II. INDICATOR SPECIES USED BY MWRA: Are the species currently used as indicator species relevant for lobsters?

The MWRA uses several indicator organisms such as mysid shrimp, inland silversides, and sea urchins to monitor the effects of their effluent. These indicators represent organisms inhabiting a vertical distribution from surface waters to the benthos. In the past, EPA has used calanoid (Acartia sp.) copepods for toxicity testing since they are extremely sensitive to various pollutants. Calanoid copepods represent the major food source for larval lobsters from all gut content studies conducted thus far. Mysid shrimp larvae also represent a potential food source for larval and postlarval lobsters (if they can catch them). Benthic postlarvae and juveniles consume amphipods, decapods, echinoderms (sea urchins and brittlestars, primarily), polychaetes, copepods, hydrozoans, fish, juvenile mussels, as well as other incidental items. Given that the toxicity testing at MWRA includes a decapod (mysid), and echinoderm (sea urchin), and a fish (silverside), and EPA has previously tested copepods for their sensitivity levels, the food items of lobsters are well-represented. If any items should be added to the testing scheme of the MWRA, we would suggest polychaete worms, mussels or oysters, and copepods. However, since larvae are relegated to the upper 3 m of the water column in coastal regions and are subjected to surface wind currents that carry them away from their original hatching location and towards the shore (along with their food, who are also subjected to the same currents), the likelihood that larvae or their food sources would be trapped in the outfall area is incredibly small.

The situation is different, though, with postlarvae and YOY juveniles. These animals are not particularly vagile (they do not move far from their shelters) once they have taken up a benthic existence. However, their behavior, as described above, indicates that they too will not be impacted by the outfall area given that it is highly unlikely that they will be found there.

Conclusion: The current species used as bio-indicators are appropriate, not only for determining what may happen to lobster food sources, but also to provide the widest range of organisms found at different vertical depths. If any changes should be made at this time, we suggest that MWRA use calanoid copepods (which are one of the more ecologically important herbivores in the water column) and add polychaete worms, mussels or scallops to the bio-indicator species list. Mussels are a main food resource for larger juvenile and adult lobsters and their byssal gland is extremely sensitive to continuous chlorination. A continuous dose of 0.25 ppm is sufficient to cause all exposed mussels to lose their holdfasts and open their shells. Higher doses delivered intermittantly cause loss of attachment, but not death (Clapp, 1947 as reported in Gentile et al., 1976). Given this reaction, MWRA should review their area surveys mentioned in Mitchell et al. (1998) and determine if mussels are present in sufficient density to warrant concern. Similar concerns exist for oysters, who are one of the most sensitive organisms to chlorines.