Chemical, histochemical, and histopathological studies on corals. Porites spp., parasitized by trematode metacercariae

The occurrence of the metacercaria of Plagioporus sp. encysted in two species of corals, Porites compressa and P. lobata, from Kaneohe Bay, Oahu, Hawaii, is reported. This parasite is covered with a bilayered metacercarial cyst the chemical compositions of which have been ascertained by histochemistry. Both of these cyst walls are believed to be secreted by the parasite. In addition, the cytochemical properties of the metacercaria and the adjacent host cells are reported.Histo- and cytopathological alterations in the epidermis and gastrodermis of the coral hosts were studied and such changes have been interpreted to have resulted from mechanical pressure exerted by the parasite.Because gross observations had revealed the presence of elevated nodules at the sites where the metacercariae occurred, chemical analysis was conducted to ascertain whether this larval trematode had induced hypercalcification in the hosts. However, calcium determinations of Decal in which pieces of parasitized coral tissue had been decalcified revealed that hypercalcification had not occurred.Examination of the cellular reactions in both species of Porites revealed that if the gastrodermis had been ruptured, partial encapsulation of the parasite occurs. The reaction cells include free cells of the mesoglea that become fused, accidentally trapped cnidoblasts and nutritive-muscular cells, and gastrodermal interstitial cells. Despite the partial encapsulation, the encysted metacercariae did not appear to be injured.