In a squeeze: Epibiosis may affect the distribution of kelp forests

The processes limiting the population recovery of the kelp Saccharina latissima after recent large‐scale loss from the south coast of Norway are poorly understood. Previous investigations do, however, suggest that the impacts of biotic interactions (epibiosis and competition) and increased water turbidity are important. We investigated the depth‐related patterns of growth, epibiosis, and mortality in two sample populations of kelp, from the south and the southwest coast of Norway. The investigations were performed over a period of seven months, in a crossed translocational study, where kelps were mounted on rigs at six depths (1, 3, 6, 9, 15, and 24 m). In a second experiment, the amounts of light blocked by different epibiont layers growing on the kelp frond were investigated. While growth decreased with depth in spring and summer, the kelp grew faster at 15 m than at shallower depths in fall. Survival was low both in shallow water and below 15 m depth. Epibionts covered the kelp growing at depths from 1 to 9 m, and the laboratory study showed that the coverage may have deprived the individuals of as much as 90% of the available light. Although the depth‐related results we present apply—in the strictest sense—only to kelp translocated on rigs, we argue that the relative patterns are relevant for natural populations. Growth and survival of S. latissima is likely to be reduced by heavy loads of epibionts, while depths where epibionts are sparse may be close to the lower limit of the kelps depth distribution along the south coast of Norway. This suggests that a vertical squeeze, or narrowing of the distribution range of kelp forests may be occurring in Norway.publishedVersio

Optimizing the use of quicklime (CaO) for sea urchin management — A lab and field study

Mass blooms of sea urchins sometimes cause kelp forest collapses that can last for decades. Quicklime has historically been used to reverse those conditions, but the efficacy of liming has varied along latitudinal and temperature gradients for reasons that are not fully understood. To evaluate the feasibility and ecological impacts of liming in a high latitude area in Northern Norway (70°N), we conducted a field pilot study in 2008–2011, a follow-up lab study in 2017, and a further field study in 2018–2019, with the latter evaluating and implementing the previous results in a site high in refuges. It was found that liming can reduce sea urchin densities sufficiently for macroalgal revegetation to occur, and that the mobile fauna species richness and abundance increased in the re-vegetated in comparison to the barren control fields. Also, the remaining sea urchins in the treated fields increased their roe content to commercial levels after 2 years. The lab experiments in 2017 indicated that the liming method is season/temperature-independent, as mortality remained at the same level irrespective of whether treatment started in the spring, when the sea temperatures were 2 °C, or in autumn when the temperatures were closer to 10 °C. The most important factor in treatment efficacy in the lab was particle size. With similar doses, the particles in the smallest size range (0–0.5 mm) caused 100% mortality, while the 0.5–2 mm and 2–4 mm fractions caused only 13% and 2% mortality respectively. In 2018–2019 we tested the fine CaO fraction (0.1–0.6 mm) and the medium fraction (0.5–2 mm) in a field experiment in areas characterized by high levels of refuges. Within 11 days, the sea urchin densities in the three fields treated with the fine lime were reduced to levels that theoretically should allow revegetation, but only in one of those fields was that potential partly realized after 1 year. The lack of effect in the two other fields was probably due to urchins protected by the substrate during treatment reappearing in sufficient numbers to prevent macroalgal regrowth, demonstrating that CaO treatment can be less effective on substrates where part of the sea urchin population hides among stones. Of the three variables held up as potential explanations for the different effects of CaO treatment in previous studies, we conclude based on our experiments that the presence of refuges and particle size were probably more important than temperature. Further improvements for larger scale treatments are discussed.publishedVersio

Genetic diversity of the NE Atlantic sea urchin Strongylocentrotus droebachiensis unveils chaotic genetic patchiness possibly linked to local selective pressure

We compared the genetic differentiation in the green sea urchin Strongylocentrotus droebachiensis from discrete populations on the NE Atlantic coast. By using eight recently developed microsatellite markers, genetic structure was compared between populations from the Danish Strait in the south to the Barents Sea in the north (56–79°N). Urchins are spread by pelagic larvae and may be transported long distances by northwards-going ocean currents. Two main superimposed patterns were identified. The first showed a subtle but significant genetic differentiation from the southernmost to the northernmost of the studied populations and could be explained by an isolation by distance model. The second pattern included two coastal populations in mid-Norway (65°N), NH and NS, as well as the northernmost population of continental Norway (71°N) FV. They showed a high degree of differentiation from all other populations. The explanation to the second pattern is most likely chaotic genetic patchiness caused by introgression from another species, S. pallidus, into S. droebachiensis resulting from selective pressure. Ongoing sea urchin collapse and kelp forests recovery are observed in the area of NH, NS and FV populations. High gene flow between populations spanning more than 22° in latitude suggests a high risk of new grazing events to occur rapidly in the future if conditions for sea urchins are favourable. On the other hand, the possibility of hybridization in association with collapsing populations may be used as an early warning indicator for monitoring purposes.publishedVersio

