March, 2000 
SCAMIT Newsletter 
Vol. 18, No. 11 
second heterospecific association was observed 
between juvenile Ophiomastix janualis and 
adults of Ophiomastix flaccida. In this case the 
juveniles clasp the aboral disc like little hats. A 
third association was observed in which 
juveniles of Ophiocoma aethiops occasionally 
occupied the genital bursae of adults. Normally 
juveniles on their own are suspected to be fair 
game for predators. We assume the above 
behaviors render survival more likely for the 
juveniles concerned. 
While in the final throes of preparation of the 
west coast bivalve monograph Gene Coan 
found time to continue his reviews of eastern 
Pacific bivalve genera and families with 
treatment of the myoid genus Sphenia (Coan 
1999). In the process he removed Sphenia 
fragilis from the synonymy of S. luticola 
indicated by Bernard (1983) and currently on 
the SCAMIT list. Both species occur in the 
southern California Bight, but can be separated 
using the criteria listed in the paper by Coan. 
Even as recently as Coan & Scott (1995) only a 
single species, Sphenia luticola , was listed 
from the Northeast Pacific. Those of you who 
(like me) have been treating all local Sphenia 
as S. luticola need to reexamine your material 
and verify that S. fragilis is not involved. If you 
find some please make note of it for the May 
meeting, where we will discuss changes and 
additions to the SCAMIT list prior to issuance 
of Ed. 4. 
Being a clam, regardless of species, can be a 
very hazardous condition - especially right 
after you settle and metamorphose from a free- 
swimming larva. Two recent articles address 
the degree to which postlarval bivalves are 
consumed by amphipods (Ejdung & Elmgren 
1998) or decapods (van der Veer et al 1998). 
With amphipods ( Monoporeia affinis and 
Pontoporeia femorata were tested) juvenile 
clams can attain a size refuge from predation 
relatively quickly, with Macoma balthica spat 
being safe from Monoporeia affinis predation 
by a size of 1mm. With the shrimps and crabs 
examined in the second paper, juveniles of 
Macoma balthica and Mya arenaria were 
consumed until at least 2mm, while juvenile 
Cerastoderma edule were still consumed at up 
to 3.5mm. Following early spring settlement 
bivalve spat density in the second study 
dropped by roughly 80% before leveling off 
through the summer. Nearly all of this 
mortality could be accounted for by the feeding 
activities of juvenile brown shrimp Crangon 
crangon. Even so, the density of the bivalve 
populations was not controlled by crustacean 
predation pressure according to the authors. 
The SCBPP in 1994 and the Bight’98 study in 
1998 have been followed in 1999-2000 by the 
WEMAP project examining very shallow water 
and estuarine benthic communities in 
California, Oregon, and Washington. It remains 
to be seen if the Benthic Response Index (BRI) 
devised to evaluate degree of disturbance 
reflected by benthic community composition 
on the continental shelf (Smith et al 1998) will 
work for these shallow samples. Other 
approaches, such as that of Engle & Summers 
(1999) may prove more useful given the nature 
of the community. Although their measure was 
designed for application in northern Gulf of 
Mexico estuaries, it does not involve species 
specific information as does the BRI, and 
should not be geographically specialized. It is a 
multimetric index utilizing a variety of 
different data types. 
Bays and estuaries, such as those examined in 
the WEMAP sampling, tend to be depots for 
terrestrial (usually anthropogenic) 
contaminants. The recent examination of 
sediment contamination in San Francisco Bay 
(Thompson et al 1999) demonstrated again that 
the patterns of contamination and benthic 
response are complex. Two sediment toxicity 
tests were used; bulk sediment assay with 
amphipods {Eohaustorius survival), and 
elutriate toxicity assay with larval bivalves 
(Mytilus or Ostrea normal development). 
Results of the two types of toxicity tests did not 
show the same patterns, rather reflecting 
different aspects of sediment toxicity and 
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