A MICROINJECTION TECHNIQUE USING A PH-SENSITIVE DYE TO DETERMINE THE GUT PH OF CALANUS-HELGOLANDICUS

By applying a microinjection technique previously used in cell biology , a pH-sensitive dye, 2',7'-bis (2-carboxyethyl)-5,6-carboxyfluorescei n) (BCECF), was injected into the gut of the copepod Calanus helgoland icus to determine pH under a range of feeding conditions. The median g ut pH of the fore- and hindguts of starved individuals was 6.86 and 7. 19, respectively. This was a consistently lower pH than that observed in copepods feeding on either the diatom Thalassiosira weissflogii, th e dinoflagellate Prorocentrum micans, or the coccolithophorid Emiliani a huxleyi (Strain 92D), all of which had a median gut pH > 7.0. In all treatments, the median pH of the foregut was more acidic than the med ian of the hindgut, implying that the foregut is the site of acid secr etion. The results, which demonstrate pH values down to 6.11, are disc ussed in terms of coccolith dissolution, pigment degradation and diges tive enzyme activity.