Forecast climate change conditions sustain growth and physiology but hamper reproduction in range-margin populations of a foundation rockweed species

Intensifying environmental changes due to climate change affect marine species worldwide. Herein, we experimentally tested if the combination of forecasted warming and hyposalinity adversely affected growth, receptacle formation, and photosynthesis of three marginal populations of the brown alga Fucus from the northern Baltic Sea. Growth was not impaired by the projected consequences of climate change but genotypes varied in their responses, suggesting existence of genetic variation in phenotypic plasticity. Climate change further prevented receptacle formation, implying that Fucus fail to reproduce sexually. Photosynthesis was not affected by climate change but varied among populations. Our results show that Fucus populations photosynthesized, grew, and survived well under the projected climate change but their sexual reproduction ceased. This suggests that the marginal populations tested herein are resilient to future conditions but only if asexual reproduction enables them to proliferate.</p

Tolerance and potential for adaptation of a Baltic Sea rockweed under predicted climate change conditions

Climate change is threating species' persistence worldwide. To predict species responses to climate change weneed information not just on their environmental tolerance but also on its adaptive potential. We tested how thefoundation species of rocky littoral habitats, Fucus vesiculosus, responds to combined hyposalinity and warmingprojected to the Baltic Sea by 2070–2099. We quantified responses of replicated populations originating from theentrance, central, and marginal Baltic regions. Using replicated individuals, we tested for the presence of withinpopulationtolerance variation. Future conditions hampered growth and survival of the central and marginalpopulations whereas the entrance populations fared well. Further, both the among- and within-populationvariation in responses to climate change indicated existence of genetic variation in tolerance. Such standinggenetic variation provides the raw material necessary for adaptation to a changing environment, which mayeventually ensure the persistence of the species in the inner Baltic Sea.</p

It takes two to stay afloat: interplay of morphology and physiological acclimation ensures long-term floating dispersal of the bladderwrack Fucus vesiculosus (Phaeophyceae, Fucales)

Floating algae can be found in high abundances at mid and high latitudes, their prolonged positive buoyancy allowing long-distance dispersal. However, despite their importance to dispersal and ecological and evolutionary meta-population dynamics, little is known about the buoyancy responses of high latitude algae to the conditions at the sea surface. Indeed, even at 60 degrees N environmental conditions during spring/summer can be challenging, and may cause the demise and sinking of floating algae. The bladderwrack Fucus vesiculosus from the Northern Baltic Sea floats on the sea surface when detached from the benthic substratum. We conducted a field experiment with tethered individuals during their reproductive period to measure variation in floating time and how that is related to morphological traits such as occurrence of vesicles and/or receptacles, and to measure growth and photosynthesis while afloat. Algal individuals with receptacles tended to sink quickly, whereas the longest floating time was evident for individuals carrying vesicles but lacking receptacles. While afloat, all individuals grew in size, showed photosynthetic acclimation to sea surface conditions and had a few invertebrates associated with them. Our results showed that rafts of F. vesiculosus were physiologically viable until their day of sinking and that morphological traits such as the occurrence of vesicles and receptacles modified their floating time. Accordingly, floating algae with a similar morphological set-up, and thus also reproductive phenology, to F. vesiculosus can have a high floating persistence, but, depending on their reproductive structures, they may mostly serve as long-range dispersal vehicles for associated organisms.</p

Low abundance of floating marine debris in the northern Baltic Sea

We determined the spatial and seasonal distribution of Floating Marine Debris (FMD) by visual ship surveys across the northern Baltic Sea between Finland and Sweden. FMD density was comparatively low, and we found the highest debris density close to major port cities. The seasonal variation in debris density was not pronounced although we observed more FMD items during the summer surveys. Plastic bags were the most common identifiable litter items, and we also found other consumer items (plastic bottles and cups). Styrofoam items suggest fishing or aquaculture activities as potential sea-based sources of FMD. These are the first data on FMD density in the Baltic Sea, and they are substantially lower than those reported for other coastal waters, which may be due to (i) lower human population densities, and (ii) higher environmental awareness in the Scandinavian countries.</p

A Comparison of Genetic Variation in Two Endemic Thermal Spring Isopods, <em>Thermosphaeroma thermophilum</em> and <em>T. milleri</em> (Crustacea - Isopoda: Sphaeromatidae)

