Marine/freshwater fauna that lives in or on the seafloor can be sampled in a number of ways using a number of different sampling devices.
Grab Sampler: Subtidal muds and soft sediments can be sampled using a grab sampler. A grab consists of a set of jaws that shut when lowered into the surface of the bottom sediment. The grab is deployed from the survey vessel and when lowered to the sediment, it will close automatically when lifted. The grab takes a ‘bite’ out of the seafloor. When the grab is returned to the vessel, the sediment is washed on the required size sieve and all fauna returns are preserved for later processing and identification.
Corer: Corers allow the retrieval of sediment cores from the seabed as opposed to ‘bites’ from the grab sampler. The corer is lowered to the seabed and by lowering a cyclindrical metal tube into the seafloor a sediment sample can be taken. In the marine environment, corers are typically used to obtain sediment samples for geological characterisations and dating or to investigate the historical input of contaminants to aquatic systems or to characterise the depth of contamination at a site. In the intertidal environment, hand-held corers are used to obtain faunal samples from along the seashore. The returned faunal samples are preserved for later processing and identification.
Dredge: Dredges are used for sampling hard bottoms such as sands, gravels and clays. A grab or corer would not be able to penetrate these hard sediments. A dredge is towed from a vessel. A the dredge moves along the seafloor, its heavy metal frame scrapes the upper layers of the seafloor, disturbing the fauna living there. This fauna is then retained in the net that is attached to the metal frame. The returned faunal samples are preserved for later processing and identification.
Trawl: Beam trawling is carried out where investigations of fish species living on the seabed is required. Beam trawling is the simplest method of bottom trawling. The mouth of a net is held open by a solid beam. The ends of the beam are attached to two solid metal plates (shoes), which slide over and disturb the seabed. All disturbed fish and epifaunal species are retained in the net. These faunal samples are preserved for later processing and identification.
Dive: Where water depths allow, some aspects of subtidal sampling can be carried out by divers. AQUAFACT have carried out in excess of 2,000 scientific logged dives in order to sample, assess, photograph and evaluate subtidal, soft bottom and hard bottom, individual species and communities. Faunal samples can be obtained by using hand-held cores. AQUAFACT’s hand-held diver SPI has been used in areas where our standard SPI machine could not gain access (e.g. under fish farms).
Kick Sampling: Kick sampling is carried out in rivers and streams where infaunal species analysis is required. It can only be carried out in water bodies where access on foot is achievable. The purpose of the kick sampling methodology is to dislodge macroinvertebrates attached to the substrata and vegetation of the stream. The kick sampling process should take approximately two minutes:
o A riffled section of the lake/river is chosen as it is likely to contain pollution-sensitive macroinvertebrates due to its higher oxygen content.
o A standard pond net of pore size 500mm is used to recover samples.
o The mouth of the net is positioned in a riffled area facing flow and the substrate disturbed in order to dislodge animal’s in-between stones.
o The acquired samples are placed in clean white buckets along with approximately a litre of stream water. The samples are then returned to the lab where the macroinvertebrates present are removed by hand and identified to genus level where possible.