Search

Live cockles were eroded from a tidal flat by a storm event and naturally transported to a nearbydike and beach. Their fate was observed regularly for two months. Some died from desiccation highon the shore, and some were consumed by oystercatchers. Others were caught by the byssusthreads of mussels inhabiting the intertidal area, while a few tried to reburrow high on the shore.These cockles were supposedly rolled while being transported to the beach and were laterobserved being rolled by the waves just below the high water line. Hence, it was concluded that theshells were subjected to abrasion and that this was the cause of the holes that some individualsdeveloped near the umbo of one or both of their (still articulated) valves. A few had repaired suchholes, supporting the hypothesis that these holes were made during rolling transportation. Similarshell assemblages of articulated cockleshells partly with subumbonal; holes were later foundelsewhere on the Wadden Sea coast of Texel. This “natural” experiment and the repair indicatedthat this abrasion occurred while the cockles were still alive, and not after their death. It may alsohelp to better discriminate between biologically and physically produced traces on shells.

Articulated, closed, empty bivalves were collected from a modern beach on the island of Texel, The Netherlands. They included many 2-year-old Spisula subtruncata (average length 25.5 mm). Experiments indicated that they could float. Normally, dead but still articulated bivalves on the beach gape; because the adductor muscles no longer pull the valves together, the ligament opens the two valves. These bivalves most probably had arrived alive on the beach after being dislodged during a storm. The animal inside desiccated on the beach, the remains of the animal glued the valves together, air was trapped inside and the next high tide brought the Spisula floating to a higher drift line on the beach. Such closed, empty bivalves may float for days and cover considerable distances as exemplified by a freshwater Dreissena polymorpha also found on the beach of Texel as a closed, floating bivalve, 20 km from the nearest place where it occurs alive. For the palaeoecologist this indicates that closed, articulated bivalves do not necessarily indicate an absence of transport.

In coastal cliffs consisting of Pliocene fine‐grained clastic sediments at El Rompido, Huelva, Spain we discovered around the high water line an extensive zone of about 1.5 m in height burrows that were made by up to 4 mm long isopods Paragnathia formica (Hesse) and small 5 mm long staphylinid beetles (Bledius cf. corniger Rosenhauer). The burrowing zone was crowded with irregular burrows 2–5 mm in diameter and extended some 5 cm deep in the cliff. The base of the cliff showed a clear (bio)erosional notch due to this burrowing activity, comparable to those produced by marine boring and scraping organisms in, for example, calcareous rocks. This indicates that the activity of Paragnathia and Bledius helps in eroding the cliffs, a phenomenon not published earlier as far as we know. A comparable but less extensive burrowed zone was found farther upstream near Cartaya. Their presence around the high tide zone also might prove these burrows to be good markers of former high tide lines in older cliffs.

Empty shells of terrestrial gastropods remain intact and become fossilized only under particular conditions. The usually thin shells are readily dissolved by rainwater, a process starting often during life. Results indicate that with this chemical weathering they may lose some 1% in weight per month. But this is not the only process by which shell biominerals disappear. During field experiments, living terrestrial gastropods have been observed to actively remove calcareous material from empty shells apparently to use for building their own shell. Empty shells lost ∼30% of their weight in 2 months, indicating this process to be much more important than simple dissolution, and explaining the rapid disappearance of empty shells in the field. Previously, mainly anecdotal mention has been made of this shell scraping. Bones of birds were not scraped by terrestrial gastropods; they lost ∼1% in weight per month at the start due to chemical weathering alone, but weight loss decreased with time and was only 6.5% after 16 months.

Models of evolutionary escalation between gastropods and their shell-breaking predators rely on the presence of a strong relation between predation intensity and repair frequency. Some previous work has suggested that both predation intensity and repair frequency have increased through geologic time. Repair frequency (the percentage of shells with at least one repair scar) in four Recent gastropods from the northern Gulf of California shows both high interspecific (7.6% in Cerithium stercusmuscarum to 87.9% in Turritella gonostoma ) and interhabitat variation (11.9–30.7% in Theodoxus luteofasciatus and 26.8–64.9% in Cerithidea albonodosa ). Habitat-mixing, time-averaging and collecting practices might diminish variation in shell repair in fossil populations. Nevertheless, the high microhabitat variation observed here indicates that trends in shell repair through geologic time should consider the variation in shell repair at any one time. Reliable estimates of repair frequencies in fossil gastropods requires samples of several species and several habitats. Measuring shell repair should be better standardized, published data are now often difficult to compare.

Predator-Prey Interactions in the Fossil Record, edited by Patricia H. Kelley, Michal Kowalewski and Thor A. Hansen, 2003. Topics in Geobiology, volume 20, xvi + 464 p., Kluwer Academic/Plenum Publ...

Michael Faraday (1791-1867) is best known as a brilliant scientist and experimenter in chemistry, electricity and magnetism; however, his biography and bibliography show that he published and lectured on a wide array of subjects (Thomas, 1991). It is apparently unknown in optical limnology and oceanography, that in 1855 Faraday experimented with a kind of Secchi disk "avant la lettre" to measure the turbidity of the River Thames. This is not mentioned in reviews and textbooks (Boguslawski, 1884; Forel, 1901; Krummel, 1923; Hutchinson, 1957; Holmes, 1957; Jerlov, 1976). Faraday's experiments were done 10 years before Secchi used a white disk and the depth of its disappearance from sight for transparency measurements in the Mediterranean in 1865. Such disks later became known as Secchi disks.

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.

