March, 2000 
SCAMIT Newsletter 
Vol. 18, No. 11 
“I see your note on p. 5 of the December 
1999 SCAMIT newsletter, which reads in 
part, ‘Dr. Jim Carlton opined that there 
was no morphological basis for 
separation of the species in the “edulis” 
group — M. edulis, M. galloprovincialis, 
and M. trossulus... Martel et al. (1999) 
disagree...’ 
If one takes a peek, again, however, at 
Martel et al. (1999), they made no 
attempt to distinguish M. gallo (MG) 
from M. trossulus (MT), they did not try 
to do so, and they offer no clear way to 
do that. They only distinguished lumped 
MG-MT (which as a species bundle they 
simply call “bay mussels”) from M. 
californianus (MC). The most telling 
evidence for this is figure 2, where they 
draw a juvenile M. californianus, but the 
juvenile bay mussel is labeled “M. 
trossulus / galloprovincialis ” — clearly 
they were unable to draw these as two 
different species! While there are 
differences in the means between MG 
and MT for some characters, the standard 
deviations are large and pretty much 
capture the mean of the other species. On 
page 162 they put the nail in the coffin, 
and say, “No attempt was made to 
distinguish true breeding...individuals 
within the bay mussel species 
complex...”. I take the point of the paper 
to be able to tell baby MC from baby MT 
or MG, whatever one might happen to 
have in the neighborhood. 
At least, that’s the way I read it — what 
do you think?” 
On reexamining the evidence provided by 
Martel et al I must admit that Dr. Carlton’s less 
sanguine assessment is more accurate. 
Although two measures (PA ratio and Dorsal 
Apex ratio, Table 4) were significantly 
different statistically between M. trossulus and 
M. galloprovincialis, the ranges are strongly 
overlapping. In practice there would be no way 
to positively separate juveniles of these two 
species using the measurements which the 
authors analyzed. One might have a suspicion, 
based on the nature of the two measurements, 
but there could be no definitive identification. 
As the two species would only co-occur in 
areas where hybridization was possible, and no 
evaluation of hybrids was attempted, the 
situation is even less favorable for species level 
morphological discrimination of the two 
species. 
As Dr. Carlton states in his e-mail, the authors 
intent was separation of Mytilus californianus 
juveniles from bay mussel species at different 
points in the M. californianus range. The 
differences they detected between M. 
galloprovincialis and M. trossulus were only a 
byproduct of their investigation, and not 
sufficient to separate juveniles of the two bay 
mussel species in areas where they might co¬ 
occur. As M. edulis is only very rarely present 
on the West Coast, our main concern has been 
with separation of the other two members of 
the edulis or bay mussel group. The only basis 
for separating these two taxa locally is 
geographic unless molecular taxonomic data is 
available for each individual. In areas of range 
overlap all bets have been, and unfortunately 
remain, off. 
PERSISTENCE 
Despite the termination of El Nino conditions 
some time ago, and reversion to a La Nina cool 
water condition in the Southern California 
Bight, a few of the warm water elements just 
refuse to go away. The target shrimp Sicyonia 
penicillata, for instance, persists in our area. 
Three specimens were taken by OCSD on 10 
January 2000, in their regular trawl sampling 
[thanks to Christina Thomas & Mike McCarthy 
for the opportunity to examine these 
specimens]. Both stations where they occurred 
were on the 60m isobath, and one of the 
returned specimens was a mature male. I 
presume that in some areas reproduction may 
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