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

An In Situ Experimental Study of Effects on Submerged Vegetation After Activated Carbon Amendment of Legacy Contaminated Sediments

Activated carbon (AC) amendment has been shown to reduce bioavailability of hydrophobic contaminants in the bioactive layer of sediment. Unwanted secondary effects of AC amendment could be particularly undesirable for ecologically important seagrass meadows, but so far, only a few studies have been conducted on effects on submerged plants. The purpose of this study was to investigate effects on growth and cover of submerged macrophytes in situ after AC amendment. Test sites were established within a seagrass meadow in the severely contaminated Norwegian fjord Gunneklevfjorden. Here we show that AC amendment does not influence neither cover nor length of plants. Our study might indicate a positive effect on growth from AC in powdered form. Hence, our findings are in support of AC amendment as a low-impact sediment remediation technique within seagrass meadows. However, we recommend further studies in situ on the effects of AC on submerged vegetation and biota. Factors influencing seasonal and annual variation in plant species composition, growth and cover should be taken into consideration.An In Situ Experimental Study of Effects on Submerged Vegetation After Activated Carbon Amendment of Legacy Contaminated SedimentsacceptedVersio

Effects of kelp harvesting on fish and crustaceans in Vikna, Nord- Trøndelag 2013

The Institute of Marine Research studied effects of kelp (Laminaria hyperborea) harvesting on near shore fish and crab abundance in Vikna (Nord-Trøndelag) in June (before) and August (after) 2013. A similar follow up survey one year after kelp harvesting in Flatanger was planned in august 2013, but had to be postponed for another year due to bad weather conditions. The “after” surveillance in Flatanger was performed in August 2014, and will be presented in a separate report. Recordings were made using fixed underwater camera systems and traditional fish and crab catching gear in kelp harvested areas and in reference kelp beds. Recordings from Vikna in 2013 indicate no significant effects of kelp harvesting on nearshore fish and crab abundances. Such effects may however be disguised by large variations in the data sets, partly because of seasonal variations in fish and crab abundances between the before (June) and after (August) surveillanc

Kelp harvesting in Nord-Trøndelag – Kelp vegetation recovery studies 2010–2014

The Institute of Marine Research monitored the kelp (Laminaria hyperborea) vegetation and sea urchin populations in Nord-Trøndelag in 2014. The survey included previously kelp harvested areas and nearby reference areas, and was performed by underwater video. In addition, kelp plants were collected from areas harvested four years earlier, for measurements of plant size, age and epiphytes. Observations in harvested areas revealed that although kelp rapidly re-monopolizes the substratum (< 2 years), plant sizes and epiphytes are still below pre-harvesting levels 4 years later. Age structure of plants collected in areas harvested in 2010, suggests that kelp recruits present as understory vegetation prior to harvesting, contribute substantially to the restocking of kelp on trawlfields. The understory density of new kelp recruits 4 years after harvesting was significantly lower than it was prior to harvesting. The density of sea urchins was generally low and grazing effects on recovering kelp plants appeared negligibl

Before and after studies of kelp (Laminaria hyperborea) harvesting in Nord-Trøndelag in 2012

The Institute of Marine Research surveyed the kelp vegetation, before and after kelp (Laminaria hyperborea) harvesting in Nord-Trøndelag in June and August 2012. Survey stations included both kelp harvested areas (harvested in 2010, 2011 and 2012) and nearby reference areas, and was performed by underwater video. In addition, kelp plants were collected for measurements of plant length, diameter, weight, age and epiphytes. Based on these observations the state of the kelp forest was considered to be healthy, with an average of 27 kg kelp biomass per m2 prior to harvesting and moderate densities of sea urchins. The recovery of kelp vegetation on fields harvested in 2010 and 2011 is ongoing, and the kelp coverage in harvested areas were 90% (21 months after the 2010 harvesting)) and 74% (11 months after the 2011 harvesting) in June 2012. The average length of the recovering generation of kelp plants was in June 2012 around 17% (11 months after the 2011 harvesting) and 28% (21 months after the 2010 harvesting) of the average kelp plant sizes prior to harvesting. The density of sea urchins was generally low and grazing effects on recovering kelp plants appeared negligible. The harvested kelp crop in Nord-Trøndelag in 2012 was 14.901 tonnes, and estimated to be around 5,5 % of the standing kelp stock on the 8 fields earmarked for kelp harvesting this year

