Finding the needle in the haystack: Comparison of methods for salmon louse enumeration in plankton samples

The economic and social implications of salmon louse (Lepeophtheirus salmonis) epidemics in salmon aquaculture drive focus of the dispersal dynamics of the planktonic larval stages. The vast spatial scale and high connectivity of the marine environment creates difficult conditions to monitor the infective planktonic louse stage, whereby the number of samples required for a representative description is bottlenecked by processing capacity. This study assessed five quantification methods for accuracy and precision in enumeration of lice in plankton samples, validated against the benchmark method of light microscopy. Visual-based (fluorescence microscopy and automated fluid imaging) and molecular-based (droplet digital PCR, quantitative fraction PCR and quantitative PCR) were tested using high- and low-density plankton samples spiked with louse copepodids, with spike numbers blind to assessors. We propose an approach to comparative assessment that uses the collective bias and deviation of a test method to determine whether it is acceptably similar to the benchmark method. Under this framework, no methods passed the comparative test, with only ddPCR comparable to light microscopy (87% mean accuracy and 74% precision). qfPCR and fluorescence microscopy were moderately efficient (88% and 67% accuracy, and 36% and 52% precision respectively). Molecular techniques are currently restricted in distinguishing between larval stages, which is an essential distinction for some research questions, but can be economical in processing numerous samples. Overall method suitability will depend on the research objectives and resources available. These results provide evidence for operational accuracy for the tested methods and highlight the direction for further development to optimize their use

Prey selection of the Red King Crab (Paralithodes camtschaticus) preying on lumpfish eggs (Cyclopterus lumpus), sea urchins (Strongylocentrotus droebachiensis) and scallops (Chlamys islandica)

The red king crab, Paralithodes camtchaticus, is a new generalist predator in the Barents Sea and may have negative effects upon the commercially fished lumpfish eggs (Cyclopterus lumpus), sea urchins (Strongylocentrotus droebachiensis) and scallops (Chlamys islandica). Generalist predators consume an array of prey types, but have been shown to select certain prey over others. To obtain knowledge on how the king crab consume, select and actively select these prey, a laboratory experiment was performed. To detect active selection, the experiment was divided in two parts: first the crabs were given one prey item (no selection) and second they were given all three prey items (selection). Prey organisms consumed was evaluated after 22 hours. There was a significant selection for eggs and scallops and a significant active selection for scallops. The consumption, selection and active selection of prey appeared to be dependent on crab size and availability of alternative prey. With increasing crab size the amount of prey consumed increased and diet composition included a wider array of prey types. Due to the juvenile crabs residence in shallow waters for 5 years until maturation and the adult crabs annual migration to these areas during moulting/spawning, the red king crab predation could have a negative effect on all three prey types

Seasonal and spatial dynamics of meroplankton in a sub-Arctic fjord With additional focus on larvae of the invasive red king crab

Many benthic marine organisms produce pelagic larvae, meroplankton, which spend from hours to months in the pelagic. During this time, they form an important part of the pelagic community. Few studies have focused on the year round dynamics of meroplankton, thus many aspects of meroplankton dynamics remains unknown at high-latitudes. In the 1960s the red king crab was intentionally introduced into Russian waters and now serves as an important resource for Norway and Russia while at the same time posing a threat to the ecosystem. Currently there is no knowledge on when and where larvae are released in Norwegian waters. The objectives of this thesis were to increase our understanding on the seasonal and spatial dynamics of meroplankton at high-latitudes, identify environmental variables responsible for spawning and the potential role of meroplankton in the pelagic. The temporal and spatial dynamics of red king crab larvae was also investigated. Sampling monthly to bi-monthly over a 1.5-years in Porsangerfjord, Norway, showed that meroplankton abundance and assemblage separate into different seasonal communities. The highest abundance and greatest number of taxa occurs in spring and summer, correlating with increased chlorophyll a and temperature. Numerically, meroplankton contributed highly to the mesozooplankton community these seasons, suggesting that they are an important component of the pelagic food web. In spring, different meroplankton assemblages were found along the fjord and correlated with temperature and chlorophyll a. This provides evidence that larval release by benthic invertebrates is coupled with variations in these environmental variables. In a warming ocean this coupling could cause a shift in reproductive phenology and a range expansion of benthic organisms. Larvae of the red king crab were continually released over a period of six months and the greatest densities of larvae was found at protected stations. Having a prolonged larval release is advantageous for this invasive species as it ensures some larvae coincides with favorable conditions. These findings coupled with a wide tolerance to environments as larvae and adults means that they have the potential to continue their expansion in Norway and north into Svalbard waters

Environmental impacts of the diver operated C disc to harvest sea urchins and for kelp restoration

