Travel Reference
In-Depth Information
the past inhabited environments very like those surrounding the reefs of
today. In accordance with the principle of uniformitarianism, we use the
lives of present reef animals to infer the biology of those now extinct.
The types of organisms found in any community, be it modern or an-
cient, are adapted to their specific environments. As environmental condi-
tions change, so do the animals and plants that make up the various com-
munities. All that said, what can we make of the inoceramid associations?
Where in the food chain do they rest? What did they eat, and who ate them?
Where do we find living analogs?
The mystery of the inoceramids
The ancient ecosystem of Sucia Island is fairly recognizable. Most of its fos-
sils are made up of clams and snails that belonged to groups (if not to species)
still living today. Most of the clams are forms that lived in the sediment,
much like the vast majority of today's clams. These types of clams, which are
called infaunal suspension feeders, burrow to escape predators. They feed by
sucking large volumes of water through their necks and then straining plank-
tonic organisms from this ingested water. Because most of the plankton is
composed of single-celled plants, these types of clams are the herbivores of
this ecosystem, the lowest rung of the food chain above the autotrophs,
which in this case are the plankton. On Sucia, the clams are thus the lowest
animal members of the trophic pyramid. Most of the snails from Sucia, on
the other hand, were carnivores, and judging from the small bore-holes left
in many of the ancient bivalves' shells, many of the snails fed on bivalves.
All in all, this assemblage of creatures on Sucia seems to make very
good ecological sense. There are about ten times as many herbivorous forms
(the clams and a few of the snails) as there are carnivores. There are a few
oddballs—the inoceramids, for instance—that sat on the sediment rather
than living in it. Yet these small forms (usually just a few inches long) are so
much like oysters that they do not seem incongruous.
On Gabriola Island, however, and at so many other localities around
the world with an abundance of
large
inoceramid clams, things are far more
