An Ecological Study of the Distribution of the Isopod Cyathura Polita (Stimpson) from Brackish Waters of Cape Cod, Massachusetts

Burbanck, W

The isopod, Cyathura polita (Stimpson), was found at 40 of 62 estuaries and tidal marshes visited along the shores of Cape Cod, Massachusetts, and nearby areas. The habitats were studied at low tide and were characterized by a stable substrate with some sand present, water in motion, and were located within the range of tidal influence. The distance upstream from the mouths of the creeks and rivers varied, but cyathurans were frequently located below tidal gates, dams, and bridges where the natural environment had been modified by man and at the level of the downstream limits of cattails in unobstructed waterways. C. polita was usually found at a depth of 5-8 em in concentrations of from 108/m2 to 1080/m2 and appears euryokous with respect to its chemical environment. No species of macroscopic animals were always associated with C. polita, but those most frequently recorded were Scolecolepides, Heteromastus, nereids, and gammarids. Of three attempts made to introduce C. polita into apparently suitable habitats where it did not naturally occur, one at Sandwich was successful and a population with a density of 432/m2 and a linear extent of about 30 m was observed three years after the initial transplant. Populations of C. polita were stable as to location and density over a period of five years, and it is suggested that the numerous populations on Cape Cod may have acted as sources of distribution of the species to more northern locations during the past ninety years. C. polita is at the first trophic level of the food chain and is known to be eaten by winter flounder, brook trout, and black duck. Possible reasons for the absence of C. polita in certain estuaries are given, and it is hoped that cognizance of such factors will aid in the preservation of natural estuarine habitats in the Cape Cod area.

An Ecological Study of the Distribution of the Isopod Cyathura Polita (Stimpson) from Brackish Waters of Cape Cod, Massachusetts

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