Aquatic Ecology Course Zoo 374

Biodiversity Despite the importance of marine ecosystems, increased human activities have caused significant damage or are serious threats to the marine biodiversity. These activities can be overfishing, pollution, introduction of exotic species or coastal development. For this reason, conservation plans are necessary to save the marine ecosystems from being lost.

Categories For the Coastal Zones the subcategories are: Rocky shores Sandy shores Continental shelf Open oceans Deep Sea Sea ice ecosystems Coral reefs Seagrass meadows Mangroves Salt marshes Estuaries

I- Rocky Shores

I- Rocky Shores A rocky shore is an intertidal area that consists of solid rocks. It is often a biologically rich environment and can include many different habitat types like steep rocky cliffs, platforms, rock pools and boulder fields. Because of the continuously action of the tides, it is characterized by erosional features. Together with the wind, sunlight and other physical factors it creates a complex environment. Organisms that live in this area experience daily fluctuations in their environment. For this reason, they must be able to tolerate extreme changes in temperature, salinity, moisture and wave action to survive.

Zonation Each region on the coast has a specific group of organisms that form distinct horizontal bands or zones on the rocks. The appearance of dominant species in these zones is called vertical zonation. It is a nearly universal feature of the intertidal zone.  

Supratidal zone When the tide retreats, the upper regions become exposed to air. The organisms that live in this region are facing problems like desiccation, temperature changes and feeding. This upper region is called the supratidal or splash zone. It is only covered during storms and extremely high tides and is moistened by the spray of the breaking waves. Organisms are exposed to the drying heat of the sun in the summer and to extreme low temperatures in the winter. Because of these severe conditions, only a few resistant organisms live here. As fungi and microscopic algae living together and sharing food and energy to grow. Also snails which are well adapted to life out of the water by trapping water in their mantle cavity or hiding in cracks of rocks. Other common animals are isopods, barnacles.

Intertidal zone (littoral zone) Because the intertidal zone is a transition zone between the land and the sea, it causes heat stress, desiccation, oxygen depletion and reduced opportunities for feeding. At low tide, marine organisms face both heat stress and desiccation stress. The degree of this water loss and heating is determined by the body size and body shape. When body size increases, the surface area decreases so the water loss is reduced.

Subtidal zone (sublittoral zone) is the region below the intertidal zone and is continuously covered by water. This zone is much more stable than the intertidal zone. Temperature, water pressure and sunlight radiation remain nearly constant. Organisms do not dry out as often as organisms higher on the beach. They grow much faster and are better in competition for the same niche. More essential nutrients are acquired from the water and they are buffered from extreme changes in temperature.

Problems and adaptations Air Light Temperature Salinity stress Desiccation stress Predation Wave action

Problems and adaptations Air: Intertidal organisms are regularly exposed to air and water. Air differs physically from seawater in important features. This influences the ability to exchange gas and their overall thermal balance with the surrounding environment. Attachment and body changes are also required. When exposed to the air, the organisms directly absorb solar radiation. The buffering capacity of water, because of the high rate of heat conductivity, disappears and the body temperature increases. In contrast to this, heat loss is much lower in air than in water. An adaptation to heating is the vaporization of internal water reserves.

Problems and adaptations Light: Sunlight is another parameter that influences the organisms. When there is too much sunlight, organisms dry out and the capacity to capture light energy can be weakened. The light that is not used or dissipated can cause damage to subcellular structures. Too little sunlight reduces the growth and reproduction of the organism, because photosynthesis is reduced. Algae can avoid absorbing too much light by changing the amount of pigments they produce. When free radicals are produced from an excess of light, they can be scavenged and deactivated.

Problems and adaptations Temperature:. The organisms must be resistant to temp. changes to survive. Most of the marine organisms are ectothermic (need the warmth from the environment to survive). When the air temperature is too low, the organisms must cope with physiological threats associated with cold stress. The body fluids can then reach their freezing point & ice crystals develop. This causes damage to cell membranes and increasing the osmotic concentration of the remaining fluids. To avoid this cold stress, organisms can migrate to habitats that are more suitable. For sessile organisms ,they can develop physiological and behavioral adaptations such as gaping shells (mussels). Some organisms have developed antifreeze proteins. When the temperature is too high, heat stress appears. Heat stress accelerates rates of metabolic processes. This can be avoided by evaporative cooling combined with circulation of body fluids.

Problems and adaptations Salinity stress: When the osmolality of the cell is lower than the surrounding medium, the cell loses water from the internal fluids to the environment (hyperosmotic stress). When the intracellular osmolality is higher than the environment, there is an influx of water into the cell from the environment (hypoosmotic stress).

Problems and adaptations Desiccation stress: Organisms are threat by desiccation during emersion at low tides. Dehydratation due to evaporative water loss is the most common mechanism. Highly mobile organisms can avoid the desiccation by migrating to a region that is more suitable. Less mobile organisms restrict various activities (reduced metabolism) and attach more firmly to the substrate. Physiological features by reduction in water permeability of membranes, reduction of metabolic and developmental rates.

Problems and adaptations Predation: strategies to escape from predation 1) calcification. It makes them tougher and less nutritious. 2) production of chemicals, These chemicals can be produced all the time such as toxins, but other chemicals are only produced in response to stimuli (inducible defense). 3) Bioluminescence, The light is used for warning, blinding, making scare, misleading or attracting the predator. 4) camouflage. This can be visually or chemically. Visual camouflage means that the prey becomes invisible to the predator by using the same colors as the environment. Chemical camouflage is the passive adsorption of chemicals. The predator does not smell the prey anymore, because the smell is masked.

Problems and adaptations Wave action: permanent attachment (Bivalves). But this strategy can not be used by organisms that have to move to feed themselves. These organisms have to make a compromise between mobility and attachment. Another way to be protected is to burrow themselves into the sediment. But an alternative is to seek protected habitats.

Why are rocky shores important? Providing a home for a lot of organisms Nursery area for many fish and crustacean species Shelter in areas where seaweeds break the waves power Providing food for fishes Algal beds important food source for rare and threatened species like sea turtles Feeding ground at low tide for wading birds Stabilization inshore sediment

Chemical aspects of the sea The chemical constituents of seawater dissolved gases major elements minor elements organic matter