Aquatic ecology and Biodiversity

Unit 12- Biodiversity and conservation

Practicals 2- Study of macrobenthic organisms
Experiment No. 2
Benthic organisms
• Macrobenthos
• Meiobenthos
• Microbenthos
Macrobenthos
Macrobenthos comprises the burrowing fauna (Infauna) of sediments and the surface living fauna (Epifauna) of both rocky and sediment grounds, together with associated bottom living fish and crustaceans. Meiobenthos consists mainly the small metazoans – nematodes, herpecticoid copepods, turbellariona, gastrotrichas, larvae of bivalves, gastropods, polychaetes. While the smallest forms – ciliate protozoans, other protozoans and organisms of bacteria size – are grouped as microbenthos. The remaining benthic organisms – polybenthos – are primary producers, comprising macroalage and unicellular living plants.
Collection of macro benthos
Sampling of macro fauna
A wide variety of grab samples are available for quantitative sampling of soft bottoms. For general purpose, Day grab is recommended, as it is simple and reliable on a wide variety of sediment types is lowered on a wire rope with the help of winches on board in opened condition. It penetrates the bottom sediment with its gravity, and closed which hauled by wire cables attached to the bucket arms. The grab is emptied into the sieving table for sorting. For collection of the larger encrusting epifaunal species, a rectangular framed natural dredge is adequate on hard rocky bottom.
Sampling at Muddy and Sandy Shore
The most usual method of macrofauna and flora sampling is by pushing a 0.1m² or 0.25m² wooden or steel frame to a depth of 30cm, into the sediment, within the frame. Sediment is excavated to the desired depth (15cm). Plastic or metal tubes (0.1m²) are also used to take an undisturbed core of sediment (10cm) from beaches.
Sampling at rocky shores
A square frame of heavy gauge wire laid on the substratum or marked, the animals within the frame being hand picked, counted, weighed, identified and transported to laboratory. For larger organisms, a frame of 0.25m² is suitable.
Preservation of benthic organisms
After initial sieving and sorting of animals samples are preserved. Add 10% solution of 40% formaldehyde (2.5 to 5% buffered formalin is used for storage). 10% of dowacil – 100 solution or 70% ethenal with 5% glycerine are also used for storage.
Sorting of macrofauna
Grab sample is emptied on a wooden or metal lined sieving table or hopper and the contents are washed through a series of sieve baskets (16,2 and 0.5mm mesh) using a jet of water. Each sieve basket is washed and agitaed to separate three size class of organisms. Each size class is transferred to a container for fixation and transferred to laboratory
Sorting
Each size class sampler are transferred into a glass tray below which black or white material is inserted to provide varying background for distinguishing animals from debris. Larger individuals are hand sorted. For smaller individuals, divide the sample into fractions by agitating the light materials into suspension and pouring it through a fine sieve and collect. Add vital stains (rose Bengal, rodamine B, casin etc) to facilitate sorting for samples containing large quantities of detritus.