An Alexandrium Spp. Cyst Record from Sequim Bay,Washington State,USA, and its Relation to Past Climate Variability1

Since the 1970s, Puget Sound, Washington State, USA, has experienced an increase in detections of paralytic shellfish toxins (PSTs) in shellfish due to blooms of the harmful dinoflagellate Alexandrium. Natural patterns of climate variability, such as the Pacific Decadal Oscillation (PDO), and changes in local environmental factors, such as sea surface temperature (SST) and air temperature, have been linked to the observed increase in PSTs. However, the lack of observations of PSTs in shellfish prior to the 1950s has inhibited statistical assessments of longer‐term trends in climate and environmental conditions on Alexandrium blooms. After a bloom, Alexandrium cells can enter a dormant cyst stage, which settles on the seafloor and then becomes entrained into the sedimentary record. In this study, we created a record of Alexandrium spp. cysts from a sediment core obtained from Sequim Bay, Puget Sound. Cyst abundances ranged from 0 to 400 cysts · cm^?3 and were detected down‐core to a depth of 100 cm, indicating that Alexandrium has been present in Sequim Bay since at least the late 1800s. The cyst record allowed us to statistically examine relationships with available environmental parameters over the past century. Local air temperature and sea surface temperature were positively and significantly correlated with cyst abundances from the late 1800s to 2005; no significant relationship was found between PDO and cyst abundances. This finding suggests that local environmental variations more strongly influence Alexandrium population dynamics in Puget Sound when compared to large‐scale changes.     

Modeling climate change impacts on overwintering bald eagles

Bald eagles (Haliaeetus leucocephalus) are recovering from severe population declines, and are exerting pressure on food resources in some areas. Thousands of bald eagles overwinter near Puget Sound, primarily to feed on chum salmon (Oncorhynchus keta) carcasses. We used modeling techniques to examine how anticipated climate changes will affect energetic demands of overwintering bald eagles. We applied a regional downscaling method to two global climate change models to obtain hourly temperature, precipitation, wind, and longwave radiation estimates at the mouths of three Puget Sound tributaries (the Skagit, Hamma Hamma, and Nisqually rivers) in two decades, the 1970s and the 2050s. Climate data were used to drive bald eagle bioenergetics models from December to February for each river, year, and decade. Bald eagle bioenergetics were insensitive to climate change: despite warmer winters in the 2050s, particularly near the Nisqually River, bald eagle food requirements declined only slightly (<1%). However, the warming climate caused salmon carcasses to decompose more rapidly, resulting in 11% to 14% less annual carcass biomass available to eagles in the 2050s. That estimate is likely conservative, as it does not account for decreased availability of carcasses due to anticipated increases in winter stream flow. Future climate-driven declines in winter food availability, coupled with a growing bald eagle population, may force eagles to seek alternate prey in the Puget Sound area or in more remote ecosystems.     

Historical Patterns and Drivers of Spatial Changes in Recreational Fishing Activity in Puget Sound,Washington

Small-scale fisheries are the primary users of many coastal fish stocks; yet, spatial and temporal patterns of recreational and subsistence fishing in coastal marine ecosystems are poorly documented. Knowledge about the spatial distribution of fishing activities can inform place-based management that balances species conservation with opportunities for recreation and subsistence. We used a participatory mapping approach to document changes in spatial fishing patterns of 80 boat-based recreational anglers from 1950 to 2010 in Puget Sound, Washington, USA. Hand-drawn fishing areas for salmon, rockfishes, flatfishes, and crabs were digitized and analyzed in a Geographic Information System. We found that recreational fishing has spanned the majority of Puget Sound since the 1950s, with the heaviest use limited to small areas of central and northern Puget Sound. People are still fishing in the same places they were decades ago, with relatively little change in specific locations despite widespread declines in salmon and bottomfish populations during the second half of the 20^th century. While the location of core fishing areas remained consistent, the size of those areas and intensity of use changed over time. The size of fishing areas increased through the 2000s for salmon but declined after the 1970s and 1980s for rockfishes, flatfishes, and crabs. Our results suggest that the spatial extent of recreational bottomfishing increased after the 1960s, when the availability of motorized vessels and advanced fish-finding technologies allowed anglers to expand their scope beyond localized angling from piers and boathouses. Respondents offered a wide range of reasons for shifts in fishing areas over time, reflecting substantial individual variation in motivations and behaviors. Changes in fishing areas were most commonly attributed to changes in residence and declines in target species and least tied to fishery regulations, despite the implementation of at least 25 marine preserves since 1970.     

