engleski

The ecological complexity of a simple shallow marine cave in the middle Adriatic revealed by temperature recordings

Due to the karstic nature of the Eastern coast of the Adriatic Sea and the Holocene sea transgression there are many submerged pits, caves, half-caves and passages along it. During the period of time from 2003 to 2006 we undertook a number of speleo-dives with the autonomous diving apparatus in order to research living organisms and communities inside the shallow marine cave “ Y” on the SW side of Dugi otok, near Brbinjšćica cove, Middle Adriatic. The cave is mostly below sea surface ; the bottom of the entrance part is on 12 m and it’ s ceiling on 6 m of depth. It is approximately 90 m long and 3 m wide. The cave has rather simple morphology: thirty meters from the entrance the main channel bifurcates ; the long arm extending in the NE direction and the short one ending in a small chamber with an air pocket. The cave bottom gradually rises from the entrance inwards to the middle part at 5 m and then slopes downward to the depth of 8 m at the end. Besides recording biota inside the cave we also measured sea temperature simultaneously on six spots during one year and light intensity on seven spots during three days. Two distinct benthic communities inhabit the cave: we recorded in the entrance part a well developed community of semi-dark caves with high species diversity and biomass, while inside the cave a community of dark caves and passages with low species diversity and biomass. The middle part of the cave represents a transition between these two communities. In some parts of the cave the absence of marine organisms and notable corrosion marks point to freshwater influence, especially on the cave ceiling and near the sea surface in the chamber with the air pocket. Measurements showed clear light gradient from the entrance towards the inside of the cave with practically no light at its end. However, one-year long temperature recordings inside the cave revealed quite complex seasonal distribution of water layers in the cave. In the presentation we will compare and discuss the findings. Results show that even the small differences in morphology of a simple shallow marine cave could have ecological implications which can easily be overlooked without simultaneous measurements of key abiotic parameters such as temperature, salinity and light on distinct spots inside the cave.

Marine cave; freshwater influence; long-term temperature recording; Dugi otok; Croatia

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