Macrofauna density and bioturbation intensity (measured with X-ray radiography), were studied in the Dutch Wadden Sea near Ameland and in Mok Bay, Texel, in September 1988. The bivalveMacoma balthica and the polychaeteHeteromastus filiformis were widely distributed in the areas studied. The cockleCerastoderma edule and the polychaeteScoloplos armiger did not occur in areas with high clay content, while the molluscsHydrobia ulvae andMya arenaria preferred fine sediments. The polychaeteNereis diversicolor preferred the higher parts of the intertidal. In the Ameland area disturbance of primary sediment structures was highest near the shore and near the middle of the tidal confluence where physical reworking was low. The sheltered Mok Bay sediments were completely reworked by deposit-feeders. Bioturbation intensity and deposit-feeder (bioturbator) density were, however, not highly correlated. A number of stations showed higher bioturbation towards the surface and this may be related to the high abundance of near surface dwelling macrofauna, due to eutrophication and organic enrichment of the sediments in recent years.

Herring gulls (Larus argentatus) are common birds in the Dutch Wadden Sea the year round. Their diet is varied but consists of ca 70% molluscs, largely bivalves (mussels and cockles). Large shells are crushed by dropping them from the air. Bivalves

The Neogene cheilostomatous bryozoan Celleporaria palmata lived facultatively in association with the scleractinian coral Culicia. For Culicia the association was obligatory; the symbiosis was most probably mutualistic. Benefits for the coral appear to have been: (1) the bryozoan provided substrate in a soft-bottom environment; (2) the coral could feed at higher levels above the sediment; (3) the feeding currents generated by the bryozoan provided the corals with food (no competition for food would occur as the coral would collect larger prey); and (4) the surrounding of the cordites by the bryozoan provided strength and lateral protection. Benefits for the bryozoan appear to have been: (1) the stinging cells of the coral provided protection against predators and settlers; (2) the positioning of the corals on the maculae saved the bryozoan subsequent energy expenditure in further construction of polymorphs and secondary calcification. Negative effects for the bryozoan might have been the inhibition of possible functions of the maculae other than as exhalant chimneys, e.g., production and generation of male gametes. ***Symbiosis, mutualism, Culicia, Cryptangia, Celleporaria, Bryozoa, Scleractinia.

In the Wadden Sea, shell repair frequency in the small gastropod Hydrobia ulvae varied from 2.8% to 11.2%. On tidal flats of the Mok, a small bay on the island of Texel, The Netherlands, in the Wadden Sea, higher repair frequencies varying from 11.8% to 41.8% were measured. The shelduck, Tadorna tadorna, a predator of Hydrobia, occurs here in densities far above average densities for the Wadden Sea. Shelducks ingest their prey whole and crush the shells of H. ulvae internally. Live specimens of H. ulvae were collected from shelduck feces. Those with intact operculum and only a damaged outer aperture rim of the shell were kept in aquaria and repaired their shell rapidly. This indicates that predators that ingest shelled prey can also leave repair scars on shells. Such scars, however, are indistinguishable from those resulting from failed predation by predators using such pre-ingestive shell breakage as decapod crustaceans.

Gulls (mainly Larus ridibundus) and Shelducks (Tadorna tadorna) make characteristic feeding traces on the Dutch tidal flat studied. Troughs up to 3 m long, ca. 15 cm wide, and ca. 3 cm deep made by L. ridibundus were most frequent from July to October. Craters made by Shelducks, ca. 10 cm deep and up to 60 cm in diameter, were most common in summer. The larger craters compare well with feeding traces reported for Eider ducks (Somateria mollissima) and rays (Hypotremata); the smaller craters compare with those of Flounder (Platichtys flesus) and Bream (Abramis brama). All illustrate uniformity in origin: benthic feeding by predators. Annually ca. 30% of the area studied was reworked by gulls and ca. 15% was reworked by Shelducks. The annual sediment reworking rate by these birds equals a sediment layer 2.5 cm thick. This volume is about one order of magnitude less than the ∼35 cm reworked annually by the most important deposit feeders of this tidal flat, collectively: the polychaetes Arenicola marina and H...

SUMMARY: Invertebrate ichnology developed separately from vertebrate ichnology; many invertebrate traces were first interpreted as fossil algae. Recent traces have helped to discover their real nature. The study of recent traces of invertebrates in the Wadden Sea played an important role in the development of ichnology. In 1928, Rudolf Richter (1881–1957) founded the first marine institute devoted entirely to Aktuogeologie and Aktuopalaontologie in Wilhelmshaven, and the school of researchers inspired by him was crucial. Their work became widely known and influential when research articles and reviews of their work in the Wadden Sea began to be published in the English language. Hantzschel's contribution on ‘Trace Fossils and Problematica’ to the Treatise on Invertebrate Paleontology and Seilacher's important contributions to the classification of trace fossils and the use of trace fossil assemblages to estimate the depth of deposition crown the work started by Richter in the Wadden Sea.

The ligament of the bivalve Mya arenaria was previously described as being composed of two layers: a fibrous and a lamellar one, the fibrous layer being more extensive. Other features described, such as the three-dimensional extent of the layers and their mode of attachment to the chondrophores, have been found to be inaccurate to a certain extent. The ligament is therefore redescribed here. It is conical in appearance and attached to the left chondrophore only at its margin, its interior being occupied by an epithelium, which is an extension of the mantle isthmus. The lamellar layer is a pyramidal body which merges into and constitutes the posterior extension of the fibrous layer. The whole structure is internal and may rotate around the dorsoventral axis, thus being suited to allow rocking of the valves. This kind of movement is used when Mya contracts the anterior adductor muscle to eject water from the mantle cavity during burrowing. In this respect the ligament is unique among those known in bivalves.

80% of floating plastic debris freshly washed ashore on a Dutch coast showed peckmarks made by birds at sea. They either mistake these debris for cuttlebones or simply test all floating objects. Ingestion of plastic is deleterious for marine organisms. It is urgent to set measures to plastic litter production.