Maria Pia Nardelli

Survival, Reproduction and Calcification of Three Benthic Foraminiferal Species in Response to Experimentally Induced Hypoxia

An experiment was conducted to test the survival rates, growth (calcification), and reproduction capacities of three benthic foraminiferal species (Ammonia tepida, Melonis barleeanus and Bulimina marginata) under strongly oxygen-depleted conditions alternating with short periods of anoxia. Protocols were determined to use accurate methods (1) to follow oxygen concentrations in the aquaria (continuously recorded using microsensors), (2) to distinguish live foraminifera (fluorogenic probe), (3) to determine foraminiferal growth (calcein-marked shells and automatic measurement of the shell size). Our results show a very high survival rate, and growth of A. tepida and M. barleeanus in all experimental conditions, suggesting that survival and growth are not negatively impacted by hypoxia. Unfortunately, no reproduction was observed for these species, so that we cannot draw firm conclusions on their ability to reproduce under hypoxic/anoxic conditions. The survival rates of Bulimina marginata are much lower than for the other two species. In the oxic treatments, the presence of juveniles is indicative of reproductive events, which can explain an important part of the mortality. The absence of juveniles in the hypoxic/anoxic treatments could indicate that these conditions inhibit reproduction. Alternatively, the perceived absence of juveniles could also be due to the fact that the juveniles resulting from reproduction (causing similar mortality rates as in the oxic treatments) were not able to calcify, and remained at a propagule stage. Additional experiments are needed to distinguish these two options.

Assessing the effect of mercury pollution on cultured benthic foraminifera community using morphological and eDNA metabarcoding approaches

Mercury (Hg) is a highly toxic element for living organisms and is known to bioaccumulate and biomagnify. Here, we analyze the response of benthic foraminifera communities cultured in mesocosm and exposed to different concentrations of Hg. Standard morphological analyses and environmental DNA metabarcoding show evidence that Hg pollution has detrimental effects on benthic foraminifera. The molecular analysis provides a more complete view of foraminiferal communities including the soft-walled single-chambered monothalamiids and small-sized hard-shelled rotaliids and textulariids than the morphological one. Among these taxa that are typically overlooked in morphological studies we found potential bioindicators of Hg pollution. The mesocosm approach proves to be an effective method to study benthic foraminiferal responses to various types and concentrations of pollutants over time. This study further supports foraminiferal metabarcoding as a complementary and/or alternative method to standard biomonitoring program based on the morphological identification of species communities.

Contribution of soft-shelled monothalamous taxa to foraminiferal assemblages in the Adriatic Sea

Monothalamous foraminifera with organic and agglutinated test walls (“allogromiids” sensu lato) deserve attention because of their importance in deep-sea and shallow-water soft-bottom communities and their crucial phylogenetic position at the base of the foraminiferal evolutionary tree. However, our knowledge of the biodiversity and ecology of monothalamous foraminifera is very incomplete and geographically patchy. Here, we present a short review based on the available data on monothalamous, soft-walled foraminiferal taxa from the Adriatic Sea in response to several environmental parameters (i.e. organic matter, oxygen, grain size, depth). The main results of the studies provide evidence of the importance of these foraminiferal taxa in this shallow, temperate latitude area; they represent a start for the identification of soft-shelled monothalamous morphotypes that could be potential bioindicators of environments influenced by inputs of fresh waters, increasing eutrophication and consequent fluctuations in bottom-water oxygenation. The contribution of this soft-shelled component to living benthic foraminiferal assemblages appears not negligible and excluding it from foraminiferal studies can potentially lead to a loss of ecological information. The study, therefore, provide an atlas of the Adriatic soft-shelled foraminiferal taxa in order to: 1) encourage the species-level description, if possible, or alternatively a basic morphotype characterization; 2) facilitate future comparisons of taxa from similar settings; 3) promote their potential use in future biomonitoring investigations together with the hard-shelled foraminifera.