Populations with reduced gene flow and restricted population size are expected to show reduced genetic variation. Using starch gel electrophoresis, we examined allozyme variation at 12 loci in two species of freshwater, sphaeromatid isopods. Thermosphaeroma thermophilum, an endangered species, inhabits a single thermal spring in central New Mexico, USA; and T. milleri, inhabits a more complex thermal spring system in northern Chihuahua, México. We found no significant differences in allelic variation between the sexes within each species. Between species, electromorphs at each locus differed significantly in both number and moiety on the gel, with T. milleri showing greater polymorphism and greater heterozygosity than T. thermophilum. Nei’s unbiased genetic distance, calculated using the nine loci common to both populations (D = 0.75), was consistent with morphological classification of T. thermophilum and T. milleri as separate species, as well as with molecular analyses suggesting that these populations have been separated since the late Cretaceous (88 myr). Moreover, consistent with the theoretical expectation that small, isolated populations will exhibit reduced genetic variation, T. thermophilum, an endangered species, exhibited significantly less genetic variation than the more numerous and less confined T. milleri. We compare our results with other recent studies using this approach to understand the population genetics of natural populations

White-tailed eagle (Haliaeetus albicilla) and great cormorant (Phalacrocorax carbo) nestlings as spatial sentinels of Baltic acidic sulphate soil associated metal contamination

Sulphate soils, characterised by low pH conditions, are found worldwide, and are potentially large sources of metal contamination, often exceeding industrial emissions. Metal leaching from sulphate soils has been shown to be harmful to aquatic organisms, but the cascading effect on exposure in apex avian predators has not been studied earlier. With the present study we aimed at evaluating the potential of white-tailed eagle (Haliaeetus albicilla) and great cormorant (Phalacrocorax carbo) nestlings, collected from nests located either in sulphate soil or control areas, for monitoring spatial contaminant trends of metals typically associated with sulphate soils.In blood of white-tailed eagles, the concentrations of aluminium and cobalt were significantly higher in sulphate soil areas. In blood of great cormorants, the concentrations of copper and manganese were so, while the concentration of zinc was found to be lower. Also, we observed an interaction between the latitude and soil type in cobalt and lithium concentrations of great cormorants, showing that concentrations in the sulphate soil associated nestlings rose more steeply towards the north than in the control group. Latitudinal trends of higher concentrations in the south were found in cadmium, manganese, and copper of white-tailed eagle nestlings, while thallium of white-tailed eagle nestlings, and thallium and zinc of great cormorant nestlings showed a latitudinal trend of higher concentrations in the north. Concentrations of several metals correlated positively within a species indicating covariation in metal exposure. Generally, the metal concentrations in both species were similar to levels reported to be below toxicity thresholds in other species. These results indicate, that white-tailed eagle and great cormorant nestling metal burdens may indicate environmental contamination from acidic sulphate soil runoff, and that they may act as indicators of latitudinal gradient identifying different contamination sources.</p

Cormorants have negligible seascape-scale impacts on benthic vegetation communities

Cormorant populations in the Baltic Sea have rapidly expanded since the 1990s, raising concerns about their ecosystem impacts. Nutrient runoff from colonies, as well as cormorant predation on fish, can affect surrounding producer communities. Past studies have found cormorant impacts on producers in the immediate vicinity of colonies, but the importance of cormorants over a larger spatial scale is unknown, especially compared to other environmental variables. We used an extensive underwater vegetation inventory dataset (~18 000 data points along the Finnish coast) to determine the effects of cormorant colonies on macroalgae and plants. We compared community structure and species abundance/occurrence in near-colony (10 km from a colony) points, and determined the importance of cormorant influence (using an index incorporating colony size and distance from the colony) in near-colony sites. We found no significant differences in community structure between near-colony and control points in most habitats, and adding cormorant index only infinitesimally improved statistical models after incorporating other environmental factors. However, the abundance of several species did differ, in particular the foundation species bladderwrack (Fucus vesiculosus) and eelgrass (Zostera marina) were either less likely to occur in near-colony points or negatively correlated with cormorant index, possibly due to the effects of nutrient enrichment from colonies. Our findings confirm that cormorants can have effects on some producer species, but highlight that these effects are negligible when taking into account the scale and magnitude of other bottom up and top-down processes occurring in the Baltic Sea.</div

