RESULTS
Seastar Biology
Taxonomy
Life History
Echinoderms
Rocky Intertidal
The Study
Introduction
Methods
Results
Discussion
Picture Gallery
Bibliography and Weblinks
Glossary
Distribution and Abundance
The abundance and distribution of seastars varied considerably between months that samples were taken. In the first sample taken in late September, fourteen seastars were counted in the 24m2 sample grid along the horizontal transect line. The mean length of these seastars was 74.9 millimeters. In both the months of October and November, seastars were completely absent from the sample grid. Seastars were located at random intervals throughout the rocky intertidal during these months but in much lower densities than was seen within the sample grid during the first month of September. The substrate upon which these seastars were found also varied quite substantially. Seastars were found in upper, mid and lower tide pools, out of tide pools between rocks, and residing on top of the Ascophyllum. Only three seastars in total were found during the trip in October. Mean length of October seastars were shorter than September at approximately 62.7 millimeters. In November, five seastars were located and showed a higher mean length than either of the previous two months, measuring 94.6 millimeters (Fig 2). This data shows that there doesn't appear to be any correlation between seastar length and month.
Temperature data
Temperature data proved more consistent with expectations and showed a steady decrease in both mean air temperature and mean water temperature as the months passed (Fig 3). However, air temperature showed a greater difference between the starting temperature in August (23ºC) and the final temperature recorded in November (4ºC), a difference of 19ºC. Water temperature recorded between August (19ºC) and November (9ºC), showed a smaller difference of 10ºC. Fig 4 shows the density in number of individuals per square meter within the sample grid.
Various habitat temperature data gathered during the first trip in August is presented in Fig 5. The temperature at the high intertidal exposed to air above the Ascophyllum canopy showed the greatest temperature difference, a decrease of 9ºC in the 71 minutes recorded. The high intertidal underneath Ascophyllum canopy also showed a difference between start and final temperatures (4ºC) though not as great a difference as at the exposed site. The other four ibuttons measuring water temperature at various tidal heights did not show much difference between starting and final temperature, though they did show a decrease in water temperature with decreasing tidal elevation. Temperatures at the mid intertidal, both exposed and sheltered, maintained a constant 19ºC with the sheltered temperature rising 0.5ºC for a brief minute and the exposed tidal pool dropping 0.5ºC only in the last five minutes recorded. The tidal pool at the low intertidal remained constant at 18ºC and similarly dropped half a degree in the last five minutes recorded. The lowest tidal elevation with seawater inflow exhibited no change and showed a constant 15.5ºC throughout the entire length of time recorded.
(Click thumbnails to enlarge)
Fig 2
Mean length (mm) of samples in
September, October and November
Fig 3
Air & Sea Temperatures, August through
November
Fig 4
Density (# individuals / m2)
in September and October/November
Fig5
Temperature variation in different
intertidal habitats