Tomasz Borszcz

Encrustation patterns on post-extinction early Famennian (Late Devonian) brachiopods from Russia

A study of patterns of episkeletobiont encrustation on the shells of two early Famennian brachiopods, Cyrtospirifer zadonicus and Ripidiorhynchus huotinus from Russia, revealed assemblages comprising seven skeletonised encruster taxa. The assemblages are dominated by spirorbiform microconchids, followed by cornulitids. Features such as shell malformations, frequent encruster growth towards the commissure of the shells, and encruster distribution in the areas adjacent to zones of possible water intake by the brachiopods indicate that these may have been colonised syn vivo. The lack of differences in encruster abundance between the two valves in C. zadonicus indicates that this species may have lived with both valves inclined at a high angle to the substrate. The significantly higher abundance of episkeletobionts on the brachial valves of R. huotinus may indicate that shells of this species were oriented with the brachial valve at a lower angle to the substrate, providing sheltered sites for coelobiotic larvae. Compared with pre-Famennian brachiopod-hosted encruster communities, this early Famennian community is impoverished in species richness and is dominated by microconchids. It is proposed that the epibionts witnessed a regression-related Frasnian–Famennian extinction event. During the recovery interval, opportunistic microconchids may have been among the first encrusters to colonise the pioneering brachiopods.

Microconchids of the species Microconchus valvatus (Münster in Goldfuss, 1831) from the Upper Muschelkalk (Middle Triassic) of Germany

In the present paper, the commonly mentioned but poorly recognised microconchid species Microconchus valvatus (Münster in Goldfuss, 1831) is redescribed on the basis of material from the Upper Muschelkalk of Germany. ESEM studies of the microconchid tubes with clear morphological and microstructural characters were compared to the existing known Triassic species. Microconchus valvatus is characterised by fine growth lines and transverse riblets. ESEM analysis shows that tubes which appear smooth under the binocular microscope are in fact abraded. Thus, taphonomy must be taken into account and scanning microscopy must be used during studies of microconchid tubes. Quantitative ecology shows that particular microconchid populations developed various size ranges punctuated by some gaps, have non-normal distributions as expected in time-averaged assemblages, and suggests that differences among populations may reflect distinct hydrologic settings. This study provides a multidimensional investigation of microconchids and offers compelling evidence that microconchids were an important faunal group during the post-recovery Middle Triassic interval.

Temporal dynamics of encrusting communities during the Late Devonian: a case study from the Central Devonian Field, Russia

Abstract. In this study we focused on the dynamics of encrusting assemblages preserved on brachiopod hosts collected from upper Frasnian and lower Famennian deposits of the Central Devonian Field, Russia. Because the encrusted brachiopods come from deposits bracketing the Frasnian/Famennian (F/F) boundary, the results also shed some light on ecological differences in encrusting communities before and after the Frasnian—Famennian (F-F) event. To explore the diversity dynamics of encrusting assemblages, we analyzed more than 1300 brachiopod valves (substrates) from two localities. Taxon accumulation plots and shareholder quorumsubsampling (SQS) routines indicated that a reasonably small sample of brachiopod host valves (n=50) is sufficient to capture themajority of the encrusting genera recorded at a given site. The richness of encrusters per substrate declined simultaneously with the number of encrusting taxa in the lower Famennian, accompanied by a decrease in epibiont abundance, with a comparable decrease in mean encrustation intensity (percentage of bioclasts encrusted by one or more epibionts). Epibiont abundance and occupancy roughlymirror each other. Strikingly, few ecological characteristics are correlated with substrate size, possibly reflecting random settlement of larvae. Evenness, which is negatively correlated with substrate size, shows greater within-stage variability among samples than between Frasnian and Famennian intervals and may indicate the instability of early Famennian biocenoses following the faunal turnover. The occurrence distribution of encrusters points to nonrandomassociations and exclusions among several encrusting taxa. However, abundance and occupancy of microconchids remained relatively stable throughout the sampled time interval. The notable decline in abundance (∼60%) and relatively minor decline in diversity (∼30%) suggest jointly that encrusting communities experienced ecological collapse rather than a major mass extinction event. The differences between the upper Frasnian and lower Famennian encrusting assemblages may thus record a turnover associated with the F-F event.

90Sr and 137Cs in Arctic echinoderms

Radionuclides in the Arctic echinoderms have seldom been studied despite their considerable environmental importance. This manuscript covers the results of 90Sr and 137Cs measurements in common echinoderm taxa collected from the Svalbard Bank in the Barents Sea and from two High-Arctic fjords (Isfjorden and Magdalenefjorden). We focused on the echinoid, Strongylocentrotus droebachiensis, the asteroid, Henricia sanguinolenta, and the ophiuroid, Ophiopolis aculeata. For all echinoderms, the analysis revealed a negative correlation between 90Sr activity and the mass. Thus, we concluded that metals are accumulated faster at a young age when the growth is most rapid. The highest average activities of 137Cs followed the order O. aculeata>H. sanguinolenta>S. droebachiensis. This suggests that bioaccumulation was highly taxon-dependent and could reflect differences in the isotope exposures associated with the diet of echinoderms. The study provides a baseline for understanding radionuclide processes in the High-Arctic benthic echinoderm communities.

Direct evidence of sea anemone predation on Arctic echinoids

Predator–prey interactions are considered a major evolutionary driver and a key biological factor affecting recent organisms, but little is known about their influence on Arctic benthic life. It is not easy to document predatorial behaviour in situ in the marine realm, especially in polar seas, and thus usually only indirect evidence is available. Palaeoecologists use several proxies to infer predation on echinoids (Wilson et al. 2015), namely drill holes, repair scars, ejecta deposits