Causes and projections of abrupt climate-driven ecosystem shifts in the North Atlantic

Warming of the global climate is now unequivocal and its impact on Earth' functional units has become more apparent. Here, we show that marine ecosystems are not equally sensitive to climate change and reveal a critical thermal boundary where a small increase in temperature triggers abrupt ecosystem shifts seen across multiple trophic levels. This large-scale boundary is located in regions where abrupt ecosystem shifts have been reported in the North Atlantic sector and thereby allows us to link these shifts by a global common phenomenon. We show that these changes alter the biodiversity and carrying capacity of ecosystems and may, combined with fishing, precipitate the reduction of some stocks of Atlantic cod already severely impacted by exploitation. These findings offer a way to anticipate major ecosystem changes and to propose adaptive strategies for marine exploited resources such as cod in order to minimize social and economic consequences.     

The fate of nitrogen and phosphorus at the land-sea margin of the North Atlantic Ocean

Five large rivers that discharge on the western North Atlantic continental shelf carry about 45% of the nitrogen (N) and 70% of the phosphorus (P) that others estimate to be the total flux of these elements from the entire North Atlantic watershed, including North, Central and South America, Europe, and Northwest Africa. We estimate that 61 · 109 moles y^–1 of N and 20 · 10⁹ moles y^–1 of P from the large rivers are buried with sediments in their deltas, and that an equal amount of N and P from the large rivers is lost to the shelf through burial of river sediments that are deposited directly on the continental slope. The effective transport of active N and P from land to the shelf through the very large rivers is thus reduced to 292 · 10⁹ moles y^–1 of N and 13 · 10⁹ moles y^–1 of P.The remaining riverine fluxes from land must pass through estuaries. An analysis of annual total N and total P budgets for various estuaries around the North Atlantic revealed that the net fractional transport of these nutrients through estuaries to the continental shelf is inversely correlated with the log mean residence time of water in the system. This is consistent with numerous observations of nutrient retention and loss in temperate lakes. Denitrification is the major process responsible for removing N in most estuaries, and the fraction of total N input that is denitrified appears to be directly proportional to the log mean water residence time. In general, we estimate that estuarine processes retain and remove 30–65% of the total N and 10–55% of the total P that would otherwise pass into the coastal ocean. The resulting transport through estuaries to the shelf amounts to 172–335 · 10⁹ moles y^–1 of N and 11–19 · 10⁹ moles y^–1 of P. These values are similar to the effective contribution from the large rivers that discharge directly on the shelf.For the North Atlantic shelf as a whole, N fluxes from major rivers and estuaries exceed atmospheric deposition by a factor of 3.5–4.7, but this varies widely among regions of the shelf. For example, on the U.S. Atlantic shelf and on the northwest European shelf, atmospheric deposition of N may exceed estuarine exports. Denitrification in shelf sediments exceeds the combined N input from land and atmosphere by a factor of 1.4–2.2. This deficit must be met by a flux of N from the deeper ocean. Burial of organic matter fixed on the shelf removes only a small fraction of the total N and P input (2–12% of N from land and atmosphere; 1–17% of P), but it may be a significant loss for P in the North Sea and some other regions. The removal of N and P in fisheries landings is very small. The gross exchange of N and P between the shelf and the open ocean is much larger than inputs from land and, for the North Atlantic shelf as a whole, it may be much larger than the N and P removed through denitrification, burial, and fisheries. Overall, the North Atlantic continental shelf appears to remove some 700–950· 10⁹ moles of N each year from the deep ocean and to transport somewhere between 18 and 30 · 10⁹ moles of P to the open sea. If the N and P associated with riverine sediments deposited on the continental slope are included in the total balance, the net flux of N to the shelf is reduced by 60 · 10⁹ moles y^–1 and the P flux to the ocean is increased by 20 · 10⁹ moles y^–1. These conclusions are quite tentative, however, because of large uncertainties in our estimates of some important terms in the shelf mass balance.     

Oceanic records of North American bats and implications for offshore wind energy development in the United States

Offshore wind energy is a growing industry in the United States, and renewable energy from offshore wind is estimated to double the country''s total electricity generation. There is growing concern that land‐based wind development in North America is negatively impacting bat populations, primarily long‐distance migrating bats, but the impacts to bats from offshore wind energy are unknown. Bats are associated with the terrestrial environment, but have been observed over the ocean. In this review, we synthesize historic and contemporary accounts of bats observed and acoustically recorded in the North American marine environment to ascertain the spatial and temporal distribution of bats flying offshore. We incorporate studies of offshore bats in Europe and of bat behavior at land‐based wind energy studies to examine how offshore wind development could impact North American bat populations. We find that most offshore bat records are of long‐distance migrating bats and records occur during autumn migration, the period of highest fatality rates for long‐distance migrating bats at land‐based wind facilities in North America. We summarize evidence that bats may be attracted to offshore turbines, potentially increasing their exposure to risk of collision. However, higher wind speeds offshore can potentially reduce the amount of time that bats are exposed to risk. We identify knowledge gaps and hypothesize that a combination of operational minimization strategies may be the most effective approach for reducing impacts to bats and maximizing offshore energy production.     

