Belichnus Traces Produced on Shells of the Bivalve Lutraria lutraria by Gulls

In February 2011, after a storm, thousands of adult, articulated, and still-living common otter shells Lutraria lutraria (L. 1758) were stranded on the North Sea beach of the Island Texel (NL). These 9 to12cm long bivalves were rapidly found and consumed by both herring- and lesser black-backed gulls. Holes, irregular in outline, were observed in some 10% of the articulated shells of these bivalves. These holes were always smaller on the outside of the valves than on the inside and varied in size from 1 to 20mm (outside) to 4 to 22mm (inside). Often the other valve was crushed indicating consumption by gulls. We concluded that these holes were made by the gulls probing the shells; in a few cases, we observed that valves were broken starting from such a hole. Such traces are described in the literature as the ichnogenus Belichnus and were until now attributed to Stomatopoda only. We also suggest that a separate ichnospecies name for two Belichnus holes in one shell should not be used, as we see them simply as a double injury due to two blows. Our findings stress once more the importance of avoiding premature phylogenetic interpretation of traces and the use of a separate ichnotaxonomy

Low juvenile mortality in fossil brachiopods, some comments

Assemblages of fossil brachiopods are often characterized by the absence af juvenile specimens. This absence may be due for instance to method of collection, transport by currents, mechanical destruction, diagenetic solution, predation, factors that all may work selectively on small specimens. In some instances, where it was assumed from a taxonomic analysis that these factors could be excluded, low or even absence of juvenile mortality was given as an explanation. These cases are reviewed and alternative explanations are proposed. So, the assemblage could be the result of mass-mortality (census-assemblage) of a population without juveniles due to the fact that this "census" was taken some time after the last successful recruitment. Another explanation is that adults and juveniles live spatially separated, the assemblage of shells accumulating at localities where the adults live then contains no juvenile specimens. Recent examples of spatial separation of adults and juveniles are given for different groups of marine organisms which shows this phenomenon to be widespread and not only occurring in vagile animals. As long as other explanations are available, low juvenile mortality should be used with great reservation to explain the absence of juveniles in fossil assemblages, as such mortalities are rarely observed in present-day marine animals. Although juvenile mortality is usually high in the planktonic larval stage it is by no means restricted to this stage as stated sometimes. Also just settled benthic organisms are highly vulnerable to predation and other causes of mortality

Een tropisch drijfzaad, Pangium edule Reinwardt (Flacourtiaceae), van het Nederlandse strand

A seed in the collection of the Rijksherbarium from the Dutch coast (1971) appears to belong to Pangium edule. Although able to drift for a long time, it is improbable that this Malaysian seed reached the Dutch coast all the way by sea currents. Transport by man to NW. Europe is the most probable explanation for its occurrence on the Dutch coast. Import of tropical seeds and fruits particularly for decoration has increased. As a result it becomes more difficult to prove longdistance transport by sea for tropical drift-seeds found on the Dutch coast

Decay rates of shells in aquatic and terrestrial habitats, some comments

Measuring decay rates of shells in a terrestrial environment should also take into account the bioeroding effects of land snails that use empty shells as a source of calcium for their own shell formation. This amounted to 30% shell weight loss in only 2 months in my experiment published earlier and was much higher than the 2 to 10% decay in 1 year measured in nylon mesh bags published recently (Ilarri et al. 2015). This bioerosion is not measured when shell decay on land is studied by placing the decaying shells in nylon mesh bags which living gastropods cannot enter freely. Moreover, shell crushing predators (birds, rats) also play an important role in shell decay. That decay in aquatic environments is 6-12 times higher than on land as published by Ilarri et al. (2015) can be questione