Community persistence in Broadstone Stream (U.K.) over three decades

1. Few detailed long-term data sets exist for fresh waters with which to examine large-scale temporal changes in community composition. Consequently, insight into community persistence has been restricted to a few, contingent case studies. We collated and analysed data for the aquatic macroinvertebrate community of Broadstone Stream in south-east England, spanning three decades. The pH of this naturally acid stream has risen progressively since the 1970s, and we sought to examine the potential effects of this environmental change upon the community.
2. Persistence within Broadstone was high when compared with other systems that have been analysed using similar methods. The stream was characterised by a `core' community of eight taxa that were always present, and contributed 75–97% of total invertebrate abundance, with a trailing limb of progressively rarer and more acid-sensitive taxa. There was little species turnover, although the time-series exceeded 20 generations for most species.
3. Despite this high persistence, a long-term response to rising pH was detected: species indicating profound acidity (identified a priori from independent studies) have declined since the 1970s, whereas indicators of moderate acidity increased. The structure of the community food web has also changed since the 1970s, with increased predator diversity and abundance, and a lengthening of food chains following the invasion of a new top predator.
4. These changes in the community appeared to be driven by an interaction between pH and climate. The unusually hot, dry summers characteristic of the 1990s may have raised pH during the more sensitive (i.e. early) stages of the life-cycle, and thus provided a window of opportunity for less acid-tolerant taxa to colonise and become established. Changes in pH appeared to set the boundaries of the available local species pool, within which biotic interactions ultimately shaped the community.     

Observations on Abundance of Bluntnose Sixgill Sharks,Hexanchus griseus,in an Urban Waterway in Puget Sound, 2003-2005

The bluntnose sixgill shark, Hexanchus griseus, is a widely distributed but poorly understood large, apex predator. Anecdotal reports of diver-shark encounters in the late 1990’s and early 2000’s in the Pacific Northwest stimulated interest in the normally deep-dwelling shark and its presence in the shallow waters of Puget Sound. Analysis of underwater video documenting sharks at the Seattle Aquarium’s sixgill research site in Elliott Bay and mark-resight techniques were used to answer research questions about abundance and seasonality. Seasonal changes in relative abundance in Puget Sound from 2003–2005 are reported here. At the Seattle Aquarium study site, 45 sixgills were tagged with modified Floy visual marker tags, along with an estimated 197 observations of untagged sharks plus 31 returning tagged sharks, for a total of 273 sixgill observations recorded. A mark-resight statistical model based on analysis of underwater video estimated a range of abundance from a high of 98 sharks seen in July of 2004 to a low of 32 sharks seen in March of 2004. Both analyses found sixgills significantly more abundant in the summer months at the Seattle Aquarium’s research station.     

Ecological implications of invasive tunicates associated with artificial structures in Puget Sound, Washington, USA

The non-native tunicates Didemnum vexillum, Ciona savignyi, and Styela clava are of concern to resource managers of Puget Sound, Washington, USA because they have been shown to threaten native species diversity and shellfish aquaculture in other regions. Invasive tunicates in Puget Sound occur mainly on man-made structures such as floating docks and aquaculture facilities. We conducted studies of the three species of concern and a fourth introduced tunicate, Botrylloides violaceus, that occur on these structures to evaluate their effects on mussels and native invertebrate communities. Because most studies of community effects of tunicates have dealt with sessile fouling organisms, we focused instead on epibenthic organisms such as meiofaunal harpacticoid copepods and macrofaunal polychaetes and amphipods that are known to be important prey for juvenile salmon and other small fish. Similar studies have shown mixed results, with negative, positive, or no effects depending on the species. We also found few community-level effects. Abundances of several species were lower when tunicates were present, but only at some of the sites. Several other species, including a non-native isopod, were significantly more abundant in the presence of tunicates. However, in most cases results were not statistically significant and more intensive, controlled sampling or experiments may be needed to demonstrate any consistent tunicate effects. Although invasive tunicates cause problems for mussel growers elsewhere, we did not find negative effects on mussels at four sites in Puget Sound. Given the large impacts known to accompany tunicate invasions elsewhere and their relatively recent invasions into Puget Sound, monitoring of their populations and effects should continue in the region.     