NIVA did a 2-day environmental evaluation of the diver operated suction device “C disc” constructed by C robotics. Because the C disc uses suction from a water pump to suck sea urchins from the seafloor, it will collect bycatch and may have some harmful effects on the seafloor. It can also be used for kelp restoration in northern-Norway. This survey tested the C disc at two sea urchin barren grounds around Tromsø (Ytre Kårvika, Kvalsundet and Berg, Balsfjord) in May 2021. Analysis of catch efficiency on target sea urchins, bycatch and effects on the sea floor using video transects and frame counts was done at both sites. About 81 – 89 % of the catch consisted of the target species sea urchins and the CPUE was on average 78 ind./min (61 – 96 ind./min). Of these 11 % were damaged by the C disc. Bycatch accounted for 11 and 19 % of the catch and reflected the local community consisting of mainly larger loose sitting organisms. There was little to no damage observed on bycatch organisms, except for barnacle and blue mussels. There was a reduction in loosely fastened organisms after using the C disc, and the most impacted organisms reflected the bycatch. If the bycatch is kept in sea water and returned to sea soon after capture, they are likely to survive. The survey is only representative for hardbottom sea urchin barrens in northern-Norway

Environmental impacts of the diver operated C disc to harvest sea urchins and for kelp restoration

Project Manager Helena Kling MichelsenNIVA did a 2-day environmental evaluation of the diver operated suction device “C disc” constructed by C robotics. Because the C disc uses suction from a water pump to suck sea urchins from the seafloor, it will collect bycatch and may have some harmful effects on the seafloor. It can also be used for kelp restoration in northern-Norway. This survey tested the C disc at two sea urchin barren grounds around Tromsø (Ytre Kårvika, Kvalsundet and Berg, Balsfjord) in May 2021. Analysis of catch efficiency on target sea urchins, bycatch and effects on the sea floor using video transects and frame counts was done at both sites. About 81 – 89 % of the catch consisted of the target species sea urchins and the CPUE was on average 78 ind./min (61 – 96 ind./min). Of these 11 % were damaged by the C disc. Bycatch accounted for 11 and 19 % of the catch and reflected the local community consisting of mainly larger loose sitting organisms. There was little to no damage observed on bycatch organisms, except for barnacle and blue mussels. There was a reduction in loosely fastened organisms after using the C disc, and the most impacted organisms reflected the bycatch. If the bycatch is kept in sea water and returned to sea soon after capture, they are likely to survive. The survey is only representative for hardbottom sea urchin barrens in northern-Norway.publishedVersio

Temporal and spatial dynamics of the invasive red king crab and native brachyuran and anomuran larvae in Norwegian waters

This study investigates the temporal and spatial patterns of larval stages of the invasive red king crab Paralithodes camtschaticus (RKC) and co-existing native brachyurans and anomurans in a Norwegian fjord. It is one of few field studies describing the larval stage of native and invasive brachyurans and anomurans in the southern Barents Sea. Larvae were collected at 6 to 18 stations at roughly 1 to 2 mo intervals over a 1.5-yr period. To help explain timing in hatch of RKC larvae, the reproductive state of females was determined. The first larval stage of RKC was found in higher abundances in shallow bays, reflecting the spawning migrations of reproducing females. RKC was the first species among anomurans and brachyurans to release their larvae in Norwegian waters, and due to an extended larval release (January-May) their larvae occurred for the longest period of time in the water column. The native boreo-Arctic Pagurus pubescens and Hyas araneus released their larvae early in the year, starting in March. In contrast, larvae of the native boreal Pagurus bernhardus, Hyas coarctatus and Munida sp. were observed later in spring and summer. The combination of protracted hatching, high fecundity and high adult abundance of RKC are likely strong contributing factors to the species’ successful establishment in the southern Barents Sea and could favour the dispersal of RKC south along the Norwegian coast and potentially north into Arctic shelf areas

Seasonal dynamics of meroplankton in a high-latitude fjord

Knowledge on the seasonal timing and composition of pelagic larvae of many benthic invertebrates, referred to as meroplankton, is limited for high-latitude fjords and coastal areas. We investigated the seasonal dynamics of meroplankton in the sub-Arctic Porsangerfjord (70°N), Norway, by examining their seasonal changes in relation to temperature, chlorophyll a and salinity. Samples were collected at two stations between February 2013 and August 2014. We identified 41 meroplanktonic taxa belonging to eight phyla. Multivariate analysis indicated different meroplankton compositions in winter, spring, early summer and late summer. More larvae appeared during spring and summer, forming two peaks in meroplankton abundance. The spring peak was dominated by cirripede nauplii, and late summer peak was dominated by bivalve veligers. Moreover, spring meroplankton were the dominant component in the zooplankton community this season. In winter, low abundances and few meroplanktonic taxa were observed. Timing for a majority of meroplankton correlated with primary production and temperature. The presence of meroplankton in the water column through the whole year and at times dominant in the zooplankton community, suggests that they, in addition to being important for benthic recruitment, may play a role in the pelagic ecosystem as grazers on phytoplankton and as prey for other organisms

