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Chapter 15 Life Near the Surface

Pelagic Zone

• – The vast open – Contains almost all of the liquid water on earth Pelagic Zone

• Pelagic zone benefits – Regulates our climate – Provides food. • Pelagic organisms live suspended in the water • Lacks the solid substrate provided by the bottom • No place for attachment, no bottom for burrowing, nothing to hide behind

Epipelagic Zone • Epipelagic – Upper pelagic – Zone from the surface down to a given depth commonly 200 m (650 ft) – Warmest – Best lit • The - area where photosynthesis can occur Epipelagic Zone

• The epipelagic zone has two main components • Coastal or Nertic – epipelagic waters that lie over the continental shelf – Lies close to shore – Supports most of the world’s marine fisheries production • Oceanic part – Waters beyond the continental shelf The Organisms of the Epipelagic The Epipelagic Zone

• Fueled by solar energy captured in photosynthesis • Nearly all primary production takes place within the epiplagic zone. • Supplies food to other communities

The Epipelagic Zone

• Lacks deposit feeders • Suspension feeders are very common • There are also many large predators like , and marine mammals • is abundant Plankton

Plankton

• Plankton - live in the and cannot swim against the current. • are autotrophs. – Perform photosynthesis • – are heterotrophs • Plankton can be grouped based on their size – Picoplankton – smallest – Nanoplankton – Microplankton – Mesoplankton – Macroplankton – Megaplankton – largest

Plankton

• Holoplankton – plankton for their entire life. • – Many and invertebrates have planktonic larvae – Temporary members of the plankton – Small larvae feed on phytoplankton – Larger larvae feed on zooplankton

Phytoplankton Net Plankton (Micro, Meso, Macro)

• Diatoms – Found everywhere – Important primary producers • Dinoflagellates – Found everywhere – Most common in warm waters – Common red tide organisms

Picoplankton

• Colonial (Trichodesmium) – mainly tropical – Can fix atmospheric nitrogen – causes red tides in the Red Sea ZooPlankton Zooplankton

• Phytoplankton form the base of the • Solar energy that they capture and store in organic matter is passed on to the other creatures of the epipelagic from minute zooplankton to gigantic whales • Herbivores eat phytoplankton

Zooplankton

• Zooplankton are heterotrophic plankton. • Zooplankton are by far the most important herbivores in the epipelagic • Very few zooplankton are strict herbivores most will eat other zooplankton Protozoan Zooplankton

• - unicellular eukaryotic organisms • Protozoans can catch tiny picoplankton and nanoplankton • Without protozoans, much of the primary production in the epipelagic would go unutilized • Some are photosynthetic and are also considered phytoplankton. • Flagellates, Ciliates, Foraminiferans, Radiolarians

Flagellates

Foraminiferans

Radiolarians

Cilliates Zooplankton

• Copepods – Small – Dominate the net zooplankton – Most abundant members of the net zooplankton practically everywhere in the ocean – 70% or more of the community – Major carnivores

Copepods Crustacean Zooplankton

• Shrimp-Like – Not as abundant as copepods but often aggregate into huge dense swarms – Dominate the plankton in the polar – Efficient filter feeders – diatoms are a favorite food, also eat detritus – Relatively big – up to 6 cm – Eaten by fishes, , great whales

Krill Non-Crustacean Zooplantkon

• Salps – transparent, planktonic herbivores – filter out plankton by pumping water through a sieve-like sac or a fine mucus net Non-Crustacean Zooplantkon • Larvaceans – float inside a house they make of mucus – beat tail to move water through the house – food particles are caught in a complicated mucus net that is inside the house

Non-Crustacean Zooplantkon

• Pteropods – Mollusks – small snails that have a foot that has been modified to form a pair of wings that they flap to stay afloat • Arrow Worms or chaetognaths – extremely important predators in the zooplankton – feed mostly on copepods Non-Crustacean Zooplantkon

• and siphonophores – large, weak swimmers that drift with the currents – carnivores

Nekton

• – Large strong swimmers – Fishes, marine mammals, squids, turtles, sea snakes, penguins – Carnivorous • Most species of nekton eat other nekton • Fishes, squids and large crustaceans are the main foods Nekton

• The larger the predator the larger the prey – Herrings (small fish) eat zooplankton • Sperm whale largest of nekton giant eat 10 m (33 ft long) Nekton Herring • Planktivorous nekton – eat plankton – includes herrings, sardines and anchovies, and the basking shark Anchovies Sardines

Surviving in the Epipelagic

• Demands of the environment cause organisms to have certain adaptations • Two main problems – Need to stay in the epipelagic zone – Need to eat and avoid being eaten • Many of the adaptations of epipelagic animals are related to their need to find food and at the same time avoid being eaten Surviving in the Epipelagic - Staying Afloat • Staying afloat – Cells and tissues are denser than water – naturally sink – Shells and skeletons are even more dense – Phytoplankton need to stay for sun – Zooplankton need to stay so they can get prey

Surviving in the Epipelagic - Staying Afloat • Increase the water resistance so that you sink slower – Drag – resistance to movement through water or any other medium – For Small organisms drag mostly depends on surface area, the higher the surface area the slower the organism sinks this is the reason plankton are so small Surviving in the Epipelagic - Staying Afloat • Increase the water resistance so that you sink slower – Shape influences surface area – parachute shape slows sinking (jellyfish) – Flat shapes slow sinking – Long projections or spines increase surface area and therefore decrease the rate of sinking – Forming chains slows sinking

