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diatoms marine ecology

Marine Ecology
Classification of organisms
Basic Ecology

Hydrothermal Vents


Diatoms are a major group of algae, and are one of the most common types of phytoplankton. Most diatoms are unicellular, although they can exist as colonies in the shape of filaments or ribbons (e.g. Fragillaria),fans (e.g. Meridion), zigzags (e.g. Tabellaria), or stellate colonies (e.g. Asterionella). Diatoms are producers within the food chain. A characteristic feature of diatom cells is that they are encased within a unique cell wall made of silica (hydrated silicon dioxide) called a frustule. These frustules show a wide diversity in form, but usually consist of two asymmetrical sides with a split between them, hence the group name. Fossil evidence suggests that they originated during, or before, the early Jurassic Period.

Diatom communities are a popular toolfor monitoring environmental conditions, past and present, and are commonly used in studies of water quality.

copepod marine ecology


Planktonic copepods are important to global ecology and the carbon cycle. They are usually the dominant members of the zooplankton, and are major food organisms for small Fish, whales, seabirds and other crustaceans such as krill in the ocean and in fresh water. Some scientists say they form the largest animal biomass on earth. They compete for this title with Antarctic krill (Euphausia superba). Because of their smaller size and relatively faster growth rates, however, and because they are more evenly distributed throughout more of the world's oceans, copepods almost certainly contribute far more to the secondary productivity of the world's oceans, and to the global ocean carbon sink than krill, and perhaps more than all other groups of organisms together.

shark fish shape marine ecology


The shape of a fish's body tells a lot about its lifestyle.  Fish with fusiform, or streamlined, bodies are usually fast swimming predators that may swim at high speeds much of the time or are capable of great bursts of speed. Many tropical fish are laterally compressed(flattened from side to side).  Fish with this shape are not very streamlined but they do not rely on speed for catching food or escaping from predators.  Their body shape is perfectly adapted for hiding in the cracks and crevices of rocks and reef.  They can move into these areas to hide, to escape predators or to get at food that cannot be reached by other fish.  Fish with this body shape, like angelfish, are very maneuverable and capable of short bursts of speed.   They are often camouflaged with disruptive coloration.

Other fish are flattened from top to bottom.  Fish with this body shape spend most of their time at the bottom.  They are usually camouflaged or can change color to match the bottom.


Marine Ecology

Basic Ecology

Ecology (from Greek: ?l???, "house" or "living relations"; -λογία, "study of") is the scientific study of the distributions, abundance and relations of organisms and their interactions with the environment. 

Ecology includes the study of plant and animal populations, plant and animal communities and ecosystems. Ecosystems describe the web or network of relations among organisms at different scales of organization. Since ecology refers to any form of biodiversity, ecologists research everything from tiny bacteria's role in nutrient recycling to the effects of tropical rain forest on the Earth's atmosphere.

Environmental factors in the marine environment include: temperature, salinity, pressure, nutrients, dissolved gases, currents, light, suspended sediments, substrate (bottom material), river inflow, tides and waves.

  • Temperature can control distribution, degree of activity and reproduction of an organism. The biology of life operates within certain ranges of temperatures. This is due to the use of enzymes within an organisms cells to perform important chemical processes. Enzymes have an optimal temperature where they have a maximum effect on a reaction. Below the optimal temperature an enzyme will function but at a slower rate which may hamper the cells functions or cause it to die. Above the optimal temperature enzymes become denatured and permanently damaged which may lead to cell death. Small Sea organisms are particularly susceptible to changes in temperature as they are directly affected by the temperature of the surrounding water. That is why organism distribution follows isotherm distribution around the world.

  • Salinity can control the distribution of organisms and force them to migrate in response to changes in salinity. The diffusion of nutrients and waste products in and out of a cell are controlled by diffusion gradients caused by differences in concentrations between solutions (cytoplasm) inside and outside of a cell. Concentrations inside and outside a cell must be similar otherwise sudden changes could cause large movements of chemicals / water in or out of the cell, causing it to swell or shrivel and burst. Some organisms can tolerate changes in salinity such as oysters by battening down the hatches when they close their shells. This a short term solution such as when there is a sudden outflow of fresh water in an estuary, but if the situation does not return to normal there could still be a mass death due to exposure to fresh water.

