Non-indigenous species and their realized niche in tidepools along the South-East Pacific coast.

Non-indigenous species (NIS) have the potential to colonize and become established in a wide range of coastal habitats. Species with broad environmental tolerances can quickly adapt to local conditions and expand their niches along environmental gradients, and even colonize habitats with extreme abiotic conditions. Here we report and document the distribution of eight marine NIS (four seaweed and four invertebrate species) found in tidepools along a 3000 km latitudinal gradient along the Pacific coast of Chile (18.4°S to 41.9°S). The seaweed NIS Codium fragile, Capreolia implexa, Schottera nicaeensis and Mastocarpus latissimus were mostly distributed towards high latitudes (i.e., more southerly locations), where temperatures in tidepools were low. The invertebrate NIS Anemonia alicemartinae, Ciona robusta, Bugula neritina and Bugulina flabellata were more common towards low latitudes, where high temperatures were registered in the tidepools. Across the intertidal gradient, seaweed NIS were mostly found in pools in the mid and low intertidal zone, while invertebrate NIS occurred mostly in pools from the mid and upper intertidal zones. The realized niche spaces of NIS (based on the Outlying Mean Index, OMI) in the study area were mainly influenced by environmental conditions of temperature and salinity (along the latitudinal and intertidal gradients), while other tidepool characteristics (depth, surface area, exposition, and complexity) only had minor effects. Five of the eight NIS exhibited a realized niche space coinciding with the average tidepool environmental conditions, while marginal niches were occupied by species with affinities for specific temperatures and salinities along the latitudinal and intertidal gradients. Our results indicate that physiological tolerances to environmental factors play a fundamental role in the distribution of seaweed and invertebrate NIS in tidepools along the Chilean coast. This study confirms that tidepools offer suitable conditions for some seaweed and invertebrate NIS, potentially facilitating their invasion into new natural habitats.

Heterozostera nigricaulis from the south-East Pacific coast of Chile: First insights into its physiology and growth.

A short stretch (27°S and 30°S) along the coast of Chile is habitat for the seagrass Heterozostera nigricaulis. The seagrass is classified as endangered and grows only clonally, but there are no data on its physiology and growth. However, this information is important to gain insights into its acclimation potential and how disturbances may affect them. We therefore studied H. nigricaulis at 27° and 30°S, and determined their growth and physiology among seasons and depths over one year. Biomass was higher at 27° than at 30°S, and was always higher in summer than in autumn and winter. Increased photosynthesis supported growth in summer, and in winter carbonic anhydrase activity was in place to maintain these evergreen meadows. Our results suggest that these seagrass meadows are adapted to local conditions, which, together with their asexual reproduction, could make them more vulnerable to disturbance. Therefore, our results serve as a basis for future studies on seagrass growth dynamics, and are important for protection and management plans.

Effect of UV-radiation on the physiology of the invasive green seaweed Codium fragile and its associated bacteria.

Invasive species such as seaweeds often have a broad tolerance, allowing them to colonize novel habitats. During invasion, also new epibacteria can be formed on seaweeds, which have important chemo-ecological effects. Since UV-radiation (UVR) is one of the main factors affecting seaweeds and their epibacteria, we tested its effect on intertidal and subtidal thalli of the invasive seaweed Codium fragile from three sites and monitored photosynthesis, antioxidant activity and epibacteria. Exposure to UV-radiation resulted in photoinhibition with a subsequent low recovery in subtidal thalli from 23°S compared to 27°S and 30°S, which both showed a higher and almost complete recovery. However, a high antioxidant activity was present in all thalli, permitting to explain its relatively high tolerance to new environments. UV-radiation modified the composition of the epibacteria community by reducing its diversity and evenness. Our results showed that C. fragile responds plastic to variable UV-radiation (depending on site and water depth), which contributes to its high invasion potential.

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.

Revealing the deposition of macrophytes transported offshore: Evidence of their long-distance dispersal and seasonal aggregation to the deep sea.

The role of coastal macrophyte beds as a carbon sink is under debate. Various studies have provided global estimates of the carbon sequestration and stocks of macrophyte beds; however, the final fate of macrophyte debris exported from coastal beds remains uncertain, and must be determined in order to fully clarify the role of coastal vegetation as a carbon sink. Here we conducted bottom-trawl surveys to investigate the extensive and seasonal aggregation of exported macrophytes on the continental shelf and slope seafloor (40-1,800 m). Sunken macrophytes showed a clear seasonal trend with highest biomasses in summer. This was mainly caused by the most collected macrophyte species Sargassum horneri. Furthermore, we used numerical simulations to verify the link between sea-surface hydrographic condition and seafloor distribution of sunken macrophytes. Our results showed that S. horneri accumulated beneath the Kuroshio Extension current, which is the western boundary current of the North Pacific subtropical gyre. Overall, floating macrophytes that became transported offshore by a stable sea-surface current, such as the western boundary current, constitute an organic carbon pathway from coastal waters to the deep sea. Our findings suggest that these buoyant macrophytes can act as a biological pump to enhance oceanic carbon sequestration.

