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Estuarine evolution

JAMES BLAKE jablake at ix.netcom.com
Thu Dec 14 23:44:53 EST 1995


Dear Annelid enthusiasts, 

I am delighted at the various directions discussions are taking with 
regard to transport of exotic species. 

David Kirtley writes in response to my comment about the relatively 
young geological age of California estuaries.

>Some of the present day estuaries may have been at their present 
>positions for relatively brief (geologic) time spans, indeed, but 
>there is little reason to imagine that there were no antecedent 
>estuarine habitats along the California coast that occupied laterally 
>contiguous positions during lower, or higher, relative sea level 
>stands.  

>Whether as the result of global glacio-eustatic rise and fall of sea-
>level or local tectonic vertical displacement and/or lateral 
>translation of fault blocks, the size and shapes and areal extent of 
>the estuarine habitats may have changed greatly  from time to time, 
>but this would not completely obviate the opportunity for the 
>evolution of endemic invertebrates in those estuarine habitats. 

>If there is evidence that at any time the California coastal margin 
>was a high, sheer, strait cliff, and all the rivers and streams were 
>dammed up so that there was no fresh water flowing into the ocean, 
>then my argument would be baseless and my conclusions dead wrong.

If you look at a map of the coastline from the Columbia River to the 
southern California Bight, you will not find very many embayments.  
Most of the coastline is composed of cliffs with debris from former 
cliffs forming extensive rocky areas just offshore.  This has created 
habitat for a wonderful rocky intertidal and subtidal fauna anf flora, 
much of it endemic and well studied.  

Most of the literature dealing with introduced invertebrates in 
California estuaries comes from San Francisco Bay, an estuary that has 
been extensively modified since siltation caused by the hydraulic gold 
mining in the 1850's and thereafter.  Extensive habitat alteration from 
that area and of subsequent land filling operations would most 
certainly have altered endemic faunas.  

However, evidence of a recent geological origin is quite evident in 
Tomales Bay where I worked throughout the 1970's.  This bay is the 
sunken rift zone of the San Andreas Fault and we were always dreading 
the day the "big one" would hit.  According to predictions, the City of 
Los Angeles will one day lie just offshore of my former laboratory, the 
Pacific Marine Station.  Who knows how many "endemic" species and 
polychaete biologists will have come and gone when that time comes. 

>From a transplanted, 3rd generation native Californian, now shoveling 
snow from the first storm of the winter in Massachusetts.

Jim Blake
ENSR
89 Water Street
Woods Hole, MA 02543





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