Co‑creating coastal sustainability goals and indicators

Indicators can be powerful tools to measure progress towards achieving societal goals, and many indicators have been developed for sustainability goals nationally and internationally. When indicators are developed solely through top-down approaches without engaging local knowledge, they often fall short of capturing local perceptions and concerns relevant to decision-making. The aim of this project was to co-create a Coastal Barometer and its component indicators, together with local knowledge-holders and communities, using the Ocean Health Index as a framework. As a frst step, local knowledgeholders from six communities dispersed across Northern Norway were invited to articulate local sustainability goals and the required knowledge for eight broad topics pertaining to global OHI goals: small-scale fsheries, food production, sense of place, tourism, food production, clean waters, carbon storage and economy and livelihoods. In this paper, our main focus is the co-design phase of the Coastal Barometer, namely eliciting sustainability goals. We thus, present locally desired sustainability goals and sub-goals and the process of eliciting these goals. We also include suggestions from local knowledge-holders on how to reach these goals (i.e. proposed management measures), along with researchers’ assessment of data availability (part of the co-production process) for developing indicators to measure progress towards these goals. Finally, we discuss the benefts and challenges of co-developing sustainability goals and indicators with local knowledge-holders. We conclude that co-design can increase the quality of sustainability assessments by enriching the view of coastal sustainability. This knowledge can subsequently be used to align indicators with local sustainability goals as well as to the local context where the indicators will be applied. Blue growth · Ecosystem services · Public participation · Sustainability indicators · Sustainable development goals · Ocean health indexpublishedVersio

Method development for mapping kelp using drones and satellite images: Results from the KELPMAP-Vega project

Prosjektleder Hege GundersenThe KELPMAP study demonstrated that high-resolution multispectral data from drones and satellites, combined with AI-based image analysis, can efficiently map kelp forests and other coastal habitats. The field campaign, conducted in 2022 within Vega and Herøy municipalities, produced orthomosaics with 9 cm GSD for multispectral and 5 cm for RGB images. Based on drone data and AI, between 11% and 65% of the study area was identified as brown algae. Satellites overpredicted kelp forests but aligned with drone data after removing uncertain predictions. In Helgeland’s clear waters, benthic species and habitats were identified down to 10 meters. Using NIVA's statistical model, drones were estimated to map almost 60% of Norwegian kelp forests and 80-90% of total kelp biomass, despite only reaching 10 meters. Upscaling habitat maps using satellite images is possible but limited by satellite resolution. Drone-based training data enhances satellite-derived map accuracy. High-resolution drone maps are ideal for local marine spatial planning, while satellite maps are suitable for national level applications like carbon accounting. More ground truth data are needed for improved species-level mapping and validation of upscaled products. The study also assessed mapping benthic habitats according to NiN 3.0, identifying kelp forests, seaweed beds, eelgrass, and various seabed types.Norwegian Environment AgencypublishedVersio

"Hanging gardens" - comparing fauna communities in kelp farms and wild kelp forests

A growing need for food is causing increased interest for seaweed farming globally. This requires knowledge of the industry’s effects on the marine environment. We therefore aimed to explore the communities hosted by a kelp farm compared to that of wild kelp forests. The study was performed in mid-western Norway. Kelp associated fauna were collected from farmed kelp (Saccharina latissima and Alaria esculenta), in wild kelp forests (S. latissima, A. esculenta and Laminaria hyperborea), and from fauna traps in the water column. The study showed that the kelp farm had lower taxa abundance and richness and a lower biodiversity than the wild kelp forests. Nonetheless, the farmed kelp hosted many associated species, with communities different from what was found on ropes without kelp (i.e., in the water column). The fauna communities among the farmed kelp were more similar to what was found in the wild L. hyperborea kelp forest than to its wild counterparts. The difference between the fauna communities of ‘old’ and ‘young’ farmed kelp (grown for 3 and 7 months, respectively) was not significant, but the fauna was dominated by the isopod species Idotea pelagica in the young forest and by amphipods, mainly belonging to the genus Caprella, in the older. The study contributes to our knowledge of kelp farms’ ecological role in the marine environment, which is of importance for today’s management as well as for ensuring a sustainable future development of the kelp farming industry.publishedVersio

Top-down release of mesopredatory fish is a weaker structuring driver of temperate rocky shore communities than bottom-up nutrient enrichment

Ecological impacts of top-down trophic cascades in combination with bottom-up nutrient enrichment are increasingly being reported. Such effects may be triggered by decline in the abundance and size of piscivore fish leading to a release of smaller-sized mesopredatory fish that are capable of reducing mesograzers and their buffering herbivorous effects, thus intensifying eutrophication symptoms. Hitherto, such mesopredator release has not been studied in controlled manner in macroalgal-dominated rocky shore communities. This study utilised twelve littoral mesocosms in southeastern Norway to investigate the impact of increased nutrient levels and increased abundance of the mesopredatory goldsinny wrasse (Ctenolabrus rupestris) over 6 months, from spring (April) to autumn (October). The study mainly revealed typical eutrophication responses in both July and in October with nutrient enrichment leading to more ephemeral algae and less perennial Fucacean and red macroalgae. Significant responses to the addition of mesopredatory fish alone or with nutrients in combination were clearly fewer in July and almost non-existent in October. Mesopredatory fish reduced the number of some mesograzers, but not others, and some herbivores even benefitted. Few joint effects occurred between fish and nutrients and the anticipated negative consequences for perennial macrophytes were largely absent; the possible reasons for these observations are discussed in depth. Curiously, the presence of mesopredatory fish seems to favour some canopy-forming macrophytes. This last finding warrants further investigation as the labrid fishery in coastal waters of southern Norway and western Sweden is increasing and a too heavy reduction of mesopredators may have its own unforeseen ecosystem implications.publishedVersio

