seem surprising, but there it is. Next, he began a comparison of the stations on the
basis of their resident faunas. There are many ways to do that. Bilyard first calculated
correlation coefficients between the abundances in the list of species for each station
pair. Some data standardization is usually employed in this, such as replacing
abundance at each station by the number of standard deviations that its estimate falls
from the mean for the species across stations. That keeps species from appearing to be
correlated just because they are among the more-abundant animals. Joining those
station pairs with the largest correlation coefficients, using straight lines on the map,
demonstrated (Fig. 14.5) a strong along-shore alignment pattern. Stations at the same
depths tend to have the same species present in roughly the same relative abundances.
Clearly, while there are no sharp breaks along the depth gradient in species presence
or absence, depth appears to be a major factor affecting the faunal assemblages. Keep
in mind, however, that depth is not simply a measure of water pressure. It is usually,
as in this North Slope study, correlated with distance from shore and thus with the rate
of supply of organic matter from the surface. Production is generally greater near
shore, so more food is available to sink. Offshore production is less, and the greater
depth gives pelagic organisms more time to find and eat sinking organic matter.
Fig. 14.4 Contour plot of the number of species found at each Beaufort Sea station.
For key, see Fig. 14.1.
(^) (After Bilyard & Carey 1979.)
Fig. 14.5 Stations with high similarities in polychaete species composition, identified
by high product-moment correlation coefficients (>0.645), connected by solid lines.
Similar stations are obviously found at similar depths. For key, see Fig. 14.1.
(^) (After Bilyard & Carey 1979.)