INVASIVE FORAMINIFERA IN COASTAL ECOSYSTEMS OF THE EASTERN MEDITERRANEAN: IMPLICATIONS FOR UNDERSTANDING LARGER FORAMINIFERAL-DOMINATED BIOFACIES IN THE CENOZOIC

Larger benthic foraminifers (LBF) were abundant in warm, shallow waters of the Paleogene, sometimes producing as much as 80% of the sediment volume. A major turnover of Tethysian LBF faunas near the Paleocene-Eocene boundary, recognized for more than 50 years, is now known to be associated with the Paleocene-Eocene Thermal Maximum (PETM). For example, in the southern Pyrenean region of Spain, a nearly monospecific lenticular Nummulites facies abruptly appeared that has been shown to incorporate the carbon isotope excursion associated with the PETM. One hypothesis for the abrupt appearance of this facies is a Tethysian-wide expansion of the range of these LBF.

The genus Amphistegina has been nearly ubiquitous in LBF assemblages through much of the Cenozoic. Near the “generalist” end of the spectrum for LBF, Amphistegina spp. can be major carbonate producers, especially in the absence of more specialized taxa. The largest and shallowest dwelling of the Indo-Pacific species is A. lobifera. In the modern eastern Mediterranean, this species is a remarkably successful invasive in coastal ecosystems, where its shell production is altering sediment textures.

An A. lobifera population from the Aegaen Sea was sampled monthly between June 2008 and May 2009 in the South Evoikos Gulf, where winter temperatures can drop below previously reported minima for the species. Monthly variations in size–frequency distributions and abundances indicated that this population reproduced asexually primarily during the summer season. Proportions of shells characteristic of gametogenesis indicated that sexual reproduction also peaked in summer, revealing predominantly a one-year life span for each generation. Comparison of these findings with previous studies of A. lobifera populations indicates a) tolerance of low winter temperatures, b) adaptation of the life cycle to strong seasonality, and c) its mixotrophic feeding strategy has allowed A. lobifera to proliferate in the exceptionally clear, low nutrient, coastal waters of the Mediterranean Sea. These attributes elucidate how rapidly LBF populations of the Cenozoic might have expanded their latitudinal ranges and invaded shallow epeiric seas during episodes of climatic warming.