Belt transect across the littoral zone.
  1. Splash zone - The zone above the highest tides. It is splashed by spray but not covered by the sea. It is not really terrestrial nor truly marine.

  2. Upper shore - The top of this zone gets covered by the sea for <1% of the year. The bottom of it for about 20% of the year.

  3. Middle shore - The top gets covered for about 20% of the year. The bottom for about 80% of the year.

  4. Lower shore - The top of this zone gets covered for about 80% of the year. The bottom for 100% of the year.

At high tide, all parts of the rocky shore except the splash zone are covered in seawater. This is called immersion. At low tide, as the water drops, the shore is exposed to drying (called emersion, the opposite of immersion).

Abiotic factors on rocky shores

Emersion becomes less the further down the shore you are.

Dessication

Dessication means drying out. It occurs as a result of emersion at low tide. Dessication influences the upper and middle shore.The basic physiology of most marine organisms is very simple: the concentration of their internal fluids is the same as that of sea water. Water may pass freely in and out so that there is no requirement for water conservation. When exposed to the air, such organisms lose water by evaporation and may eventually die from dehydration. The further up the shore that they live the greater the period of emersion (time out of water) and the greater the problem of water loss

Light

Light intensity increases up the rocky shore. Light is needed for photosynthesis. Seaweeds need to be in seawater for this to occur. However, the water will filter off some of the wavelengths of light and reduce the intensity. Little red light - the wavelengths most useful for photosynthesis - penetrates more than 5m into the sea

Temperature

The key change up the shore is the size of the diurnal temperature range. The further up the shore that organisms live the greater the period of emersion and the greater the temperature fluctuation they must endure.

Wave action

The strong force produced by powerful wave action can dislodge living organisms and affect growth. Wave action is greatest where waves are breaking, so it tends to be most damaging at the middle of the shore, where waves break on both the rising tide and the fallling tide.

Salinity

Marine organisms, in osmotic balance with seawater, will absorb water by osmosis and swell up in fresh or brackish water. Elimination of such excess water may result in the associated loss of valuable ions from organisms unable to resorb such substances from their urine. By contrast they will lose water from their bodies if placed in more concentrated media. As the salinity of the environment changes so does the salinity of the organism’s body tissues.

Transect Procedure

1. Spend some initial time surveying the study site, looking for obvious bands of zonation and selecting the general area for your first transect. As a team, decide on about twelve “key species” of plants and animals to census. Not all organisms will be present in every zone – some will be specialists found only in the Splash zone, but will be there in obvious abundance – some will be present in all zones, such as small scavengers. Make sure you include at least one marine plant in each of the zones – they represent food available for grazers.

2. Make your selections based on the range of distribution of each species within the intertidal zone, its abundance, and ease of identification. Remember that many of these animals are small, often camouflaged, and may be hiding. Get down on your hands and knees for a closer look. Be sure to examine the undersides of rocks (please replace them in their original position), ledges, and even blades of algae when choosing which species are most dominant along your WHOLE selected transect line.

3. Use your field guides and test each other to make sure that everyone on the team can identify these organisms with equal accuracy.

 

4. Extending your tape measure (or rope) perpendicular to shore, begin at splash zone and extending outwards towards the ocean until knee deep. You will need to sample TEN quadrat areas along the transect line. Use a half meter square quadrat. Secure your tape at either end. Based upon the length of the section, the interval to the next quadrat can be anything from zero to 2 m.

5. Identify and count the individuals of each key species within the quadrat. If the number of individuals of a species is too large for convenient counting (over 100), put “100+”). Mark data in data table #1.

6. Continue down towards the ocean until you have 10 quadrats from one transect.

7. Collect as much information as you can relating to such factors as substrate (silt, small rocks, algae-covered boulders, etc.), food preferences, feeding behavior, and associations with other plants and animals, which may be helpful in understanding the role of the plant or animal in the intertidal community.

Data/Observations

 

Once all the data had been collected, the team should first decide which quadrats fell within each tidal zone (ex: Quadrats 1 +2 – Splash zone; quadrats 3 + 4 = High Tide Zone; quadrats 5, 6, 7, 8 = Mid Tide Zone; quadrats 9 + 10 = Low Tide Zone.) Add all the data from similar quadrats together and average the data by the number of quadrats sampled (Mid Tide Zone = 45 mussels, 68 mussels, 54 mussels, 66 mussels/4 = a mean of 58 mussles/ 1/4m quadrat.)

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