Succession in aquatic ecosystems

  • Communities develop over time
  • In facilitation, each succeeding species makes itshabitat more favorable for subsequent species
  • In inhibition, each species inhibits the species thattry to succeed it
  • In tolerance, a species neither facilitates norinhibits its successors
  • Species richness usually increases during succession
  • Biotic processes, such as herbivory, competition, andmycorrhizae, can deflect the path of succession
  • Succession: gradual changes in a community that are predictableand orderly
  • Primary succession:when plants invade an area in which no plants have grown before
  • Secondary succession:a modification of longer-term primary succession. It does not occur on virginpreviously un-inhabited aquatic ecosystems.

Effects aquatic pollution on organisms, colonization and succession

  • Changes in waterquality affect the entire biosphere. i.e. Plants, animals and other organismsliving in water may suffer physiological changes.
  • The specificeffects of aquatic pollution vary depending on the type of pollutant thatenters the environment.
  • Sometimes waterpollution, e.g. eutrophication causes the excessive proliferation or growth ofan invasive or local plant/organism. For example, harmful algal blooms (HABs) arepromoted by increased levels of nitrogen and phosphorus in the environment.
  • The excessivegrowth of algae and cyanobacteria changes the succession and communitystructure of phytoplankton and macrophytes in the aquatic environment, aprocess that can sometimes have devastating consequences on the environment.
  • HABs are usuallycomposed of algal and cyanobacterial species that produce deadly toxins and aresometimes known as “red tides” or “brown tides” for their appearance in water.
  • The toxinsproduced and released by HABs can kill fish, marine mammals and seabirds andharm humans.
  • The death ofalgae and cyanobacteria species that make up the blooms, bacteria may use upall the oxygen from the water as the algae and cyanobacteria decompose, leadingto a condition called hypoxia.
  • Hypoxia creates a“dead zone” where fish cannot live, and more than 400 areas around the worldhave been identified as experiencing eutrophication and 169 of them arehypoxic.

Adaptations to Aquatic Environments

Aquatic plants evolved from terrestrial plants. Like whales and other marinemammals, aquatic plants evolved from land back to aquatic habitats. Aquaticplants modified terrestrial features to withstand emerged, submerged, orfloating conditions.

plant adaptations to aquatic environment:

Emergents plants:

Aeration of Roots:

  • Formation of aerenchyma: large open spaces between cells, which is important to carry oxygen down to the root zone. 
  • Formation of prop roots (Red Mangrove)
  • Formation of pnuematophores (Black Mangrove)
  • Anaerobic respiration: plants will form ethylene, then more aerenchyma tissue and adventitious tissue. The plant elongates and forms fatty acids from the ethylene. Ethylene is a common gas in swamps due to decay.

Reproduction: Sexual reproductionis rare, more commonly used methods are:

  • Fragmentation, pieces break off and float away to another location where they get embedded in the substrate.
  • Rhizomes: underground stems send up shoots to start a new plant.
  • Stolon: same as rhizomes except these are above ground stems which form into shoots and start a new plant.

Seed germination:Plants have different strategies for seeds:

  • Timing of seed production to occur during the non-flood season either by delayed or accelerated flowering.
  • Production of buoyant seeds that float on high unflooded ground.
  • Seeds germinate while still attached to the plant.

Photosynthesis: Gas exchange: Asthe water gets deeper, the wavelength of light gets shorter until its gone. Thered and blue wavelengths are lost, and the green (not so good forphotosynthesis) remains. Adaptations include:

  • Wetland plants often use C4 biochemical pathway of photosynthesis instead of C3.
    -C4 provides a possible pathway for recycling CO2 from cell respiration
    -plants using C4 have low photorespiration rates and the ability to use even the most
    intense sunlight efficiently.
    -C4 plants are more efficient than C3 plants in the rate of carbon fixation and amount of water used per unit carbon fixed.


  • Barriers prevent or control the entry of salts -root and leaf cell membrane act like ultra-filters.
  • Organs specialized to excrete salts -selectively remove certain ions from the vascular tissue of the leaf.

