Effects of terrestrial sediment on the burial behaviour of post-settlement Macomona liliana
Terrestrial and marine environments are connected ecosystems that are similarly vulnerable to the effects of anthropogenic stressors. Climate change and other anthropogenically-induced stressors have resulted in an increased rate of supply (mass per time per area) of terrestrial (land-derived) sediment. This sediment is exported from catchments to rivers, and subsequently, to estuarine and marine systems. Episodic events result in the catastrophic deposition of terrestrial sediment, while small-scale spatial deposition of terrestrial sediment is widespread, and frequent. One pressing issue is the effect of thin depositions of terrestrial sediment on one ecosystem function, such as recruitment of benthic fauna.
The tellinid bivalve Macomona liliana is an important component of estuarine and coastal benthos throughout New Zealand, representing one of the most common community dominants across marine ecosystems. Significantly, M. liliana is a sensitive ecological indicator of change. Post-settlement juveniles have been demonstrated to actively avoid adverse local conditions, including sediments affected by the deposition of thin terrestrial sediment. This behavioural response may be triggered by deposit-induced changes in the porewater chemistry of the deposit-underlying sediment, but not by contact of the juveniles with the terrestrial sediment.
A laboratory flume experiment was conducted to assess the effect of millimetre-thick terrestrial sediment deposits on porewater chemistry, and the burial behaviour of M. liliana post-settlement juveniles. Terrestrial sediment deposits impeded the diffusion of solutes across the visible sediment surface. This impedance, however, had a negligible effect on the sediment porewater chemistry as a result of resident infauna mediating the exchange of solutes between porewater and bottom water. As such, the deposition of millimetre-thick terrestrial sediment did not negatively affect the burial behaviour of post-settlement juveniles.
This study has highlighted the need for a greater understanding of the contribution of bioturbation by resident infauna to solute exchange in sediments affected by periodic deposition of terrestrial sediment. Bioturbation appears to be one of the most important variables to consider when investigating the effects of terrestrial deposits on juvenile M. liliana burial behaviour.