Grabs and box corers have been used successfully to monitor changes in benthic environments over time (Maurer et al. 1993, Ruso et al. 2007, Frid 2011, Clare et al. 2015), although the challenge of revisiting sites mean that multiple samples across a representative area of a given habitat type may be necessary to detect trends (Morrisey et al. 1992a,b, Rogers et al. 2008, Spencer et al. 2011). In addition, repeated sampling using grabs and corers in the same area may result in habitat disturbance and associated statistical artefacts (Skilleter 1996). Grabs and corers can also provide species inventories or biodiversity assessments which can then be applied to a monitoring program as baseline data or to inform the interpretation of imagery (Przeslawski et al. 2013). In this way, they are similar to sleds and trawls, but grabs and corers sample a much smaller spatial area (< 1 m2, often considered a point location) rather than the hundreds of square metres often traversed by a sled. This characteristic needs to be considered in environments of low faunal abundance (e.g. some deep sea areas) or high heterogeneity.
In addition to their collection of fauna, grabs and corers are also useful to marine monitoring for their ability to characterise substrate and provide environmental baseline data. For example, EMODNet has harmonised data from disparate sediment samples to produce classification schemes at regional and national scales (Kaskela et al. 2019).
However, because they are a point location, grab and box corer sampling is a very effective method for quantifying heterogeneity at a range of spatial scales (i.e. within- and between-site heterogeneity), as long as the GPS position for each ‘drop’ is recorded and the sampling area is constrained for comparability of analysis (replicate samples are all collected within a standardised distance from the target position at every site).