Tolerance to climate change of the clonally reproducing endemic Baltic seaweed, Fucus radicans: is phenotypic plasticity enough?

To predict the effects of climate change, we first need information on both the current tolerance ranges of species and their future adaptive potential. Adaptive responses may originate either in genetic variation or in phenotypic plasticity, but the relative importance of these factors is poorly understood. Here, we tested the tolerance of Fucus radicans to the combination of hyposalinity and warming projected by climate models for 2070-2099. We measured the growth and survival responses of thalli in both current and future conditions, focusing on variations in tolerance among and within different clonal lineages. Survival was 32% lower in future than in current conditions, but the weight and length of the thalli which survived was respectively 267% and 178% higher when exposed to future conditions. The relatively high tolerance to the future conditions suggests that F. radicans is likely to persist in its current distributional range, which is limited to the Gulf of Bothia and Estonian coast in the Baltic Sea. Furthermore, this species may be able to expand its distribution southward and replace its congener F. vesiculosus, which, in previous studies, has not tolerated the future conditions as well. In addition, we discovered variation in tolerance to future conditions within one of the clonal lineages, which have been hitherto presumed to lack adaptive variation. The discovery of intra-clonal phenotypic plasticity means that this alga has the potential for adaptive responses to climate change, which may be the key to the future persistence of F. radicans in the Baltic Sea.

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.

High acclimation potential in floating Macrocystis pyrifera to abiotic conditions even under grazing pressure - a field study.

The persistence of floating seaweeds, which depends on abiotic conditions but also herbivory, had previously been mostly tested in outdoor mesocosm experiments. In order to investigate if the obtained mesocosm results of high seaweed persistence under natural environmental conditions and under grazing pressure can be extrapolated to field situations, we conducted in situ experiments. During two summers (2007 and 2008), Macrocystis pyrifera was tethered (for 14 d) to lines in the presence and absence of the amphipod Peramphithoe femorata at three sites (Iquique, Coquimbo, Calfuco). We hypothesized that grazing damage and seaweed persistence vary among sites due to different abiotic factors. By incubating the sporophytes in mesh bags, we were either able to isolate (grazing) or exclude (control) amphipods. To test for a mesh bag artifact, a set of sporophytes was incubated without mesh bags (natural). Mesh bags used to exclude herbivores influenced sporophyte growth and physiological performance. The chlorophyll a (Chl a) content depended largely on grazers and grazed sporophytes grew less than natural and control sporophytes within the two summers. A decrease in Chl a content was found for the sites with the highest prevailing irradiances and temperatures, suggesting an efficient acclimation to these sea surface conditions. Our field-based results of sporophyte acclimation ability even under grazing pressure widely align with previous mesocosm results. We conclude that M. pyrifera and other temperate floating seaweeds can function as long-distance dispersal vectors even with hitchhiking mesoherbivores.

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 we need information not just on their environmental tolerance but also on its adaptive potential. We tested how the foundation species of rocky littoral habitats, Fucus vesiculosus, responds to combined hyposalinity and warming projected to the Baltic Sea by 2070-2099. We quantified responses of replicated populations originating from the entrance, central, and marginal Baltic regions. Using replicated individuals, we tested for the presence of within-population tolerance variation. Future conditions hampered growth and survival of the central and marginal populations whereas the entrance populations fared well. Further, both the among- and within-population variation in responses to climate change indicated existence of genetic variation in tolerance. Such standing genetic variation provides the raw material necessary for adaptation to a changing environment, which may eventually ensure the persistence of the species in the inner Baltic Sea.

Genetic variation of a foundation rockweed species affects associated communities.