  • Hydrostatic pressure is the pressures exerted by a column of water surrounding an organism. IT has generally been thought that aquatic animals, which lack gas-filled spaces in their bodies, would not perceive variations in hydrostatic pressure due to small changes in depth, since their bodies are permeated with fluid of very slight compressibility. Only animals possessing gas-filled spaces, such as fishes, with their swim bladders, and certain aquatic insects, with special pressure gauges connected to the tracheal system, had been shown to respond to pressure changes, until recently. Then the discovery that decapod larvæ swim upwards, in response to pressure increases, suggested that tests for pressure sensitivity should be carried out on animals not known to possess gas organs.

Selective Adaptive Strategies

If an organism has a trait which provides them with a selective advantage (i.e. has an adaptive significance) in a new environment natural selection will likely favor it. Adaptive significance therefore refers to the beneficial qualities in terms of increased survival and reproduction a trait conveys. Therefore organisms within the plankton, nekton and benthos groups will have developed their own traits to help them survive within their own environments.

These include:

Plankton include plants (phytoplankton) and animals (zooplankton). More than 90% of marine plants are algae and most are unicellular and microscopic.

  • To photosynthesize (produce organic material from inorganic matter and sunlight) plants must remain within the photic zone.
  • Diatoms are single-celled plants enclosed in a siliceous frustrule (shell) that is shaped like a pillbox.
  • Dinoflagellates are single-celled plants with two whip-like tails (flagella).
To help plankton remain in the photic zone they have developed a lare surface area to volume ratio. This is because settling rates depend on body size and frictional drag, the smaller the cell, the larger it's friction with the surrounding water.

Zooplankton include the copepods and foraminifera.

  • Copepods are small herbivores (plant-eating organisms) that filter diatoms from the water.
  • Foraminifera are single-celled animals which build shells of calcium carbonate.
A copepod increases its filtering efficiency by moving its cephalic appendages to generate a current that directs photoplankton to the mouth region

The morphology of fish has evolved to allow them to move through the water easily.

  • The fish’s body must overcome three types of drag (resistance): surface drag, form drag, and turbulent drag.
  • Aspect ratio is the ratio of the square of the caudal fin height to caudal fin area:
    AR = (Caudal Fin Height)2/Caudal Fin Area.
  • Speed of a fish is dependent upon body length, beat frequency, and the aspect ratio of the caudal fin.
  • There are three basic modes of fish locomotion, each adapted to a different life style.
  • There is a strong correlation between predation success and mode of locomotion.

Swiming efficiency in fishes is achieved by minimising the drag created by friction, turbulence and body form. The "torpedd" shape, hydrodynamically efficient for cruising at high speeds, is the final result of taking these types of drag into account. An excellent example is the Tuna which is capable of extreme bursts of speed to catch their prey.

Intertidal benthonic communities generally are arranged in distinctive bands, termed vertical zonation.

  • Zonation reflects the amount of time the area is submerged and the ability of the organism to survive the stress of exposure.
  • Benthonic communities also vary in response to substrate (bottom material). Some organisms are adapted to rocky, sandy, or muddy sea bottoms.
Along the rocky shorelines of the midlatitudes, the benthic biota may display a banded distribution termed vertical zonation. Each of the bands possesses a unique assemblage of organisms. The upper boundary of each zone is related to the degree of tolerance to exposure to air. The lower boundaries reflect competition and predation pressure.

Banded Benthic Communities

A complex interaction among kelp, sea urchins, and sea otters controls the kelp community.

  • Macrocytis is a brown algae that grows up to 40m long in extensive beds on North America’s Pacific continental shelf.
  • Sea urchins feeding on kelp detach them from this holdfast and devastate the kelp beds.
  • Sea otters feed on sea urchins and control the size of their population.
  • Where sea otters abound, sea urchins are few, kelp beds thrive and sea otters feed mainly on fish.
  • Where sea otters are few, sea urchins abound and kelp bed are thin. Sea otters then mainly eat sea urchins

In the Amchitka islands of Alaska, sea otters control the size of the sea-urchin population, which in turn regulates the extent and growth of the kelp beds there. Due to hunting by humans and predatation by killer whales sea otter numbers have been reduced resulting in the destruction of the kelp forest ecosystems, which has had a knock on effect to local fish stocks.

Here is a powerpoint presentation which will help reinforce some of the point covered above. Marine Ecology


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