Per R. Jonsson

MULTIPLE FUNCTIONS INCREASE THE IMPORTANCE OF BIODIVERSITY FOR OVERALL ECOSYSTEM FUNCTIONING

Biodiversity is proposed to be important for the rate of ecosystem functions. Most biodiversity-ecosystem function studies, however, consider only one response variable at a time, and even when multiple variables are examined they are analyzed separately. This means that a very important aspect of biodiversity is overlooked: the possibility for different species to carry out different functions at any one time. We propose a conceptual model to explore the effects of species loss on overall ecosystem functioning, where overall functioning is defined as the joint effect of many ecosystem functions. We show that, due to multifunctional complementarity among species, overall functioning is more susceptible to species loss than are single functions. Modeled relationships between species richness and overall ecosystem functioning using five empirical data sets on monocultures reflected the range of effects of species loss on multiple functions predicted by the model. Furthermore, an exploration of the correlations across functions and the degree of redundancy within functions revealed that multifunctional redundancy was generally lower than single-function redundancy in these empirical data sets. We suggest that by shifting the focus to the variety of functions maintained by a diversity of species, the full importance of biodiversity for the functioning of ecosystems can be uncovered. Our results are thus important for conservation and management of biota and ecosystem services.

Analysis of behavioural rejection of micro-textured surfaces and implications for recruitment by the barnacle Balanus improvisus.

Experiments performed in the field and in the laboratory show that the barnacle, Balanus improvisus, preferentially settles on smooth surfaces. Settlement and recruitment of B. improvisus was evaluated on micro-textured surfaces with scales of surface texture ranging from 1 to 100 µm in profile heights. Surface texture with profile heights within a topographic range of 30-45 µm reduced settlement and recruitment by 92% as compared to smooth surfaces. The reduction in recruitment on micro-textured surfaces is best explained by behavioural responses to surface topography. Behavioural experiments show that cyprids have a higher propensity for smooth surfaces than for micro-textured surfaces. Cyprids spend more time exploring smooth surfaces and more time swimming when exposed to micro-textured surfaces. Micro-textured surfaces are more often rejected by cyprids after exploration than smooth surfaces. It is suggested that some scales of surface texture could be exploited to improve future anti-fouling techniques in geographical areas where Balanus improvisus is a severe fouling problem.

Surface active adrenoceptor compounds prevent the settlement of cyprid larvae of Balanus improvisus

The barnacle Balanus improvisus is the major fouling macroorganism in Swedish waters and it colonizes most man‐made surfaces submerged in the sea. New or impending legislation restricts the use of traditional, hazardous antifouling coatings based on heavy metals, mainly copper and tin. This calls for the development of new non‐toxic methods that prevent barnacle settlement. In this work several adrenoceptor compounds are shown to be very efficient in preventing the settlement of cyprid larvae of B. improvisus. The settlement rate of laboratory‐reared cyprids was studied in hydrophilised polystyrene dishes containing adrenoceptor antagonists and agonists dissolved in seawater. Two of these drugs, medetomidine and clonidine, repeatedly inhibited settlement at concentrations between 1 nM and 10 nM. In the vertebrate adrenoceptor classification system, which separates pharmacological substances according to their receptor affinity, both of these substances are classified as α2 adrenoceptor agonists. An inhibiting effect on presyn‐aptic receptors is suggested, but the localization of the receptor effect requires futher studies. Experiments also revealed that the inhibiting effect of medetomidine was reversible. Cyprids incubated with medetomidine for 20 h attached and metamorphosed into juvenile barnacles after washing and transferrence to seawater. The antagonizing compound atipamezole reversed the effect of medetomidine. This observation supports the assumption that this substance acts at the receptor level. Studies of the surface affinity of medetomidine revealed a strong tendency to accumulate in solid/ liquid phase boundaries. This ability makes it particularly attractive as a candidate for the development of a slow‐release carrier in marine coatings. Panels coated with medetomidine in an acrylate polymer and exposed in the field reduced the recruitment of B. improvisus by 96% after 4 weeks and by 70% after 8 weeks.

