Symbiotic associations among the microplankton in oligotrophic marine environments, with special reference to the Gulf of Aqaba,

Abstract. Instances of symbiotic consortia in the microplankton of highly oligotrophic seas are discussed on the basis of case studies and long-term observations off the Israeli coast of the Gulf of Aqaba, Red Sea, and the inshore and offshore waters of the Eastern Mediterranean. Associations described include diatoms with filamentous cyanophytes, diatoms with protozoans, tintinnids with attached or encrusted diatoms, and acantharians with algal endosymbionts. Noted among the case studies is the frequent occurrence of the endosymbiont cyanophyte Richelia intracellularis, capable of molecular nitrogen fixation, in diatoms, including three species of Hemiaulus. For one of these associations, seemingly with Hemiaulus sinensis, this is the first photographic record. The consortia are considered in relation to their seasonal distribution in depth profiles from the northern end of the Gulf of Aqaba, and in relation to their occurrence in the Eastern Mediterranean and also worldwide in similar environments. These aspects and the easily identifiable symbiotic nature of the consortia described herewith make them useful as indicator species of warm water oligotrophic seas