Double-edged sword of desalination: Decreased growth and increased grazing endanger range-margin Fucus populations

Coastal ecosystems worldwide are facing intense and diverse pressures caused by anthropogenic climate change, which compromises physiological tolerance of organisms, as well as causes shifts in their biotic interactions. Within-species genetic variation plays an important role in persistence of populations under such changes by providing building blocks for adaptation. The brackish-water Baltic Sea is predicted to experience a significant desalination by the end of this century. The Baltic Sea is dominated, in terms of biomass, by a few species with locally adapted populations, making it a suitable model for studying shifting biotic interactions under changing abiotic conditions. We exposed two foundation species of brown algae, Fucus vesiculosus and Fucus radicans, to end-of-the-century projected salinity together with grazing pressure in experimental tanks. We measured growth, grazing and phlorotannin content and compared these traits between the current and projected future salinity conditions, between Fucus species, and between high and low genotypic diversity groups. Grazing, phlorotannin content and growth of both F. radicans and F. vesiculosus all showed genotypic variation. Future decreased salinity hampered growth of F. vesiculosus irrespective of genotypic diversity of the experimental population. Furthermore, the growth response to desalination showed variation among genotypes. F. radicans was more susceptible to grazing than F. vesiculosus, and, in the high genetic diversity group of the latter, grazing was higher in the future than in current salinity. Climate change induced hyposalinity will thus challenge Fucus populations at their range margins in the Baltic Sea both because of the growth deterioration and changes in grazing. Differences between the species in these responses indicate a better ability of F. radicans to cope with the changing environment. Our results emphasize the complexity of biotic interactions in mediating the climate change influences as well as the importance of genetic diversity in coping with climate change

Trophic Dynamics of Mercury in the Baltic Archipelago Sea Food Web: The Impact of Ecological and Ecophysiological Traits

We investigated trophic dynamics of Hg in the polluted Baltic Archipelago Sea using established trophic magnification (TMFs) and biomagnification factors (BMFs) on a comprehensive set of bird, fish, and invertebrate species. As different ecological and ecophysiological species traits may affect trophic dynamics, we explored the effect of food chain (benthic, pelagic, benthopelagic) and thermoregulatory strategy on trophic total Hg (THg) dynamics, using different approaches to accommodate benthopelagic species and normalize for trophic position (TP). We observed TMFs and most BMFs greater than 1, indicating overall THg biomagnification. We found significantly higher pelagic TMFs (3.58-4.02) compared to benthic ones (2.11-2.34) when the homeotherm bird species were excluded from models, but not when included. This difference between the benthic and pelagic TMFs remained regardless of how the TP of benthopelagic species was modeled, or whether TMFs were normalized for TP or not. TP-corrected BMFs showed a larger range (0.44-508) compared to BMFs representing predator-prey concentration ratios (0.05-82.2). Overall, the present study shows the importance of including and evaluating the effect of ecological and ecophysiological traits when investigating trophic contaminant dynamics

Global patterns in the impact of marine herbivores on benthic primary producers

Despite the importance of consumers in structuring communities, and the widespread assumption that consumption is strongest at low latitudes, empirical tests for global scale patterns in the magnitude of consumer impacts are limited. In marine systems, the long tradition of experimentally excluding herbivores in their natural environments allows consumer impacts to be quantified on global scales using consistent methodology. We present a quantitative synthesis of 613 marine herbivore exclusion experiments to test the influence of consumer traits, producer traits and the environment on the strength of herbivore impacts on benthic producers. Across the globe, marine herbivores profoundly reduced producer abundance (by 68% on average), with strongest effects in rocky intertidal habitats and the weakest effects on habitats dominated by vascular plants. Unexpectedly, we found little or no influence of latitude or mean annual water temperature. Instead, herbivore impacts differed most consistently among producer taxonomic and morphological groups. Our results show that grazing impacts on plant abundance are better predicted by producer traits than by large‐scale variation in habitat or mean temperature, and that there is a previously unrecognised degree of phylogenetic conservatism in producer susceptibility to consumption