Influence of peat substrate on the distribution and behaviour patterns of sand shrimp, <i>Crangon septemspinosa</i>, under experimental conditions

Peat harvesting is a lucrative industry in New Brunswick, Canada, and is for the most part located along the coast. Current methods of mining peatlands are such that high levels of peat fibers are transported by runoff into fresh and marine waters. To understand better the influence of peat substrate on aquatic organisms living in peat-impacted habitats, the sand shrimp (Crangon septemspinosa) was used as a bioindicator. A series of laboratory experiments was conducted in which shrimp were provided with a choice between sand and peat. Long-term studies on starved shrimp confirmed that whereas foraging activities took place on both substrates, shrimp display an overall preference for sand (73% of all shrimp observed were on sand, n=60). When food was deposited on each of the substrates, shrimp generally opted to feed on sand (75% of all shrimp observed were on sand, n=60). After all food on sand was consumed, shrimp tended to move to peat. This was followed by a short period of foraging on both sand and peat with an eventual return to sand in most instances. The presence of food on both substrates did not influence their preference for sand. However, shrimp will move onto a peat substrate to forage if food is present only there. This observation suggests that, although there is a marked preference for sand, peat is not completely repellent to them. Finally, histological investigations of the shrimp digestive system revealed that peat was ingested with food particles and processed in the gastric mill. There was, however, no discernible discrimination between the two substances during ingestion. Finally, starved shrimp on peat substrate did not ingest peat fibers, suggesting that peat is not perceived as an alternative food source.