Frithjof E. Moy

Large-scale shift from sugar kelp (Saccharina latissima) to ephemeral algae along the south and west coast of Norway

Abstract Sugar kelp forests (Saccharina latissima) normally dominate the sublittoral rocky sea bed in medium exposed to sheltered areas of the Norwegian coast. In 2002, a large-scale disappearance of sugar kelp was observed, and a survey of more than 600 sites along the coast of southern Norway (58–63°N, 6–11°E) during 2004–2009 recorded a large-scale shift from anticipated sugar kelp forests to communities dominated by filamentous, ephemeral macroalgae. The loss of sugar kelp was most severe in the Skagerrak region, and a comparison with earlier studies supported the observed changes in the community structure and regional differences between the Skagerrak region and the west coast. Filamentous red algae dominated the sublittoral communities at the Skagerrak coast, whereas coarsely branched and filamentous brown algae were most abundant at the west coast sites with low or no abundance of sugar kelp. The cause of this large-scale shift is not clear, but our observations suggest eutrophication (nutrient and particle pollution) and climate change (increase in temperature) as the two main drivers synergistically contributing, alongside other factors, to the demise of S. latissima. If the ephemeral algae community represents an alternative stable state, it will have implications for marine coastal zone production and management.

The Response of Experimental Rocky Shore Communities to Nutrient Additions

The aim of this study was to determine whether the experimental nutrient enrichment of littoral rocky shore communities would be followed by a predicted accumulation of fast-growing opportunistic algae and a subsequent loss of perennial benthic vegetation. Inorganic nitrogen (N) and potassium (P) was added to eight concrete mesocosms inhabited by established littoral communities dominated by fucoids. The response to nutrient enrichment was followed for almost 2 1/2 years. Fast-growing opportunistic algae (periphyton and ephemeral green algae) grew significantly faster in response to nutrient enrichment, but the growth of red filamentous algae and large perennial brown algae was unaffected. However, these changes were not followed by comparable changes in the biomass and composition of the macroalgae. The biomass of opportunistic algae was stimulated only marginally by the nutrient enrichment, and perennial brown algae (fucoids) remained dominant in the mesocosm regardless of nutrient treatment level. Established rocky shore communities thus seem able to resist the effects of heavy nutrient loading. We found that the combined effects of the heavy competition for space and light imposed by canopy-forming algae, preferential grazing on opportunistic algae by herbivores, and physical disturbance, succeeded by a marked export of detached opportunistic algae, prevented the fast-growing algae from becoming dominant. However, recruitment studies showed that the opportunistic algae would become dominant when free space was available under conditions of high nutrient loading and low grazing pressure. These results show that established communities of perennial algae and associated fauna in rocky shore environments can prevent or delay the accumulation of bloom-forming opportunistic algae and that the replacement of long-lived macroalgae by opportunistic species at high nutrient loading may be a slow process. Nutrient enrichment may not, in itself, be enough to stimulate structural changes in rocky shore communities.

Global patterns of kelp forest change over the past half-century

Significance Kelp forests support diverse and productive ecological communities throughout temperate and arctic regions worldwide, providing numerous ecosystem services to humans. Literature suggests that kelp forests are increasingly threatened by a variety of human impacts, including climate change, overfishing, and direct harvest. We provide the first globally comprehensive analysis of kelp forest change over the past 50 y, identifying a high degree of variation in the magnitude and direction of change across the geographic range of kelps. These results suggest region-specific responses to global change, with local drivers playing an important role in driving patterns of kelp abundance. Increased monitoring aimed at understanding regional kelp forest dynamics is likely to prove most effective for the adaptive management of these important ecosystems. Kelp forests (Order Laminariales) form key biogenic habitats in coastal regions of temperate and Arctic seas worldwide, providing ecosystem services valued in the range of billions of dollars annually. Although local evidence suggests that kelp forests are increasingly threatened by a variety of stressors, no comprehensive global analysis of change in kelp abundances currently exists. Here, we build and analyze a global database of kelp time series spanning the past half-century to assess regional and global trends in kelp abundances. We detected a high degree of geographic variation in trends, with regional variability in the direction and magnitude of change far exceeding a small global average decline (instantaneous rate of change = −0.018 y−1). Our analysis identified declines in 38% of ecoregions for which there are data (−0.015 to −0.18 y−1), increases in 27% of ecoregions (0.015 to 0.11 y−1), and no detectable change in 35% of ecoregions. These spatially variable trajectories reflected regional differences in the drivers of change, uncertainty in some regions owing to poor spatial and temporal data coverage, and the dynamic nature of kelp populations. We conclude that although global drivers could be affecting kelp forests at multiple scales, local stressors and regional variation in the effects of these drivers dominate kelp dynamics, in contrast to many other marine and terrestrial foundation species.

