Undersøkelser av sedimentsamfunn offshore – sammenlignende kvantitativ utprøving av 0,1 m² vs. 0,25 m² van Veen grabb

På bakgrunn av mulig bruk av Mareanos faunadata som bakgrunnsreferanse ved petroleumsindustriens forurensningsovervåking rundt offshore-installasjoner på norsk sokkel, er det utført en sammenlignende kvantitativ undersøkelse av fangstegenskapene for van Veen grabb med innsamlet bunnareal på henholdsvis 0,25 m² som hittil er benyttet av Mareano, og 0,1 m² som benyttes av petroleumsindustrien grunnere enn 500 m. Undersøkelsen ble utført på fire upåvirkede lokaliteter fra 287 til 963 m dyp, der det ble samlet inn sedimentfauna fra 1,0 m2 bunnareal pr. grabbstørrelse. Det er ikke funnet entydige statistisk signifikante forskjeller i faunasammensetningen mellom de to grabbstørrelsene. For standard offshore prøvetatt bunnareal på 0,5 m2 indikerer ikkesignifikante multivariate statistiske resultater forskjeller i faunasammensetning på 32–39 % på de respektive lokalitetene, hvorav inntil 6 % utgjør forskjeller mellom liten og stor grabb (Bray-Curtis ulikhet). For kvalitativ artsfangst (antall taksa) er forskjellen mellom grabbstørrelsene ved 0,5 m² prøvetatt areal 7–10 %, der liten grabb samlet inn høyest prosentandel på tre av fire lokaliteter. Både for liten og stor grabb er antall taksa innsamlet ved 0,5 m² prøvetatt areal mindre enn 60 % av totalt antall innsamlede taksa på de respektive lokalitetene (2 m2 pr. lokalitet).publishedVersio

Fauna analyses of a possible electrical cable corridor in the Hardanger fjord

In relation to a possible cable pathway on the sea floor through the inner half of the Hardanger fjord, the Institute for Marine Research has carried out ROV inspections of the benthic faunal communities along 17 selected bottom transects. The surveyed area was restricted to the inner half of the Hardanger fjord – from Sima to Norheimsund in the period 9–29 November 2010. The deep horizontal seabed along the midline of the investigated part of the fjord was dominated by the crustacean Munida sp and its borrow, the sea cucumbers Bathyplotes sp and Stichopous sp, sea-pens, and the echiuran Bonellia sp. The steep walls along the sides of the investigated fjord were populated with less abundant but still relatively frequently-occurring taxa such the sea star Brisingia sp, the large bivalve Acesta sp, and several species of sponges. Though any local recovery time is unknown, we do not consider these populations to be threatened by the possible cable-laying activities. These are not listed in the Norwegian redlist and are not considered as threatened by the OSPAR Convention. However, in the outer part of the investigated area (transects named Kvamsøy cliff wall and Øystese), the vulnerable corals Lophelia pertusa and Anthomastus grandiflorus (redlisted) and Primnoa sp were observed. To avoid threatening impacts to these groups of corals, we therefore recommend using video monitoring during any cable-laying activities

Fauna analyses of a possible electrical cable corridor in the Hardanger fjord

In relation to a possible cable pathway on the sea floor through the inner half of the Hardanger fjord, the Institute for Marine Research has carried out ROV inspections of the benthic faunal communities along 17 selected bottom transects. The surveyed area was restricted to the inner half of the Hardanger fjord – from Sima to Norheimsund in the period 9–29 November 2010. The deep horizontal seabed along the midline of the investigated part of the fjord was dominated by the crustacean Munida sp and its borrow, the sea cucumbers Bathyplotes sp and Stichopous sp, sea-pens, and the echiuran Bonellia sp. The steep walls along the sides of the investigated fjord were populated with less abundant but still relatively frequently-occurring taxa such the sea star Brisingia sp, the large bivalve Acesta sp, and several species of sponges. Though any local recovery time is unknown, we do not consider these populations to be threatened by the possible cable-laying activities. These are not listed in the Norwegian redlist and are not considered as threatened by the OSPAR Convention. However, in the outer part of the investigated area (transects named Kvamsøy cliff wall and Øystese), the vulnerable corals Lophelia pertusa and Anthomastus grandiflorus (redlisted) and Primnoa sp were observed. To avoid threatening impacts to these groups of corals, we therefore recommend using video monitoring during any cable-laying activities

Infaunal and epifaunal secondary production in the Barents Sea, with focus on snow crab (Chionoecetes opilio) prey resources and consumption