Interactions between wave action and grazing control the distribution of intertidal macroalgae

Canopy-forming macroalgae are key species on temperate rocky shores. However, there is a lack of understanding of how the relative balance of physical and biological factors controls the establishment and persistence of intertidal macroalgae. Here we present an integrated study of the relative importance of wave-induced forces and grazing for the recruitment and survival of the canopy-forming intertidal macroalgae Fucus vesiculosus and F. spiralis. A set of overtopped breakwaters provided a nearly unconfounded gradient in wave exposure between seaward and landward sides. A biomechanical analysis was performed based on empirical measurements of maximum drag forces in breaking waves, a model of long-term maximum wave height, and the breaking stress of Fucus spp. The estimated maximum flow speed (7-8 m/s) on the seaward side of the breakwaters was predicted to completely dislodge or prune Fucus spp. larger than approximately 10 cm, while dislodgment was highly unlikely on the landward side for all sizes. Experimental transplantation of Fucus spp. supported the biomechanical analysis but also suggested that mechanical abrasion may further limit survival in wave-exposed locations. Experimental removal of the limpet Patella vulgata, which was the principal grazer at this site, resulted in recruitment of Fucus spp. on the seaward side. We present a model of limpet grazing that indicates that limpet densities >5-20 individuals/m2 provide a proximate mechanism preventing establishment of Fucus spp., whereas wave action >2 m/s reduces persistence through dislodgment and battering. In a conceptual model we further propose that recruitment and survival of juvenile Fucus spp. are controlled indirectly by wave exposure through higher limpet densities at exposed locations. This model predicts that climate change, and in particular an increased frequency of storm events in the northeast Atlantic, will restrict fucoids to more sheltered locations.

Disturbance-diversity models: what do they really predict and how are they tested?

The intermediate disturbance hypothesis (IDH) and the dynamic equilibrium model (DEM) are influential theories in ecology. The IDH predicts large species numbers at intermediate levels of disturbance and the DEM predicts that the effect of disturbance depends on the level of productivity. However, various indices of diversity are considered more commonly than the predicted number of species in tests of the hypotheses. This issue reaches beyond the scientific community as the predictions of the IDH and the DEM are used in the management of national parks and reserves. In order to compare responses with disturbance among measures of biodiversity, we used two different approaches of mathematical modelling and conducted an extensive meta-analysis. Two-thirds of the surveyed studies present different results for different diversity measures. Accordingly, the meta-analysis showed a narrow range of negative quadratic regression components for richness, but not evenness. Also, the two models support the IDH and the DEM, respectively, when biodiversity is measured as species richness, but predict evenness to increase with increasing disturbance, for all levels of productivity. Consequently, studies that use compound indices of diversity should present logical arguments, a priori, to why a specific index of diversity should peak in response to disturbance.

Mass mortality of the bivalve Cerastoderma edule on the swedish west coast caused by infestation with the digenean trematode Cercaria cerastodermae I

Abstract The trematode Cercaria cerastadermae I, a parasite of the cockle Cerastaderma edule, is recorded for the first time in Scandinavian waters. More than 20% of the investigated population of C. edule was infested by C. cerastodermae I, and most individuals showed severe tissue damage. Infestation intensity and tissue damage together with field observations strongly indicate that infestation by C. cerastodermae I was responsible for the mass mortality of C. edule during the summer of 1991. Patterns of infestation intensity, damage to the bivalve foot and an experiment on burrowing behaviour suggest that infestation by C. cerastadermae I impairs burrowing ability. The resulting large numbers of C. edule lying on the sediment surface may be misinterpreted as being caused by other factors e.g. oxygen deficiency.

HETEROGENEOUS GENOMIC DIFFERENTIATION IN MARINE THREESPINE STICKLEBACKS: ADAPTATION ALONG AN ENVIRONMENTAL GRADIENT

Evolutionary divergence among populations occupying ecologically distinct environments can occur even in the face of on‐going gene flow. However, the genetic underpinnings, as well as the scale and magnitude at which this differentiation occurs in marine habitats are not well understood. We investigated the patterns and degree of genomic heterogeneity in threespine sticklebacks (Gasterosteus aculeatus) by assessing genetic variability in 20 nongenic and 20 genic (associated with genes important for freshwater adaptation) microsatellite loci in samples collected from 38 locations spanning the entire Baltic Sea coast to the North Sea boundary. Population divergence (FST ≈ 0.026) and structuring (five genetic clusters) was significantly more pronounced in the genic as compared to nongenic markers (FST ≈ 0.008; no genetic clusters). Patterns of divergence in the genic markers—45% of which were identified as outliers—correlated with local differences in salinity. Yet, a strong positive correlation between divergence in genic and nongenic markers, and their association with environmental factors suggests that adaptive divergence is reducing gene flow across the genome. Apart from providing a clear demonstration of heterogeneous genomic patterns of differentiation in a marine species, the results are indicative of adaptive population structuring across the relatively young Baltic Sea in spite of ample opportunities for gene flow.