Tareundersøkelser i Nordland i 2019

Havforskningsinstituttet har i perioden 2013-2019 gjennomført undersøkelser i forbindelse med prøvehøsting av stortare (Laminaria hyperborea) på kyststrekningen Sømna (65° 20’ N) – Vega (65° 33’ N) i Nordland. Det ble i 2019 gjennomført oppfølgende undersøkelser av taresamfunnene på felt som ble prøvehøstet i 2013, 2014 og 2017, samt i nærliggende områder som ikke har vært tarehøstet tidligere (referanseområder). I tillegg ble det gjennomført kartlegging av tarevegetasjonen og kråkebolleforekomster i utvalgte breddegradssektorer på kyststrekningen fra Herøy (66° 02’ N) til Bodø (67° 22’ N). Tarevegetasjonen ble undersøkt ved hjelp av undervannsvideo og innsamlinger av tareplanter for studier av morfologi, alder, veksthistorikk, epifytter og kråkebollerekrutter. Undersøkelsene i de tidligere prøvehøstede områdene viser at selv om høstefeltene raskt rekoloniseres av små stortareplanter og tarebiomassen restitueres i løpet av fire år, kreves en hvileperiode på seks år for reetablering av epifyttstruktur og rekruttvegetasjon. Videoobservasjonene viser at tettheten av kråkebolle var lav på de fleste stasjoner undersøkt i Nordland i 2019, og kråkebollebeiting har hatt liten effekt på tarevegetasjonens reetablering i de tidligere prøvehøstede områdene. På kyststrekningen Herøy - Bodø er stortarevegetasjonen best utviklet i ytre, vestlige deler av de undersøkte sektorene. Tettheten av juvenile grønne kråkeboller (Strongylocentrotus droebachiensis) observert i de innsamlede tareplantenes festeorgan (hapter) økte fra sør til nord. Veksthistorikkanalyser av innsamlede tareplanter indikerer at den årlige stilktilveksten er langsommere på kyststrekningen Herøy – Bodø, enn i sørligere områder.publishedVersio

Tareundersøkelser i Nordland i 2017

Havforskningsinstituttet har i perioden 2013-2017 gjennomført undersøkelser i forbindelse med prøvehøsting av stortare (Laminaria hyperborea) sør i Nordland. I forkant av prøvehøstingen i 2017 ble tarevegetasjonen undersøkt ved hjelp av undervannsvideo og tareinnsamlinger for studier av morfologi, alder, veksthistorikk og epifytter. Det ble også gjennomført oppfølgende undersøkelser av taresamfunnene på felt som ble prøvehøstet i 2013-2016 og i nærliggende områder som ikke har vært tarehøstet tidligere (referanseområder). Undersøkelsene viste god gjenvekst av stortare på høstefeltene som til nå har vært lite påvirket av beiting fra kråkeboller. Forekomstene av rød kråkebolle (Echinus esculentus) ser imidlertid ut til å ha økt i forhold til tidligere år i den nordligste delen av det undersøkte området på både høstede og ikke-høstede stasjoner. Fire år etter den første prøvehøstingen i 2013 var stortarevegetasjonens størrelses-, alder- og epifyttstruktur, samt tettheten av tarerekrutter i undervegetasjonen, fortsatt ikke tilbake på samme nivå som før høsting. Tarevegetasjonens- og kråkebollebestandenes utvikling i området bør derfor følges videre for å framskaffe et bedre kunnskapsgrunnlag for en framtidig bærekraftig forvaltning av stortareressursene i denne regionen. Fiskeundersøkelser som ble startet før prøvehøsting i 2017 vil bli fulgt opp med nye undersøkelser i 2018 for å teste eventuelle effekter på fisk og skalldyr.publishedVersio

Kelp studies in Nordland in 2018

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

The influence of permanently submerged macrophytes on sediment mercury distribution, mobility and methylation potential in a brackish Norwegian fjord

Embargo until 30 August 2019.Macrophytes are shown to affect the microbial activity in different aqueous environments, with an altering of the sediment cycling of mercury (Hg) as a potential effect. Here, we investigated how a meadow with permanently submerged macrophytes in a contaminated brackish fjord in southern Norway influenced the conditions for sulfate reducing microbial activity, the methyl-Hg (MeHg) production and the availability of MeHg. Historically discharged Hg from a chlor-alkali plant (60–80 tons, 1947–1987) was evident through high Hg concentrations (491 mg Tot-Hg kg− 1, 268 μg MeHg kg− 1) in intermediate sediment depths (10–20 cm) outside of the meadow, with reduced concentrations within the meadow. Natural recovery of the fjord was revealed by lower sediment surface concentrations (1.9–15.5 mg Tot-Hg kg− 1, 1.3–3.2 μg MeHg kg− 1). Within the meadow, vertical gradients of sediment hydrogen sulfide (H2S) Eh and pH suggested microbial sulfate reduction in 2–5 cm depths, coinciding with peak values of relative MeHg levels (0.5% MeHg). We assume that MeHg production rates was stimulated by the supply and availability of organic carbon, microbial activity and a sulfide oxidizing agent (e.g. O2) within the rhizosphere. Following this, % MeHg in sediment (0–5 cm) within the meadow was approximately 10 × higher compared to outside the meadow. Further, enhanced availability of MeHg within the meadow was demonstrated by significantly higher fluxes (p < 0.01) from sediment to overlying water (0.1–0.6 ng m− 2 d− 1) compared to sediment without macrophytes (0.02–0.2 ng m− 2 d− 1). Considering the productivity and species richness typical for such habitats, submerged macrophyte meadows located within legacy Hg contaminated sediment sites may constitute important entry points for MeHg into food webs.acceptedVersio