Chapter 15 Life Near the Surface

Vast open sea – pelagic realm Contains almost all of the liquid water on earth

How the Open Sea Effects You Regulates our climate Conditions our atmosphere Provides food and many resources

Life in the Pelagic Pelagic organisms live suspended in their liquid medium Lacks the solid physical structure provided by the bottom No place for attachment, no bottom for burrowing, nothing to hide behind

Epipelagic Upper pelagic Zone from the surface down to a given depth commonly 200 m (650 ft) Warmest Best lit Similar to the photic zone (area where photosynthesis can occur)

Pelagic 1. Epipelagic 2. Mesopelagic 3. Bathypelagic 4. Abyssopelagic Benthic 5. Littoral, Sub-littoral 6. Bathyal 7. Abyssal 8. Ultra-abyssal

Two Main Components 1.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 Pelagic Realm Fueled by solar energy captured in photosynthesis Nearly all primary production takes place within the epiplagic system itself Gets almost no external input of organic matter Supplies food to other communities

Lacks deposit feeders Suspension feeders are very common There are also many large predators like fishes, squids and marine mammals

The Plankton: A New Understanding

Scientist used to study plankton by catching them in tow nets This practice limited what organisms were caught

Recent developments in collecting plankton have lead to the discovery of many new groups of plankton and have changed how the plankton interactions are currently looked at

Plankton can be grouped based on their size Picoplankton – smallest Nanoplankton Microplankton Mesoplankton Macroplankton Megaplankton – largest

Phytoplankton – perform photosynthesis Zooplankton – cannot perform photosynthesis - heterotrophs

Phytoplankton – Major Groups

Net Plankton (Micro, Meso, Macro) Diatoms – found everywhere – important primary producers Dinoflagellates found everywhere, most common in warm waters – common red tide organisms

Dinoflagellates Diatoms

Colonial cyanobacteria (Trichodesmium) – mainly tropical – can fix atmospheric nitrogen – causes red tides in the Red Sea

Nanoplankton Coccolithophorids – important primary producers in nutrient poor waters Cryptophytes – very important primary producers Silicoflagellates – sometimes form blooms

Coccolithophorids

Picoplankton Unicellular cyanobacteria (Prochlorococcus) dominant primary producers, especially in nutrient poor water Various protists – presence of many groups recently discovered

ZooPlankton

Phytoplankton form the base of the food web 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 are by far the most important herbivores in the epipelagic Very few zooplankton are strict herbivores – will eat other zooplankton Most zooplankton species are primarily carnivorous and hardly eat phytoplankton at all

Protozoan Zooplankton Protozoans can catch tiny picoplankton and nanoplankton Without protozoans, much of the primary production in the epipelagic would go unutilized Flagellates, Ciliates, Foraminiferans, Radiolarians

Foraminiferans Radiolarians

Copepods Small crustaceans 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

Other Crustaceans – Shrimp-Like Krill Not as abundant as copepods but often aggregate into huge dense swarms Dominate the plankton in the polar seas

Efficient filter feeders – diatoms are a favorite food, also eat detritus Relatively big – up to 6 cm Eaten by fishes, seabirds, 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 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

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

Jellyfish and siphonophores – large, weak swimmers that drift with the currents – carnivore

Holoplankton Spend their whole lives as plankton

Meroplankton Many fish and invertebrates have planktonic larvae Temporary members of the plankton Small larvae feed on phytoplankton

Larger larvae feed on zooplankton Larvae can grow while in the plankton and change trophic levels

The Nekton

Large strong swimmers Fishes, marine mammals, squids, turtles, sea snakes, penguins Carnivorous

Planktivorous nekton – eat plankton – include herrings, sardines and anchovies, whale shark and the basking shark

Herring Sardines Anchovies

Most species of nekton eat other nekton Fishes, squids and large crustaceans are the main foods Epipelagic predators are not fussy, just need to be the right size

In general the larger the predator the larger the prey Herrings (small fish) – zooplankton Sperm whale largest of nekton – giant squid 10 m (33 ft long)

Living 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

Staying Afloat Cells and tissues are denser than water – naturally sink Shells and skeletons are even more dense Phytoplankton need to stay for sun and the others need to stay so they can get prey

How to stay afloat if you can not swim Increase the water resistance so that you sink slower Make yourself more buoyant

Increased Resistance Drag – resistance to movement through water or any other medium Small organisms – drag mostly depends on surface area – higher the surface area the slower the organism sinks – reason plankton are so small

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

Swimming organisms rarely have spines as this would increase water resistance and make swimming harder They generally have adaptations that reduce drag

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 Many adult fish store lipids – especially sharks and tuna

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

Bony fish have swim bladders – disadvantage – gases expand and contract as the fish moves in the water column

The Floaters Neuston – organisms that live right at the sea surface but remain underwater Pleuston – organisms whose bodies project through the sea surface into the air Most common method is to have a gas-filled structure

By-the-wind-sailor – (Velella) – colonial jellyfish-like cnidarian that is specialized as a float Portuguese man-of-war (Physalia) – powerful sting – part 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 Velella

Janthina

Predators and their Prey Many of the adaptations of epipelagic animals are related to their need to find food and at the same time avoid being eaten

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

Coloring and Camouflage Protective coloration or camouflage Nearly universal among epipelagic organisms that are large enough to be seen One way – transparent – jellyfish, salps, larvaceans, comb jellies

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

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

Swimming: The Need for Speed 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)

Laterally compressed bodies are also common – reduce the size of the silhouette 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

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 – for sustained cruising

White muscle – provides short burst of power Epipelagic sharks, tuna and billfishes have evolved a system to conserve the heat generated by their muscles and keep their internal temperatures above that of the surrounding water

Vertical Migration Pelagic waters are dangerous but they also contain the most food Some zooplankton spend only part of their time near the surface and then retreat to safer, deeper water Usually live at least 200m or 650 ft down

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

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 food chains usually have many steps and are generally longer than in other ecosystems Tropical usually have more levels than colder waters

Epipelagic is an exception to the 10% rule Herbivores pass on 20% and the carnivores pass on more than 10% also

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

Ocean Productivity         Red areas contain the most life, while the purple areas are nearly empty of life. Ocean areas of high productivity support more life than less productive areas. It is as simple as more food = more fish. More oxygen is produced and carbon dioxide consumed in these highly productive areas of the ocean.

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

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

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 Deep water is usually nutrient rich

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

Upwelling 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

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