Seasonal and Ontogenetic Changes in Movement Patterns of Sixgill Sharks

Background

Understanding movement patterns is fundamental to population and conservation biology. The way an animal moves through its environment influences the dynamics of local populations and will determine how susceptible it is to natural or anthropogenic perturbations. It is of particular interest to understand the patterns of movement for species which are susceptible to human activities (e.g. fishing), or that exert a large influence on community structure, such as sharks.

Methodology/Principal Findings

We monitored the patterns of movement of 34 sixgill sharks Hexanchus griseus using two large-scale acoustic arrays inside and outside Puget Sound, Washington, USA. Sixgill sharks were residents in Puget Sound for up to at least four years before making large movements out of the estuary. Within Puget Sound, sixgills inhabited sites for several weeks at a time and returned to the same sites annually. Across four years, sixgills had consistent seasonal movements in which they moved to the north from winter to spring and moved to the south from summer to fall. Just prior to leaving Puget Sound, sixgills altered their behavior and moved twice as fast among sites. Nineteen of the thirty-four sixgills were detected leaving Puget Sound for the outer coast. Three of these sharks returned to Puget Sound.

Conclusions/Significance

For most large marine predators, we have a limited understanding of how they move through their environment, and this clouds our ability to successfully manage their populations and their communities. With detailed movement information, such as that being uncovered with acoustic monitoring, we can begin to quantify the spatial and temporal impacts of large predators within the framework of their ecosystems.     

Present-day and future climate pathways affecting Alexandrium blooms in Puget Sound,WA, USA

This study uses a mechanistic modeling approach to evaluate the effects of various climate pathways on the proliferative phase of the toxin-producing dinoflagellate Alexandrium in Puget Sound, WA, USA. Experimentally derived Alexandrium growth responses to temperature and salinity are combined with simulations of the regional climate and Salish Sea hydrology to investigate future changes in the timing, duration, and extent of blooms. Coarse-grid (100–200 km) global climate model ensemble simulations of the SRES A1B emissions scenario were regionally downscaled to a 12-km grid using the Weather Research and Forecasting model for the period 1969–2069. These results were used to: (1) analyze the future potential changes and variability of coastal upwelling winds, and (2) provide forcing fields to a Regional Ocean Model System used to simulate the circulation of the Salish Sea, including Puget Sound, and the coastal ocean. By comparing circa-1990 and circa-2050 climate scenarios for the environmental conditions that promote Alexandrium blooms, we disentangle the effects of three climate pathways: (1) increased local atmospheric heating, (2) changing riverflow magnitude and timing, and (3) changing ocean inputs associated with changes in upwelling-favorable winds. Future warmer sea surface temperatures in Puget Sound from increased local atmospheric heating increase the maximum growth rates that can be attained by Alexandrium during the bloom season as well as the number of days with conditions that are favorable for bloom development. This could lead to 30 more days a year with bloom-favorable conditions by 2050. In contrast, changes in surface salinity arising from changes in the timing of riverflow have a negligible effect on Alexandrium growth rates, and the behavior of the coastal inputs in the simulations suggests that changes in local upwelling will not have major effects on sea surface temperature or salinity or Alexandrium growth rates in Puget Sound.     

Genetic Evidence of Postglacial Population Expansion in Puget Sound Rockfish (Sebastes emphaeus)

Several rockfish species (genus Sebastes) along the northeastern Pacific Ocean have rapidly declined in abundance owing in part to overfishing. A striking exception is the dwarf-like Puget Sound rockfish Sebastes emphaeus, whose densities have increased by several orders of magnitude over the last several decades. To describe their genetic structure, we sequenced 395 bp from the mitochondrial control region of 128 S. emphaeus adults from 5 locations spanning approximately 120 km of the Northwest Straits of Washington state. We detected no significant genetic differentiation among these populations and substantial genetic variation within populations, a pattern that may indicate high levels of ongoing gene flow. Preliminary data from 2 microsatellite loci are also consistent with panmixia. The mtDNA sequences also suggest that Puget Sound rockfish populations have expanded substantially since the retreat of Pleistocene glaciers made habitat in Puget Sound region available approximately 12,000 years ago.     

