Per Aberg

University of Gothenburg | GU · Department of Marine Sciences

The cultivation of kelp typically involves two stages, where an indoor hatchery phase preceedes the grow-out phase at-sea. The in situ adhesion of microscopic propagules onto specifically designed substrates using binders has been proposed as an alternative to conventional hatchery methods where juvenile seaweeds are cultured on seeded twine, aimed...

The cultivation of kelp typically involves two stages, where an indoor hatchery phase proceeds the grow-out phase at-sea. The in situ adhesion of microscopic propagules onto specifically designed substrates using binders has been proposed as an alternative to conventional hatchery methods where juvenile seaweeds are cultured on seeded twine, aimed...

Interactions in the Marine Benthos - edited by Stephen J. Hawkins August 2019

The allocation of resources to different life-history traits should represent the best compromise in fitness investment for organisms in their local environment. When resources are limiting, the investment in a specific trait must carry a cost that is expressed in trade-offs with other traits.In this study, the relative investment in the fitness re...

Persistence of populations at range edges relies on local population dynamics and fitness, in the case of geographically isolated populations of species with low dispersal potential. Focusing on spatial variations in demography helps to predict the long-term capability for persistence of populations across the geographical range of species' distrib...

Blooming filamentous algae recurrently overgrow macroalgae and seagrass in many coastal ecosystems, leading to potential losses in the functions and services these habitats provide. The seasonal reoccurrence of algal blooms is partly caused by excessive input of nutrients into coastal ecosystems. At the same time, overfishing of top predators has l...

Disturbance is an important structuring factor in intertidal communities. This study aimed at experimentally testing the effects of three important sources of disturbance to intertidal rocky habitats (abrasion, sediment deposition and herbivory) on the survivorship and growth of embryos of canopy forming fucoid species (Fucus vesiculosus and Fucus...

Empirical field studies in seagrass have revealed that overgrowth by filamentous algae which reduces seagrass growth can be explained by a top-down cascading effect caused by declines in top predators, which is enforced by eutrophication. On the Swedish west coast, 60% of the seagrass has disappeared since the 1980s. We hypothesised that overfishin...

The recovery of Ascophyllum nodosum, and the associated benthic community, was followed after repeated trampling disturbance at different intensities, from 2005 to 2010, at its southern limit (41�4102700N; 8�5005700W). The cover of A. nodosum and associated organisms and the demography of A. nodosum individuals in the most disturbed areas were foll...

Marginal populations are often geographically isolated, smaller, and more fragmented than central populations and may frequently have to face suboptimal local environmental conditions. Persistence of these populations frequently involves the development of adaptive traits at phenotypic and genetic levels. We compared population structure and demogr...

Aim Ascophyllum nodosum (L.) Le Jolis is a dominant fucoid seaweed occurring along sheltered, rocky shores throughout the North Atlantic (but not in the Pacific), where it is a foundational species of the intertidal community. Its large size and vulnerability to ice-scour have led to the hypothesis that contemporary populations in the north-west At...

The importance of external and internal population processes in determining variation in reproductive output and variation in population size were quantified with model simulations for open populations of the sequentially hermaphroditic limpet Patella vulgata using field data from the Isle of Man and South West Ireland. Cross-correlation analyses o...

For matrix population models, analyses of how sensitive the population growth rate is to changes in vital rates (i.e. perturbations) are important for studies of life history evolution as well as for management and conservation of threatened species. There are two types of sensitivity analyses corresponding to absolute (sensitivity) or relative (el...

Understanding the demography and function of biotope-forming seaweed species is of great importance for the conservation of the target species itself, as well as its associated organisms. The brown seaweed Ascophyllum nodosum is fundamental for the functioning of coastal marine ecosystems in the North Atlantic. In this study, we use a data-based si...

Seagrasses have declined in many places around the world, and the Swedish Skagerrak coast is no exception. Between the 1980s and 2000, the cover of eelgrass (Zostera marina L.) on the Swedish Skagerrak coast decreased about 60%. In the present study, the sites that were investigated in the 1980s and 2000 were revisited (1655 ha) in 2003 and 2004 to...

Using observations, experiments and model simulations we investigate the possibility and range of long-distance dispersal by seed rafting in eelgrass, Zostera marina, at the Swedish west coast. A field experiment showed that the breaking strength of post-flowering rhipidia decreased significantly over a 30-day period, indicating that ontogenetic ch...

The most commonly used birth function in two-sex demographic models is the harmonic mean birth function. This function treats all individuals of one sex as identical, i.e., stage specific fecundity is not taken into account. In the analysis presented here, the harmonic mean birth function is developed to incorporate size and sex specific fecunditie...

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 r...

1. The climate is changing and data-based simulation models can be a valuable tool for predicting population response to such changes and investigate the mechanisms of population change. In this study, a data-based two-species matrix model was constructed to explore the possible effects of elevated sea surface temperature (i.e. climate change) on t...

It is critical for our knowledge of biodiversity and ecosystem processes to understand how individual species contribute to ecosystem processes and how these contributions vary in space and time. We used a manipulative field experiment in five locations over 17 degrees of latitude [from southern Portugal to the Isle of Man (British Isles)] to deter...

