To study and compare the density of cthamalus montagui (shield shaped barnacles) on an exposed and sheltered shore.

 

Equipment: Watchmakers eye lens, quadrat, ranging pole, sighter, gloves, and measuring tape.  

Hypothesis:

I predict that a higher density of the ‘Ctamalus montagui’, the shield shaped barnacles will be found at the exposed shore compared to the sheltered shore. The reasons being:-

       

• On the exposed shore, there are less competition for food, space and less presence of predators as the strong wave motions on the exposed shore prevent most organisms from settling there.
• Organisms such as seaweeds, muscle and algae that usually compete with the barnacles for space get washed away by strong wave motions but the much more strongly attached (the chemical ‘cement’ that attaches the barnacle to the rock is one of the strongest natural adhesives known) barnacles do not.
•  Absences of other organisms such as periwinkles (which are not that commonly found on exposed shores due to strong wave motions) that compete for food with the barnacles also allow more growth in population of the barnacles.
•  Another reason would be the absence of the barnacle’s predators such as worms and whelks(which are known to be able to wipe out entire colonies of barnacles) which prefer less rough habitats. The lack of these organisms on exposed shores allows the barnacles to live, breed and eat more comfortably on exposed shores.
• On an exposed shore a higher concentration of minerals and food (plankton) as the flow of water (which carry the food and minerals) on an exposed shore is stronger and more direct. Therefore it can reach higher distances up the shore giving a larger area for the barnacles to colonise.
• Less organisms and a more water gives the barnacles ample supply of oxygen, which is needs thus allowing easier gas exchange to take place.
• A more direct flow of water which allows the water to move further up the shore allows barnacles further up the shore to keep moist (an essential survival action) more easily.
• All these elements allow a bigger population of barnacles to live in exposed shores. A more dense area of barnacles also allows it to breed more easily. As a barnacles can only breed when its eggs are fertilized by its neighbour, a bigger population increases the chances of reproduction.

Variables:

               

   Independent Variables: -As the experiment is carried out outside the lab, there are many independent variables which can’t be controlled.

             

1. Temperature – The temperature might be slightly different at different shores                                             depending on the amount of sunlight and water that hits the area studied. (*Note= The temperature measurement was taken and it was found that the temperature on both shores were almost the same).A difference in temperature could effect the population of barnacles but only in a very small way as barnacles are very tough organisms.
2. Water salinity – The salinity of water samples taken were found to be different on the exposed and sheltered shores. Difference in salinity could cause the barnacles to prefer an exposed shore to a sheltered shore although there is no concrete evidence to support this.
3. Gas availability – The oxygen and carbon dioxide could not be measured as no proper instruments and apparatus was available.
4. PH – The pH values of water and rock surfaces were variables that could not be controlled.
5. Wave action – Wave actions influence the experiment heavily, as it washed away the barnacles competitors and predators. This is an unavoidable variable on exposed shores.

 

Different areas of the shore will be affected differently by each if the above factors. Because of this, the barnacles will be adapted to these different areas. This is called zonation.

Dependent Variables: -Among the variables that were kept constant to ensure a balanced study     on both shores were: -

1. The vertical distance of both areas was kept constant in order for a solid     comparison to be drawn. Both areas were at mid-shore.
2. The area studied was kept constant so that the densities of barnacles could be compared. (Each area consisted of 4 quadrats of same size)
3. The count was done 4 times, to increase precision and accuracy.

Implementing:

Method: As the time and height of low tide was found out earlier, a suitable time to carry out the experiment was chosen. It started at 1300 hours 30 minutes before low tide, so that sufficient time could be allocated for each shore and as a safety measure.

1. A sighter and ranging pole was used to measure the vertical distance from the shoreline of the area covered. But a modification to the method had to be done, as the shoreline was not at its final low tide, due to time constraints and safety measures a sighting downwards the shore had to be done.

2. 4 quadrats of 0.25m2 were laid side by side parallel to the exposed shoreline. Each barnacle that was identified (using the eye lens) as Cthamalus montagui was counted and recorded in a data table. The whole process was then repeated on a sheltered shore. The area to be covered was sighted first on the sheltered shore before any counting began so that a proper vertical distance could be measured.

The data tables are shown below.