Why some foraminifera love frequent anoxia disturbance: The success of lifestyle-switchers in the northwestern Adriatic Sea

Category Other
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Duijnstee, Ivo۱; Ernst, Sander۱; De Nooijer, Lennart۲; Van der Zwaan, Bert۱
Holding Date 17 September 2008

Foraminifera are important elements in most benthic marine ecosystems. Yet, surprisingly little is known about foraminiferal biology, possibly because they are often ignored in biological studies. Their fossil remains, however, are studied extensively by earth scientists, as they constitute a major source of paleo-environmental and paleo-oceanographical information. For instance, fossil foraminiferal assemblages reflect the anthropogenic eutrophication history of the northwestern Adriatic Sea, which is characterized by increasing incidence of sea-floor anoxia. Here, many species were pushed towards local extinction over the last 100 years or so, while others seemed to benefit from the increasingly variable environment. After combining results from a variety of field studies and laboratory experiments, we conclude that it was the increased variability of bottom water oxygenation, or more particularly the increased frequency of anoxic episodes, that caused the composition of the foraminiferal community to change so drastically. Furthermore, we discovered that the thriving taxa have the capacity to switch back and forth between alternate behavioral and life-history strategies, depending on the environmental conditions: during episodes of massive deposition of organic matter and subsequent anoxia, they change their distribution pattern in the sediment, and switch to rapid and early reproduction. Once the adverse conditions ameliorate, they change back to their original life-style. This facultative opportunism enables them to profit from anoxia disturbance, and yet persist during inter-crisis conditions when more competitive equilibrium species should recover. Due to their post-crisis perseverance, even ephemeral crises become detectable in the fossil record. Dominance of these lifestyle-switchers in fossil assemblages is a good proxy for high disturbance frequencies, however not for long-lasting mildly stressful conditions such as prolonged hypoxia, as often suggested.