Comparison of the particle size distributions of sediment collected from sandy seafloor using a Van Veen grab and cone dredge

Abstract

Sediment particle size is an important environmental parameter that influences benthic species composition and is frequently used in habitat and ecosystem classification systems. In South Africa, benthic grabs are regularly used to collect seafloor sediment samples for particle size analysis. However, grab sample failures are a common, time-consuming and costly exercise, particularly in deep-sea work. This study compares replicate sediment samples collected using a custom-designed cone dredge and a conventional Van Veen grab, deployed at nine stations, ranging from 355 to 508 m in depth, in the Southern Benguela Sandy Shelf Edge ecosystem off the west coast of South Africa. No significant differences were detected between sediment properties of the samples collected by the different devices (all grain size categories [particles <3.9 to >2 000 μm]: D = 0.101, p = 0.693; fine grain size categories [particles ≤63 μm]: D = 0.177, p = 0.480). This finding suggests that, despite its different mode of operation, the cone dredge collected an appropriate sediment sample for a particle size analysis of this ecosystem, and thus the device might be usefully applied in other areas of a similar nature. The cone dredge can be considered a cost-effective and efficient alternative for sampling seafloor sediment at depth. However, further comparative analyses are required for different substrates and ecosystem types.