Geographical shift of zooplankton communities and decadal dynamics of the Kuroshio–Oyashio currents in the western North Pacific

We investigated temporal and spatial variations in the zooplankton community structure in the Oyashio and Transition region of the subarctic western North Pacific from 1960 to 1999 using principal component analysis (PCA) and zooplankton samples from the historical Odate Collection. In particular, we examined the influence of Kuroshio and Oyashio decadal dynamics on geographical variations in the zooplankton community. The first principal component (PC1) closely represented the interannual variation in cold-water, large copepod species, while the second PC (PC2) represented the variation in warm-water, small copepod species. Using Rodionov's regime-shift method, we detected a significant increase in the PC score after 1976 and 1981 for PC1 and PC2, respectively. After the shift years, (1) warm-water species increased in the Transition zone, (2) the distribution center of the cold-water species shifted southward, and (3) copepod abundance and species diversity increased in the Transition zone as a result of (1) and (2). The timing of these shifts in the zooplankton community roughly coincided with the North Pacific climatic regime shift in 1976/1977. From the mid-1970s to the early 1980s, the southern boundary of the Oyashio shifted southward and increased geostrophic transport was observed in the Kuroshio, indicating spin up of the Kuroshio–Oyashio system. Change in atmospheric circulation during the 1976/1977 regime shift is thought to have caused the spin up of these currents, which subsequently affected the regional zooplankton community through advective processes.     

Limited realized dispersal and introgressive hybridization influence genetic structure and conservation strategies for brown rockfish, <Emphasis Type="Italic">Sebastes auriculatus</Emphasis>

Understanding patterns of connectivity among marine fish populations with demersal adults and pelagic larvae is critical for effective conservation of west coast rockfishes. The brown rockfish (Sebastes auriculatus) occurs in nearshore habitat and is common from northern Baja California, Mexico to northern California, rare off the outer coast of Oregon and Washington and again common in the inland waters of Puget Sound, Washington. Here we examine patterns of microsatellite DNA diversity from throughout the species’ range as an indirect measure of long-term trends in larval dispersal. Genetic divergence was large and highly significant over all populations (F _ST=0.056, P<0.0001), and was significantly correlated with geographic distance when considering coastal populations. The best estimates of mean coastal dispersal distance were on the order of 10 km or less per generation. Diversity was relatively low in the Puget Sound, suggesting that Puget Sound rockfish populations experienced a post-glacial founder effect followed by genetic isolation and low effective population size. Puget Sound individuals appeared to have recent mixed ancestry as a result of introgression with S. maliger and S. caurinus. Genetic isolation of Puget Sound fish provides a basis for consideration as a Distinct Population Segment (DPS) under the provisions of the Endangered Species Act. We recommend that coastal brown rockfish fisheries be managed at regional rather than coast-wide scales, and that design of marine reserve networks considers the surprisingly low realized dispersal distance of some species with high dispersal potential.     

Environmental Factors Influencing Hairy-Nosed Wombat Abundance in Semi-Arid Rangelands

