Chantal De Ridder

Possible effects of global environmental changes on Antarctic benthos: a synthesis across five major taxa

Because of the unique conditions that exist around the Antarctic continent, Southern Ocean (SO) ecosystems are very susceptible to the growing impact of global climate change and other anthropogenic influences. Consequently, there is an urgent need to understand how SO marine life will cope with expected future changes in the environment. Studies of Antarctic organisms have shown that individual species and higher taxa display different degrees of sensitivity to environmental shifts, making it difficult to predict overall community or ecosystem responses. This emphasizes the need for an improved understanding of the Antarctic benthic ecosystem response to global climate change using a multitaxon approach with consideration of different levels of biological organization. Here, we provide a synthesis of the ability of five important Antarctic benthic taxa (Foraminifera, Nematoda, Amphipoda, Isopoda, and Echinoidea) to cope with changes in the environment (temperature, pH, ice cover, ice scouring, food quantity, and quality) that are linked to climatic changes. Responses from individual to the taxon-specific community level to these drivers will vary with taxon but will include local species extinctions, invasions of warmer-water species, shifts in diversity, dominance, and trophic group composition, all with likely consequences for ecosystem functioning. Limitations in our current knowledge and understanding of climate change effects on the different levels are discussed.

Iron microbial communities in Belgian Frasnian carbonate mounds

SummaryThe Belgian Frasnian carbonate mounds occur in three stratigraphic levels in an overall backstepping succession. Petit-Mont and Arche Members form the famous red and grey “marble” exploited for ornamental stone since Roman times. The evolution and distribution of the facies in the mounds is thought to be associated with ecologic evolution and relative sea-level fluctuations. Iron oxides exist in five forms in the Frasnian mounds; four are undoubtedly endobiotic organized structures: (1) microstromatolites and associated forms (blisters, veils...), possibly organized in “endostromatolites”; (2) hematitic coccoids and (3) non dichotomic filaments. The filaments resemble iron bacteria of theSphaerotilus-Leptothrix “group”; (4) networks of dichotomic filaments ascribable to fungi; (5) a red ferruginous pigment dispersed in the calcareous matrix whose distribution is related to the mound facies type. The endobiotic forms developed during the edification of the mounds, before cementation by fibrous calcite. The microbial precipitation of iron took place as long as the developing mounds were bathed by water impoverished in oxygen.

Is the Species Flock Concept Operational? The Antarctic Shelf Case

There has been a significant body of literature on species flock definition but not so much about practical means to appraise them. We here apply the five criteria of Eastman and McCune for detecting species flocks in four taxonomic components of the benthic fauna of the Antarctic shelf: teleost fishes, crinoids (feather stars), echinoids (sea urchins) and crustacean arthropods. Practical limitations led us to prioritize the three historical criteria (endemicity, monophyly, species richness) over the two ecological ones (ecological diversity and habitat dominance). We propose a new protocol which includes an iterative fine-tuning of the monophyly and endemicity criteria in order to discover unsuspected flocks. As a result nine « full » species flocks (fulfilling the five criteria) are briefly described. Eight other flocks fit the three historical criteria but need to be further investigated from the ecological point of view (here called « core flocks »). The approach also shows that some candidate taxonomic components are no species flocks at all. The present study contradicts the paradigm that marine species flocks are rare. The hypothesis according to which the Antarctic shelf acts as a species flocks generator is supported, and the approach indicates paths for further ecological studies and may serve as a starting point to investigate the processes leading to flock-like patterning of biodiversity.

Sea urchin Arbacia dufresnei (Blainville 1825) larvae response to ocean acidification

Increased atmospheric CO2 emissions are inducing changes in seawater carbon chemistry, lowering its pH, decreasing carbonate ion availability and reducing calcium carbonate saturation state. This phenomenon, known as ocean acidification, is happening at a faster rate in cold regions, i.e., polar and sub-polar waters. The larval development of Arbacia dufresnei from a sub-Antarctic population was studied at high (8.0), medium (7.7) and low (7.4) pH waters. The results show that the offspring from sub-Antarctic populations of A. dufresnei are susceptible to a development delay at low pH, with no significant increase in abnormal forms. Larvae were isometric between pH treatments. Even at calcium carbonate (CaCO3) saturation states (of both calcite and aragonite, used as proxies of the magnesium calcite) <1, skeleton deposition occurred. Polar and sub-polar sea urchin larvae can show a certain degree of resilience to acidification, also emphasizing A. dufresnei potential to poleward migrate and further colonize southern regions.

