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Faunal Bed (Biotic Class)

Component: Biotic

Unique Identifier: 391

Biotic Setting Benthic/Attached Biota
Biotic Class Faunal Bed
Biotic Subclass Attached Fauna
Soft Sediment Fauna
Inferred Fauna

Definition Seabeds dominated or characterized by a cover of animals that are closely associated with the bottom, including attached, clinging, sessile, infaunal, burrowing, laying, interstitial, and slow-moving animals, but not animals that have created substrate (Reef Biota). Unlike Reef Biota, Faunal Bed biota cannot (or are not sufficiently abundant to) construct identifiable substrate. "Slow-moving" animals included in the Faunal Bed class are defined as being incapable of moving outside the boundaries of the classification unit within one day. Faunal Bed organisms are aquatic, but they may be able to withstand periods of exposure to air.

Faunal Bed food webs may receive basic trophic inputs from benthic photosynthesis or chemosynthesis, plankton, allochthonous detritus and debris, or other sources. In nature, Faunal Bed habitats are often composed of complex mixes and associations of animals of different phyla, sizes, feeding strategies, and habits, and these areas can be difficult to classify. Faunal Bed classifications are determined in CMECS by greatest percent cover of fauna or faunal structures, or (particularly for infauna) by estimates of greatest biomass. The inherent complexity of these areas is addressed through Co-occurring Elements and Associated Taxa Modifiers (Sections 10.6.2 and 10.3.1).

In the photic zone, primary producers often constitute the greatest biotic percent cover of substrate, and so define the biotic group of an area (e.g., Filamentous Algal Bed, Microphytobenthos). Faunal Bed organisms, when present in these areas, are classified in CMECS as Co-occurring Elements, for example: "Biotic Group: Coralline/Crustose Algal Bed with Co-occurring Element: Strongylocentrotus purpurata".

In waters deeper than the photic zone, however, most Faunal Bed biotic groups and communities are defined by immobile or slow-moving suspension-feeders and detritivores that dominate percent cover or biomass, and create a distinct living environment for other fauna. Other Faunal Bed biotic groups and communities are defined by slow-moving grazers or predators (e.g., urchins, starfish), when these are the clearly dominant fauna. However, practitioners should attempt to identify a biotic group that is providing "forage" for these predatory or herbivorous species. If a "forage" biotope is present, it will often dominate percent cover, and practitioners should characterize the area accordingly as (for example): "Biotic Community: Nassariid Bed with Co-occurring Element: Pisaster". The Co-occurring Elements modifier (see Section 10.6.2) is used to describe areas where any two (or more) biotic groups, biotic communities, or other biotic classification units described in CMECS occur simultaneously. In these cases, the classification units exist together, as a mix, in a single location, and the non-dominant units are termed Co-occurring Elements. Further local research may indicate that the mix of biotic groups and co-occurring elements is, in fact, a repeatable unit that should be designated as a single defined biotic group or biotope.

Other common animals in seafloor environments include opportunistic predators or herbivores that are capable of moving outside the bounds of the classification unit within one day, such as portunid crabs, cancrid crabs, horseshoe crabs, cephalopods, other mobile benthic crustaceans, fishes, and other nekton. These animals actively move over the seafloor searching for prey, and are defined in CMECS as Associated Taxa (see Section 10.3.1).

As in other BC classes, practitioners may apply Genus and/or species names to define local biotic communities that are not listed in the current version of CMECS. In these cases, observations in the field must verify that these new biotic communities are predictable and repeating aggregations or assemblages of dominant or characteristic species. These names should be submitted as part of the CMECS Dynamic Content Standard (see Section 13).

Faunal Beds are highly dependent on substrate type. Individual species and entire biotic communities have adapted specialized anatomies and behaviors for survival on hard substrates; other species and communities have specialized and developed adaptations for life on soft substrates. Generalist fauna also occur (e.g., certain holothurians, crustaceans, and sponges) that can succeed on both substrate types. However, substrate type is such a defining aspect of the Faunal Bed class that CMECS Faunal Bed subclasses are assigned as physical-biological associations involving both biota and substrate.

The Faunal Bed class is arranged into two major subclasses: Attached Fauna, and Soft Sediment Fauna. Each subclass presents alphabetized biotic groups that are defined by ecological characteristics, followed by alphabetized biotic groups that are defined by taxonomic characteristics. Within biotic groups and communities, the term "Bed" is used to identify soft sediment faunal areas.