Eli Rinde

Distribution, structure and function of Nordic eelgrass (Zostera marina) ecosystems: implications for coastal management and conservation

This paper focuses on the marine foundation eelgrass species, Zostera marina, along a gradient from the northern Baltic Sea to the north-east Atlantic. This vast region supports a minimum of 1480 km2 eelgrass (maximum >2100 km2), which corresponds to more than four times the previously quantified area of eelgrass in Western Europe. Eelgrass meadows in the low salinity Baltic Sea support the highest diversity (4–6 spp.) of angiosperms overall, but eelgrass productivity is low (<2 g dw m-2 d-1) and meadows are isolated and genetically impoverished. Higher salinity areas support monospecific meadows, with higher productivity (3–10 g dw m-2 d-1) and greater genetic connectivity. The salinity gradient further imposes functional differences in biodiversity and food webs, in particular a decline in number, but increase in biomass of mesograzers in the Baltic. Significant declines in eelgrass depth limits and areal cover are documented, particularly in regions experiencing high human pressure. The failure of eelgrass to re-establish itself in affected areas, despite nutrient reductions and improved water quality, signals complex recovery trajectories and calls for much greater conservation effort to protect existing meadows. The knowledge base for Nordic eelgrass meadows is broad and sufficient to establish monitoring objectives across nine national borders. Nevertheless, ensuring awareness of their vulnerability remains challenging. Given the areal extent of Nordic eelgrass systems and the ecosystem services they provide, it is crucial to further develop incentives for protecting them.

Distribution, structure and function of Nordic eelgrass (Zostera marina) ecosystems

This paper focuses on the marine foundation eelgrass species, Zostera marina, along a gradient from the northern Baltic Sea to the north-east Atlantic. This vast region supports a minimum of 1480 km2 eelgrass (maximum >2100 km2), which corresponds to more than four times the previously quantified area of eelgrass in Western Europe. Eelgrass meadows in the low salinity Baltic Sea support the highest diversity (4–6 spp.) of angiosperms overall, but eelgrass productivity is low (<2 g dw m-2 d-1) and meadows are isolated and genetically impoverished. Higher salinity areas support monospecific meadows, with higher productivity (3–10 g dw m-2 d-1) and greater genetic connectivity. The salinity gradient further imposes functional differences in biodiversity and food webs, in particular a decline in number, but increase in biomass of mesograzers in the Baltic. Significant declines in eelgrass depth limits and areal cover are documented, particularly in regions experiencing high human pressure. The failure of eelgrass to re-establish itself in affected areas, despite nutrient reductions and improved water quality, signals complex recovery trajectories and calls for much greater conservation effort to protect existing meadows. The knowledge base for Nordic eelgrass meadows is broad and sufficient to establish monitoring objectives across nine national borders. Nevertheless, ensuring awareness of their vulnerability remains challenging. Given the areal extent of Nordic eelgrass systems and the ecosystem services they provide, it is crucial to further develop incentives for protecting them.

Regrowth of kelp and colonization of epiphyte and fauna community after kelp trawling at the coast of Norway

The kelp Laminaria hyperborea is regularly harvested along the Norwegian coast. Kelp trawling is regulated by restricting this to every 5th year in specified areas. The kelp plants form dense forests, 1–2 m high, and house a large number of epiphytes and associated invertebrates. Kelp, epiphytes, and holdfast (hapteron) fauna were sampled at two different regions in untrawled kelp forest and at sites trawled different number of years ago. We have examined the rate of kelp regrowth after trawling, and in what time scale the associated flora and fauna colonize the trawled areas. The trawl removed all adult kelp plants (the canopy plants), while small understorey kelp plants were left undisturbed. These recruits, given improved light conditions, made the new generation of canopy-forming kelp plants, exceeding a height of 1 m within 2–3 y. The recruitment pattern of the kelp ensures maintenance of kelp forest dominance despite repeated trawling. Both percent cover, abundance and number of epiphytic species increased with time post trawling, but epiphytic communities were not totally re-established before the next trawling episode. Colonization of most species of fauna inhabiting the kelp holdfast were found as early as one year after trawling, but increasing size of the habitat by age of kelp gave room for increasing numbers of both individuals and species. Slow colonization rate by some species might be due to low dispersal potential. Due to a higher maximum age and size of kelp plants in the northernmost region studied, restoration of both kelp and kelp forest community was slower there.

