Marine And Coastal Ecosystems

BAT 213: MARINE AND COASTAL ECOSYSTEMS

LECTURE 6

SOME PROBLEMS OF SHORE LIFE:

SOME PROBLEMS OF SHORE LIFE • • • • •

Water Loss Wave Action Temperature Fluctuation Salinity Fluctuation Fluctuation of Oxygen, Carbon Dioxide and pH • Range of Illumination • Predation; and • Immersion

SOME PROBLEMS OF SHORE LIFE: Water

Loss

• Most are aquatic organisms; when exposed to air may loose water through evaporation. May die of dehydration; • Organisms must have means to reduce water loss; • Danger of dying most severe if also exposed to sun and wind;

SOME PROBLEMS OF SHORE LIFE: Water

Loss

• Water loss can be fatal in many ways: – Disturbances of metabolism resulting in increasing conc. of internal fluids; – Asphyxia; • Organisms require continuous current of water over gills for adequate gas exchange; • Those that can temporarily survive in air need film of water over respiratory surfaces; • In fish, when not supported by water, the gill lamellae collapse and unable to function adequately.

SOME PROBLEMS OF SHORE LIFE:

Wave Action

SOME PROBLEMS OF SHORE LIFE:

Wave Action

• Enormous forces transmitted to shore by breaking waves; • May contain stones, sand etc.; • When waves churn beach deposit, burrowing organisms in danger of being crushed; • Dislodgement; • Continuous wave action presents difficulties for settlement and attachment of spores and larvae, and may prevent colonization except in crevices and sheltered parts.

SOME PROBLEMS OF SHORE LIFE:

Temperature Fluctuation • During low tide, wide and rapid changes in temperature; • Strong sunshine produces high temperature on exposed shore; • Shallow pools on tropical coasts may have temperatures as high as 50oC; • In temperate countries intertidal organisms may be exposed to severe frosts;

Small tide pool

SOME PROBLEMS OF SHORE LIFE:

Salinity Fluctuation • Organisms may be exposed to low salinity due to heavy rain; • Tidal pools may have very high salinity due to evaporation • Increased salinity and raised temperature usually occur together.

Small tide pool

SOME PROBLEMS OF SHORE LIFE:

Fluctuation of Oxygen, Carbon Dioxide and pH • Occur in shore water in association with photosynthesis and bacterial activities; • In bright light photosynthesis in small pools raise O2 content but decrease CO2;

SOME PROBLEMS OF SHORE LIFE:

Range of Illumination • Varies widely with rise and fall of tide; • When tide recedes, shore directly exposed to light; • At high tide, illumination much reduced; • Inadequate light one of factors limiting downward spread of some algae; • Direct exposure to light good for plant growth but high intensity may be lethal to many red algae; • Very strong sunlight bad for organisms due to combined effects of radiation, heating and drying.

SOME PROBLEMS OF SHORE LIFE: Predation

• Exposed to two sets of predators; – Study in South Wales reported oystercatchers (Haematopus ostralegus) can eat few hundred cockles per day

• In other areas, during high tide, more bivalves taken by flatfish than by waders,

SOME PROBLEMS OF SHORE LIFE: Immersion

• Majority shore animals utilize oxygen dissolved in seawater, but few are airbreathing; – Some evolved from land-form eg. Insects Petrobius and Lipura and gastropod Otina and Leucophytia – Others evolved from marine forms where respiratory organs adapted to absorb atmospheric air eg. amphipod Orchestia and periwinkles Littorina sp.

• Too long immersion may be fatal for both.