This chart reflects some of the ecological differences among sites: the species richness (from the student counts) varies by nearly a factor of three between the most (Eagle Cove) and least species rich (False Bay) habitats. It is important to keep in mind that the sampling effort may have been different across the six sites. For example, some student groups may have focused carefully on finding a large number of different species, while other groups focused on examining the natural history of the most abundant or prominent species. The percentages of species exclusive to each site was strongly correlated with the overall species diversity, especially at Eagle Cove which had the largest number of species and the largest proportion of species not found elsewhere.

79 of the 169 total species reported were found at more than one site: Below is a chart of the number of species shared by pairs of field sites.

These data may be converted to a measure of overall similarity:

These similarity figures may then be used to graphically describe the relative similarity among the six field sites using a branching tree diagram (like a genealogy): sites that are closely related to each other on the tree (such as Eagle Cove and Cattle Point) arise from a branch point with a high similarity score, while sites that are not alike (such as Garrison Bay and Cobble Beach) must trace their similarity back to a branch point with a relatively low similarity score:

Bray-Curtis similarity dendrogram of the six habitats using presence/absence data for 169 species.
Generated using Primer5 software package.

This tree drawing (called a dendrogram) is especially interesting because it reflects the quantitative differences among the six sites, which many of the student researchers also noted qualitatively: the three rocky sites are the most similar to one another, each being more exposed to wave action than the other three sites, and having a similar slope with respect to tidal height. Garrison Bay and Argyle Creek, though they differ in terms of substrate type (mud versus rocky creek), are both protected and far flatter than the rocky sites. Finally, False Bay is the most different from any other field site with respect to its fauna, as it is a very broad, soft-bottom habitat that contains a large variety of sediment types.

The survey and this statistical analysis of its results did not indicate strongly similar faunas at the two soft sediment sites (Garrison Bay and False Bay). This seems surprising because the two locations look similar (mud) and seem to have many similar faunal elements (many burrowing bivalves and polychaete worms). In part, the differences between them could reflect some more particular differences between the two sediments: False Bay includes more sand, and is flushed more vigorously by tidal action than Garrison Bay, which has more very fine mud and clay plus a very rich upper layer of diatoms. Perhaps as a result of such physical differences, the two bays have some striking faunal differences in what are superficially similar habitats (e.g., burrowing thallassinid shrimp in False Bay but not Garrison Bay). The differences could also reflect different sampling efforts by the student groups who studied the two sites. At Garrison Bay, the specific mud site chosen for study was just a few meters from a rocky outcropping where some typical rocky shore animals (e.g., Nucella snails) were found and included in the faunal survey. At False Bay, many similar rocky outcroppings are present at the margins of the bay but were not included by that student group because the rocks and their animals were hundreds of meters away from the sediment areas that those students focused on.

Comparative Assemblage Discussion

• Only two species were found in all six habitats: the hermit crabs Pagurus hirsutiusculus and P. caurinus.
  Both hermit crabs are known to be ecological generalists, which may explain why they are found across so broad a range of habitats. These crabs are detritus feeders, so they do not seem to be restricted to one habitat type by their diet. While these crabs could conceivably be limited by the availability of shells in which to take refuge (suitable shells might be found only in habitats where the appropriate living snails are able to occur), these Pagurus may find shelter in the shells of any number of gastropod species, many of which are similarly widespread. Because none of the snail species were also found alive in all six habitats, there must be some differences among the habitats in which snail shells are used by Pagurus. A study of this variation in shell use across habitats might be something interesting for another student group to pursue.
  
• Other species that were commonly found in at least five of the six habitats include nereid worms (a polychaete family), a nemertean (Paranemertes peregrina), two brachyuran crabs ( Cancer productus and Hemigrapsus nudus), a chiton (Mopalia sp.), and four gastropods (Lacuna sp., Nucella lamellosa, Lottia digitalis, and Lottia scutum).
  It is interesting that both nereids and Paranemertes are found so broadly. While nereids tend to be omnivorous and ecological generalists, Paranemertes have a more specialized diet: nereids.
  
• The other widespread species were all ecological generalists, omnivorous animals that may serve as detritivores. The dietary breadth of these species may in part explain why they are found in such diverse habitats.
  

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