Nutrient Addition to Experimental Rocky Shore Communities Revisited: Delayed Responses, Rapid Recovery

Coastal eutrophication may alter the dominance patterns of marine macroalgae, with potential consequences for the associated fauna and the entire ecosystem. Benthic macroalgae and animals in control and nutrient-enriched mesocosms were monitored to investigate eutrophication-induced changes in rocky shore communities. During a 3-year project, nutrient addition had only minor effects on the community structure, such as increased cover and biomass of green Ulva spp. and increased abundance of certain animal species at high nutrient levels. This study is a 4-year extension of a previously reported project, with 2 extra years of effect studies (altogether 5 years) and a subsequent 2 years for recovery. During the 4th year of nutrient enrichment, the cover of Fucus vesiculosus and Fucus serratus started to decline. In the 5th year, these canopy species crashed and there was an evident take-over by green algae at high nutrient addition levels. The previously observed abundance stimulation for fauna disappeared later in the time series, probably due to the loss of the macroalgal canopy. After less than 2 years on regular seawater, the algal and animal communities had returned to within the range of normal variability. The results indicate that established rocky shore communities of perennial algae with associated fauna are able to persist for several years, even at very high nutrient levels, but that community shifts may suddenly occur if eutrophication continues. They also indicate that rocky shore communities have the ability to return rapidly to natural undisturbed conditions after the termination of nutrient enhancement.

Seasonal Patterns of Sporophyte Growth, Fertility, Fouling, and Mortality of Saccharina latissima in Skagerrak, Norway: Implications for Forest Recovery

On the Skagerrak coast the kelp Saccharina latissima has suffered severe stand reductions over the last decade, resulting in loss of important habitats. In the present study, healthy kelp plants were transplanted into four deforested areas and their patterns of growth, reproduction, and survival were monitored through subsequent seasons. Our main objective was to establish whether the kelp plants were able to grow and mature in deforested areas. We observed normal patterns of growth and maturation at all study sites. However, heavy fouling by epiphytes occurred each summer, followed by high kelp mortality. The study shows that the seasonal variations and the life stage timing of S. latissima make formation of self-sustainable populations impossible in the present environment. Most noteworthy, we suggest that fouling by epiphytes is involved in the lack of kelp forest recovery in Skagerrak, Norway.

Accumulation and depuration of organic micro-pollutants in marine hard bottom organisms

Abstract A method used in to estimate uptake of hydrophobic pollutants in marine hard bottom organisms is described. Radio-labelled toxicants (14C-PCB77 and 14C-BaP) were used in a closed continuous-flow system without making use of solvents. Concentrations of PCB77 and BaP in the water were relatively high and stable during the experimental periods (14 days). The experimental set-up gave a satisfactory dispersion of the toxicants in the water and the use of radiochemicals made analyses quick and inexpensive. Algae (Fucus vesiculosus) and mussels (Mytilus edulis) were exposed to the toxicants and uptake was principally rapid and significant. Algae exposed to PCB77 reached a steady-state level within 24 h. No steady-state level was observed for BaP during exposure. Mussels showed an approximately linear uptake rate with no steady state observed for either of the toxicants. Organisms moved to a clean environment showed no reduction in PCB77 content. For BaP a slow depuration rate was observed. The rapid uptake of PCB and BaP by the organisms, and the accumulation and retention of the substances in the tissue for a long time, may result in a considerable pool of toxicants stored in these organisms.

Identifying Rocky Seabed Using GIS-Modeled Predictor Variables

Mapping the seabed along the Norwegian coast is costly and time consuming. Hence, finding a modeling method to separate rocky seabed from other substrate types will provide digital maps that may be used to develop cost-effective sampling designs to predict species and habitat distribution. Our approach was to use geophysical data that were quantitative and objectively defined, generalized additive models (GAMs), and Akaike information criterion (AIC) to develop statistical models and select among them. We found that slope, terrain curvature, wave exposure, and depth predicted rocky seabed occurrence with a high degree of certainty.

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

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 (60-80tons, 1947-1987) was evident through high Hg concentrations (491mgTot-Hgkg-1, 268μgMeHgkg-1) in intermediate sediment depths (10-20cm) outside of the meadow, with reduced concentrations within the meadow. Natural recovery of the fjord was revealed by lower sediment surface concentrations (1.9-15.5mgTot-Hgkg-1, 1.3-3.2μgMeHgkg-1). Within the meadow, vertical gradients of sediment hydrogen sulfide (H2S) Eh and pH suggested microbial sulfate reduction in 2-5cm 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 (0-5cm) 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 (0.1-0.6ngm-2d-1) compared to sediment without macrophytes (0.02-0.2ngm-2d-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.

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

AbstractActivated 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. Graphical AbstractThe effects of activated carbon amendment to growth and cover of submerged macrophytes were tested in an in situ experiment

Ecosystem Services : In the Coastal Zone of the Nordic Countries

People are dependent on the ocean and coasts and their resources for their survival and well-being. Coastal ecosystems of the Nordic countries, such as kelp forests, blue mussel beds, eelgrass mead ...