Lack of sea urchin settlement may explain kelp forest recovery in overgrazed areas in Norway

In this study, we investigated whether failure of sea urchin recruitment can explain an ongoing phase shift from overgrazed, barren grounds to kelp forests along the coast of mid- Norway. Settlement of sea urchins on artificial substrates deployed in mid-Norway and North Norway was compared on barren grounds and in kelp forests. Settlement varied in time and space, and was low in mid-Norway—the area where kelp is recovering. Settlement did not differ between kelp forest and barren grounds. Densities of adult and juvenile sea urchins were estimated and gonad index (GI) was measured in order to relate sea urchin settlement to local population structure and the reproductive potential of the sea urchin populations. Sea urchin density was generally lower in mid-Norway than in North Norway, but reproductive potential did not differ significantly between the areas. Increasing water temperature is considered a critical factor for sea urchin larval development and may be partly to blame for the recent sea urchin recruitment failure in mid-Norway. Lack of sea urchin recruitment may explain the recovery of kelp in mid-Norway.publishedVersio

Hva bestemmer egenskaper og økologisk funksjon i ålegrasenger?

Juni 2014 ble 27 ålegrasenger i Aust-Agder undersøkt for å analysere hvilke miljøfaktorer som bestemmer egenskaper som tetthet og høyde til ålegrasplanten i engene, og om enger med tett ålegrasvegetasjon er leveområde for et annet dyresamfunn enn glisne enger. Tett ålegrasvegetasjon er hovedsakelig knyttet til områder grunnere enn 5 m dyp.; ålegrasets høyde øker med økt bølgepåvirkning og med økt helningsgrad av terrenget.; de største engene med hensyn til areal var i områder med relativt lite bølgepåvirkning. På tross av disse generelle påvirkningene av miljøfaktorene dyp, skråning og bølgepåvirkning var det en del tilfeldig variasjon knyttet til de ulike engenes egenskaper. Ved å sammenlikne tre enger med tett ålegrasvegetasjon med tre enger med spredt ålegrasvegetasjon fant vi også stor variasjon i forekomst og sammensetning av assosierte arter av smådyr og fisk. Det var store likheter mellom prøvene innenfor hver eng, mens forskjellene i tetthet av dyr var store fra eng til eng. Undersøkelsen viser at ålegrasenger har en viktig økologisk funksjon uavhengig av om de har høy eller lav ålegrasbiomasse og enten plantene er høye eller lave. Det er derfor viktig å ivareta enger med både høy og lav ålegrastetthet for å ivareta biologisk mangfold, forekomst av smådyr og næringsområder for fisk. Store ålegrasenger, enten de har høy eller lav ålegrastetthet, vil ha større økologisk betydning enn små gjennom økt habitatstørrelse, høyere total primærproduksjon og totalt større mengde assosiert flora og fauna

Predation mortality from ambush and cruising predators on newly-settled 0-group gadoids

We investigated predation from an ambush predator (shorthorn sculpin) and two cruising predators (Atlantic cod and saithe) on bottom-settled 0-group cod and saithe juveniles in a fjord in northern Norway. Stomach contents of potential fish predators caught by gill net in shallow waters (depth of 3–10 m) during September in 2013–2015 were analysed. The frequency of occurrence (FO) of 0-group gadoid prey was highest for shorthorn sculpin (FO = 10%) and cod (FO = 9%), while it was lower for saithe (FO = 0.8%). Each predatory fish species had different alternative prey to 0-group gadoids: shrimps for cod; sandeels for saithe; and Brachura/Anomura for shorthorn sculpin. Amongst the fish predators, shorthorn sculpin had the highest catch rates in gill nets. The mean number of 0-group cod and saithe in shorthorn sculpin stomachs increased with increasing abundance of prey as measured by beach seine hauls. Predation mortality from shorthorn sculpin was estimated based on abundance of shorthorn sculpins, number of 0-group cod and saithe juveniles in predator stomachs, prey recognition times and abundance of 0-group cod and saithe. The average predation mortality rate from shorthorn sculpin on 0-group gadoid juveniles varied from 0.40 to 1.14 month−1 between years and the pooled estimate from 2013 to 2015 was 0.70 month−1 (95%CI: 0.30, 1.73). This is comparable to mortality rates from other studies on newly-settled 0-group Atlantic cod, other gadoid species and plaice. Based on gill-net catches and stomach data from this study and literature values for gill-net catching area, calculated predation mortalities from the cruising cod and saithe were less than 47% of the sculpin predation mortality rates. This show that predation mortality from the ambush sculpin predator was much higher than from the cruising Atlantic cod and saithe.publishedVersio