Identification and Distribution of Endosymbiotic Diatoms in Larger Foraminifera

Abstract

The diatom endosymbionts have been isolated in culture from over 2,000 specimens of larg iner a (Amphistegina lessonii, A. lobifera, Heterostegina depressa, Borelis schlumbergi, Operculina ammonoides, Calcarina calcar) harvested from Red Sea, Indian Ocean, Hawaii, Palau, and the Great Barrier Reef stations. Twenty different species or varieties of diatoms were collectively isolated from the 6 host species in the total samples. Nitzschia frustulum var. symbiotica was the most commonly (33.7% of total hosts) isolated endosymbiont. Next most common were Nitzschia panduriformis var. continua, Fragilaria shiloi, Nitzschia laevis, and Amphora roettgerii, respectively, representing 14.5, 9.9, 8.7, and 6% of the isolations. More than half of the isolations were made in the vacinity of the H. Steinitz Marine Biology Laboratory on the Gulf of Elat, Red Sea so that the results have to be interpreted with that bias in mind. N. frustulum var. symbiotica was the most frequently isolated endosymbiont at all sites where more than 75 organisms were studied. Significant numbers of N. frustulum var. symbiotica, N. laevis and N. panduriformis var. continua were isolated from hosts collected at every depth. Fragilaria shiloi, in contrast, was rarely isolated from hosts at depths greater than 25m. Achnanthes maceneryae, Amphora sp.(J) and Protokeelia hottingeri were only collected in hosts harvested at depths greater than 25m. Although host species harbored more than one endosymbiont species some bias was observed. Nitzschia laevis and F. shiloi were the most common symbionts of B. schlumbergeri. A. maceneryae and N. laevis were isolated in over 55% of all the 0. ammonoides studied. Most larger foraminifera were the hosts for only a single species of symbiont (71%) at a time; a second symbiont species was found in the remainder. Studies of the microflora on substrates on which larger foraminifera were feeding showed no correlation between potential diet and the endosymbiotic diatoms present in foraminifera harvested from the same substrates. Endosymbiotic diatoms were extremely rare (<0. 5%) in the habitat where the foraminifera were feeding.