Understanding environmental factors influencing the abundance of species is important for developing strategies to manage wildlife effectively. Long-term studies provide the most reliable information upon which to base management decisions. This is particularly important when considering threatening processes, like drought and climate change, and a species' future security. We collected data on abundance of southern hairy-nosed wombats (Lasiorhinus latifrons) on Kooloola Station in South Australia's Murraylands during nightly spot-lighting excursions in winter and spring between 1993 and 2014. Wombat numbers declined significantly after the early-mid 1990s, and were lowest in 2002–2003 in the middle of the millennium drought (late 1996–mid-2010). Despite an observed decline in grazing competition from domestic sheep and rabbits (Oryctolagus cunniculus) after 2003 and above-average rainfall in 5 of the next 11 years, the wombat population failed to recover to early–mid-1990s levels, remaining at approximately 50% of estimated abundance pre-drought. The study provides evidence that rainfall has a significant effect on southern hairy-nosed wombat population size, most likely through improvements in the availability of palatable plant species. Historical information suggests that there was a change in the grass and herbaceous layer on Kooloola Station in the mid-1970s from a pasture dominated by summer-germinating native grass and forb species, the natural diet of the southern hairy-nosed wombat, to one dominated by winter-germinating introduced weeds. Several consecutive years of above-average rainfall are needed before effective wombat population increase occurs and the size of yearly winter and spring rainfall events is strongly linked to population trends the following year. Historical information and first-hand observations suggest that dietary components (either native grasses or introduced weed species) and level of grazing competition may also interact to affect wombat survival and population recovery from drought, although this requires further testing. Together with rainfall, these factors have important implications to develop appropriate conservation and management strategies for this species in a changing climate likely to be dominated by increased drought frequency and duration. © 2020 The Wildlife Society.     

Nuclear DNA identification of migrating bull trout captured at the Puget Sound Energy diversion dam on the White River,Washington State

Bull trout (Salvelinus confluentus) is a char listed as threatened under the United States Endangered Species Act throughout its range in the coterminous United States. Substantial morphological similarities between bull trout and Dolly Varden (S. malma) make field identification difficult. This has resulted in an incomplete understanding of their distribution and abundance in Washington State where these two species occur sympatrically. We used three diagnostic nuclear loci to determine the species of char collected at a trap on the White River in southern Puget Sound (Washington State, USA). Each of the 104 samples revealed the expected bull trout genotype at all three loci. This work presents three principle results: (i) the presence of a migratory bull trout population in southern Puget Sound; (ii) no evidence of migratory Dolly Varden over 3 years; and (iii) no evidence of hybridization was detected. These results also demonstrate how molecular markers can provide information essential to the conservation and management of these species.     

Profiles of Alexandrium catenella cysts in Puget Sound sediments and the relationship to paralytic shellfish poisoning events

The magnitude of paralytic shellfish poisoning (PSP) toxins in shellfish and the geographical scope of shellfish closures in Puget Sound have increased in recent decades. PSP, monitored by the Washington Department of Health, has spread from Sequim Bay in the 1950s into central Puget Sound in the 1970s and throughout Puget Sound by the 1990s. Alexandrium catenella, the species responsible for PSP toxins, produces a benthic resting cyst that, upon germinating, can seed blooms. This study examined whether there is a relationship between profiles of cysts in the sediment and temporal variation in PSP in shellfish and if the history of the toxin's southward expansion through Puget Sound can be seen in the cyst record. To address this question, sediment cores were collected from three Puget Sound basins, Sequim Bay, Penn Cove, and Carr Inlet, and cyst profiles were determined. Activities of ²¹⁰Pb were fitted to a depth-dependent diagenetic model to date the sediment cores and determine mixing and sediment-accumulation rates. In order to compare historical variation in PSP with cyst profiles that have been altered by bioturbation, a depth and time-dependent diagenetic model was then used to predict vertical profiles of cysts that would occur under the assumption that cyst deposition rates are proportional to PSP concentration in shellfish measured over several decades at each site. The cyst profiles predicted by the model were compared to measured cyst profiles. These comparisons suggested that Alexandrium blooms and resulting PSP concentration in shellfish are more closely linked to cyst germination and deposition at some stations than at others. Sequim Bay had relatively large numbers of cysts and it is likely that the persistent toxicity here is the result of recurrent seeding from the cyst bed. Penn Cove and Carr Inlet had few cysts despite occasional blooms, suggesting that blooms are transported into those areas, perhaps from other sites of cyst germination. Sequim Bay and Penn Cove had cysts from top to bottom of the cores so it was not possible to determine the date when cysts were first introduced into these bays, but it is likely that A. catenella has been in Penn Cove since at least 1955 or for about two decades before the WDOH PSP toxicity data would indicate. The cyst profile in Carr Inlet suggested a first appearance date of 1985 that is consistent with the first appearance of PSP in shellfish in 1988.     

