The symbiotic case study of zooxanthellae living inside the jellyfish Cotylorhiza tuberculata

Abstract

The symbiotic association between the zooxanthellae Symbiodinium sp. and its host jellyfish, the rhizostome scyphozoan Cotylorhiza tuberculata was studied. Measurements were carried out in two different sections of the medusa body to investigate de distribution of the alga in hospite: oral arms (OA) and umbrella (UM). Medusa carbon and nitrogen composition were higher in the OA section than UM (4.43 ± 0.3 and 3.7 ± 0.26 respectively). No significant differences were found in the chlorophyll a content among the two sections. However, zooxanthellae density was higher in OA than UM tissue. A total of 13 different pigments was revealed by the High Performance Liquid Chromatography (HPLC) method, the most representative pigments were chlorophyll c2 peridin and diadinoxanthin, typical pigments of dinoflagellates. Cell diameter was significantly higher in hospite (8.71 ± 0.94 μm) than in culture (6.78 ± 0.85 μm), whose growth rate value was 0.285 (± 0.09) d-1. Cultures of Symbiodinium sp. observed by light microscopy, cytograms, and SEM micrographs, showed three subpopulations of autotrophic cells: a bigger and a smaller coccoid stage, and a motile flagellate stage. The presence of zooxanthellae living in symbiosis with C. tuberculata may be a reason added to explain the population success of this jellyfish.