Original scientific paper

Microbial community structure in two anchialine caves on Mljet Island (Adriatic Sea)

Nada KRSTULOVIĆ ; Institute of Oceanography and Fisheries, Šetalište Ivana Meštrovića 63, 21 000 Split, Croatia
Mladen ŠOLIĆ ; Institute of Oceanography and Fisheries, Šetalište Ivana Meštrovića 63, 21 000 Split, Croatia
Danijela ŠANTIĆ ; Institute of Oceanography and Fisheries, Šetalište Ivana Meštrovića 63, 21 000 Split, Croatia
Jasna MARŠIĆ-LUČIĆ ; Institute of Oceanography and Fisheries, Šetalište Ivana Meštrovića 63, 21 000 Split, Croatia
Marin ORDULJ ; University of Split, Centre of Marine Studies, Livanjska 5/III, 21 000 Split, Croatia
Stefanija ŠESTANOVIĆ ; Institute of Oceanography and Fisheries, Šetalište Ivana Meštrovića 63, 21 000 Split, Croatia

Abstract

The microbial abundances, including bacteria, viruses, and heterotrophic nanoflagellates, were determined for two anchialine caves located on the Island of Mljet (Adriatic Sea): Bjejajka Cave and Lenga Pit. Both caves are situated approximately 100 m from the coast with extensive subterranean connections to the sea, resulting in noticeable marine and terrestrial, influences. Because of the shallow settings of the studied caves, they represent habitats with a minimal light or complete darkness where photosynthesis is minimal or not possible. Thus, during the surveys there was no evidence of cyanobacterial cells in either caves, but the presence of bacteria, viruses and heterotrophic nanoflagellates (HNF) was established. Further, bacterial abundance was higher in caves in comparison to surrounding open seawater. In the surrounding seawater the predominance of the LNA group over HNA is determined, which also indicates the differences in relation to the studied caves. In fact, the dominance of HNA group of bacteria in caves together with higher total bacterial abundance indicates that the caves are of higher trophic level than the surrounding seawater. With regard to bacterial diversity, both caves had a unique makeup of bacterial populations and low diversity, with the chemolithoautotrophic Epsilonproteobacteria representing the most abundant taxonomic group. To examine the mechanisms regulating bacterial abundance in these habitats, we observed the relationship between bacteria and heterotrophic nanoflagellates (HNF) and between bacteria and viruses. The importance of predation in controlling bacteria (top down control) and, consequently, the domination of bottom up control of HNF were observed in both caves.

Keywords

anchialine caves; cyanobacteria; bacteria; viruses; heterotrophic nanoflagellates

Hrčak ID:

117139

URI

https://hrcak.srce.hr/117139

Publication date:

1.12.2013.

Article data in other languages: croatian

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