The long-living species Ascophyllum nodosum dominates the mid-shore of sheltered rocky sites in NW Europe, forming near-monospecific stands. We aimed to determine the effects of small-scale disturbance on such shores, through manipulative experiments over a long period (almost 7 yr). We tested the general hypothesis that small-scale disturbance all...

Coastal areas play a crucial role in the economical, social and political development of most countries; they support diverse and productive coastal ecosystems that provide valuable goods and services. Globally flooding and coastal erosion represent serious threats along many coastlines, and will become more serious as a consequence of human-induce...

Coastal defence structures to protect sedimentary coastlines from erosion and flooding are increasingly common throughout Europe. They will become more widespread over the next 10–30 years in response to rising and stormier seas and accelerating economic development of the coastal zone. Building coastal defences results in the loss and fragmentatio...

Effects of environmental pollutants are most obvious when mortality is increased. However, there are other nonlethal factors that may affect population size significantly. Endocrine disruption as a mechanism of action for pollutants recently has received much attention. Observations of effects likely caused by endocrine disruptors in pulp mill effl...

Sargassum polyceratium is widely distributed around the island of Curaçao (Netherlands Antilles) where it inhabits strongly contrasting habitats. Changes in population structure have been followed in three bays with increasing levels of wave exposure at two depths: shallow (0 m) and deep (18 m). The effects of increasing wave exposure were investig...

Stochastic, stage-based matrix models were used to investigate the life history strategy of the seaweed Sargassum polyceratium in shallow intertidal and deep-water (18m) populations. Matrix models were parameterized with 3years of yearly transitions among four plant stages quantified from three bays on Curaçao (Netherlands Antilles). There were yea...

Isolated populations or those at the edge of their distribution are usually more sensitive to changes in the environment, such as climate change. For the barnacle Semibalanus balanoides (L.), one possible effect of climate change is that unpredictable spring weather could lead to the mismatching of larval release with spring phytoplankton bloom, he...

The relative importance of recruitment and post-recruitment processes in determining adult density among marine species varies considerably between species and populations. This study aimed to investigate the relative effects of variation in recruitment and survival rates on the density dynamics of 3 spatially separated natural populations of the b...

The effects of small-scale disturbances (80×30-cm plots) of canopy and grazers on intertidal assemblages were investigated in this 4-year experiment on sheltered rocky shores on the Swedish west coast. Canopy disturbances due to ice scouring were mimicked by removal of adult plants of the seaweed Ascophyllum nodosum (L.) Le Joli. Density of the mai...

Many brown macroalgae contain substantial concentrations of polyphenolic compounds, known as phlorotannins. Previous studies have shown that much of the variation in phlorotannin concentration is correlated with taxonomy and biogeography, but little is known about patterns of variation within species and populations. In this study, we examined intr...

The temporal and multiple-scale spatial variation in the density of mobile epifauna and grazing damage was investigated in populations of the brown seaweed Ascophyllum nodosum (Fucales: Phaeophyta). The relationship between density of grazers and grazing marks was also analyzed. The study was carried out in two locations of the northeastern Atlanti...

Grazing susceptibilities of gametophytic and tetrasporophytic fronds of Chondrus crispus Stack. from the Swedish west coast were examined in laboratory experiments. The overall consumption, irrespective of stage, as well as the feeding preference was tested on both adult and juvenile fronds. The mesoherbivores used in the experiments were the gastr...

Optimal defense theory (ODT) predicts that plants should have the highest defense levels in parts that have the highest value in terms of fitness. Assumptions about differences in fitness value among plant parts have previously been based on general reasoning, e.g., that reproductive tissue is more valuable than vegetative tissue since fitness ulti...

Summary1.Barnacles are a good model organism for the study of open populations with space-limited recruitment. These models are applicable to other species with open supply of new individuals and resource limitation. The inclusion of space in models leads to reductions in recruitment with increasing density, and thus predictions of population size...

The effects of density on the vital rates of the modular seaweed Ascophyllum nodosum (L.) Le Jol. were investigated in 2 areas of the northern Atlantic Ocean: the Isle of Man, in the Irish Sea, and Tjarno, on the Swedish west coast. The densities of plants (genets) were manipulated in the field, The impact of density on survival, growth and reprodu...

Spatial variability in the population dynamics of the intertidal acorn barnacle Semibalanus balanoides was investigated using a hierarchical sampling programme. Variability in a number of population parameters (size distribution, density, % cover, absolute growth and instantaneous mortality) was determined separately for new recruits and adults ove...

Summary • Many red seaweeds are characterized by a haploid-diploid life cycle in which populations consist of dioecious haploid (gametophyte) and diploid (tetrasporophyte) individuals as well as an additional diploid zygote-derived sporangium (carposporophyte) stage. A demographic analysis of Gracilaria gracilis populations was carried out to explo...

A manipulative experiment was done on the Swedish west coast to test hypotheses about effects of grazing on assemblages of algae and sessile animals on moderately exposed shores. The experiments, which lasted for 15 mo, involved a total of 144 experimental units at 16 sites in 2 areas 3 km apart. Experimental treatments involved fences to exclude g...

