DECAPOD CRUSTACEANS OF THE WEST EDDIES 43 



All of the streams on the island are subject to torrential floods, 

 and the water level in some of them, such as the Layou River, may- 

 rise 6 to 10 feet within a few hours. With the steepness of the gradients, 

 the streams just as quickly return to their more usual levels. 



From the standpoint of their decapod faunas, three types of 

 permanent streams are recognizable on Dominica: (1) those in which 

 the gradient is steep from source almost to mouth, usually with 

 clear water, and without estuarine or subestuarine development — 

 examples include the Belfast River, stations 7, 18, 118, 123, and the 

 Rosalie River (pi. 2a), stations 19, 20, 21, 22, 122; (2) those in which 

 the gradient is steep but with the lower stream bed well below sea 

 level, usually with clear water — examples include the Layou River 

 (pi. 2b), stations 13, 14, 15, and the Castle Bruce River, stations 66, 

 67, 68, 69, 127; (3) those in which the gradient is more gradual, with 

 the lower stream bed below sea level, subestuarine, usually with 

 cloudy water — examples include the Mero River, stations 38, 44, and 

 the Salisbury River, Stations 37, 107 (essentially similar to the stream 

 pictured by Mitchell, 1966, pp. 86-87). 



The faunas of the three river-types differ chiefly in the lowermost 

 portions. Those above the first rifl^e area in all of the permanent 

 streams are almost identical. 



There are three lakes on Dominica — Boeri, Boiling, and Fresh- 

 water — all located in the south-central part of the island. It is im- 

 probable that any decapods exist in Boiling Lake; none were found 

 in Freshwater Lake; and only the crab Ouinotia dentata is known to 

 occur in Boeri Lake (pi. 5). 



A number of hours were spent in observing the decapod fauna 

 of a small pool, approximately 4 feet wide, 10 feet long, and with 

 a maximum depth of 2 feet, on Mannet's Gutter, a mountain trib- 

 utary of the Layou River on the Clarke HaU Estate in Dominica. 

 Here, at an altitude of some 350 feet, the stream has cut a deep 

 V-shaped valley, and boulders from the eroded walls have fallen into 

 the stream bed, deflecting the current or obstructing the flow so that 

 pools are interspersed between cascades and rifile areas. Except after 

 heavy rains the water is clear, flowing over a rocky, sandy bottom 

 overlain in the pools with a shallow layer of silt. Many of the larger 

 trees along the 45 to 80 degree slopes have been cut and bananas 

 have been planted between the felled trunks; as a result, during a 

 short period in the day, the time depending upon the orientation of 

 the adjacent slopes, fuU sunlight reaches the stream bed. Marginal 

 shrubs do inhibit direct light from reaching portions of the stream. 

 The pool referred to here received sunlight for about two hours before 

 noon in mid-March. 



The macroscopic fauna of the pool consisted of what the observer 

 believed to be a single species of gobioid fish scarcely exceeding 



317-180 — 69 5 



