Lars-Ove Loo

Improving marine water quality by mussel farming : a profitable solution for Swedish society

Abstract Eutrophication of coastal waters is a serious environmental problem with high costs for society globally. In eastern Skagerrak, reductions in eutrophication are planned through reduction of nitrogen inputs, but it is unclear how this can be achieved. One possible method is the cultivation of filter-feeding organisms, such as blue mussels, which remove nitrogen while generating seafood, fodder and agricultural fertilizer, thus recycling nutrients from sea to land. The expected effect of mussel farming on nitrogen cycling was modeled for the Gullmar Fjord on the Swedish west coast and it is shown that the net transport of nitrogen (sum of dissolved and particulate) at the fjord mouth was reduced by 20%. Existing commercial mussel farms already perform this service for free, but the benefits to society could be far greater. We suggest that rather than paying mussel farmers for their work that nutrient trading systems are introduced to improve coastal waters. In this context an alternative to nitrogen reduction in the sewage treatment plant in Lysekil community through mussel farming is presented. Accumulation of bio-toxins has been identified as the largest impediment to further expansion of commercial mussel farming in Sweden, but the problem seems to be manageable through new techniques and management strategies. On the basis of existing and potential regulations and payments, possible win-win solutions are suggested.

Marine eutrophication induced oxygen deficiency: Effects on soft bottom Fauna, Western Sweden

Abstract Marine eutrophication is studied in a multidisciplinary project in the Kattegat, western Sweden. Input of nutrients has increased several fold during this century; nitrogen ≈ 6 times, phosphrorus ≈ 10 times. This has caused elevated concentrations of nutrients in the water and increased primary production. Some adverse effects at the bottom have been noted annually from about August through October in the 1980s, e.g. fish catches have dropped and mortalities have been reported for fish and benthic animals including Nephrops noruegicus. In this paper we evaluate the effects on benthic macrofauna which are suggested to be caused mainly by oxygen deficiency occurring especially around the depth ofa strong halocline (≈ 15m), but also along a bottom transect down to 57 m. At some sites the benthic communities were impoverished, and at others only some species seemed to be especially sensitive, e.g. the bivalve Abra alba and the brittle star Amphiura filijormis. In shallow < 10 m) exp.sed waters an an...

Bivalve suspension-feeding dynamics and benthic-pelagic coupling in an eutrophicated marine bay

Abstract The open exposed Laholm Bay in the Kattegat is eutrophicated through riverine input, mainly of N. The benthic macrofauna down to 10 m depth (60 km 2 ) is dominated by the suspension-feeding bivalves Cardium edule and Mya arenaria . To estimate the seasonal and annual consumption of seston by the suspension-feeders in Laholm Bay, we carried out three sets of observations. (1) The abundance and biomass of the macrofauna in this depth interval were assessed along eight transects. (2) The secondary production of the two bivalves was estimated over a 10-month period in two sampling squares. (3) The filtration rate of C. edule was determined in natural seawater in laboratory experiments during different seasons. The bivalves can in theory filter all of the water volume down to 10 m in 3 days and, thus, make a significant impact on the phytoplankton concentration. In our study, however, they filtered only approximately half of their potential feeding capacity, perhaps because food availability was low due to low turnover close to the bottom or due to physical disturbance. The majority of the phytoplankton is exported from the bay. Bivalve abundance, biomass, production and growth rate were moderate and generally lower than in adjacent areas to the north. In autumn, the bivalves consumed >90% of the seston in comparison with net-zooplankton consumption. An energy-flow diagram for the bivalves is presented including estimates of bivalve N excretion and biodeposition.

Hypoxia, salinity and temperature as structuring factors for marine benthic communities in a eutrophic area

Abstract During 1983 to 1990 the benthic macrofauna was studied at eight stations along a depth gradient from 5 to 53 m in the SE Kattegat on the Swedish west coast. The area is almost non-tidal and characterized by a strong halocline at about 15 m with brackish water (S=12 to 25) at the surface and oceanic water (S=32 to 34) below the halocline. Increasing eutrophication of the area has caused annual periodic below-halocline oxygen deficiency in the 1980s. In this paper, we present spatial and temporal benthic-community structural differences between the fauna above, around and below the halocline. As a consequence of the extensive and severe hypoxia below the halocline, especially in autumn 1988, significant reductions of the benthic fauna were recorded. We conclude that the salinity variation around the halocline in combination with oxygen stress at these depths and just below the halocline have great impact on the benthic faunal structure and biomass. Our long-term field observations suggest that benthic sub-littoral communities can survive lower oxygen concentrations than previously presented.

Production, dynamics and demography of an Amphiura filiformis population

Secondary product~on and popula t~on dynamics of the bnttle star Amphiura fillformis (0 F Muller) were studied between June 1990 and November 1991 at 40 m depth In the Skagerrak west Sweden Mean abundance of individuals > 1 mm in disc diameter was stable around 280 ind m After a spawnlng maximum In June and July settling post-larvae (ca 7000 ind m-2) occurred In autumn 1991 DISC growth and gonad product~on accounted for ca 68 9 % (1 8 g AFDW m- yr-l) of the total annual product~on in the populat~on About 13 3 % (0 34 g AFDW m-2 yr.) of the total production was allocated to regeneration of arms probably a result of cropping by predators Mean regenerated b ~ o mass In percent of total blomass for adult A hliformls was between 12 and 30% (mean 22 %) Annual production/b~omass ratio was 0 46 yr. The Input of energy to arm regeneration indicates the m p o r tance of A fi l l forms as an ~mportant food source

Production and energy budget in marine suspension feeding populations : Mytilus edulis, Cerastoderma edule, Mya arenaria and Amphiura filiformis