Variation in the level of settlement and recruitment in the intertidal barnacle Semibalanus balanoides was studied using a hierarchical sampling programme. The effect of three spatial scales, 10s of metres (sites), 1000s of metres (shores) and 100s of kilometres (locations), was determined. The largest spatial scale represented the distance between...

1 The potential cost of polyphenolic (phlorotannin) production in the brown seaweed Ascophyllum nodosum was investigated by testing for phenotypic trade-offs between phlorotannin content and annual growth. Relationships between tissue nitrogen and phlorotannin content, as well as between tissue nitrogen content and annual growth, were also examined...

Mortality soon after settlement is typically high and spatial distribution of germlings is usually very variable in seaweeds. This is the case for Ascophyllum nodosum (L.) Le Jol, which is a very common brown alga on sheltered rocky shores of the northern Atlantic. In this paper, the interactive effects of several factors on the survival of germlin...

Habitat and feeding preferences of crustacean mesoherbivores inhabiting the brown alga Ascophyllum nodosum (L.) Le Jol. and its macroepiphytes were examined on the Swedish west coast. After an initial survey of the epifauna, three species of mesoherbivores, the isopods Idotea granulosa Rahtke and Jaera albifrons Leach, and the amphipod Gammarus loc...

This study was designed to investigate spatial and temporal variation in Gelidium canariensis populations at two shores in northern Gran Canaria during two years. Spatial scales ranged from some hundred meters (distance between shores), 10 to 30 m (distance between plots) to less than 3 m (distance between quadrats). Gelidium individuals were defin...

Observation of spatial and temporal variation in the distribution and abundance of organisms is often the starting point from which questions and hypotheses about ecological processes arise. This study was designed to investigate spatial variability in abundance of macrorecruits and adults of the brown alga Ascophyllum nodosum using hierarchical sa...

The survival of germlings of the brown alga Ascophyllum nodosum on the west coast of Sweden were investigated in two field experiments. In the first experiment the role of Littorina fabalis, L. littorea, L. obtusata and L. saxatilis for the survival of 5 days old germlings were tested at two spatial scales, by comparing plots cleared of Littorina s...

Models and experiments seeking to explain intraspecific variation in brown algal phlorotannins (polyphenolics) have mainly focused on the effect of 2 factors, herbivory and resource availability (carbon/nutrients). The possible importance of other biotic and abiotic factors, e.g. pathogenic micro-organisms, heavy metals and UV radiation, has often...

The pattern of allocation of reproductive biomass in the brown alga Ascophyllum nodosum (L.) Le Jol. was investigated in 2 populations on the Swedish west coast. An analysis of the demography of A. nodosum in these stochastic environments suggested 2 specific hypotheses about the reproductive allocation. First, the annual reproductive effort [annRE...

The spatial variation in the proportion of gametophytes to tetrasporophytes of the red alga Chondrus crispus Stackhouse was investigated in two areas, Tjarno and Idefjorden, on the Swedish west coast. Tjarno represents a marine environment and Idefjorden an estuarine, polluted environment, where C. crispus on the regional scale is close to the limi...

Spatial variation in polyphenolic content in annual shoots of the brown alga Ascophyllum nodosum was quantified using a hierarchical sampling design. Three sampling levels, covering distances of 100–106 m, were used. Comparisons were made between two areas, Tjrn on the Swedish west-coast and the Isle of Man in the Irish Sea, with very different typ...

Phycological studies of Nordic coastal waters : a festschrift dedicated to Prof. Mats Waern on his 80th birthday, ISBN 91-7210-078-8: eds. I. Wallentinus, P. Snoeijs, Acta phytogeographica Suecica, ISSN 0084-5914 ; 78, 49-63 Records of attached seaweeds new to the flora of Sweden and records of very rare and otherwise interesting species from the w...

Ambio, ISSN 0044-7447, vol. 21, nr. 8, 511-516 Results from aerial surveys of hauled-out harbor seals, Phoca vitulina, in the entire Kattegat-Skagerrak, the Limfjord and the western part of the Baltic Sea in 1989-1991 are compared with results from surveys conducted soon after the seal epizootic in 1988. The results suggest that an increase in rela...

Very little is known about the demography in size-structured seaweed populations, and this is especially true for populations in variable environments. Thus, the demography of the brown alga Ascophyllum nodosum was analyzed with a matrix population model. This was built on a 3-yr study in two populations on the Swedish west coast, where >1100 indiv...

Large variations in vital rates are found among individuals in populations of Ascophyllum nodosum along the Swedish W coast due to temporal variation in the environment (years with or without ice). A matrix model with a set of three population projection matrices for each population described the demography during three different types of years (en...

A nondestructive method for measuring the size of the brown alga Ascophyllum nodosum (L.) Le Jol. has been modified in order to esbmate the dry weight of tagged ind~viduals for a size-based demographic study. There is a very strong positive correlation between the dry weight (dw) of an individual and a crude measurement of its volume. A total of 78...

British phycological journal, ISSN 0007-1617, vol. 24, 183-190