Submerged plants:


  • Vallisneria produce a coiled peduncle (female), which straightens out so the stigma can reach above the water surface. The spathe (male) also straightens out so its petals float on the surface. Its three leaves and anthers form a sailboat. The spathe floats along until hopefully it bumps into a stigma.
  • Ceratophyllum: uses a strategy of hydrophily: the male releases pollen into the water where it floats until it sinks again, hopefully landing on a female plant.
  • A chinese lotus can lay dormant for over 1,000 years.     


Algal blooms can block the sunlight and nutrients to submerged plants.

Aeration of Roots –

Oxygen is transmitted from the leaves to the roots and rhizomes by lacunae(air spaces forming channels in leaves, stems, and roots). Lacunae also have astructural role. Lacunae take up about 60% of the plants volume.

An experiment was done to demonstrate the oxygen gradient in plants.  It was found that a plant has 20% oxygen inits leaves, 15% in its stem,10% in the root parts, and only 2- 5% in the roothairs. The oxygen is taken in from the air by photosynthesis and travelsthrough the plant and out of the root hairs.

When low oxygen levels are present, plants use other mechanisms to adjustfor respiration. Aquatic plants can respire anaerobically. This has been shownexperimentally by bubbling N2 or O2 into the water with rhizomes, and thenmeasuring the ethanol production. At <3% O2 , ethanol is produced by Typha, Scirpus, Nuphar, andothers. Some aquatic plants have developed air roots along their stems forrespiration in water. Aquatic trees have developed pnuematophores, which areextensions of the root system reaching above the water level. Pnuematophorestake in oxygen through small holes at their tips.

Other challenges that aquatic plants must adapt to include: flooding,desiccation (drying out) nutrient uptake, and vegetative reproduction.

Adaptation of animals in aquatic habitat

  • Changes in body organization to exploit water asa habitat are known as aquatic adaptation.
  • All classes of vertebrates have theirrepresentatives partially or totally adapted to aquatic life.
  • An aquatic animal should have the ability toswim to overcome the resistance of the surrounding medium.
  • Therefore, they must have a streamlined bodywith an organ or ability to float.
  • The animal should also have to overcome theproblem of osmoregulation.
  • There are two types of animals living in thepresent day water, which have undergone aquatic adaptation.
  • According to their origin, they are primary andsecondary aquatic animals.
  • Primary aquatic animals are those animals whoseancestors lived in water and they are still living in the water. Therefore,primary aquatic animals never had a terrestrial ancestry. They exhibit perfectaquatic adaptions. All fishes are primary aquatic animal.
  • Secondary aquatic animals are those whoseancestors were lung breathing land animals, migrated to the water for somereason and ultimately got adapted to live in aquatic habitat.
  • Some secondary animals live partially whileothers live totally in the water.
  • All aquatic reptiles, aves and mammals arerepresentatives of secondary aquatic animals.
  • Amphibians are in a transitional form betweenprimary and secondary aquatic life.
  • Respiratory organs are the gills in perfectly adaptedaquatic forms such as fishes but in the air breathing forms nostrils arelocated near the top of the head to enable them to go to surface frequently toinhale air.
  • Locomotary organs are developed as the fins toswim in water easily. There are different types of fins including dorsal fin,ventral fin, caudal fin, pectoral fins and pelvic fins.
  • All the fins help in swimming but the caudal finhelps them to balance the body in water.
  • Some aquatic forms like amphibians have a thinfold of skin in between the digits of the hind limbs which are called web. Webhelps to increase the surface area for swimming.
  • Aquatic animals like turtles have fin likeorgans called paddles for swimming and whales have the flippers as the swimmingorgan.
  • Body is covered by scales which make the bodysoft and slippery so as to escape from the enemies and also helps them to protectthe internal soft organs of the body.
  • Some fishes have a hydrostatic organ called airbladder for adjusting them in the different depths of water according to theirneed by increasing the amount of gas or by decreasing the amount of gas insidethe air bladder.

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