Declining water yield from forested mountain watersheds in response to climate change and forest mesophication

Climate change and forest disturbances are threatening the ability of forested mountain watersheds to provide the clean, reliable, and abundant fresh water necessary to support aquatic ecosystems and a growing human population. Here, we used 76 years of water yield, climate, and field plot vegetation measurements in six unmanaged, reference watersheds in the southern Appalachian Mountains of North Carolina, USA to determine whether water yield has changed over time, and to examine and attribute the causal mechanisms of change. We found that annual water yield increased in some watersheds from 1938 to the mid‐1970s by as much as 55%, but this was followed by decreases up to 22% by 2013. Changes in forest evapotranspiration were consistent with, but opposite in direction to the changes in water yield, with decreases in evapotranspiration up to 31% by the mid‐1970s followed by increases up to 29% until 2013. Vegetation survey data showed commensurate reductions in forest basal area until the mid‐1970s and increases since that time accompanied by a shift in dominance from xerophytic oak and hickory species to several mesophytic species (i.e., mesophication) that use relatively more water. These changes in forest structure and species composition may have decreased water yield by as much as 18% in a given year since the mid‐1970s after accounting for climate. Our results suggest that changes in climate and forest structure and species composition in unmanaged forests brought about by disturbance and natural community dynamics over time can result in large changes in water supply.     

Eight decades of sampling reveal a contemporary novel fish assemblage in coastal nursery habitats

In order to adequately monitor biodiversity trends through time and their responses to natural or anthropogenic impacts, researchers require long time series that are often unavailable. This general lack of datasets that are several decades or longer makes establishing a background or baseline of diversity metrics difficult – especially when attempting to understand species composition changes against a backdrop of climate and ecological variability. Here, we present an analysis of a community of juvenile nearshore fishes based on nearly 8 decades of highly standardized Norwegian survey records. Using multivariate statistical techniques, we: (i) characterize the change in taxonomic community composition through time, (ii) determine whether there has been an increase in warm‐water affinity species relative to their cold water affinity counterparts, and (iii) characterize the temporal change in the species’ functional trait assemblage. Our results strongly indicate a shift toward a novel fish assemblage between the late 1990s and 2000s. The context of changes within the most recent two decades is in stark contrast to those during the 1960s and 1970s, but similar to those during the previous warm period during the 1930s and 1940s. This novel assemblage is tightly linked to the warming temperatures in the region portrayed by the increased presence of warm‐water species and a higher incidence of pelagic, planktivorous species. The results indicate a clear influence of ocean temperature on the region's juvenile fish community that points to climate‐mediated effects on the species assemblages of an important fish nursery area.     

Synergistic Effects of Climate and Fishing in a Marine Ecosystem

Current climate change and overfishing are affecting the productivity and structure of marine ecosystems. This situation is unprecedented for the marine biosphere and it is essential to understand the mechanisms and pathways by which ecosystems respond. We report that climate change and overfishing are likely to be responsible for a rapid restructuring of a highly productive marine ecosystem with effects throughout the pelagos and the benthos. In the mid-1980s, climate change, consequent modifications in the North Sea plankton, and fishing, all reduced North Sea cod recruitment. In this region, production of many benthic species respond positively and immediately to temperature. Analysis of a long-term, spatially extensive biological (plankton and cod) and physical (sea surface temperature) dataset suggests that synchronous changes in cod numbers and sea temperature have established an extensive trophic cascade favoring lower trophic level groups over economic fisheries. A proliferation of jellyfish that we detect may signal the climax of these changes. This modified North Sea ecology may provide a clear indication of the synergistic consequences of coincident climate change and overfishing. The extent of the ecosystem restructuring that has occurred in the North Sea suggests we are unlikely to reverse current climate and human-induced effects through ecosystem resource management in the short term. Rather, we should understand and adapt to new ecological regimes. This implies that fisheries management policies will have to be fully integrated with the ecological consequences of climate change to prevent a similar collapse in an exploited marine ecosystem elsewhere. Author Contributions  RRK conceived the project and GB analysed the data. RRK, GB and JAL co-wrote the paper.     

