Marine Invertebrate Neoichnology - Trace Fossils as Indicators of Sedimentary Environments - page 280

FIGURE 7 Summary chart of the effects of various physico-chemical stresses on trace diversity
and trace density. The thickness of the bar reflects the relative density or diversity of burrowing
where thicker more. Note that transitions in bar thickness are more abrupt in the burrow density

diagram; this reflects the ability of specific animals to thrive in settings considered stressful by most
infauna (e.g., Corophium volutator in the upper estuary; Howard et al., 1975 ). Data is based on
recent neoichnological studies conducted by the authors.

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observed and burrowing is dominated by crustaceans and bivalves and, uncom-
monly, by polychaetes (e.g., Polydora spp.; Dashtgard et al., 2008; Gingras
et al., 2001; Yang et al., 2009 ). The limitations of bioturbation into firmgrounds
are that the firm surface must be exposed for a substantial amount of time to
permit animal recruitment, and overly compacted, but uncemented, sediment