|Stormy part ii – a sequel flume study. Finding the connection between the burrowing capacity and body size for C. Edule & R. Philippinarium at low temperature|
Teeuw, L. (2020). Stormy part ii – a sequel flume study. Finding the connection between the burrowing capacity and body size for C. Edule & R. Philippinarium at low temperature. BSc Thesis. NIOZ Royal Netherlands Institute for Sea Research: Yerseke. 36 pp.
As a result of climate change, storms occur with higher frequency and higher intensity during winters in the Netherlands. The sediment erosion on tidal areas during these storms might have an impact on coastal macro-benthic ecosystems. This study aims to understand how different bivalve populations are influenced by winter storms in tidal areas. To study the effect of sediment erosion on benthic species, the STORMY flume was built at the royal Netherlands Institute of Sea Research (NIOZ). During a pilot study (A. Slabon 2019), the flume was tested and the burrowing capacity during erosion events of a group of Cerastoderma edule (the common cockle) was determined for several sediment types. A follow-up study was recommended to determine the relation between the individual size and burrowing capacity of burrowing bivalves. Furthermore, as more erosion events like storms occur during autumn and winter, when benthic organisms are expected to be less active, the experiments from the pilot study needed to be repeated with a water temperature of 6 °C. An extra cooling system was built to cool the STORMY flume water down to 6 °C. Next, the burrowing capacity at sediment erosion speeds of 5,3 10,6 and 15,9 cm h-1 was determined for burrowing bivalve species Cerastoderma edule & Ruditapes philippinarum in a sediment type with high erodibility and an average grain size of 246 μm. The burrowing capacity was compared between two categories of individual body size and between species. C. edule was found to be able to keep up with higher erosion rates than R. philippinarum. At a sediment erosion rate of 5,3 cm h-1, 100% of C edule stayed burrowed, whereas only 40% of R. philippinarum managed to stay burrowed. At sediment erosion rates of 10,6 and 15,9 cm h-1, all R. philippinarum were dislodged, while the majority of the individuals of C. edule still managed to stay burrowed. Besides their burrowing capacity, a difference in behavior was found between the two species. While R. philippinarum showed very little burrowing activity, no individuals were carried away by the water current once dislodged from the sediment. Contrarily, C. edule was immediately displaced by the water current, as soon as it was dislodged from the sediment. So, both species seem to withstand high sediment erosion rates such as during storms in their own way. In extreme cases however, R. philippinarum falls vulnerable to predators and C. edule will be dragged away by the current, impairing their chances for survival.