INCREASING INTRASPECIFIC DIVERSITY ENHANCES SETTLING SUCCESS IN A MARINE INVERTEBRATE

Theoretical and empirical research during the last decade suggests that increasing species richness often enhances ecosystem processes such as productivity, nutrient cycling, or resistance to disturbance. By analogous reasoning, it can be hypothesized that genetic diversity within species will have equivalent effects; however, this hypothesis has rarely been tested. We present experimental support for the positive effects of intraspecific diversity on a key trait: larval settlement in a marine invertebrate, the barnacle Balanus improvisus. Varying within-species diversity levels of an animal over nine experiments, we found increasing larval settlement with increasing diversity (one, two, or three parental broods). Possible mechanisms explaining this pattern include: (1) facilitation of gregarious response through the presence of founder genotypes, and (2) ensuring genetic complementarity to increase future reproductive potential. Our results indicate that changing intraspecific genetic diversity could have hitherto unrecognized community-scale implications for larval recruitment and space occupancy.

Reduction of barnacle recruitment on micro‐textured surfaces: Analysis of effective topographic characteristics and evaluation of skin friction

This study investigates five designed micro‐textured surfaces and their effects on barnacle fouling and hydrodynamic drag. Three of the micro‐textures were developed in the present study and evaluated together with two commercial riblet films. All micro‐structures were arranged as longitudinal grooves with different profile depths, widths and angles of inclination. In field tests the recruitment of the barnacle Balanus improvisus on micro‐textured surfaces and smooth controls was evaluated. All micro‐textured surfaces reduced recruitment, and the most efficient texture reduced recruitment by 98%. For some micro‐textures the reduction of recruitment declined as settlement intensity increased. In a correlative analysis, the trigonometric inclination of the micro‐structures explained most of the recruitment reduction. The steepest angle of inclination caused a massive reduction in barnacle settlement. Surface micro‐structures may affect the boundary‐layer flow and the hydrodynamic drag (skin friction) of the surface. The skin friction was empirically measured in a flow channel using a sub‐set of the tested micro‐textures. The measurements of skin friction showed that the orientation of the microstructures is important, with a minimum friction when the grooves are parallel to the flow. For one of the micro‐textures the skin friction was ca 10% lower compared to a hydraulically smooth surface. It is concluded that, depending on the flow speed, micro‐textures will not significantly increase skin friction when arranged parallel to the flow, even at moderate protrusion through the viscous sub‐layer.

Roughness-dependent Removal of Settled Spores of the Green Alga Ulva (syn. Enteromorpha) Exposed to Hydrodynamic Forces from a Water Jet

Topographic features change the hydrodynamic regime over surfaces subjected to flow. Hydrodynamic microenvironments around topographic structures may have consequences for recruitment and removal of propagules of marine benthic organisms. The settlement and adhesion of zoospores from the green alga Ulva linza (syn. Enteromorpha linza) to defined topographies was investigated. A range of topographic size scales (Rz: 25u200a–u200a100u2009μm) was manufactured from plankton nets, creating patterns with ridges and depressions. The topographic scales span a roughness similar to that of natural substrata and antifouling coatings. Spores were removed from the surfaces by a calibrated water jet. Fewer spores were removed from the smallest topographic structure tested (Rz: 25u2009μm) compared to both the smooth (Rz: 1) and the roughest (Rz: 100u2009μm) structures. Zoospores that settled in depressions were less likely to be removed compared to spores on the ridges. The results in terms of the interaction between surface topography and hydrodynamic forces have implications for both natural substrata exposed to wave action and antifouling surfaces on ships hulls. The possible effects of topography on increasing zoospore adhesion and offering a refuge from hydrodynamic forces are discussed.