Spatial patterns of spring meroplankton along environmental gradients in a sub-Arctic fjord

The spatial patterns in abundance and composition of benthic invertebrate larvae (meroplankton), the correlation between these patterns and environmental variables (temperature, salinity and chl a) and the relative abundance of meroplankton in the mesozooplankton community were investigated in the sub-Arctic Porsangerfjord, Norway (70° N). Zooplankton samples and CTD-profiles were collected at 17 stations along the fjord in April 2013. A total of 32 morphologically different larval types belonging to 8 phyla were identified. Meroplankton were found at all stations, and their community and abundance differed significantly along the fjord. Meroplankton abundance in the inner and outer parts of the fjord was low and was dominated by Gastropoda and Echinodermata. The greatest numbers were recorded in shallow bays and the middle part of the fjord where Cirripedia and Polychaeta were dominant. Meroplankton contributed significantly to the mesozooplankton community in the bays (30 to 90%) and mid-fjord (13 to 48%) areas. These changes in community structure were attributed to spatial gradients in environmental variables such as chl a, salinity and temperature. The different communities suggested a seasonal succession in reproductive events from the fjord mouth toward the head. Considering that spring is an important season for reproduction in pelagic organisms, meroplankton may play a role in the pelagic ecosystem of high-latitude fjords as grazers and prey. Furthermore, the spatial dynamics and reproductive timing of benthic and holoplanktonic organisms are sensitive to local hydrographical features, illustrating their sensitivity to changing environments

Finding the needle in the haystack: Comparison of methods for salmon louse enumeration in plankton samples

The economic and social implications of salmon louse (Lepeophtheirus salmonis) epidemics in salmon aquaculture drive focus of the dispersal dynamics of the planktonic larval stages. The vast spatial scale and high connectivity of the marine environment creates difficult conditions to monitor the infective planktonic louse stage, whereby the number of samples required for a representative description is bottlenecked by processing capacity. This study assessed five quantification methods for accuracy and precision in enumeration of lice in plankton samples, validated against the benchmark method of light microscopy. Visual-based (fluorescence microscopy and automated fluid imaging) and molecular-based (droplet digital PCR, quantitative fraction PCR and quantitative PCR) were tested using high- and low-density plankton samples spiked with louse copepodids, with spike numbers blind to assessors. We propose an approach to comparative assessment that uses the collective bias and deviation of a test method to determine whether it is acceptably similar to the benchmark method. Under this framework, no methods passed the comparative test, with only ddPCR comparable to light microscopy (87% mean accuracy and 74% precision). qfPCR and fluorescence microscopy were moderately efficient (88% and 67% accuracy, and 36% and 52% precision respectively). Molecular techniques are currently restricted in distinguishing between larval stages, which is an essential distinction for some research questions, but can be economical in processing numerous samples. Overall method suitability will depend on the research objectives and resources available. These results provide evidence for operational accuracy for the tested methods and highlight the direction for further development to optimize their use

Finding the needle in the haystack: Comparison of methods for salmon louse enumeration in plankton samples

The economic and social implications of salmon louse (Lepeophtheirus salmonis) epidemics in salmon aquaculture drive focus of the dispersal dynamics of the planktonic larval stages. The vast spatial scale and high connectivity of the marine environment creates difficult conditions to monitor the infective planktonic louse stage, whereby the number of samples required for a representative description is bottlenecked by processing capacity. This study assessed five quantification methods for accuracy and precision in enumeration of lice in plankton samples, validated against the benchmark method of light microscopy. Visual-based (fluorescence microscopy and automated fluid imaging) and molecular-based (droplet digital PCR, quantitative fraction PCR and quantitative PCR) were tested using high- and low-density plankton samples spiked with louse copepodids, with spike numbers blind to assessors. We propose an approach to comparative assessment that uses the collective bias and deviation of a test method to determine whether it is acceptably similar to the benchmark method. Under this framework, no methods passed the comparative test, with only ddPCR comparable to light microscopy (87% mean accuracy and 74% precision). qfPCR and fluorescence microscopy were moderately efficient (88% and 67% accuracy, and 36% and 52% precision respectively). Molecular techniques are currently restricted in distinguishing between larval stages, which is an essential distinction for some research questions, but can be economical in processing numerous samples. Overall method suitability will depend on the research objectives and resources available. These results provide evidence for operational accuracy for the tested methods and highlight the direction for further development to optimize their use