Foraminiferal species responses to in situ, experimentally induced anoxia in the Adriatic Sea

Abstract

Abstract. Anoxia was successfully induced in four benthic chambers installed at 24 m depth in the northern Adriatic Sea for periods varying from 9 days to 10 months. During the 10-month period, species richness significantly decreased. Although no significant change in Shannon diversity and evenness was observed, the composition of the foraminiferal assemblages changed with time. This change is due to interspecific differences in tolerance to anoxia. Reophax nanus, Textularia agglutinans and Quinqueloculina stelligera all showed a significant decrease with time, strongly suggesting they are sensitive to anoxia. Conversely, Eggerella scabra, Bulimina marginata, Lagenammina atlantica, Hopkinsina pacifica and Bolivina pseudoplicata appeared to be resistant to the experimental conditions. Quinqueloculina seminula was apparently sensitive to anoxia but showed a clear standing stock increase during the first month of the experiment, which we interpret as an opportunistic response to increasing organic matter availability due to the degradation of the dead macrofaunal organisms. None of the anoxia-sensitive species is able to accumulate intracellular nitrates. Nitrate accumulation could be shown for some tested specimens of the dominant anoxia-tolerant species E. scabra and B. marginata. However, tests on the denitrification capacity of these taxa yielded negative results, suggesting that their resistance to long-term anoxia is not due to their ability to denitrify.

Tropical Atlantic climate and ecosystem regime shifts during the Paleocene–Eocene Thermal Maximum

“…In apparent contrast is an increase in the abundance of organic linings of benthic foraminifera. Some benthic foraminifera, however, tolerate low oxygen concentrations for substantial periods (Langlet et al, 2014) and may outcompete metazoans in such conditions (Woulds et al, 2007). This signal is surprisingly similar to that found in shelf sections of the Gulf of Mexico and Nigeria .…”

“…Interestingly, the reduction in carbonate accumulation was most severe at Walvis Ridge and the Caribbean , both located towards the borders of the tropical band, which is in sharp contrast to sustained carbonate deposition in the Atlantic Southern Ocean sites 689 and 690 (Kelly et al, , 2010. Although carbonate wt % at Pacific tropical sites remains high (Colosimo et al, 2006;Leon-Rodriguez and Dickens, 2010), this is largely due to very low accumulation rates of the sole other sedimentary component, clay, and bioturbation, complicating robust estimates of carbonate accumulation through time.…”

“…Long-term gradual warming during the late Paleocene and early Eocene (∼ 59-53 Ma) is recorded in the deep ocean Littler et al, 2014), as well as Southern Hemisphere Hollis et al, 2012) and Northern Hemisphere (Frieling et al, 2014) midlatitude and high-latitude surface oceans and the equatorial Atlantic (Cramwinckel et al, 2018). Superimposed, the PaleoceneEocene Thermal Maximum (PETM) represents a transient period of rapid global warming, associated with the massive input of strongly 13 C-depleted carbon into the oceanatmosphere system (Dickens et al, 1995;Zeebe et al, 2009).…”

Structural and functional responses of harpacticoid copepods to anoxia in the Northern Adriatic: an experimental approach

“…Studies within a given habitat typically concluded that of all permanent meiobenthic taxa, foraminiferans (see also Langlet et al, 2013) and nematodes are best adapted to hypoxia/anoxia and that crustaceans (e.g. copepods) are the least tolerant (see review by Wetzel et al, 2001).…”

CellTracker Green labelling vs. rose bengal staining: CTG wins by points in distinguishing living from dead anoxia-impacted copepods and nematodes

“…drug-multicellular parasites relation (TrejoChávez et al, 2011), phytoplankton ecology (Peperzak and Brussaard, 2011); and microbenthology -i.e. benthic microalgae, ciliates, flagellates and foraminiferans (Bernhard et al, 2003(Bernhard et al, , 2006Pucci et al, 2009;First and Hollibaugh, 2010;Figueira et al, 2012, Langlet et al, 2013a. The use of CTG for metazoan organisms, however, has so far been limited to dysoxic laminated sediments in 400 to 600 m water depth (oxygen minimum zone in the Santa Barbara Basin; Bernhard et al, 2003), and deep-sea (3300 to 3600 m) anoxic sediments (Mediterranean; Danovaro et al, 2010).…”