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►Ecology and Ecosystems

►Ecosystems in the Open Sea

►Coastal Ecosystems

►Polar Ecosystems

►Deep-Sea Ecosystems

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The Science of Ecology

Ecology is the science that studies how organisms relate to each other and their environment. It embraces a wide range of disciplines: Biology, Physics, Geology,

Climatology, Oceanography, Paleontology, and Astronomy. Ecology considers biotic (living) and abiotic (nonliving) factors.

Abiotic includes temperature, wind, pH, currents, minerals and sunlight.

Biotic includes the quantity and type of organisms in an environment.

Ecology studies the relationships and interactions of the abioticand biotic aspects of the environment. The goal is to understandhow changes in an environment will affect the organisms in the environment.

In marine ecology the four branches that come together are: Biological Oceanography, Chemical Oceanography, Geological

Oceanography, and Physical Oceanography.Ec

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Ecology Terminology

Ecosystem – a distinct entity, with clearly defined physical boundaries, distinct abiotic conditions, an energy source, and a community of interacting organisms through which energy is transferred.

Community – a collection of different organisms living in an ecosystem. Includes all species and types of organisms.

Population – is a group of the same species living and interacting within a community.

Habitat – includes the area and conditions in which you find an organism.

Microhabitat – exists on a very small scale.For example: tiny worms living between sand grains on the seafloor.

Niche – is an organism’s role in its habitat. Very different species can occupy the same niche.

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Energy Flow and Nutrient Cycles

Energy flow through the food web affects an ecosystem by determining how much energy is available for organisms at higher trophic levels.

The carbon nutrient cycle is the basis for most of the biomass inall ecosystems.

The nitrogen nutrient cycle is thought to be more limited inmarine ecosystems than interrestrial ecosystems.

Temperate ecosystems have less overall sunlight, but receive far more nutrients. For that reason, the most productive marine ecosystems are found in cold, temperate regions.E

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Neuston Ecosystems

Neuston – plankton that live afloat on the surface – make up an ecosystem a few millimeters thick. Despite being thin, this forms a major ecosystem receiving maximum sunlight and covering about 71% of the Earth’s surface.

Cyanophyte, diatom and dinoflagellate populations – may be 10,000 times more numerous here than in the water just a few millimeters deeper.

In some areas photosynthesis and primary productivity are higher below the neuston ecosystem. This may be due to: Photoinhibition, prevalent in tropical seas, may be one cause –

UV light gets though because there’s little water to protectneuston organisms.

A second factor may be pollutants – a concern to scientists with respect to global warming. Pollutants concentrate in the neuston layers, just like beneficial nutrients.

The world’s largest floating ecosystem is the Sargasso Sea in the middle of the North Atlantic gyre.

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The Continental Shelf

The neritic zone is a significant marine ecosystem because it is the most productive region in the ocean. Continental-shelf depth seldom

exceeds 200 meters (656 feet). This helps to keep nutrients in

the shallow photic zone and helps retain heat from the sun.

Nutrients come from river runoff near shore and rise with currents fromdeep water.

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Upwellings

Upwelling plays a significant role in the balance of coastal ocean ecosystems.

Upwellings are important to open-ocean ecosystems because they bring nutrients from deeper water to shallow, more productive depths.

The role of upwellings is unmistakable. Areas with the highest upwelling activity

also have the highest nutrient levels. These in turn correspond with many

of the ocean’s highest productivityregions including: Waters offshore of Peru. The Bering Sea. The Grand Banks in the Atlantic. The deep water surrounding Antarctica.C

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©Current Publishing Corp. 2006

Worldwide upwelling

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High Productivity Marine Environments

Coastal ecosystems are highly productive ecosystems forseveral reasons: 1. Benefit from nutrient-rich runoff from land. 2. Being shallow, the benthic organisms in these ecosystems live in the

upper photic zone, instead of the bottom as in the open sea. 3. Salt-tolerant plants can grow in the well-lit shallows, providing shelter. 4. These plants act as the foundation for several different types of

ecosystems that cannot exist in the open ocean. A combination of nutrients, ample light, and shelter make coastal ecosystems

diverse and rich. Human activities have wide-ranging potential effects on coastal ecosystems.

Because people live near water, this means that many of our activities potentially affect coastal ecosystems. We can’t always anticipate consequences to the ecosystems. Two examples are agricultural fertilizer and pollutants.

Eutrophication is an overabundance of nutrients that causes an ecological imbalance. It is a stimulus to some species and a detriment to others. Red tides are caused by eutrophication.

