A Red Tide Caused by the Marine Ciliate Mesodinium rubrum in Passamaquoddy Bay, Including Pigment and Ultrastructure Studies of the Endosymbiont

Abstract

A red tide caused by Mesodinium rubrum was observed in Passamaquoddy Bay, New Brunswick, during August 1975. The chlorophyll and phycoerythrin composition and ultrastructure of the endosymbiotic alga are similar to those described for M. rubrum from Ecuador and British Columbia, including the fact that the endosymbionts do not appear to contain a nucleus. Special ultrastructural features are a complete endoplasmic reticulum surrounding symbiont chloroplast, pyrenoid, and starch bodies, ciliate trichocysts with electron-dense and electron-translucent regions, and curious symbiont mitochondria–ciliate macronuclei associations.