Genetic Evidence Confirms Polygamous Mating System in a Crustacean Parasite with Multiple Hosts

Mating systems are diverse in animals, notably in crustaceans, but can be inferred from a limited set of parameters. Baeza and Thiel (2007) proposed a model predicting mating systems of symbiotic crustaceans with three host characteristics and the risk of predation. These authors proposed five mating systems, ranging from monogamy to polygynandry (where multiple mating occurs for both genders). Using microsatellite loci, we tested the putatively mating system of the ectoparasite crab Dissodactylus primitivus. We determined the mating frequencies of males and females, parentage assignment (COLONY & GERUD software) as well as the contents of female spermathecae. Our results are globally consistent with the model of Baeza and Thiel and showed, together with previous aquarium experiments, that this ectoparasite evolved a polygamous mating system where males and females move between hosts for mate search. Parentage analyses revealed that polyandry is frequent and concerns more than 60% of clutches, with clutches being fertilized by up to 6 different fathers. Polygyny is supported by the detection of eight males having sired two different broods. We also detected a significant paternity skew in 92% of the multipaternal broods. Moreover, this skew is probably higher than the estimation from the brood because additional alleles were detected in most of spermathecae. This high skew could be explained by several factors as sperm competition or cryptic female choice. Our genetic data, combined with previous anatomic analyses, provide consistent arguments to suggest sperm precedence in D. primitivus.

Description and significance of a peculiar intradigestive symbiosis between bacteria and a deposit-feeding echinoid

Abstract Individuals of the deposit-feeding echinoid Echinocardium cordatum (Pennant) harbour peculiar irregular to round-shaped nodules in their intestinal caecum. The nodules have a well-defined structure being made of a central detrital core originating from the gut content and surrounded by actively growing bacteria. These bacteria consist of chains of rod-shaped, usually sheathed cells. They form a core-embedding stratified coat, the thickness of which allows estimation of the relative age of the nodules. The selective penetration of the core-forming detritus into the caecal lumen is explained in terms of the fluid properties of the gut sediment. Nodule formation takes place repeatedly within the caecum where newly-arrived potential cores are progressively colonized by bacteria. The oldest nodules tend to be eliminated through the anus of the echinoids. Nodule bacteria appear to be important for the echinoids well-being as their activity presumably results in avoiding the reduction of the intradigestive sediment in the echinoids hindgut.

Accumulation of a ferric mineral in the biofilm of Montacuta ferruginosa (Mollusca, Bivalvia). Biomineralization, bioaccumulation, and inference of paleoenvironments

Abstract Infrared absorption spectra of the amorphous and phosphorus-rich ferric mineral associated with the biofilm of Montacuta ferruginosa , a marine bivalve, were obtained by applying the KBr disc method. Phosphate absorption bands due to PO stretching vibrations were observed at 1100 and 1020 cm −1 . This result, as well as the similarity of spectra with other well known (bio)minerals, suggests that the mineral is an amorphous iron oxyhydroxide gel with phosphate sorbed on its surface rather than a pure ferric phosphate. It is suggested that phosphate ions are of microbial origin because phosphate-producing enzymes were detected in vivo. Apart from iron, the mineral phase is devoid of other heavy metals. Despite its similarity with other abiotically precipitated phases, it is argued that the mineral is the result of in situ microbial biomineralization processes in the biofilm and not the result of a simple bioaccumulation process. This is supported by microscopic observations. A geological implication is that the simple presence of such iron minerals in ancient sedimentary environments, where microbes have not been fossilized, might be considered as an indicator of microorganisms performing biomineralization. By comparison with the present-day environment of M. ferruginosa , precise paleoenvironmental conditions may be inferred.

The holothuroids, echinoids and asteroids (echinodermata) collected by the Snellius-II expedition

Abstract Together the holothuroids, echinoids and asteroids collected by the Snellius-II Expedition represent 144 different species (40 species of holothuroids, 45 species of echinoids and 59 species of asteroids). The collection includes 14 species new to science. Among the remaining 130 species there are five new records for the Austro-Malayan region and 13 new records for the Indonesian seas.

Presence of a seawater-filled caecum in Echinocardium cordatum (Echinoidea: Spatangoida)

Heart urchins (Echinoidea: Spatangoida) are considered infaunal, deposit feeding sea urchins that utilize the surrounding sediment as a source of nutrients. Sediment occupies most of the digestive tract lumen but never enters the gastric caecum, a prominent structure that is filled with a transparent fluid. The aim of this study was to shed light on the nature of the fluid found inside the gastric caecum of a well-studied spatangoid species, Echinocardium cordatum. Our conclusions are based on a three-step-approach: firstly, by following the movement of dyed seawater from the mouth up to the caecal lumen; secondly, by comparing the osmolarity of various body fluids; and thirdly, by describing the particulate content of the gastric caecum. In addition, we employed magnetic resonance imaging (MRI) to reveal the absence of sediment within the gastric caecum. Our osmolarity measurements show that the coelomic fluid is significantly more concentrated than the caecal fluid, which in turn has an osmolarity similar to seawater. MRI reveals that the gastric caecum, in contrast to the rest of the digestive tract, is always devoid of sediment. Light and electron microscopy observations reveal the presence of a variety of detrital particles suspended in the caecal fluid that are identical to those occurring in seawater sampled over the seafloor. We argue that the fluid filling the gastric caecum must be predominantly seawater, and we propose a scenario that explains seawater circulation in E. cordatum. In this context, the gastric caecum could act as an internal trap for suspended particulate organic matter. We hypothesize that spatangoid sea urchins could have adopted internal suspension feeding as a secondary feeding mode in addition to deposit feeding.