Saddleback Journal of Biology - Saddleback College

Fall 2009 Biology 3B Paper
60
Relative Density(org./sq. inch)
50
40
30
20
10
0
-10
Green Sea
Anemones
California
Mussels
Black Turban
Snails
Blue Banded
Hermit Crabs
Doheny
Laguna
Figure 1. Bar graph displaying the mean relative densities of all the listed organisms at both locations
(p=0.99±S.E.M.) Results showed no significant difference for relative density. Error bars indicating Standard
Deviation.
Discussion
There is no perfect method to determine
abundances of animals. For this reason, our results
could have been a factor for not having a significant
difference in relative density between both locations.
There are problems of arbitrary definitions of available
habitat, of these make the techniques less than ideal,
but they do not mean that current methods need to be
abandoned, or even that they should be necessarily
modified. Results indicated to having no significant
difference could have been caused because results were
based at low tide. At high tide, numerous other species
move into previously immersed areas and some of
them may interact with members of the resident
community. Having sampled at low tide, it is
considerably easier than at high tide, particularly on
rocky shores. Consequently, most intertidal
observations and collections are made when the tide is
out.
Accuracy of the measurements will vary from
organism to organism along a spectrum starting with
large, non-cryptic, stationary organisms, each of which
can be unambiguously identified and counted, and
ending with highly mobile species that react to the
process of being counted (Lessios, H.A. 1996b.)
Repeatability will often be low, making large sample
sizes necessary. At one end, determinations of an
organism’s density should only include areas at which
it is physically present, in which case, the density of all
organisms is only dependent on the size of each
individual. At the other end, to determine densities of
any organism, one would need to sample (and average
over) the entire ocean (Pfister 2007).
The most important action one can take to
improve matters as much as possible is to consider
commonly bias sources, the ways in which this bias
can affect conclusions, and the means of determining
exactly how the measurements are being distorted by
the techniques. Further research will be required to
allow for prominent comparisons of population
densities.
Literature Cited
Caldeira K, Wickett ME. 2003. Anthropogenic carbon
and ocean pH. Nature pp.425:365-365
Catherine A. Pfister (2007) Intertidal invertebrates
locally enhance primary production. Ecology: Vol.
88, No. 7, pp. 1647-1653
Cha HR, Buddemeier RW, Fautin DG, Sandhei P. 15
November 2004. Distribution of seaanemones
(Cnidaria, Actiniaria) in Korea analyzed by
environmental clustering. Hydrobiologia. 430(Sp.
Issue):497-502
Lessios, H.A. 1996b. Methods for quantifying
abundance of marine organisms. Smithsonian Tropical
Research Institute, Balboa, Panama pp. 149-157
Jayalakshmy KV, Saraswathy M, Nair M. 20 August
2008. Effect of water quality parameters on the
distribution of Pleuromamma (Copepoda-Calanoida)
species in the Indian Ocean: a statistical approach.
Environmental Monitoring and Assessment. 155(1-4):
373-392
137
Saddleback Journal of Biology
Spring 2010