Long‐term declines in an intertidal foundation species parallel shifts in community composition

The earth is in the midst of a biodiversity crisis, and projections indicate continuing and accelerating rates of global changes. Future alterations in communities and ecosystems may be precipitated by changes in the abundance of strongly interacting species, whose disappearance can lead to profound changes in abundance of other species, including an increase in extinction rate for some. Nearshore coastal communities are often dependent on the habitat and food resources provided by foundational plant (e.g., kelp) and animal (e.g., shellfish) species. We quantified changes in the abundance of the blue mussel (Mytilus edulis), a foundation species known to influence diversity and productivity of intertidal habitats, over the past 40 years in the Gulf of Maine, USA, one of the fastest warming regions in the global ocean. Using consistent survey methods, we compared contemporary population sizes to historical data from sites spanning >400 km. The results of these comparisons showed that blue mussels have declined in the Gulf of Maine by >60% (range: 29–100%) at the site level since the earliest benchmarks in the 1970s. At the same time as mussels declined, community composition shifted: at the four sites with historical community data, the sessile community became increasingly algal dominated. Contemporary (2013–2014) surveys across 20 sites showed that sessile species richness was positively correlated to mussel abundance in mid to high intertidal zones. These results suggest that declines in a critical foundation species may have already impacted the intertidal community. To inform future conservation efforts, we provide a database of historical and contemporary baselines of mussel population abundance and dynamics in the Gulf of Maine. Our results underscore the importance of anticipating not only changes in diversity but also changes in the abundance and identity of component species, as strong interactors like foundation species have the potential to drive cascading community shifts.     

What is the role of disturbance in catalyzing spatial shifts in forest composition and tree species biomass under climate change?

Mounting evidence suggests that climate change will cause shifts of tree species range and abundance (biomass). Abundance changes under climate change are likely to occur prior to a detectable range shift. Disturbances are expected to directly affect tree species abundance and composition, and could profoundly influence tree species spatial distribution within a geographical region. However, how multiple disturbance regimes will interact with changing climate to alter the spatial distribution of species abundance remains unclear. We simulated such forest demographic processes using a forest landscape succession and disturbance model (LANDIS-II) parameterized with forest inventory data in the northeastern United States. Our study incorporated climate change under a high-emission future and disturbance regimes varying with gradients of intensities and spatial extents. The results suggest that disturbances catalyze changes in tree species abundance and composition under a changing climate, but the effects of disturbances differ by intensity and extent. Moderate disturbances and large extent disturbances have limited effects, while high-intensity disturbances accelerate changes by removing cohorts of mid- and late-successional species, creating opportunities for early-successional species. High-intensity disturbances result in the northern movement of early-successional species and the southern movement of late-successional species abundances. Our study is among the first to systematically investigate how disturbance extent and intensity interact to determine the spatial distribution of changes in species abundance and forest composition.     

The influence of trophic status and large-scale climatic change on the structure of fish communities in Perialpine lakes

1. A recurrent question in ecology is the influence of environmental factors, particularly nutrients and climatic variables, on community structure and functioning, and their interaction with internal community processes (e.g. competition). 2. Perialpine lakes have been subject to two main kinds of human-induced changes over the last 50 years: eutrophication-reoligotrophication, represented by lake-specific changes in total phosphorus concentration (TP), and long-term global climatic change, captured by average winter temperature (AWT). 3. Changes in fish communities (abundance of seven species from fishery data) in 11 Perialpine lakes during 31 years (1970-2000) were investigated in relation to variation in TP and AWT using models incorporating the effects of fish maturation age, and potentially discriminating effects on adult survival and recruitment. 4. We show that phosphorus concentration affects fish abundance in species-specific ways. These effects are mediated by recruitment rather than by adult survival. Phosphorus effects are probably modulated by interspecific interactions, as increasing TP enhances total community biomass, which in turn is either positively or negatively associated with species abundance depending on species position in trophic chains. 5. Climatic change has very little effect on fish abundances, which is not consistent with the prediction of larger changes in species near their southern distribution boundary. 6. We propose several hypotheses to account for those findings, and place our study in the wider framework of community ecology.