Marine Benthic Invertebrates Basics

Biologica analyzes marine benthos samples from grabs and cores, as well as offering video and photo analysis of benthic invertebrate communities.
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Organisms living in or on the sediment on the seafloor are called benthos. Marine benthic invertebrate communities are dominated by polychaete annelids, molluscs, crustaceans, and echinoderms, but include members of many lesser known animal phyla. Organisms that live on hard substrates above the sediment are called epibenthos – or epifauna (e.g., barnacles, anemones) and organisms that live in the sediment are called infauna. Most infauna live in the top 4-5cm of sediment, but many taxa can burrow much deeper. Many sedentary benthic organisms have developed specialized structures to collect detritus and other particles through deposit-feeding, suspension-feeding or both. Mobile forms may be voracious predators and scavengers.

Given their relatively stationary existence the community structure of the benthos can reveal localized impacts such as organic pollution or contamination. Some polychaetes in particular, such as the Family Capitellidae, are well-established indicators of organic pollution when they occur in high numbers.

Marine benthic samples are typically collected with a grab sampler that is deployed with a winch. This sediment is screened in the field to reduce the sample volume and allow for sufficient preservation of organisms. Standard screen sizes vary throughout various habitats, but 1.0mm is most common as this captures most adult-sized organisms.

Benthic samples are labour intensive because these require sorting (removal of organisms from sample debris) before identification. Our sorting procedure involves examining the sediment in small portions under a dissecting scope to ensure >95% of organisms are retrieved from the sample debris. Sorting is an important and often-overlooked milestone in taxonomic analysis; after all, if sorting is done poorly or inconsistently, there is no good basis for comparing samples. Samples undergo rigorous quality control to ensure our clients receive reliable data. Our taxonomists are specialists with expertise in annelids, crustaceans, molluscs, and miscellaneous phyla.

For more information on taxonomic analysis of Marine Benthos, please consult our Services page.

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