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Estuaries

Factors that limit productivity are: Organisms in the ecosystem must tolerate wide salinity ranges. Variations in salinity tend to reduce the variety of species to only euryhaline. Osmotic stress caused by tides mixing with fresh water is fatal to many

organisms. The tendency of decomposition to deplete the oxygen level.

Estuaries serve as nurseries for more than 75% of the commercial fish species. Estuaries contribute to the productivity of adjacent marine ecosystems:

1. By providing surviving juvenile species with shelter for them to mature. By increasing the number of individuals that survive the hazardous larval and juvenile stages.

2. By providing nutrients to adjacent ecosystems while trapping sediment and other materials in runoff from rain and storms. By reducing eutrophication and other runoff damage were the runoff to reach the open sea.

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Salt Marshes

Salt marshes exist in estuaries and along the coasts. The upper marsh includes the areas only rarely flooded by the tides. The lower marsh includes areas flooded by salt water and a regular

part of the tidal cycle. Organisms living here must tolerate significantly more osmotic stress than species with niches in the upper marsh.

Halophytes are plants that have adaptations that allow them to survive in salt water.

Lower marsh halophytes deal with constant osmotic stress and have adaptations to deal with it. Adaptations include: Pores in the leaves through which it breathes. Concentrates salts in its roots. Salt glands on leaves and stem.

Upper marsh halophytes have muchreduced osmotic stress. Adaptations include: Sacrificial leaves.C

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Mangrove Swamps

Red mangroves grow above the waterline on stilt-like roots allowing oxygen to get to the roots.

Black mangroves have roots that grow in the sediment below the waterline. They aerate their roots with snorkel-like tubes that carry air from above to the roots.

White mangroves lack special root adaptations. They are very saltwater tolerant, but thrive high on the tideline.

All species of mangroves share two important characteristics that make them the basis of mangrove ecosystems. First, strong, tangled roots that provide habitats for

juvenile fish and invertebrates. This provides a nursery for nearby marine ecosystems, particularly coral reefs.

Second, due to size they hold the soil well, protecting the habitat and coast from erosion from storm surges, waves, and weather.

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Seagrasses

Seagrasses differ from other halophytes in several ways: They are the only plants, living entirely underwater except during rare,

very low tides. They have no means of extracting fresh water from seawater. They extract oxygen from the seawater and have internal air canals. They do not need to have a freshwater source because they have an

internal salinity the same as seawater. They reproduce by releasing pollen into the water,

much like land-based plants release polleninto the wind.

They differ from other halophyte-basedecosystems because: They do not need to have a freshwater source

and they can exist in deep water. They are edible and provide food for ecosystem

inhabitants like microbes, invertebrates, fish, turtles, manatees, and dugongs.C

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Intertidal Zones

Ecosystems in the intertidal zones exist in areas that may be above the waterline at times. Other portions reach depths of 10 meters (32.8 feet).

The supralittoral zone is the area only submerged during the highest tides. The greatest challenges facing organisms that live in this zone are

drying out, thermal stress, and water motion. With the constant spray of seawater evaporating, high salt levels

can also be a problem. The littoral zone is the area between high and low tide.

The organisms here must also deal with drying out, thermal stress, and water motion.

With ample water nutrients, and sunlight, this is a highly productive region. One challenge to life here, therefore is massive competition.

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Beaches

Beaches are rich and productive ecosystems; they have important roles that affect other marine ecosystems. The first way beaches affect the ecosystem is the sand protects the

coastline by reducing sedimentation caused by coastal erosion. Complex organisms, (worms, mollusks, and fish) live in the submerged

beach sand. Algae and nonanimal organisms live among the sand grains.

The second way beaches affect other marine ecosystems is the interaction between water motion and the meiofauna.

The meiofauna – benthic organisms – live in the spaces between sand grains.

The physical and organic process in the beachecosystem break down organic and inorganicmaterials making the beach a giant filter thatprocesses compounds from runoff to the seaor washed up from the sea.

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Kelp and Seaweed Ecosystems

Kelp provides a clear example of why it is important to study ecology, not simply individual organisms. Until protected, in some areas the sea otter was hunted nearly to extinction. Amazingly, in these areas the kelp began to die off rapidly. Few organisms eat kelp. The sea urchin is one that does. They

especially like the rubbery holdfast that anchor the kelp. The sea urchin is one of the sea otter’s primary foods and the

sea otter eats a substantial number of sea urchins. Killing the sea otters disrupted the kelp forest’s ecological

balance by removing the sea urchin’s chief predator. This allowed the sea urchin population

to rise relatively unchecked. More urchins meant more grazing on kelp holdfasts.

In the end, the sea urchins ate the kelp faster than it could grow.

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Coral Reefs

Coral reefs are the most taxonomically diverse of all ecosystems on Earth. While diverse, they are also fragile.

