Biology of shallow marine ichnology: a modern perspective

Abstract

This study considers the construction and functionality of biogenic structures made by marine, vermiform nemerteans, polychaetes and hemichordates; marine crustaceans; motile bivalves; motile echinoderms; and sponges and sea anemones. We report on a range of modern biogenic structures similar to several known ichnogenera. Vermiform animals dominantly occupy vertical burrows that range from simple through helical shafts to Y-and U-shapes. Horizontal traces made by worms range in form, but are dominated by branching and variably sinuous to meandering burrows. Crustaceans primarily excavate open burrow systems that possess a range of architectures that are similar to either Thalassinoides or Psilonichnus. Smaller crustaceans, such as amphipods, mix the sediment. Bivalve traces vary in form, but generally preserve evidence of vertically oriented filter or interface-deposit feeding from a stationary location, rapid vertical escape, or horizontal grazing. Echinoderms dominantly preserve body impressions and motility traces, such as Asteriacites. An important class of biogenic structure, Scolicia and Bichordites, are made by urchins. Finally, sea anemones can generate large, penetrative, conical biogenic structures. Large, open horizontal networks serve as domiciles and deposit-feeding structures for crustaceans, but with worms similar burrow types are used more for passive carnivory and establishing an interface-feeding network. We report that the trace fossil Gyrolithes potentially represents mechanical ramps for shrimp, but is used as a sediment holdfast when made by worms. Finally, Y-shaped burrows are used for filter feeding in shrimp, and interface-deposit feeding in worms. These examples emphasize that inferences of behavior in the rock record are interpretive.

Neoichnology of Thyonella gemmata: A Case Study for Understanding Holothurian Ichnofossils

“…The X-radiographs revealed that cup-in-cup structures were produced as the holothurians gradually moved upward in response to sediment aggradation [13]. Field observations of Thyone have shown that they produce irregular U-shaped burrows similar to those of T. gemmata in intertidal settings although these have not been described in detail [16,17]. Laboratory experiments with H. scabra indicated that this species burrowed in response to daylight and decreasing salinity, however, neither the burrowing method nor the burrows were described in this study [4].…”

“…The extant holothurians Thyone briareus [5,[13][14][15][16][17], Holothuria scabra [4], and Protankyra bidentata [18] are three exceptions. Pearse [5] conducted various experiments with T. briareus including some designed to observe the animals burrowing methods.…”

Bioturbation in aquatic environments: linking past and present

“…Their results show that we can be fairly confident about the origin of some trace fossils, but also that similar structures can be produced by different taxa behaving in very different ways. Traces morphologically equivalent to the ichnogenus Gyrolithes, for example, are produced by worms anchoring themselves to the seabed, and by ramp-building shrimps (Gingras et al 2008). This highlights the risk of interpreting trace fossils definitively, but further studies of this kind can provide greater clarity.…”

The effects of temperature on oxygen uptake and nutrient flux in sediment inhabited by molluscs

“…Most of these invertebrates actively rework the sediment, a process that may disturb the natural deposited stratification, facilitate the horizontal movement of particles, and restyle the microtopography of the sediment (Gerino et al, 2003;Gingras et al, 2008;Maire et al, 2008). Indeed, to respire, feed, and excrete metabolites, benthic invertebrates must renew their burrow water through bioirrigation (Kristensen and Kostka, 2005).…”