August, 1999 
SCAMIT Newsletter 
Vol. 18, No. 4 
Carcinus maenas and the Chinese Wooly- 
Handed Crab Eriocheir sinensis. Fortunately 
the latter two have yet to penetrate into the 
waters of the southern California Bight, but 
they are on their way. 
We have a much more established invader still 
garnering its share of attention in the literature, 
the south-east Asian clam Musculista 
senhousia. We usually do not see this animal, 
as it is restricted to harbors, bays, and estuaries. 
During Bight ‘98, however, we encountered it 
in abundance. In the upcoming EMAP West 
Coast estuarine investigations it will also be 
prominent. Two recent papers provide 
additional information on the status of M. 
senhousia in southern California (Reusch 1998, 
Reusch & Williams 1998). In the first of these 
the author addresses how indigenous predators 
affect the invasion success of the introduced 
exotic. In this case the predator is the muricid 
snail Pteropurpurafestiva. It feeds 
preferentially on M. senhousia rather than co¬ 
occurring indigenous bivalves, probably 
because the locals have much thicker shells. In 
exclusion experiments he demonstrated that 
predation can potentially prevent establishment 
of the high density nest-beds of M. senhousia 
which smother subsurface fauna and prevent 
establishment of eel-grass, strongly impacting 
the indigenous biota. 
The relationship between M. senhousia and the 
eel-grass Zostera marina is a spatial 
competitive one. Both establish high density 
contiguous populations to the detriment of the 
other. It has been shown previously that M. 
senhousia byssal mat provides an inhospitable 
environment for the establishment of eel-grass 
beds, and now Reusch & Williams (1998) 
demonstrate that conversely eel-grass 
decreases growth and increases mortality of M. 
senhousia. 
It has often been observed that infaunal 
community composition and abundance are 
modified in ecotonal areas around benthic hard 
bottoms such as reefs (and outfalls). The 
mechanism is not always clear, and 
undoubtedly varies with the case examined. 
Dahlgren et al (1999) examined the effect of 
reef-based bioturbators on the adjacent infauna. 
They found that the sea-cucumber Holothuria 
princeps was the dominant bioturbator of the 
system, and that it’s activities in turning over 
surface sediments are of sufficient impact to be 
a significant structuring element of the infaunal 
community adjacent to the reef. Predation 
associated with reef attracted or reef resident 
fish and invertebrates is probably of even 
greater impact, but they found the bioturbation 
component far from negligible. 
Results of this study may not be directly 
applicable to the activities of Parastichopus 
californicus in our area, because, unlike H. 
princeps , our local species does not burrow. 
The authors’ results do, however, point to an 
effect which should be considered in 
examination of local hard/soft bottom 
ecotones. 
Childress & Seibel (1998) examine the 
adaptations of animals at another ecotone; that 
between oxic and anoxic waters. They 
specifically address the animals living in 
oxygen minimum layers such as that found off 
California. While the discussion is primarily 
illustrated with examples of midwater forms, 
the types of respiratory adaptations they exhibit 
also apply to benthic animals in the zone of 
impingement of the minimum layer on the 
upper slope. They point out that adaptations to 
this stable long-term minimum layer differ in 
kind from those of fluctuating or temporary 
low oxygen exposures such as intertidal mud¬ 
flats. 
Such environmental stresses as low oxygen, 
pollution, extremes of temperature, etc., impact 
the presence and abundance of parasites. In 
NPDES and other monitoring permits it is 
usually assumed that anthropogenic pollutants 
result in higher incidence and severity of 
parasite infestation. Lafferty & Kuris (1999) 
review how stress and parasites interact on host 
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