Exploring movement patterns and changing distributions of baleen whales in the western North Atlantic using a decade of passive acoustic data

Six baleen whale species are found in the temperate western North Atlantic Ocean, with limited information existing on the distribution and movement patterns for most. There is mounting evidence of distributional shifts in many species, including marine mammals, likely because of climate‐driven changes in ocean temperature and circulation. Previous acoustic studies examined the occurrence of minke (Balaenoptera acutorostrata) and North Atlantic right whales (NARW; Eubalaena glacialis). This study assesses the acoustic presence of humpback (Megaptera novaeangliae), sei (B. borealis), fin (B. physalus), and blue whales (B. musculus) over a decade, based on daily detections of their vocalizations. Data collected from 2004 to 2014 on 281 bottom‐mounted recorders, totaling 35,033 days, were processed using automated detection software and screened for each species' presence. A published study on NARW acoustics revealed significant changes in occurrence patterns between the periods of 2004–2010 and 2011–2014; therefore, these same time periods were examined here. All four species were present from the Southeast United States to Greenland; humpback whales were also present in the Caribbean. All species occurred throughout all regions in the winter, suggesting that baleen whales are widely distributed during these months. Each of the species showed significant changes in acoustic occurrence after 2010. Similar to NARWs, sei whales had higher acoustic occurrence in mid‐Atlantic regions after 2010. Fin, blue, and sei whales were more frequently detected in the northern latitudes of the study area after 2010. Despite this general northward shift, all four species were detected less on the Scotian Shelf area after 2010, matching documented shifts in prey availability in this region. A decade of acoustic observations have shown important distributional changes over the range of baleen whales, mirroring known climatic shifts and identifying new habitats that will require further protection from anthropogenic threats like fixed fishing gear, shipping, and noise pollution.     

Links between viruses and prokaryotes throughout the water column along a North Atlantic latitudinal transect

Viruses are an abundant, diverse and dynamic component of marine ecosystems and have a key role in the biogeochemical processes of the ocean by controlling prokaryotic and phytoplankton abundance and diversity. However, most of the studies on virus–prokaryote interactions in marine environments have been performed in nearshore waters. To assess potential variations in the relation between viruses and prokaryotes in different oceanographic provinces, we determined viral and prokaryotic abundance and production throughout the water column along a latitudinal transect in the North Atlantic. Depth-related trends in prokaryotic and viral abundance (both decreasing by one order of magnitude from epi- to abyssopelagic waters), and prokaryotic production (decreasing by three orders of magnitude) were observed along the latitudinal transect. The virus-to-prokaryote ratio (VPR) increased from ∼19 in epipelagic to ∼53 in the bathy- and abyssopelagic waters. Although the lytic viral production decreased significantly with depth, the lysogenic viral production did not vary with depth. In bathypelagic waters, pronounced differences in prokaryotic and viral abundance were found among different oceanic provinces with lower leucine incorporation rates and higher VPRs in the North Atlantic Gyre province than in the provinces further north and south. The percentage of lysogeny increased from subpolar regions toward the more oligotrophic lower latitudes. Based on the observed trends over this latitudinal transect, we conclude that the viral–host interactions significantly change among different oceanic provinces in response to changes in the biotic and abiotic variables.     

The relationship between marine fronts and fish diversity in the Patagonian Shelf Large Marine Ecosystem

