San Francisco Bay Study / Polydora origins

JAMES A. BLAKE jablake at
Mon Nov 4 14:59:06 EST 1996

Dear Annelid workers,

As promised, here is the URL for the San Francisco Bay introduced 
species study:

Cohen, A.N. and J.T. Carlton. (1995, December). Nonindigenous Aquatic 
Species in a United States Estuary: A Case Study of the Biological 
Invasions of the San Francisco Bay and Delta.  Report for the U.S. Fish 
& Wildlife Service and the National Sea Grant College Program, 
Connecticut Sea Grant (NOAA Grant No. NA36RG0467).

The document is a government report, and what we call Grey Literature.  
However, because it is online and accessible, perhaps not now so grey.

I had some problems calling up the document on Netscape, but was 
successful with my AOL browser.  I printed the document from Netscape 
off-line after saving the htm file from AOL.

My copy printed out at 241 pages.  The majority of the text is a 
species by species review of introductions that includes everything 
from plants to vertebrates.  An extensive literature review is posted 
for each species along with a large bibliography and several 
appendices. A few references in the text are not in the bibliography, 
but otherwise it is an impressive compilation of information on a very 
important subject.

Annelids are well represented with 8 oligochaetes and 13 polychaetes.  
I was surprized to notice that Marenzellaria viridis has now been 
identified in the SF Bay system, another spionid genus and species now 
in California, and to be added to the planned revision of Light's 

One of the spionids listed as an introduced species warrants some 
comment: Polydora ligni Webster, 1879.  

As most of you know, (Blake and Maciolek, 1987: Bull. Biol. Soc. Wash. 
7) referred this species to synonymy with the type species of Polydora, 
P. cornuta Bosc, 1802.  This synonymy has now been widely accepted and 
the name P. cornuta is regularly appearing in published accounts of the 

Regardless, Cohen and Carlton state: "Polydora ligni is native to the 
northern Atlantic where it is found in mudflats, fouling...., and 
oyster beds.....  They note that the first record from the Pacific was 
in 1932 from British Columbia.  

The statement that the species is native to the Atlantic is, in my 
mind, not substantiated.  In fact, there is systematic evidence that 
the species very likely originated in the Pacific.  

The two species most closely related to P. cornuta are Polydora 
nuchalis Woodwick, 1953 from central and southern California and P. 
cirrosa Rioja, 1943 which ranges from southern California to Ecuador 
(Blake, 1983: Antarctic Res. Series 39).  

Thus, the two species that are morphologically most similar to P. 
cornuta have restricted ranges in the eastern Pacific, suggesting a 
point of origin for P. cornuta in the Pacific not the Atlantic.  Just 
because a species was not collected prior to 1932 is no reason to 
suspect it was not there earlier.  Notice that P. cirrosa and P. 
nuchalis were not discovered until 10 and 20 yrs after the first P. 
cornuta (ligni) record in the Pacific.  P. nuchalis at least, is a very 
common species in certain bays and estuaries in California, yet was not 
formally described until 1953.

I would welcome discussion on this issue.

Jim Blake
(jablake at

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