Short-term dispersal of kelp fauna to cleared (kelp-harvested) areas

The kelp Laminaria hyperborea forms large forests and houses a numerous and diverse fauna, especially in the kelp holdfast and stipe epiphytes. Kelp harvesting creates cleared areas and fragmentizes the kelp forest. We investigated the dispersal ability of kelp fauna to cleared, harvested areas by studying their colonization pattern to artificial substrata (kelp mimics) exposed for a short (3 days) and longer time period (35 days) at different sites within the kelp forest (one site) and at a cleared area (two sites). Most of the kelp fauna (111 species) showed a rapid dispersal and colonized the artificial substrata within the cleared area. The similarity of the faunal community in the mimics with the natural kelp holdfast community increased with the length of the exposure period. During the experiments, 87% of the mobile species in the kelp plants were found in the kelp mimics, indicating good dispersal for slow-moving animals like gastropods, polychaetes and tube-building crustaceans. Relating the frequency of the different faunal groups in the untrawled kelp forest to their frequency in the kelp mimics, showed gastropods, amphipods and decapods to have relatively high dispersal rates, whereas isopods, bivalves, polychaetes and tanaids showed a lower dispersal rate than expected. Amphipods dispersed as juveniles and adults. No significant differences were found between the faunal composition and number of species in the mimics placed inside the kelp forest and in the cleared area. Remaining holdfasts and pebbles were identified as refuges/alternative habitats in the harvested area, and may together with the nearest kelp vegetation, serve as sources for colonization to new substrata. The high dispersal ability of most of the kelp fauna provides maintenance of the faunal composition of disturbed habitats and ensures colonization of recovering algal habitats regardless of reproduction strategy.

Status, trends and drivers of kelp forests in Europe: an expert assessment

A comprehensive expert consultation was conducted in order to assess the status, trends and the most important drivers of change in the abundance and geographical distribution of kelp forests in European waters. This consultation included an on-line questionnaire, results from a workshop and data provided by a selected group of experts working on kelp forest mapping and eco-evolutionary research. Differences in status and trends according to geographical areas, species identity and small-scale variations within the same habitat where shown by assembling and mapping kelp distribution and trend data. Significant data gaps for some geographical regions, like the Mediterranean and the southern Iberian Peninsula, were also identified. The data used for this study confirmed a general trend with decreasing abundance of some native kelp species at their southern distributional range limits and increasing abundance in other parts of their distribution (Saccharina latissima and Saccorhiza polyschides). The expansion of the introduced species Undaria pinnatifida was also registered. Drivers of observed changes in kelp forests distribution and abundance were assessed using experts’ opinions. Multiple possible drivers were identified, including global warming, sea urchin grazing, harvesting, pollution and fishing pressure, and their impact varied between geographical areas. Overall, the results highlight major threats for these ecosystems but also opportunities for conservation. Major requirements to ensure adequate protection of coastal kelp ecosystems along European coastlines are discussed, based on the local to regional gaps detected in the study.

The Influence of Physical Factors on Kelp and Sea Urchin Distribution in Previously and Still Grazed Areas in the NE Atlantic