The conditions coral requires for life are narrow and specific: Clear water; dinoflagellates coexisting in the polyps need light for

photosynthesis. Water that’s in moderate motion as this prevents sediments from

accumulating on polyps. Water that is relatively free of nutrients. Lack of nutrients actually protect

coral from other organisms. With too many nutrients, algae grows displacing coral and plankton grows reducing water clarity and the amount of sunlight. When a body of water is choked by plant life it is called eutrophication.

Threats to coral reefs include: Eutrophication levels have been rising over

the last several decades. Thermal stress also threatens coral reef ecosystems. Coastal dredging and construction cause sediment

to accumulate on the polyps faster than water motioncan remove it.

Coral diseases are more common. Co

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The Arctic

For the following reasons life is relatively scarce under the ice cap. Marine ecosystems in the Arctic face the challenges of reduced sunlight

under the ice and water that’s barely above freezing. Much of this sea is a permanently frozen ice cap on top of the Earth.

At the edge of the cap, life intensifies during the warmer months. As the sun melts ice in the spring, water flows off the ice, sinking into deep water. Warm currents from the south interact with the cold water and that churns up nutrients from the shelf bottom.

Extremely high productivity occurs along an arc in the North Pacific and across the North Atlantic from April to August. Massive fisheries, marine mammals and other organisms take advantage of the nutrients.

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The Antarctic

Antarctica is a continent, not a frozen sea, and it hasit’s own continental shelf. Antarctic winters have widespread freezing and the

continent almost doubles in size as the ice sheet expands. When summer comes, the melting of this sheet sets

off an explosion of bioproductivity. Cold melt water sinks. This downwelling results in an

upwelling from the deep ocean. The nutrient-rich water reaches the surface at the Antarctic Divergence,

located at 65° to 70° south latitude. This area extends northward to an area called the Antarctic Convergence located at about 50° to 60° south latitude.

This is the largest nutrient-rich area on Earth. There are massive phytoplankton blooms from November through the

southern summer. The copepod and krill populations are larger than any other species population found in any other ecosystem. The krill swarms have been estimated as exceeding 100 million tons!

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The Abyssal Zone

The abyssal zone covers about 30% of the Earth’s surface. Without sunlight, there’s no photosynthesis; consequently, there’s no

primary productivity in most of the deep ocean. Marine snow makes the deep ocean rich in nutrients.

Marine snow is the constant fall of sediment, dead organisms, fecal pellets, and other nutrients fromthe productive shallow water above.

Without primary productivity the abyssal zone lacks dense life concentrations. However, there is a vast species diversity. Without photosynthesis there are not many multicellular

organisms. Those that do survive are primarily echinoderms, such as sea cucumbers, sea lilies, and brittle stars.

Submersibles have seen rattails, deep-sea dogfishes, catsharks, crustaceans, mollusks and many species of deep-ocean fish.

The diversity is found in the meiofauna. Representatives from almost all the animal phyla can be found living in the deep-ocean mud or sediment.

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Whale Falls

A whale fall is exactly what the name says – a place where a dead whale comes to rest on the deep-ocean floor. Stages of whale fall ecosystems are:

1. During the first stage the scavengers arrive. They consume the whale’s soft tissues in a few months. Hagfish, grenadiers, deep-sea spider crabs and sleeper sharks are associated with this stage.

2. Stage two lasts about a year. Worms, small crustaceans, and other small organisms feed on the remaining soft tissue and the tissue dispersed around the whale as detritus.

3. The final stage involves the decay of the skeleton. This can last several years or even decades. The bones provide a steady supply of sulfide as they’re broken down. Chemosynthetic bacteria live on this sulfide and in turn create a food source. These bacteria appear to be the same as those associated with hydrothermal vents.

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Hydrothermal Vents and Cold Seeps

Hydrothermal vents are sources of primary productivity. Chemosynthesizing bacteria consume sulfides dissolved in the heated water emerging from the vents. These bacteria act as the base of a trophic pyramid for a diverse community living in these deep-ocean ecosystems.

Cold seeps are areas where hydrocarbons and sulfide-rich fluid seep from the underlying rock in the ocean floor. Heated by geothermal energy from inside the Earth. They are called “cold” seeps because they’re cool compared to hydrothermal vents.

The Hadal Depths – Ocean Trenches Scientists know little about the hadal zone ecosystems primarily because of

the limits of technology. Depth and pressure make it expensive and difficult. Depths range from 5,000 to 6,000 meters (16,404 to 19,685 feet). Some spots

are as deep as 11,000 meters (36,089 feet). Few submersibles exist that can go to these depths.

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