Because of over harvesting, shark populations are decreasing • Population off North Carolina Bony Fish ~25,000 species usually overlapping flat scales. Body shape of fish varies and depends on the needs of their habitat. Tuna : active swimmers have fusiform (torpedo shaped) bodies with a high narrow tail. Tuna Regulate body temperature by using countercurrent circulatory networks that consist basically of paired ingoing and outgoing blood vessels. In this way the heat of the warm blood going to the gills is transferred to the cooled blood coming from the gills, and the heat is kept within the fish's body. By using these networks, tuna are able to keep their body temperature from about 5° to almost 12° C above the water temperature. By keeping their body temperature up, this allows them to be more active in cold waters. Body shape depends on the needs of their habitat. Fish living in sea grasses or coral reefs have laterally compressed body to navigate easily through a complex environment. They are agile but not fast. Body shape depends on the needs of their habitat. Bottom dwellers have depressed or flattened bodies, such as flounder. Designed to hide from predators and surprise prey. Body shape depends on the needs of their habitat. Sedentary (not active) Fish have globular bodies, such as anglerfish (toadfish). Not built for speed or agility but to suddenly grab prey . Body shape depends on the needs of their habitat. Burrowing fish are long and narrow, such as the moray eel. Moray Eel has a modified gill raker Moray Eel has a modified gill raker which jumps forward when biting. Like a second set of jaws. Coral reef fish have disruptive coloration making it difficult to identify the head and direction in which they are going to move. A swim bladder is used by some fish to maintain neutral buoyancy so the fish can remain at one depth and not constantly swim. A network of blood vessels in the bladder adds or removes gasses. When a fish descends, it adds gas to keep the bladder from being compressed. Active swimmers such as tuna, sharks and mackerel do not have swim bladders. Migrations: Fish often make use of ocean currents. Usually they spawn in one place and feed and grow up in another to take advantage of ample food and good spawning conditions in different places. Examples Salmon & Eel. Salmon must adapt to living in freshwater vs. seawater and eels do the opposite. Salmon are anadromous. There are six species of Pacific Salmon. Adults die after spawning (Atlantic salmon can spawn more than once). Salmon are guided by odor (or taste) of water to their birth stream. Eels are catandromous….breed in the ocean but live adult lives in freshwater. Spawn in Sargasso Sea (Atlantic) at 300 meters depth and the adults then die. Takes 3 years for larvae to reach Europe and North America. Marine Organisms must maintain constant internal osmotic Marine Organisms must maintain constant internal osmotic pressure in the face of changing external salts when they go between fresh & salt water. The salts in salmon blood are about half that of seawater • When salmon migrate from • freshwater to saltwater their internal fluids lose H2O and gain salts. They compensate by drinking seawater and excreting salts through their gills. When they go back to freshwater their gills pump in salts to compensate for loss of salts. Every species of salmon has a Every species of salmon has a different life cycle • As an example, the Chinook (King) Salmon young spend from 1­18 months in freshwater after eggs hatch • They then migrate downstream and spend 6 months in the estuary • After that they spend 1­8 yrs in the ocean, then migrate to their home stream to spawn, then die Eel Transparent leaf shape larvae called leptocephalus. Drift in Sargasso 1-3 yrs off coast of N. America. When they get to the coastal waters they metamorphose into elvers, which resemble adults. American eels spawn in the American eels spawn in the Sargasso Sea • The size of the larvae caught in a plankton net increases as you get closer to the streams they will inhabit as adults Salmon Life Cycle Schooling provides some defense from predators. There is less of a chance a fish will be eaten when schooling and non-randomly distributed. Ice Fish : Notothenioids This family has radiated out into different niches in Antarctica. How they survive in cold waters: The blood of marine fish is more dilute (fewer salts) than seawater. Their fish blood should freeze at -0.2°C, while seawater freezes at about -1.5oC.. How they live in the cold cntnd… Notothenioids have glycopeptides that act as antifreeze. Their structure is such that they fit into the slots in an ice crystal and this prevents the ice crystal from growing. Additionally there are antibodies that hunt ice crystals. How they live in the cold continued… In regular fish blood, when very cold, the hemoglobin and red blood cells make the blood very viscous, requiring a lot of energy to pump the blood. In Notothenioids, hemoglobin and red blood cells are not required (so many species have none) to carry oxygen to the cells and instead oxygen is acquired via oxygen dissolved in the blood plasma. Notothenioids also have wide blood vessels and a large heart, and in some cases, lack red blood cells altogether. Marine fish are very fecund (many eggs). salmon = 5 x 103 eggs cod = 10 x 106 eggs Cod eggs usually laid in midwater and drift with plankton. Salmon, herring and sand-eel are the few exceptions, and their eggs are laid either in sediments or they attach to solid objects. Most eggs develop ~3 wks then hatch. (salmon eggs take 5 months to develop) The cod & salmon have two different The cod & salmon have two different approaches to reproduction • The cod releases millions of eggs but with little yolk (food reserves) directly into the water column. The hope is that there are so many eggs that some would survive. • The salmon releases fewer eggs into a nest in a stream, and each egg has a lot of yolk. In a gravel nest there is less chance of being eaten, so fewer eggs are required. At the end of the larval stage they metamorphose and become juveniles which look like adults. Juveniles usually live in nursery grounds several years. Larvae can survive the first two weeks on the yolk (lower left), after which they feed on copepod nauplii. If no food is available they die. Most Fish have indeterminate growth (not like us) and continue to grow throughout life. Most adult fish migrate seasonally searching for food. Winter flounder move inshore and off shore ~15 mi. Plaice in the North Sea migrate ~200mi. Herring in the North Sea migrate ~450mi. Bigger fish tend to migrate farther than smaller fish. Spawning in all fish in temperate waters is at a regular time of the year and does not vary more that a week from year to year. In the tropics it is more variable year to year since food availability is more predictable. Year class survival depends on availability of food. Spawning is timed to occur so the eggs hatch when there is plenty of food. If food is lacking, starvation occurs and there is a poor year class. Fish Populations and Human impact. Patagonia Toothfish : AKA Chilean Sea Bass. A Notothenoid, little known about the biology of this fish. Most fishing for it is illegal because it occurs in Antarctic waters. Don’t eat Chilean Sea Bass! Cephalopods are molluscs (related to Cephalopods are molluscs (related to clams) most of which are active swimmers Reptiles and Birds have salt excreting organs associated with their nasal passages which help them deal with excess salts in their food and the saltwater they drink. The salt is excreted near their eye so they look like they are crying Cetaceans • Two suborders: Toothed whales and Baleen • Baleen whales are able to filter plankton and can take up to 10 tons of krill at a single feeding • Toothed whales eat seals, fish, squid etc. • Have no external ears or projecting nostrils • Many whales make seasonal migrations. Humpback whales feed in northern waters in summer and breed and birth in equatorial waters in winter. Study Guide Study Guide • • • • • • • • • • • What are Nekton? Give examples What is Trophic Level? 3 groups of fishes, examples & characteristics How fish get O2 in blood Why sharks excrete urea? How sharks sense electric fields & prey Shark eyes How tuna regulate body temperature Disruptive coloration Swim bladder­how work & why have it? Anadromous vs Catandromous give examples Study Guide Study Guide • Osmotic Pressure – how regulated in Fresh vs • • • • • • • salt water Ice Fish – how live in cold. Blood characteristics Cod vs salmon egg size vs numbers Year class survival. What depend on? Cephalopods ­ examples What reptiles in sea? How birds drink seawater and live? Toothed vs baleen whales ...
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