ECOLOGY AND COMMUNITY STRUCTURE OF MODERN INTERTIDAL FORAMINIFERA FROM CORFU ISLAND (GREECE): INSIGHTS FROM PROPAGULE EXPERIMENTS

Our understanding of the ecology and community structure of modern foraminiferal assemblages is traditionally based on field observations or bio-monitoring. Recently, experimental approaches, including in-situ and laboratory studies are used more commonly. Among them, the Propagule Method offers a wide range of potential applications. It focuses on the reactions of isolated assemblages of small juveniles (“propagules”) to controlled environmental conditions, by analyzing the experimental assemblages that were able to grow from these juveniles after a certain time.

In the present study, we applied the Propagule Method to intertidal foraminiferal assemblages from two lagoons on Corfu Island (Greece, Mediterranean Sea). Both lagoons offer comparable environmental settings and were sampled at two different seasons of the year (spring and fall). The fine fraction (<53 μm) of the sampled sediment, which contains the propagules, was isolated and set up in the laboratory under controlled conditions (26–30°C, 40 ppt and different additional substrates including phytal and rubble) for six weeks.

The foraminiferal assemblages that grew from these experiments revealed that despite their ecological comparability, both lagoons contain specific assemblages of foraminiferal propagules, which were defined by a varying amount of allochthonous juveniles that do not normally live at the respective study sites. Significant differences between the two seasons show that the juvenile assemblages are shaped by individual reproduction patterns as well as seasonal variations in propagule transport. While additional phytal or rubble substrates did not have a significant effect, the relative increase in organic content within the fine sediment lead to an increased abundance of certain ecological groups of foraminifera (e.g., opportunists).

Our results deepen our understanding of the ecology and community structure of intertidal foraminiferal assemblages. They further highlight the potentially important role that these “hidden” juvenile assemblages might play with regard to ongoing environmental changes such as ocean warming, sea-level rise, or changes in nutrient supply.