BACKGROUND ILLUMINATION AS A FACTOR IN THE ATTACHMENT OF BARNACLE CYPRIDS

¹ University of Miami Marine Laboratory, Centro Research Laboratories, and the University of Alabama

1. Experiments were conducted to determine the effect of contrasting surroundings upon the frequency of attachment of Balanus eburneus larvae to opaque black and opal glass collecting surfaces. Further experiments were carried out to determine to what extent the number of attachments of transparent collectors was influenced by black and opal backgrounds placed at varying distances.

2. Greater numbers of attachments occurred upon the under side of horizontal rather than vertical, and upon black rather than opal collectors, thus confirming the observations of previous authors.

3. No correlation was found between the degree of contrast shown in the collector and surroundings, and the frequency of attachments.

4. Both black and opal surfaces were found to increase frequency of attachment when placed behind transparent collectors up to distances of six inches.

5. A definite dependence was found to exist between the frequency of attachment and a decrease in the intensity of general illumination in the area immediately beneath horizontal opal collectors. Similarly, the influence of movable backgrounds appeared to be in the nature of a shadow effect. It is suggested that "shading" acts as a stimulus which brings about favorable physiological conditions for the subsequent attachment of barnacle larvae and that the amount of light reflected from the collecting surface is only important insofar as it affects the general "shading" in the vicinity.