Mussel Physiology as Sewage Bioindicator
Figure 1. Median survival in air (LT50) and byssal
threads produced every 48 hours for mussels from two sewage outfalls and two
reference sites. Values are reported as a percent of the response elicited from
reference site mussels. Asterisks indicate significant difference (P<0.05) from
paired reference site mussels.
Mussels (Mytilus trossulus), were sampled from four Juneau-area beaches
in Southeast Alaska: one beach that received untreated sewage for several
years, a second beach adjacent to a secondary wastewater outfall, and
two nearby reference beaches. Average shell length measured 43 mm. Survival
time of the mussels in air, byssal thread production rate, and the prevalence
of trematode parasites were determined for each group. Tolerances to aerial
exposure were significantly lower at both sewage outfall sites than at
reference sites. Mussels exposed to untreated sewage produced fewer byssal
threads and had a significantly higher prevalence of encysted trematodes
than mussels from the other beaches, including the secondary wastewater
site (Fig. 1 above). Survival in air, byssal thread production, and trematode
prevalence in mussels may be useful indicators in evaluating the long-term
health of beaches exposed to sewage.
By Adam Moles.
Substrate Preferences of Juvenile Tanner and Red King Crabs
Behavioral preference tests were done in the laboratory to determine whether
sediment selection plays a role in habitat choice in juvenile Tanner crab
(Chionoecetes bairdi) and red king crab (Paralithodes camtschaticus).
Two-year-old juvenile Tanner crab selected bryozoan-hydroid assemblages (34%) as habitat
but otherwise buried in either sand (16%) or mud (38%). Burial in the shell
hash, shale, or cobble was impossible, although shell hash and shale were
selected occasionally. In the 1,800 observations conducted, Tanner crab
never selected cobble. The two-year-old red king crabs preferred the bryozoan-hydroid
assemblages (39%) or cobble (36%). Shale and shell hash were selected in
12% and 10% of the tests, respectively. Sand and mud were seldom selected
(<3%). Habitat which affords some measure of cover and protection from
predation is preferred by juvenile crabs.
By Adam Moles.
quarterly July-Sept 2003 sidebar
Auke Bay Lab