Abstract The pelagic primary production and the secondary production of four species of benthic suspension feeders were frequently measured over a period of approximately one year in four different habitats. Simplified energy budgets over one-year periods are presented including ingestion, absorption, faeces production, respiration and secondary production. The production of a Mytilus edulis culture exceeded primary production by about 6.25 times, whereas semi-exposed shallow-water populations of Cerastoderma edule and Mya arenaria had a production roughly equal to primary production. In an exposed area, the latter species had a secondary production: primary production ratio of 0.15:1, whereas for a deeper-living (40 m) Amphiura filiformis population this relation was 0.0034:1. M. edulis followed by C. edule and M. arenaria in the semi-exposed habitat had the comparatively lowest Respiration: Absorption ratios and the highest Production: Absorption ratios. This study emphasizes the ecological importance of horizontal advective processes for energy transfer from the pelagic to the benthic system.

Suspension feeding in adult Nephrops norvegicus (L.) and Homarus gammarus (L.) (decapoda)

Abstract Suspension feeding in adults of the Norway lobster Nephrops norvegicus (40–74 g) and the European lobster Homarus gammarus (280–350 g) was tested in experiments offering planktonic food items of different sizes from 200 to 600 μm and measuring the clearing capacity. Both lobster species were found to effectively clear water of food particles comprising nauplii of the brine shrimp Artemia salina of about 600 μm in size. These were reduced to 50% of the initial concentration within 5 h and to 90% within 12 h. When N. norvegicus was offered food particles averaging 200 μm, a significant reduction in average size occurred, indicating that the minimum retention size is around 200 μm. Fluorescently dyed Artemia salina were recovered in the stomach and intestine of lobsters proving that the filtered particles are passed to the digestive tract. Results from other experiments, using the blood pigment (haemocyanin) concentration as an index of nutritional state, indicated that the lobsters can get some nutritional advantage from suspension feeding. Suspension feeding in larger decapods has not been described previously, so the significance of this finding is discussed with respect to changes in behavioural and ecological role.

Seascape genetics and biophysical connectivity modelling support conservation of the seagrass Zostera marina in the Skagerrak-Kattegat region of the eastern North Sea

Maintaining and enabling evolutionary processes within meta‐populations are critical to resistance, resilience and adaptive potential. Knowledge about which populations act as sources or sinks, and the direction of gene flow, can help to focus conservation efforts more effectively and forecast how populations might respond to future anthropogenic and environmental pressures. As a foundation species and habitat provider, Zostera marina (eelgrass) is of critical importance to ecosystem functions including fisheries. Here, we estimate connectivity of Z. marina in the Skagerrak–Kattegat region of the North Sea based on genetic and biophysical modelling. Genetic diversity, population structure and migration were analysed at 23 locations using 20 microsatellite loci and a suite of analytical approaches. Oceanographic connectivity was analysed using Lagrangian dispersal simulations based on contemporary and historical distribution data dating back to the late 19th century. Population clusters, barriers and networks of connectivity were found to be very similar based on either genetic or oceanographic analyses. A single‐generation model of dispersal was not realistic, whereas multigeneration models that integrate stepping‐stone dispersal and extant and historic distribution data were able to capture and model genetic connectivity patterns well. Passive rafting of flowering shoots along oceanographic currents is the main driver of gene flow at this spatial–temporal scale, and extant genetic connectivity strongly reflects the “ghost of dispersal past“ sensu Benzie, . The identification of distinct clusters, connectivity hotspots and areas where connectivity has become limited over the last century is critical information for spatial management, conservation and restoration of eelgrass.

Substantial changes in the depth distributions of benthic invertebrates in the eastern Kattegat since the 1880s

Abstract Bottom trawling and eutrophication are well known for their impacts on the marine benthic environment in the last decades. Evaluating the effects of these pressures is often restricted to contemporary benthic data, limiting the potential to observe change from an earlier (preimpact) state. In this study, we compared benthic species records from 1884 to 1886 by CGJ Petersen with recent data to investigate how benthic invertebrate species in the eastern Kattegat have changed since preimpact time. The study shows that species turnover between old and recent times was high, ca. 50%, and the species richness in the investigation area was either unchanged or higher in recent times, suggesting no net loss of species. Elements of metacommunity structure analysis of datasets from the 1880s, 1990s, and 2000s revealed a clear change in the depth distribution structure since the 1880s. The system changed from a Quasi‐nested/Random pattern unrelated to depth in the 1880s with many species depth ranges over a major part of the studied depth interval, to a Clementsian pattern in recent times strongly positively correlated with depth. Around 30% of the 117 species recorded both in old and in recent times, including most trawling‐sensitive species, that is large, semiemergent species, showed a decrease in maximal depth of occurrence from the deeper zone fished today to the shallower unfished zone, with on average 20 m. Concurrently, the species category remaining in the fished zone was dominated by species less sensitive to bottom trawling like infauna polychaetes and small‐sized Peracarida crustaceans, most likely with short longevity. The depth interval and magnitude of the changes in depth distribution and the changes in species composition indicate impacts from bottom trawling rather than eutrophication. Furthermore, the high similarity of results from the recent datasets 10 years apart suggests chronic impact keeping the system in an altered state.

Reference conditions and EQOs for aquatic vegetation and macrozoobenthos

Development of a methodological approach to define and characterise type areas of selected elements of the ecosystems in the open parts of the Skagerrak and Kattegat. The selected elements are aquatic vegetation on hard substrate and macrozoobenthos. Furthermore, the project will develop quantitative ecological relationships and empirical models that describe the relationship between anthropogenic pressures and biological elements.