Trine Bekkby

GIS Modeling of Wave Exposure at the Seabed: A Depth-attenuated Wave Exposure Model

Several studies have documented relationships between wave exposure and distribution, density, and size of marine species. Hence, this factor is at a high level in the hierarchical habitat classification system EUNIS and is one of the Water Framework Directive water typology criteria of coastal waters. Isæus (2004) has developed a continuous simplified wave model (SWM) that has been applied to several Nordic countries. Here we refine this model by introducing depth-attenuation, giving us the advantage of a model for wave exposure as it will actually work at the seabed. The values of the depth-attenuated model SWM(d) are approximately similar to the SWM model in shallow areas but noticeably lower in deep areas. The two models were compared in an analysis of the distribution of seabed substrate in the Stockholm archipelago. Using the depth-attenuated wave exposure instead of the SWM model as predictor in substrate modeling improved these models considerably.

A Landscape Ecological Approach to Coastal Zone Applications

Managing complex environments requires suitable tools to integrate data from a variety of sources and efficiently analyse and present them within a geographical context. Recently there has been a growing interest in the integration of geographical, environmental and behavioural data for use in coastal zone management and planning. Our study shows how easily accessible information on bathymetry, terrain variation and wind conditions may be integrated into a georeferenced model applied to the study of key species and ecosystems of the Norwegian coastal zone. Through case studies, we predicted kelp forest ( Laminaria hyperborea ) distribution and analysed harbour seal ( Phoca vitulina ) habitat selection. Combining information on depth and wind exposure derived from a digital terrain model was a suitable approach to predict kelp forest distribution, even though the prediction showed deviations from information provided by kelp harvesters. Including information on sea-bed sediment improved the predictive ability drastically, and more investigation is needed to continue this kind of modelling. This approach is relevant for making decisions concerning site selection of kelp forest harvesting and restoration. Integrating the kelp forest prediction model with information on depth and the presence of slopes, islands and georeferenced behavioural data, we developed a technique for classifying habitats and studying resource selection.

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.

Impact of Scale and Quality of Digital Terrain Models on Predictability of Seabed Terrain Types

The local and regional distribution of seabed terrain types depends on factors such as slope and terrain ruggedness. Digital bathymetrical models (DBM) are therefore essential for mapping and predictive modeling of marine habitats. DBMs vary considerably with respect to scale and quality, and this variation is likely to influence the predictive ability of marine habitat models built with use of DBM-derived environmental predictor variables. We studied the interpretability of seabed terrain types from four different DBMs in two ways: by visual inspection of hillshade representation of the DBMs and by subjecting sets of variables derived from each of the four DBMs to maximum entropy (MaxEnt) predictive modeling of six seabed terrain types. Our results show that DBMs based on multibeam echo sounder data, resampled at resolutions up to 50 m, enable identification of concentrations of seabed terrain types characterized by moraine-ridge assemblies and plough-mark fields. Variables derived from models interpolated from contours of existing marine maps and bathymetric databases have strong limitations and merely enable separation of terrain dominated by rugged bedrock seabed from soft sediment flats. Interpolated DBMs are currently the only type of bathymetrical data that cover all Norwegian coastal waters. Their poor quality is an important obstacle to predictive modeling and classification of seabed habitats.

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.

What is the impact of kelp forest density and/or area on fisheries?

BackgroundKelp forests are highly productive ecosystem engineers of rocky cold-water marine coastlines, providing shelter, habitat and food for a variety of associated organisms. Several factors have been related with an observed trend of kelp deforestation in some regions of the globe. The effect of this trend on fisheries has been poorly studied. The European directives addressing the conservation of marine habitats highlight the need to increase the knowledge about the relationship between kelp forests and fisheries, which will also be very valuable for the definition of fisheries management measures. This protocol describes the methods that will be used to conduct a systematic review to answer the following question: What is the impact of changes in kelp forest density and/or area on the abundance and diversity of fisheries?Methods/designThis systematic review will be focused primary in studies that report on positive, negative or no quantitative relationships between kelp forests (abundance and/or presence) and the health of fisheries (including adults and young life stages). The measurement of fisheries health will include abundance, presence and diversity of fisheries, mortality, fertility and recruitment rates and feeding behavior.

Joint diving behaviour of harbour seal (Phoca vitulina) females and pups in the lactation period

We studied the behaviour of harbour seal (Phoca vitulina) female–pup pairs during joint diving sessions in the lactation period. During this period, females and pups most often started diving simultaneously. However, at night the pups most often started the diving events. The pair rarely resurfaced simultaneously, and there was no pattern in who resurfaced first. There was no difference in the dive duration of females and pups when they were swimming together. The pups occasionally dived alone, leaving their mothers at the surface. However, they returned faster to the surface when diving alone than when diving with their mothers. This was also the case when the females dived without the pups.

Historical and present distribution of Zostera marina in the high north (Troms County, northern Norway) – a decline over the last century

Abstract Eelgrass meadows (Zostera marina) have been mapped in Troms (Norway), in the temperate northeast Atlantic, north of the polar circle, from 2008 to 2011. In this region, there is little knowledge of the distribution of the eelgrass meadows. Northern Norway has an extensive coastline with many pressures and stakeholders. Old records (back to 1900) have been revisited and new locations surveyed based on a combination of spatial modeling, using digital information on depth, slope, and wave exposure and stakeholder recommendations. The results showed that 42% of the previously mapped locations had disappeared. However, we found Z. marina meadows at seven locations where they had not previously been recorded. Most meadows (66%) were smaller than 10,000 m2. The largest meadow covered an area of 325,000 m2, and was located in Balsfjorden. The results clearly show that Z. marina is able to form actively growing stands even at ∼70°N. Three of the meadows were first registered over 100 years ago, indicating long-lived stands in stable conditions. This study cannot explain the causes for the observed decline, and only discusses possible relations. The eelgrass meadows are genetically isolated but yet diverse. Management at fjord range level is required to maintain healthy and stable stands of eelgrass meadows in this region.

Red sea urchins (Echinus esculentus) and water flow influence epiphytic macroalgae density

Abstract The importance of forests of the kelp Laminaria hyperborea along the Norwegian coast is related to the three-dimensional structure that they create together with the associated macroalgae. Today, kelp forests have recovered in several areas after an extensive overgrazing by green sea urchins (Strongylocentrotus droebachiensis). However, red sea urchins (Echinus esculentus) have been observed grazing on kelp and algae in recently recovered kelp forests. Apart from grazing pressure, the abundance of algae depends on environmental conditions, such as light and water flow. The main aim of this study was to analyse how densities of red sea urchins, wave exposure and current speed influence densities of epiphytic macroalgae associated with kelp stipes. Our results show that the density of red sea urchins had a negative effect on macroalgal densities. In the well-developed kelp forest (i.e. in a late successional stage found in the southern region), macroalgal density decreased with depth and increased with water flow, both in terms of waves and currents. Wave forces had a higher effect than tidal-driven currents. In the recently recovered kelp forests (in the northern region), we found lower densities of epiphytic macroalgae in shallow compared to deep waters, most likely caused by red sea urchin grazing. Our study concludes that water flow is important for the ecological function of the kelp forest through the influence on habitat-forming epiphytic macroalgae, and that grazing by red sea urchins might severely affect kelp forest resilience in recently recovered areas.