Rock Platforms: Spray Zone - Results from the Barnacle Experiment

Think again about growth rates of barnacles (ie. size of operculae in 1-year-old barnacles) in the different tidal zones.

What key factor could be limiting growth in the spray zone? (Select the best answer.)

availability of water

availability of food

ability to reproduce

try again

Yes. Water supply is fundamental to barnacle growth. Barnacles in the spray zone are rarely inundated and spend much of their time sealed inside the test.
True. Barnacles can only feed when splashed by waves, so animals growing high up in the spray zone do have a limited supply of food. However, this is not the only limiting factor. Try again.
Although reproduction in the spray zone is limited to times when barnacles are wet, this affects rate of reproduction rather than rate of growth. Try again.
barngraph.swf john john john john john

Examine the graph by moving the mouse over it.

This bar shows the size of barnacles from the intertidal zone. The intertidal zone is generally inundated twice each day (a hazard for the zoologists measuring them).

This bar shows the size of barnacles from the lower part of the spray zone. This area was covered by water a number of times each month.

This bar shows the size of barnacles from the spray zone. The site was only sprayed with water and not covered at extreme high tides.

Height above sea level is measured relative to a physical marker, as sea level varies with the tides

This is the mean width of a sample of barnacles' opercula reached in the first year of adult life, ie. it is a measure of growth rate.