Genetic variation in a foundation species may affect the composition of associated communities as well as modify ecosystem function. While the ecological consequences of genetic diversity of foundation species have been widely reported, the ability of individual genotypes to support dissimilar communities has been documented only in forest ecosystems. Here, for the first time in a marine ecosystem, we test whether the different genotypes of the rockweed Fucus vesiculosus harbor distinct community phenotypes and whether the genetic similarity of individual genotypes or their defensive compound content can explain the variation of the associated communities. We reared replicated genotypes in a common garden in the sea and analyzed their associated communities of periphytic algae and invertebrates as well as determined their contents of defense compounds, phlorotannins, and genetic distance based on neutral molecular markers. The periphytic community was abundant in mid-summer and its biovolume, diversity and community composition varied among the rockweed genotypes. The diversity of the periphytic community decreased with its increasing biovolume. In autumn, when grazers were abundant, periphytic community biomass was lower and less variable among rockweed genotypes, indicating different relative importance of bottom-up regulation through heritable variation of the foundation species and top-down regulation through grazing intensity. Similarly, composition of the invertebrate community varied among the rockweed genotypes. Although the genotype explained about 10-18% of the variation in associated communities, the variation was explained neither by the genetic distance nor the phlorotannin content. Thus, neither neutral genetic markers nor a single phenotypic trait could provide a mechanistic understanding of the genetic basis of community specificity. Therefore, a more comprehensive mapping of quantitative trait variation is needed to understand the underlying mechanisms. The community specificity implies that genetic variation within a foundation species is crucial for the biodiversity and assembly of associated organisms and, thus, for the functioning of associated communities. The result highlights the importance of ensuring the genetic variation of foundation species as a conservation target.

Genetic variation in photosynthetic performance and tolerance to osmotic stress (desiccation, freezing, hyposalinity) in the rocky littoral foundation species Fucus vesiculosus (Fucales, Phaeophyceae).

Genetic diversity may play an analogous role to species diversity, as it can contribute to ecosystem function and stability, and provision of ecosystem services. In the Baltic Sea, perennial algal beds are often comprised of only Fucus vesiculosus and the amount of genetic variation in fitness-related traits (i.e., the ability of the alga to photosynthesize or withstand stress) will thus determine the alga's local persistence in a changing environment. To study genetic variation in the crucial traits behind persistence we grew replicate vegetative branches that came from the same genotype in common gardens. We quantified osmotic stress tolerance and recovery responses by exposing branches to desiccation, freezing, and hyposalinity regimens. Our results show that genetic variation among genotypes was apparent for some photosynthetic parameters (maximal electron transport rate, saturation irradiance for electron transport, nonphotochemical quenching) and growth. Algae tolerated freezing (1,440 min at -2.5°C) and hyposalinity (1,560 min at 2.5) well, but did not recover from desiccation (70 min at 12°C, causing ~94% water loss). Furthermore, we found very little if any evidence on genetic variation in tolerance to these stressors. Our results suggest that low salinity and cold winters in the northern marginal populations selected for hyposalinity and freezing tolerant genotypes, possibly eroding genetic variation in tolerance, but that tolerance to harsh desiccation has been lost, likely due to relaxed selection. The overall availability of genetic variation in fitness related traits might be supportive for F. vesiculosus during adaptation to gradual changes of its environment.

Unusual distribution of floating seaweeds in the East China Sea in the early spring of 2012.

Floating seaweeds play important ecological roles in offshore waters. Recently, large amounts of rafting seaweed have been observed in the East China Sea. In early spring, juveniles of commercially important fish such as yellowtail accompany these seaweed rafts. Because the spatial distributions of seaweed rafts in the spring are poorly understood, research cruises were undertaken to investigate them in 2010, 2011, and 2012. Floating seaweed samples collected from the East China Sea during the three surveys contained only Sargassum horneri. In 2010 and 2011, seaweed rafts were distributed only in the continental shelf and the Kuroshio Front because they had become trapped in the convergence zone of the Kuroshio Front. However, in 2012, seaweed was also distributed in the Kuroshio Current and its outer waters, and massive strandings of seaweed rafts were observed on the northern coast of Taiwan and on Tarama Island in the Ryukyu Archipelago. Environmental data (wind, currents, and sea surface height) were compared among the surveys of 2010, 2011, and 2012. Two factors are speculated to have caused the unusual distribution in 2012. First, a continuous strong north wind produced an Ekman drift current that transported seaweed southwestward to the continental shelf and eventually stranded seaweed rafts on the coast of Taiwan. Second, an anticyclonic eddy covering northeast Taiwan and the Kuroshio Current west of Taiwan generated a geostrophic current that crossed the Kuroshio Current and transported the rafts to the Kuroshio Current and its outer waters. Such unusual seaweed distributions may influence the distribution of fauna accompanying the rafts.

Seabird guano fertilizes Baltic Sea littoral food webs.