Since the first observation of snow crab (Chionoecetes opilio) in the Barents Sea in 1996, the population has increased significantly, supporting a commercial fishery on the Norwegian shelf since 2012. To investigate whether the availability of benthic prey organisms may support a continued geographical snow crab expansion, benthic invertebrate production was studied across the central parts of the Barents Sea and around Svalbard, where snow crabs are currently absent or at low densities. Annual productivity (P/B ratio) from 66 stations collected by grab and beam trawl was estimated using a multiparameter artificial neural network model. Mean infaunal productivity and production were 0.43 yr−1 and 38.4 g ww m−2 yr−1, respectively, while the epifaunal production was considerably lower with 2.5 g ww m−2 yr−1. The proportions of epi- and infaunal production suitable as prey for snow crab were 98 and 96%, respectively. Areas close to the Polar Front represent the most attractive snow crab foraging region, having the highest benthic secondary production, high estimated primary production, and bottom water temperatures within the snow crab’s preferences. At snow crab densities of 12800 ind. km−2, high enough to support commercial fishing, their mean consumption rate was estimated to be around 1.5 g ww m−2 yr−1, which amounts to 4% of mean infaunal prey production. Food availability is, therefore, not expected to be a hindrance to further population expansion of the snow crab in the Barents Sea.publishedVersio

Benthic invertebrates in Svalbard fjords—when metabarcoding does not outperform traditional biodiversity assessment

To protect and restore ecosystems and biodiversity is one of the 10 challenges identified by the United Nations’s Decade of the Ocean Science. In this study we used eDNA from sediments collected in two fjords of the Svalbard archipelago and compared the taxonomic composition with traditional methods through metabarcoding, targeting mitochondrial CO1, to survey benthos. Clustering of 21.6 mill sequence reads with a d value of 13 in swarm, returned about 25 K OTU reads. An identification search with the BOLD database returned 12,000 taxonomy annotated sequences spanning a similarity range of 50% to 100%. Using an acceptance filter of minimum 90% similarity to the CO1 reference sequence, we found that 74% of the ca 100 taxon identified sequence reads were Polychaeta and 22% Nematoda. Relatively few other benthic invertebrate species were detected. Many of the identified sequence reads were extra-organismal DNA from terrestrial, planktonic, and photic zone sources. For the species rich Polychaeta, we found that, on average, only 20.6% of the species identified from morphology were also detected with DNA. This discrepancy was not due to missing reference sequences in the search database, because 90–100% (mean 96.7%) of the visually identified species at each station were represented with barcodes in Boldsystems. The volume of DNA samples is small compared with the volume searched in visual sorting, and the replicate DNA-samples in sum covered only about 2% of the surface area of a grab. This may considerably reduce the detection rate of species that are not uniformly distributed in the sediments. Along with PCR amplification bias and primer mismatch, this may be an important reason for the limited congruence of species identified with the two approaches. However, metabarcoding also identified 69 additional species that are usually overlooked in visual sample sorting, demonstrating how metabarcoding can complement traditional methodology by detecting additional, less conspicuous groups of organisms.publishedVersio

Does grab size influence sampled macrofauna composition? A test conducted on deep-sea communities in the northeast Atlantic

In deep-sea surveys, heavy gears are often preferred to effectively collect macro benthos while smaller samplers are sufficient in coastal and shallow areas. However, there are few comparative studies of the samples retained and results gained from different-sized grabs. To study the differences in sampling properties between a small (sampling area of 0.1 m2) and a large (0.25 m2) van Veen grab, 1 m2 of seafloor was sampled with each of the grab sizes at four test sites in the Barents- and Norwegian Sea; one inside a fjord and three offshore, across a depth range of 287–963 m. Overall, the small and large grab collected a comparable number of species and individuals: 248 and 233 species, and 6074 and 6143 individuals, respectively. The large grab retrieved the most species at the deepest location while the small grab collected more species at the other test sites. Based on internationally recommended 0.5 m2 sampling units, a variation in the total species richness per test site of 7–13% was found while the diversity indices (ES100 and H′) varied by less than 10%. Independent of grab size, a cluster and nMDS analysis showed four clearly separated sample-groups that correspond to the four test stations although the multivariate dispersion was consistently higher for the small grab. A SIMPROF test showed no grab size-dependent differences. ANOSIM and PERMANOVA tests showed differences between grab sizes for the deepest station, where a similar difference occurred also between samples of the same grab size. This station displayed the least faunal heterogeneity, indicating that faunal patchiness may influence any grab-size differences. The results indicate that the two van Veen grabs tested deliver comparable quantitative faunal compositions. For the small grab, however, numerous samples were rejected due to poor performance, resulting in increased sampling time, ship costs and a suggested biased sampling towards less heterogeneous sediments at the fjord site