Surviving in the Epipelagic - Staying Afloat

• Swimming organisms rarely have spines as this would increase water resistance and make swimming harder • They generally have adaptations that reduce drag Surviving in the Epipelagic - Staying Afloat • Increase buoyancy – Reduces the tendency to sink – Store lipids (Oils or fats) – Lipids are less dense so they tend to float – Diatoms, copepod and fish eggs contain a drop of oil. – Whales, seals and other marine mammals have a great deal of buoyant fat in a thick layer of blubber under the skin – Pocket of gas is another adaptation

Surviving in the Epipelagic - Staying Afloat • Increase buoyancy – Bony fish have swim bladders – disadvantage – gases expand and contract as the fish moves in the water column Surviving in the Epipelagic - Staying Afloat • The Floaters - Increase Buoyancy – Neuston – organisms that live right at the sea surface but remain underwater – – organisms whose bodies project through the sea surface into the air • Most common method is to have a gas- filled structure

Surviving in the Epipelagic - Staying Afloat • Floaters - Increased Buoyancy – By-the-wind-sailor (Velella) • colonial jellyfish-like cnidarian that is specialized as a float – Portuguese man-of-war (Physalia) • powerful stingpart of the colony acts as a sail – Violet shell (Janthina) • makes a rafts of mucus filled with bubbles from which it hangs upside down Physalia

Velella

Janthina Surviving in the Epipelagic - Sense Organs

• Highly developed • Vision is important – many have good eyesight • Vision is especially important to the nekton because there are no solid structures to avoid concealment • Lateral line – remote sensing system that sense vibrations in the water – used to stay with school mates and detect predators Surviving in the Epipelagic - Coloring and Camouflage • Protective coloration or camouflage • Nearly universal among epipelagic organisms that are large enough to be seen • Transparent – jellyfish, salps, larvaceans, comb jellies Surviving in the Epipelagic - Coloring and Camouflage • Countershading – dorsal surface (back) is dark usually green, blue or black and the belly (ventral surface) is white or silver – Looking down – ocean depths are dark blue and it is hard to see the prey – Looking up – bright light is filtered down and it is hard to see the prey Surviving in the Epipelagic - Coloring and Camouflage • Laterally compressed bodies are also common – reduce the size of the silhouette • Silvery sides – reflect light – help to blend in • Vertical bars or irregular patterns – help to break up their outline in the dappled under water light Surviving in the Epipelagic - Swimming • Whether the prey gets away or the predator gets a meal depends on which swims faster • Emphasis is on sheer speed • Epipelagic contains the worlds most powerful swimmers • Practically all epipelagic nekton have streamlined bodies that make swimming easier & more efficient • Do not have features that increase resistance (like spines, bulging eyes)

Surviving in the Epipelagic - Swimming • Bodies are firm and muscular • Force is delivered mainly by the tail • The tail is high and narrow • Fins tend to be stiff – provides maneuverability and lift Surviving in the Epipelagic - Swimming • Fishes have two types of muscle – red and white – red muscle gets its color from the high concentration of myoglobin (stores oxygen) • Red muscle – best suited for long sustained effort • White muscle – provides short burst of power

Epipelagic Food Webs Epipelagic Food Webs

• Of great interest, especially because epipelagic fishes provide food and employment to millions • Trophic Levels and Energy Flow – Very complex – Epipelagic contains vast numbers of different species – Feeding habits of most of them are poorly known – Most of the animals eat a variety of prey often from different trophic levels Epipelagic Food Webs

• Most epipelagic animals consume different prey at different times in their lives • The basic flow of energy in the epipelagic can be depicted as phytoplankton  zooplankton  Small nekton  Large nekton top predators • Epipelagic is an exception to the 10% rule • Herbivores pass on 20% of their energy and the carnivores pass on more than 10% Epipelagic Patterns of Production Epipelagic Patterns of Production • Epipelagic food webs are complex but they all share one simple feature – primary production by phytoplankton is the base • Some areas of the epipelagic are among the most productive on earth and some are “deserts” • Phytoplankton need 2 main things to perform photosynthesis – Sunlight – Supply of essential nutrients Epipelagic Patterns of Production - Light Limitation

• Must get all their light during the day • May be light-limited during the winter • Total primary production also depends on how far down light penetrates into the water column

Epipelagic Patterns of Production - Nutrients

• Nitrogen, iron and phosphorus play a major part in controlling primary production • Nitrogen is most often the limiting nutrient • Most nutrients come from the recycling of nutrients Epipelagic Patterns of Production - Nutrients

• Much of the organic matter ends up as detritus (fecal pellets, dead bodies) • Often the detritus sinks past the epipelagic zone before it releases its nutrients • The surface is usually nutrient poor • Deep water is usually nutrient rich Epipelagic Patterns of Production - Nutrients

• Seasonal Patterns – Can cause nutrient laden cold water to come to the surface – As the water cools it sinks, breaks up the thermocline and allows surface waters to mix with deep nutrient rich water

Epipelagic Patterns of Production - Nutrients

• – Caused by Ekman Transport – Occur mainly along the eastern sides of ocean basins where the prevailing winds blow parallel to the coast – Ekman transport carries the warm surface water offshore

Epipelagic Patterns of Production - Nutrients • Upwelling – This allows the deeper nutrient rich water to move to the surface – Major coastal upwelling areas are among the most productive waters of the epipelagic – In the pacific there can be equatorial upwelling