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Mussel Physiology as Sewage Bioindicator

Figure 1 graph, see caption

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.


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