Bio 320 Tropical Biology - San Salvador Spring 2015

Rocky Intertidal Shore Transect Survey

Objectives: Examine the diversity, abundance, and distribution of flora and fauna of a tropical marine rocky intertidal shore.

Quantitative Observations

  1. Establish a string transect line extending from the Mean High Water level (assumed to be the bottom edge of the "black" zone/upper limit of barnacles) down to the water's edge at low tide (At the time of our intertidal study, the low water level will likely be several cm above Mean Low Water). If your transect line is not long enough to reach the water's edge, you will need to move it down the shore, keeping track of the horizontal distance from the Mean High Water level. The transect line may need to be secured at each end.
  2. Note: If your transect doesn't include any tide pools, several pools should be located and examined at another location (see below).
  3. Use a plastic (PVC) quadrat sampler to delineate study quadrats (0.25 m x 0.25 m = 0.0625 m2) at 1 meter intervals along your transect. The quadrat sampler should be placed on one side or the other of the transect line at the meter marks - place the sampler on the same side of the line each time.
  4. Within each study quadrat, estimate the percent of surface area covered by attached organisms, i.e., encrusting coralline algae, algal mats, foliose algae, and invertebrates. For free-living invertebrates, such as snails, crabs, etc., count the total number within the quadrat.
  5. All organisms observed in your study quadrats should be identified to species, if possible (this may be difficult for some of the algae you find). If you have difficulty making identifications in the field, a few small specimens may be saved in zip-lock plastic bags and examined in the laboratory; be sure to mark all bags so you know which quadrats they came from.
  6. Note: If you take specimens back to the lab, it is your responsibility to make sure they survive the journey - keep the bag out of the sun, and be sure the water is well aerated at all times. Check with one of the instructors about how to maintain the organisms in the lab.
  7. If there are large rocks along your transect line, if may be possible to lay your quadrat sampler on the rock surface for quantitative observations. If a rock is too small for the quadrat sampler, make observations about the relative abundance and location of organisms on the rock.

    Qualitative Observations (Roving Surveys)

  8. Examine the distribution of algae and invertebrates as a function of height (relative to Mean High Water level) on the large rock outcrops at the study site. All organisms should be identified to species, if possible. What trends do you see?
  9. Examine some large tide pools in the vicinity and make general observations about the diversity and abundance of flora and fauna. If tide pools were examined along your transect, compare the various pools with respect to size, position on the shore, and diversity and abundance of organisms. What trends do you see?

    Data Analysis

  10. Describe any observed differences in the abundance (e.g., numbers per unit area) and diversity (e.g., species richness; species diversity) of organisms as a function of horizontal and vertical position on the shore. Use the intertidal zonation classification on page 4 (from the Kaplan Caribbean Seashore field guide).
  11. Describe the species composition of your tide pools, and relate this to the physical characteristics of the pools (location, area, depth, time of exposure). Be sure to distinguish between organisms that are true intertidal residents and subtidal residents that seek refuge in tide pools during low tide.
  12. Your analysis should consider the importance of physical-chemical factors (e.g., wave action, duration of exposure to air, temperature, salinity, etc.) and biological factors (e.g., competition, predation, etc.) in determining the abundance, diversity, and distribution of organisms on rocky intertidal shores.
  13. Compare your findings to observations you make on intertidal zones elsewhere on San Salvador. What conclusions can you draw about the biogeography and ecology of intertidal organisms found on San Salvador?
  14. Compare your findings to those in published studies of rocky shores in other areas of the greater Caribbean. What conclusions can you draw about the biogeography and ecology of intertidal organisms found on San Salvador?

Field Report

If you are writing up your intertidal study as the required field report for BIO 320, you will be expected to make use of the extensive published scientific literature on the ecology of tropical marine rocky shores, and cite a minimum of five refereed journal articles. Five references are given below to get you started; they are available for downloading on the course website: For access to these copyrighted materials you need the username:________________ and password:_____________________. Be aware that grade deductions will be made for listing articles not actually cited, for not listing cited articles, and for making a citation without having thoroughly read the article! (Yes, faculty can tell when you cite something you have not actually read!)

Your literature cited section should provide complete citations in CSE/CBE style of all library references and all field guides that you do choose to incorporate into your paper…in alphabetical order. Consult your biology writing guide (Pechenik or Knisely) for specific instructions on format and style. The style below is acceptable.

Selected References

Good, T. P. (2004) Distribution and abundance patterns in Caribbean rocky intertidal zones. Bulletin of Marine Science 74: 459-468.

Smith, T. B., J. Purcell, and J. F. Barimo (2007) The rocky intertidal biota of the Florida keys: Fifty-two years of change after Stephenson and Stephenson (1950). Bulletin of Marine Science 80: 1-19.

Stephenson, T. A. and A. Stephenson (1950) Life Between tide-marks in North America: The Florida Keys. The Journal of Ecology 38:354-402.

[JSTOR link:] Note: The Stephenson and Stephenson article available at JSTOR is an archived version of the original article published in hard copy. Thus, you do not have to list the URL for this online copy; this also applies to current journal articles that are published simultaneously in hard copy and online at the journal website - they are the same article so the version you read is irrelevant; cite the hard copy version. You must, however, cite the URL and access date for web pages that can, and often do, change over time, keeping in mind that such web pages are generally not acceptable reference sources for scientific papers or laboratory reports.

Thomas, M. L. H. (1985) Littoral community structure and zonation on the rocky shores of Bermuda. Bulletin of Marine Science 37: 857-870.

Vermeij, G. J. (1973) West Indian molluscan communities in the rocky intertidal zone: a morphological approach. Bulletin of Marine Science 23: 351-386.

Rev. 5/15