Improving the estimation of deep-sea megabenthos biomass: dimension to wet weight conversions for abyssal invertebrates

Abstract

Deep-sea megafaunal biomass has typically been assessed by sampling with benthic sledges and trawls, but non-destructive methods, particularly photography, are becoming increasingly common. Estimation of individual wet weight in seabed photographs has been achieved using equations obtained from measured trawl-caught specimens for a limited number of taxa. However, a lack of appropriate conversion factors has limited estimation across taxa encompassing whole communities. Here we compile relationships between measured body dimensions and preserved wet weights for a comprehensive catalogue of abyssal epibenthic megafauna, using 47 000 specimens from the Porcupine Abyssal Plain (NE Atlantic) housed in the Discovery Collections (National Oceanography Centre, Southampton, UK). The practical application of the method is demonstrated using an extremely large dataset of specimen measurements from seabed photographs taken in the same location. We also collate corresponding field data on fresh wet weight, to estimate the impact of fixation in formalin and preservation in industrial denatured alcohol on the apparent biomass. Taxa with substantial proportions of soft tissues lose 35 to 60% of their wet weight during preservation, while those with greater proportions of hard tissues lose 10 to 20%. Our total estimated fresh wet weight biomass of holothurians and cnidarians in the photo graphic survey was ~20 times the previous estimates of total invertebrate biomass based on trawl catches. This dramatic uplift in megabenthic biomass has significant implications for studies of standing stocks, community metabolism, and numerical modelling of benthic carbon flows.

Monitoring mosaic biotopes in a marine conservation zone by autonomous underwater vehicle

“…Data from AUVs can improve the quantification of conservation metrics (Durden et al. ) and may be of particular value in habitats where remote sampling methods are ineffective, such as reef or rock habitats (Tolimieri et al. ).…”

“…They offer rapid, nondestructive data collection, access to a wide range of habitats, and reduced survey costs (Wynn et al 2014). Data from AUVs can improve the quantification of conservation metrics (Durden et al 2016a) and may be of particular value in habitats where remote sampling methods are ineffective, such as reef or rock habitats (Tolimieri et al 2008).…”

Abyssal deposit‐feeding rates consistent with the metabolic theory of ecology

“…An additional species‐specific relationship was developed for A. abyssorum (preserved wet mass [g] = 0.0002 × length [mm] 2.57 , R 2 = 0.94; converted to fresh wet mass using Durden et al. ). Where such conversions were not available, individual fresh wet masses were estimated as follows: (1) echinoid test volume was calculated as a regular tetrahedron, tissue volume estimated as 25% of test volume (Ebert ), and converted to fresh mass assuming a density of 1 g/cm 3 ; (2) enteropneust fresh wet mass was estimated from body width and mean body length (from Smith et al.…”

“…100, No. 1 fresh wet mass using Durden et al [2016]). Where such conversions were not available, individual fresh wet masses were estimated as follows:…”

“…(2) enteropneust fresh wet mass was estimated from body width and mean body length (from Smith et al 2005), and computed using the body geometry method of Jones et al (2013); and (3) echiuran fresh wet mass was estimated as the geometric mean of trawl-caught specimen preserved wet mass, converted to fresh wet mass (per Durden et al 2016). Ingestion was estimated by taxon (t) and site (x) as I tx = R tx S t DC x , where I is ingestion rate (mg C/h), R is the geometric mean tracking rate (cm 2 /h), S is the sediment thickness ingested (cm), D is the sediment bulk density (g dry mass/cm 3 ), and C is site-specific sediment organic carbon content (mg C/g).…”