The Effects of Temperature on the Physiology of PHATARIA UNIFASCIALIS : and its Implications for the Species\u27 Distribution in the Gulf of California

Populations of the asteroid Phataria unifascialis were sampled subtidally in the Gulf of California at Loreto, well within the species\u27 distribution, and at Bahia de los Angeles (the Bay of LA), at the northern end of its distribution on several occasions between 1989 and 1991 to determine the influence of water temperature on species\u27 physiology at each location. The starfish was much more abundant at Loreto, and though both locations had similar indices of pyloric caeca and gonad development, the population at Loreto was distinctly separated by depth into a shallow reproducing population and a deeper feeding population. No such distinct reproducing population was found at the Bay of LA. In addition, the Bay of LA population was relatively depauperate in the smaller size classes. The low winter temperatures in the Bay of LA result in reduced rates of activity and aerobic metabolism. This suggests that the lower temperatures of the Bay of LA may be in part directly responsible for the lower success there