THE INFLUENCE OF THE ORIENTATION, ROUGHNESS, AND WETTABILITY OF SOLID SURFACES ON THE BEHAVIOR AND ATTACHMENT OF PLANULAE OF CYANEA (CNIDARIA: SCYPHOZOA)

¹ Department of Biology, Trinity College, Hartford, Connecticut 06106

In the laboratory the planulae of Cyanea are exposed to a choice of substrates. Their behavior, the length of time required for them to attach, and the size they attain after attachment differs between glass (hydrophilic) and plastic (hydrophobic) surfaces. The correlation of these differences with wettability is shown by giving planulae a choice of six substrates exhibiting different degrees of wettability (determined by measurement of contact angles); planular attachment to these surfaces is directly proportional to the hydrophobicity of the substrate for those with contact angles from 17° to 82°, but their response is variable and relatively weak to the more hydrophilic surfaces. The same relationship between planular settlement and surface wettability is possibly shown by the preferred attachment of scyphozoan planulae (three species) to roughened plastic surfaces paralleling the increased hydrophobicity of this surface that roughening effects. However, a favorable surface (plastic) does not supercede the requirement that it also must be horizontally oriented to permit attachment to its lowermost surface; planulae rarely attach to uppermost surfaces, nor to vertically oriented surfaces.

Planulae exposed to natural substrate do not usually attach to clean shells in the laboratory nor are they found attached to fresh shells in the field, both of which have wettabilities equivalent to or less than that of glass. Aged shells, on the other hand, possessing organic and bacterial films, show increased hydrophobicity, and have a high incidence of planular attachment in the field.

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