Annelid, peracarid crustacean and mollusc macrofauna (>300 μm; 95.7% of macrofaunal individuals) were identified to species or morpho-species level.
Samples were classified as being collected from ‘active’ chemosynthetically-fuelled (13 samples), ‘transition’ (13 samples) or ‘background’ photosynthetically-fuelled (12 samples) environments based on visual indicators of seep. Visual indicators of high seep chemosynthetic activity included high seafloor cover of microbial mats and non-sedimented authigenic carbonates, and high densities of seep-associated megafauna.
Taxonomic and functional biodiversity were quantified using richness (number of species/functional categories), diversity (Shannon Index), and evenness (Pielou’s Index) metrics in R 3.4.2 using the package ‘vegan’. Functional diversity was quantified based on the scoring of taxa for 32 traits in 7 trait groupings. Taxon-specific scores for traits were weighted by taxon abundance and totaled across all taxa present per sample, producing a sample (rows) by trait abundance (columns) matrix.
Standing stock (macrofaunal wet biomass per sample) was measured to 0.00001 g using an electronic balance (A&D GR-202). Excess liquid was wicked from specimens using paper tissue, and sample weights were recorded following a standardised two-minute period after removal from preservative. Faunal density was calculated as the total number of polychaete, peracarid crustacean and mollusc individuals per 64.3 cm2 sample (two cores, each with a surface area of 32.17 cm2), multiplied by 155.42 to express this as number of individuals per m2. Average individual body size (biomass) per sample was calculated by dividing sample biomass by macrofaunal abundance.
Values stated are for combined sample consisting of two push cores collected adjacent to each other.
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