Marine Organisms

Marine vs. Terrestrial Life

Marine Terrestrial Organisms – similar density as Organisms – much higher density than environment (salt water) less energy to air … than to walk or fly. float/swim… small effect of gravity High gravity impact (fall down)

Water supports bodies, no need to put Need strong skeletal material (animals: energy in skeletons bones; trees: trunks) Plenty of water for life May become water limited Temperature variation low Temperature varies strongly Light limited: reflection of light at sea Light energy substantially higher than in surface and rapid light absorption with aquatic systems, low absorption by air water depth Nutrient limited: nitrate, phosphate, High nutrient concentrations in natural silicate, iron soils

Major part of nutrient regeneration in Nutrient regeneration in soil close to plant the dark deep-sea uptake Physically unstable habitats Physically stable environment

Classification by habitat

Plankton are those organisms that live suspended in the water column and are too small to be able to swim counter to typical ocean currents, they include phytoplankton, zooplankton and bacteria.

Those animals that move in the water column, but they are (اﻟﺴﻮاﺑﺢ:) Nekton capable of more powerful swimming and can move against a current or through turbulent water. They range from small fish, to the largest whales.

Include those animals and plants that live attached to the bottom (اﻟﻘﺎﻋﻴﺔ):Benthos or on or in the bottom.

ƒ Infaunal: Animals that live in the bottom within the sediment such as clams.

ƒ Epifaunal: Animals that live on or attached to the surface of the bottom, e.g. oysters and barnacles.

ƒ Semi-infaunal: Those animals that are partially burrow in the bottom e.g Artina.

70 Neuston Nekton

Plankton

Boring Epifaunal

Benthos Semi-faunal Infaunal

Plankton

Phytoplankton are photosynthetic planktonic protists and plants, and usually consist of single-celled organisms or of chains of cells.

Zooplankton all heterotrophic plankton, their size range from 2 µm (heterotrophic flagellates, protists) up to several meter (jellyfish)

Mixoplankton are photosynthetic protists, but also can ingest other plankton.

Meroplankton are plankton for only part of their life cycle. They include the planktonic larval stages of many benthic invertebrate groups.

Holoplankton, are those planktonic organisms that spend all their life cycles as plankton, i.e., Planktonic throughout life.

Neuston are the plankton associated with the water surface, such as bacterial films.

Pleuston: Planktons that have a float protruding above the sea surface, e.g. Portuguese man-of-war.

Classification of Planktonic organisms according to their size

• Ultraplankton or picoplankton (<2 µm), • Nanoplankton (2-20 µm), • Microplankton (20-200 µm), • Mesoplankton (0.2-20 mm)

71 • Macroplankton (2-20 cm), • Megaplankton (20-200 cm).

Plankton is traditionally sampled by plankton nets with a mesh size of various pore size.

Fig. Paired plankton nets are placed overboard. The length of wire and angle of entry are measured to find the depth of sampling. A calibrated propeller gives the volume of water sampled.

Plankton Life

As we have mentioned before, Plankton are the plants and animals that drift around on the oceans’ currents. Phytoplankton are the microscopic plants that convert sunlight and nutrients to starch and organic matter. Not only do phytoplankton form the base of the oceans’ food chain, they also produce at least 80% of the oxygen that we breathe. Zooplankton on the other hand, are the animal members of the marine planktonic community. Most zooplankton occupy the second or third trophic level of the marine food web. As such, these herbivores and small carnivores play an exceptionally important role in marine food webs. Planktonic organisms usually depend upon the surface waters for survival. Phytoplankton will die unless they are near a source of sunlight for photosynthesis. Zooplankton on the other hand, depend upon phytoplankton, or at least upon animals that consume phytoplankton. Zooplankton, therefore, also must remain in the surface waters. How do plankton keep near the surface or avoid sinking?

A particle will remain suspended in water if it is less dense than seawater. Many planktonic organisms however are somewhat denser than seawater and will therefore sink in a quiet water column. Plankton reduce their density relative to that of the surrounding water and avoid sinking to the bottom or to depths greater than a depth at which they can photosynthesize (in case of phytoplankton) or survive by one or more of the following mechanisms:

72 1. By storing (accumulating) oils and other fluids of low density • Diatoms and other organisms such as copepods, and fish eggs and larvae, contain droplets of oil which reduce their density and can serve as food reserves. • Some blue-green bacteria have vacuole-like structures that contain low- density gaseous nitrogen. 2. By having flattened bodies and appendages, spines, and other body projections that increases their surface area and reduces settling velocity.

• The bell-shaped jellyfish has flat bottom and tentacles combine to slow sinking relative to a sphere of the same shape and bulk composition. • Some diatoms, such as Chaetoceros, form twisted chains, which spiral as they sink slowly. 3. By having Flotation structures • Portuguese man-of-war Physalia for example have a large gas-filled sac that acts as a float from which the rest of the colony is suspended. 4. By replacing heavier ions with lighter ones • Many zooplankton are replacing dense magnesium, calcium, and sulfate ions with lower-density ammonium, sodium, and chloride. 5. By accumulating ions of low specific gravity • The dinoflagellate Noctiluca, for example, accumulates ions of low specific gravity, which reduces their density.

6. By having the ability to swim sea butterfly) for example, has two lateral winglike) ( ﻣﺠﻨﺤﺔ اﻷﻗﺪام) Pteropods • projections, and the snails flap through the water. • Jellyfish move in pulses, through rapid compressions of circular muscles, which compress the bell and force water backward. • Crustaceans such as copepods use assorted appendages to push against the water to move forward. • Arrow worms swim by undulation. All these swimming methods are effective means of countering sinking.

7. By depending upon water turbulence which keeps organisms suspended in the water column.

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