1554 



Roberts, Morris H. , Jr., Robert J. Diaz, Michael E. Bender, and Robert J. Huggett. 

 1975. 



Acute toxicity of chlorine to selected estuarine species. J. Fish. Res. Bd. 

 Canada 32(12): 2525-2528. 



Larvae of Meraenaria mercenaria were among various life-history stages of 

 several species tested. Hard clam larvae were among the most sensitive forms 

 tested. EC50 value at 48 hr was 0.006 mg/1 of total residual chlorine, and 

 TL50 value estimated at 0.001 mg/1. Thus, it is not necessarily true that 

 small residues in sewage plant effluents are harmless. - J.L.M. 



1555 



Robertson, James D. 1964. 



Osmotic and ionic regulation. Chapter 9 in Physiology of Mollusca. Vol. 1. 

 K. M. Wilbur and C. M. Yonge (eds.) . Academic Press, New York: 283-311. 



Blood plasma of M. meraenaria is in osmotic equilibrium with seawater across 

 permeable membranes such as gills, where isosmoticity is within 1%. Cole 

 (1940) found blood 1.76A°C and seawater 1.76A°C. In slightly diluted sea- 

 water it was blood 1.39A°C and seawater 1.34A°C. This slight hypertonicity 

 in dilute seawater was possibly only apparent, because no details were given 

 about the equilibration period. V. mercenaria tissues show anomalous re- 

 actions to decreased salinity: gills and mantle increase and muscles decrease 

 in oxygen consumption (Hopkins 1949). Mytilus is the same. - J.L.M. 



1556 



Robinson, Peg. 1973. 



Clam dredges too effective for Fla. beds. Natl. Fisherman 54(4): 2C . 



From the late 30s to mid-40s, the state's clam industry was in full swing, 

 but otherwise the clam fishery has been small. At its height, these beds 

 were possibly the largest known. The reasons for the disappearance of the 

 major beds are not known. Recent surveys have shown that mechanical 

 harvesting equipment should be prohibited in grass covered and vegetated 

 areas. - J.L.M. 



1557 



Robinson, W. E. 1980. 



Statistical analysis of digestive gland tubule variability in Meraenaria 

 meraenaria (L.), Ostrea edulis L. and Mytilus edulis L. Natl. Shellf. 

 Assn., Abstracts, Technical Sessions 19 (abstract). 



Recent investigations show that bivalves apparently demonstrate rhythms of 

 intracellular digestion, often correlated with the tidal cycle. Evidence 

 is based primarily, and often solely, on the diverse histological appear- 

 ances of the digestive gland tubules from different individuals over a 

 period of time. Four main tubule types, signifying various stages of 

 intracellular digestion, can be recognized: 1) holding; 2) absorptive; 

 3) fragmenting; and 4) reconstituting. Digestive tubules and similar tubule 

 types are not randomly distributed within the digestive gland, but are 

 grouped together around common secondary ducts. This necessitates use of a 

 cluster sampling technique for proper statistical analysis. In all three 

 species, variability of tubule types is high within individual digestive 

 glands as well as between individuals sampled at the same time. Based on 

 calculations to minimize total variance, it is better to sample a small area 

 from numerous individuals rather than a large area from a few animals. 

 Intra-animal variability is similar in all three species. Similarly, inter- 

 animal variability is the same in the subtidal quahog and mid-intertidal 

 mussel, but much less in the low intertidal oyster. Problems imposed by 

 variability and tubule clustering have not adequately been considered in 

 previous investigations of bivalve digestion. - J.L.M. 



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