The spatial distribution of kelp (Laminaria hyperborea) and sea urchins (Strongylocentrotus droebachiensis) in the NE Atlantic are highly related to physical factors and to temporal changes in temperature. On a large scale, we identified borders for kelp recovery and sea urchin persistence along the north-south gradient. Sea urchin persistence was also related to the coast-ocean gradient. The southern border corresponds to summer temperatures exceeding about 10°C, a threshold value known to be critical for sea urchin recruitment and development. The outer border along the coast-ocean gradient is related to temperature, wave exposure and salinity. On a finer scale, kelp recovery occurs mainly at ridges in outer, wave exposed, saline and warm areas whereas sea urchins still dominate in inner, shallow and cold areas, particularly in areas with optimal current speed for sea urchin foraging. In contrast to other studies in Europe, we here show a positive influence of climate change to presence of a long-lived climax canopy-forming kelp. The extent of the coast-ocean gradient varies within the study area, and is especially wide in the southern part where the presence of islands and skerries increases the area of the shallow coastal zone. This creates a large area with intermediate physical conditions for the two species and a mosaic of kelp and sea urchin dominated patches. The statistical models (GAM and BRT) show high performance and indicate recovery of kelp in 45–60% of the study area. The study shows the value of combining a traditional (GAM) and a more complex (BRT) modeling approach to gain insight into complex spatial patterns of species or habitats. The results, methods and approaches are of general ecological relevance regardless of ecosystems and species, although they are particularly relevant for understanding and exploring the corresponding changes between algae and grazers in different coastal areas.

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.

Increased spreading potential of the invasive Pacific oyster (Crassostrea gigas) at its northern distribution limit in Europe due to warmer climate

The Pacific oyster, Crassostrea gigas, is an invasive species with a large increase in prevalence globally, and with potential of spreading even more because of climate-change effects. We examined how future climate might affect its potential for spread at its northern distribution limit in a temperate ecoregion, by simulating spawning, larval dispersal, larvae settlement and adult survival, given different climate scenarios. The simulations were performed using a three-dimensional current model (GEMSS) and a specially designed oyster module, applied at the study site in the Oslofjord, Norway. The simulations showed that the expected climate in the middle and latter part of this century, with warmer summers and winters, very likely will lead to increased prevalence of the species within northern Europe. The warmer summers will more often provide favourable temperature conditions for oyster spawning and settlement, and warmer winters will more seldom cause high winter mortality. The simulations gave a realistic picture of the relative frequency and the main distribution pattern observed, given the current climate. The future climate-scenario simulations indicated influence of local differences in temperature on the dispersal pattern. The study indicated increased dispersal and successful establishment at the outer edge of the species present distribution in the future and, hence, an increased risk to native species and habitats in temperate regions.

Mapping biological resources in the coastal zone: an evaluation of methods in a pioneering study from Norway.

For many years, the planning and management of terrestrial areas has been supported by a detailed knowledge of the distribution of habitats and their associated species. However, the detailed mapping of biological resources in extent coastal areas, such as the Norwegian coastal zone, is unrealistic due to its enormous coastline. Here, we present a useful and feasible approach and a set of simple, cost-effective methods which are suitable for providing a broad-scale overview of marine habitats and fish resources. This approach was developed in conjunction with a pioneer study conducted along the southern coast of the Skagerrak, where we combined knowledge gathered from local fishermen with scientific knowledge of important species and nature types to establish a coastal sea mapping program. GIS modeling tools were used in both the mapping program and to integrate local and scientific knowledge into digital maps made available to local area management. This multi-faceted approach, which combines local knowledge and scientific methods, provides valuable information with respect to marine biodiversity, and has been used extensively by local environmental management.

A snap shot of the short-term response of crustaceans to macrophyte detritus in the deep Oslofjord

A test deployment of a time-lapse camera lander in the deep Oslofjord (431 m) was used to obtain initial information on the response of benthic fauna to macroalgal debris. Three macroalgal species were used on the lander baited plate: Fucus serratus, Saccharina latissima and Laminaria hyperborea and observed during 41.5 hours. The deep-water shrimp Pandalus borealis were attracted to the macroalgae rapidly (3 min after the lander reached the seafloor), followed by amphipods. Shrimp abundances were significantly higher in areas covered by macroalgae compared to the adjacent seafloor and the number of shrimp visiting the macroalgae increased with time. Amphipods arrived 13 hours later and were observed mainly on decaying L. hyperborea. The abundance of amphipods on L. hyperborea increased rapidly, reaching a peak at 31 h after deployment. These initial observations suggest that debris from kelp forests and other macroalgal beds may play an important role in fuelling deep benthic communities in the outer Oslofjord and, potentially, enhance secondary production of commercial species such as P. borealis.