Nutrient enrichment in coastal marine systems can have profound impacts on trophic networks. In the Baltic Sea, the population of Great Cormorant (Phalacrocorax carbo sinensis) has increased nearly exponentially since the mid-1990 s, and colonies of these seabirds can be important sources of nitrogen enrichment for nearby benthic communities due to guano runoff. In this study we used stable isotope analyses and diet mixing models to determine the extent of nitrogen enrichment from cormorant colonies, as well as to examine any possible changes in herbivore diet preferences due to enrichment. We found significantly higher levels of δ(15)N in samples from colony islands than control islands for producers (the dominant macroalga Fucus vesiculosus, filamentous algae, and periphyton) and herbivores, as well as a positive correlation between enrichment and nest density in colony sites. We also found that enrichment increased over the breeding season of the cormorants, with higher enrichment in late summer than early summer. While the amount of total nitrogen did not differ between colony and control sites, the amount of guano-based nitrogen in algae was >50% in most sites, indicating high nitrogen enrichment from colonies. Herbivores (the isopod Idotea balthica and the gastropod Theodoxus fluviatilis) preferred feeding upon the dominant macroalga Fucus vesiculosus rather than on filamentous algae or periphyton in both control and colony, and there was a significant increase in periphyton consumption near colony sites. Overall, guano from cormorant colonies seems to have effects on both producers and herbivores, as well as the potential to modify algae-herbivore interactions.

PHYSIOLOGICAL PERFORMANCE OF FLOATING GIANT KELP MACROCYSTIS PYRIFERA (PHAEOPHYCEAE): LATITUDINAL VARIABILITY IN THE EFFECTS OF TEMPERATURE AND GRAZING(1).

Rafts of Macrocystis pyrifera (L.) C. Agardh can act as an important dispersal vehicle for a multitude of organisms, but this mechanism requires prolonged persistence of floating kelps at the sea surface. When detached, kelps become transferred into higher temperature and irradiance regimes at the sea surface, which may negatively affect kelp physiology and thus their ability to persist for long periods after detachment. To examine the effect of water temperature and herbivory on the photosynthetic performance, pigment composition, carbonic anhydrase (CA) activity, and the nitrogen (N) and carbon (C) content of floating M. pyrifera, experiments were conducted at three sites (20° S, 30° S, 40° S) along the Chilean Pacific coast. Sporophytes of M. pyrifera were maintained at three different temperatures (ambient, ambient - 4°C, ambient + 4°C) and in presence or absence of the amphipod Peramphithoe femorata for 14 d. CA activity decreased at 20° S and 30° S, where water temperatures and irradiances were highest. At both sites, pigment contents were substantially lower in the experimental algae than in the initial algae, an effect that was enhanced by grazers. Floating kelps at 20° S could not withstand water temperatures >24°C and sank at day 5 of experimentation. Maximal quantum yield decreased at 20° S and 30° S but remained high at 40° S. It is concluded that environmental stress is low for kelps floating under moderate temperature and irradiance conditions (i.e., at 40° S), ensuring their physiological integrity at the sea surface and, consequently, a high dispersal potential for associated biota.

EFFECT OF TEMPERATURE AND GRAZING ON GROWTH AND REPRODUCTION OF FLOATING MACROCYSTIS SPP. (PHAEOPHYCEAE) ALONG A LATITUDINAL GRADIENT(1).

Macroalgal rafts frequently occur floating in coastal waters of temperate regions of the world's oceans. These rafts are considered important dispersal vehicles for associated organisms with direct development. However, environmental factors may limit the floating potential of kelp and thereby the dispersal of associated organisms. To examine the effect of water temperature and grazing on growth, reproductive output, and survival of floating Macrocystis spp., experiments were conducted in outdoor tanks during austral summer 2006/2007 at three sites along the Chilean Pacific coast (20° S, 30° S, 40° S). At each site, Macrocystis spp. was maintained individually at three different water temperatures (ambient, ambient - 4°C, ambient + 4°C) and in the presence or absence of the amphipod grazer Peramphithoe femorata for 14 d. High water temperatures (>20°C) provoked rapid degradation of Macrocystis spp. rafts. At moderate temperatures (15°C-20°C), algal survival depended on the presence of associated grazers. In the absence of grazers, algal rafts gained in biomass while grazing caused considerable losses of algal biomass. Algal survival was the highest under cooler conditions (<15°C), where raft degradation was slow and grazer-induced biomass losses were compensated by continuing algal growth. Our results indicate that floating kelp rafts can survive for long time periods at the sea surface, but survival depends on the interaction between temperature and grazing. We suggest that these processes limiting the survival of kelp rafts in warmer temperatures may act as a dispersal barrier for kelp and its associated passengers.