Marine Nekton Lecture 4 PDF

Lecture 4  Nekton/swimmers o Marine organisms having swimming capabilities o Move independent of currents Heterotrophs Have patchy distribution o Dependent on primary production Have large size range e.g., fish, squid, octopus, sharks and mammals  Nektons are pelagic o Epipel...

Lecture 4  Nekton/swimmers o Marine organisms having swimming capabilities o Move independent of currents Heterotrophs Have patchy distribution o Dependent on primary production Have large size range e.g., fish, squid, octopus, sharks and mammals  Nektons are pelagic o Epipelagic o Mesopelagic o Bathypelagic  Have specialized structures to swim and float on water Diverse group varying in size Usually pelagic but some are bathypelagic Heterotrophs – herbivores, carnivores or omnivores Maintain osmotic regulation of their bodies by keeping an isotonic environment to the seawater Swim in great distances to search for food  Reproduce by producing eggs others live birth o Birds and turtles produce shelled eggs on land o Fishes spawn eggs that float and undergo development in seawater o Mammal e.g., whales - live birth Move by S-shaped contractions (undulations throughout the body)  Vertebrates o Major group of nektons o Chordates Invertebrates o Minor group of nektons o Crustaceans and mollusks  Chordates o Fishes Sharks, o Reptiles Turtles and sea snakes o Birds - penguins o Mammals Whales, dolphins , porpoises , Mollusks Squid and octopus Arthropods o Crabs and lobsters  Most bio-diverse and abundant nekton – over 32000 species Most abundant species are epipelagic Majority are plankton feeders and have high fecundity e.g., herring, sardines, anchovies  Fewer deeper water fish species o Tend to be small in size o Many species have photophores and use bioluminescence to locate or lure either prey or mates, or to evade predators  Ectothermic – cold blooded – temperature is dependent on environment Vertebral column Fins for propulsion and balance o tail fin, a matching pair of side fins, dorsal fins, and an anal fin Scales cover their bodies – protect them from injuries and diseases (some do not have e.g., pufferfish)  Gills for breathing Swim bladder - regulates swimming depth and floatation Lateral line – sensitive to vibrations in water, detect motions in water Habitat – all fish live in water  Jawless fish – super class Agnatha Jawed fish – infraphyla Gnathostomata o Cartilaginous fish - class Chondrichthyes o Bony fish – super class Osteichthyes Most abundant and diverse (anatomy, behavior and ecology) - over 20000 species Form most profitable marine fisheries  Class Chondrichthyes -cartilaginous fishes o No true bones o 5 to 7 gill clefts in sealachii o Rigid dorsal fin, fins and fin spines Subclass Elasmobranchii (e.g., sharks, rays, sawfishes, guitarfishes, skates, and stingrays o 5–7 pairs of gill clefts not covered by a fold of skin, opening separately to the exterior  Subclass Holocephali (e.g., Chimaeras) o Upper jaw completely fused to cranium o Unmodified branchial arches below cranium o Scales do not grow once formed Superclass Osteichthyes (bony fishes) o Class Class Actinopterygii (ray-finned fishes) Fins supported by dermal bones Scales grow continuously Swim bladder present Skeleton well ossified  Class Sarcopterygii (fleshy- lobe finned fishes) e.g., coelacanth and lungfishes o Cranium not divided into movable parts  Class Cephalaspidomorphi (e.g., lampreys) o Bottom dwelling fishes o No dermal ossification o Pectoral appendages absent o 1 to 16 pairs of external gill openings o Feed by suction – dead flesh Class Myxini (e.g., hagfishes) o No dermal ossification o Bottom dwellers o 7 pairs of external gill openings o Suctorial – blood and juices of live fishes  Mollusk - cephalopods Have eight short arms and two long tentacles o Tentacles have sucker rings/hooks at the tip They are active predators - common prey Many are adapted for life at great depth Size - 2 cm to 20 m (Architeuthus) No chambers in active swimmers Have siphons used in jet propulsion Commercially important  Squid driftnet fishing is unselective and vast numbers of seabirds, fish, turtles, and marine mammals are captured and killed by this method Alternative more selective squid fishing techniques are available, but they are costly  110 species of marine mammals e.g., whales, pinnipeds (seals, sea lions and walruses), and sirenians (manatees and dugongs) Largest mammal are the baleen whales Feed by filtering zooplankton Population is decreasing o Population recovery is low o Hunting pressure is high coupled with low reproduction and long maturity time makes them vulnerable to depletion (most are endangered)  Cetaceans (whales, dolphins, and porpoises), Pinnipeds - “fin footed”(seals, sea lions, and walruses), o Shortly stay on land to reproduce and rest Sirenians (manatees and dugongs), and Fissipeds (polar bears and sea otters) o Spend most time on land and get into water for feeding  Deep sea – bottom/abyssal Hostile conditions – dark, extreme pressure and temperature Examples of organisms: black hagfish, viperfish, a sleeper shark  Dead plants, live/ dead animals and animal wastes (marine snow) o Organisms are Scavengers or Predators Chemoautotrophy - bacteria use chemical reactions to produce food o Form the base of food webs o Around hydrothermal vents  Large eyes o Highly sensitive and adapted to seeing in low light intesnites Heightened scent and touch Photophores – emit bluish-green light o Bioluminascence - lure prey, scare predators or attract mates Vertical migration – move to epipelagic at night and back at dawn - safety e.g., Copepods Red body color – makes them difficult to be spotted by predators (red - long wave length, cannot reach the bottom)  Pressure: Buoyancy adjustment – regulate oxygen or fats in the swim bladder o Metal amour – crustaceans have a metallic exoskeleton (aluminum) to avoid crushing Low temperatures (4oC) o Slow movement – bodies adapted to low energy consumption Chemotropism https://youtu.be/JtV-FP212Uc  Abyssal plain o Fairly flat o Squat lobsters, red prawns, and various species of sea cucumbers Whale fall o Death and sinking of whales to the bottom o Scavengers fist for months Hydrothermal vents o Exist in volcanic active areas  Seawater sinks in cracks and is heated by hot magma Absorbs minerals on its way to the ocean floor Black smokers – emit iron sulfide White smokers – emit calcium, barium and silicon  Super salt pools on the ocean floor Remnants of ancient seas  Cold seeps o Hydrocarbon (methane) fluids and gases trapped deep in the earth percolate up to the seafloor through cracks o Mussels and shrimps Canyons and seamounts o Walls, edges, and bottoms of canyons form habitats for a variety of organisms o Mollusks, worms, deep sea corals and fish o Seamounts - influence flow of currents o Crabs, corals, anemones, sea stars, and fish  Deep sea reef o Exist individually or as diverse colonies comprised of more than one species o Serve as habitats for sea stars and sharks  Increasing our understanding of factors causing natural fluctuations in the abundance of fish Providing near real-time oceanographic data in connection with the actual process of fishing; better information on the location of fish schools can reduce the fishing costs  Assignment