Department of Biological Sciences, Burnaby, Canada
*This report is a class project NOT peer-reviewed science
How is the density of barnacles different both at varying distances up the beach as well as between freshwater and saltwater?
We expect that density measurements taken closer to the sea will show a higher the density of barnacles (H1). Further, we expect that at sample sites run through a freshwater stream will find a decrease in the density of barnacles compared to areas that are only exposed to tidal seawater (H2).
We aimed to describe how barnacle distribution changed from the bottom to top of the beach as well as from freshwater to saltwater. We chose 7 points 5-m apart along the shoreline, two of which occurred in the freshwater stream. From each of these points we ran line transects 14-m up the beach perpendicular to the shoreline. We measured the percent coverage of barnacles within a 30-cm2 quadrat at every 1-m interval of each line transect. Each interval constituted one experimental unit. To estimate percent coverage, we averaged the opinion of three researchers to avoid individual bias as much as possible, each estimate constituted one measurement unit. We took considerations for the change of the position of the shoreline to ensure a relevant reference point was used for the positioning of all transects.
Barnacles were the densest at sampling locations that were moderately close to the shoreline with all transects having their peak measured barnacle density at this range (Figure 1). In the two transects that were taken in the freshwater stream, the density of barnacles was lower than the transects that only ever receive tidal sea water. This held for the area of the beach that was close to the water, however higher on the shore the freshwater and non-freshwater transects were the same, with no barnacles being found at this highest point (Figure 2).
Figure 1. We sampled multiple line transects set perpendicular to the shoreline and 5-m apart for barnacle density up the beach at 1-m intervals, at each of which we estimated percent barnacle coverage in a 30-cm2 quadrat. Each line represents one line transect of barnacle density measurements.
Figure 2. We sampled multiple line transects set perpendicular to the shoreline and 5-m apart for barnacle density up the beach at 1-m intervals, at each of which we estimated percent barnacle coverage in a 30-cm2 quadrat. Freshwater data was taken in a stream on the same beach, and seawater data were taken in areas that only receive tidal water.
Our data support H1, however we found that at our lowest points the barnacle density was much lower, suggesting that the barnacles primarily occupy a small range of the beach bounded by an upper and lower limit. Previous intertidal work suggests that this is due to abiotic factors determining the upper limit and competition for space and resources determining the lower limit. Further studies should take measurements at low tide at the same beach to determine whether this is indeed the case.
Our data also supported H2, with barnacles occring much more frequently in transects that were not interrupted by the freshwater stream. This is likely due to the constant disturbance posed by the stream as well as the low salinity of the water that barnacles are not adapted to. Due to sampling limitations we were only able to take 2 transects with this freshwater dissruption, so more data on the density of barnacles in this situation is necessary in future studies to make for a more well-supported conclusion on this phenomena.