MODIFICATION OF THE RESPONSES OF TWO SPECIES OF BUGULA LARVAE FROM WOODS HOLE TO LIGHT AND GRAVITY : ECOLOGICAL ASPECTS OF THE BEHAVIOR OF BUGULA LARVAE

Abstract

1. The larvae of both B. flabellata and B. turrita are photopositive in diffuse light during the first 3-4 hours after release from the ovicells and then become photonegative. They became photonegative immediately, however, when they were placed in sea water buffered to a pH of 9.6 or diluted by 50 per cent; sea water containing copper chloride either reduced the intensity of the photopositive phase or caused a reversal of phototropism depending on the concentrations that were used. These organisms became indifferent to light in mixtures of 80 cc. sea water per 20 cc. of either normal calcium chloride or magnesium chloride.2. Larger numbers of larvae attached in the red end of a test tube illuminated by red and blue light passing through Wratten filters than in the opposite end.3. Heating sea water to 30° C. hastened metamorphosis and favored surface attachment, but development was poor or entirely lacking at this temperature. Darkness delayed metamorphosis and also caused attachment to the surface film; development ceased after a fair amount of growth and a slight degree of differentiation.4. In mixtures of equal amounts of sea water and normal solutions of sodium, potassium, magnesium and calcium chlorides the larvae became geopositive on entering the medium and remained so during the experiments.5. Some ecological problems of the distribution of three species of Bugula are discussed and tentative suggestions for their solution are offered.