Aim To evaluate the relationship between marine fronts and (1) fish diversity patterns, (2) fish biomass distribution, and (3) fish assemblage structure. Location Patagonian Shelf, Southwestern Atlantic Ocean. Methods Three main frontal systems and eight nearby zones (frontal vs. non‐frontal areas) were compared. An extensive fishery database, obtained during an a priori sampling scheme (spatial resolution 1 × 1) from 1978 to 1979, was employed. Analyses of 248 trawling stations were performed using a combination of diversity measures (species richness, Shannon diversity and evenness), biomass analyses and multivariate analyses [nonparametric analysis of similarity (ANOSIM), non‐metric multidimensional scaling ordination (NMDS) and similarity percentages (SIMPER)] to evaluate the effect of fronts on fish communities. Results In total, 46 fish taxa were identified. Demersal fish diversity increased at the tidal front of Península Valdés but decreased in the frontal zones of the Southern Shelf‐Break and Magellan frontal systems. The richness and biomass of pelagic fish were higher at the Península Valdés Tidal Front, while the biomass of demersal fish was higher at its non‐frontal counterpart. Fish diversity did not differ consistently along the Northern Shelf‐Break Front. However, a higher fish biomass was registered at the non‐frontal zone. Demersal and pelagic fish assemblages differed between frontal and non‐frontal zones. Main conclusions The Patagonian Shelf Large Marine Ecosystem has diverse frontal types that appear to have different effects on fish diversity and assemblage structure. Seasonal (tidal) or permanent fronts have different effects on the parameters analysed, which could be due to productivity–diversity relationships. The Península Valdés Tidal Front, a relatively short temporal scale system, demonstrates a stronger influence on fish diversity, biomass and assemblage structure than the other frontal areas studied. The seasonality of nutrient input owing to frontogenesis, which begins during the austral spring, may play an important role in determining local diversity. At permanent frontal features, diversity decreases when the nutrient availability is high. This is potentially because, when food resources increase, a few species become dominant.     

Species range size distributions for some marine taxa in the Atlantic Ocean. Effect of latitude and depth

The range size distributions of 6643 species in ten different fish and invertebrate taxa dwelling in pelagic (latitudinal range sizes) and benthic (latitudinal and depth range sizes) habitats on both sides of the Atlantic Ocean (80°N−70°S) were studied. The objectives were to analyse: (1) the range size distribution patterns for the various taxa and whether they have right/left skewed or lognormal distributions; (2) the geographical species distributions, to ascertain whether the distribution ranges change with latitude (Rapoport's rule); and (3) the relationship between the depth ranges of benthic species and their maximum depth of occurrence and how depth range size distributions change with latitude. The pelagic taxa exhibited larger range sizes than did the benthic taxa, continental slope/rise species excepted. On the other hand, the boundaries between geographical provinces for both benthic taxa and pelagic taxa tended to occur in association with major oceanographic processes. The shape of the latitudinal range frequency distributions (LRFDs) of the pelagic organisms were distinctly left‐skewed, and the LRFDs for most taxa were significantly different from lognormal. There was no common pattern for the distributions of the benthic organisms, which were lognormal in Cephalopoda, Stomatopoda, and Crustacea Decapoda and tended to be left‐skewed and significantly different from lognormal in Pisces. The applicability of Rapoport's rule was not clearly inferable from the results, and the rule appears to be conditioned by the location of biogeographical boundaries and the endemism rate in the different biogeographical provinces. A clear increase in depth range size with maximum depth range was observable for benthic species, confirming previous studies. Species’ depth range distributions displayed a discernible latitudinal pattern, right‐skewed at high latitudes and left‐skewed at low latitudes. The location of biogeographical boundaries, and endemism rate by biogeographical province were considered to be the factors most useful in explaining species’ distribution patterns and their conformity or nonconformity to Rapoport's rule. © 2003 The Linnean Society of London, Biological Journal of the Linnean Society, 2003, 80 , 437–455.     

Phylogeography of North Atlantic intertidal tardigrades: refugia,cryptic speciation and the history of the Mid‐Atlantic Islands

Aim To analyse the phylogeographical history of intertidal tardigrades in the North Atlantic in order to improve our understanding of geographical differentiation in microscopic organisms, and to understand the potential importance of the Mid‐Atlantic Islands as stepping stones between the American and European coasts of the Atlantic Ocean. Location Twenty‐four localities from the Mid‐Atlantic Islands (Greenland, Iceland and the Faroe Islands) and both sides of the North Atlantic Ocean. Methods A mitochondrial marker (cytochrome c oxidase subunit I) was sequenced from individual tardigrades belonging to the genus Echiniscoides. The existence of cryptic species was detected using generalized mixed Yule coalescence analysis; lineage ages were estimated with relaxed clock methods; and the degree of geographical differentiation was analysed with samova analyses, haplotype networks and Mantel tests. Results Echiniscoides hoepneri, previously known only from Greenland, was recovered throughout the Mid‐Atlantic Islands. The Faroe Islands population was isolated from Greenland and Iceland, but overall genetic variation was low. The morphospecies Echiniscoides sigismundi had high genetic variation and consisted of at least two cryptic species. A northern and a southern species were both recovered on both sides of the Atlantic, but only the northern species was found on the Mid‐Atlantic Islands. The northern species showed signs of long‐term isolation between the Western and Eastern Atlantic, despite the potential of the Mid‐Atlantic islands to act as stepping‐stones. There was no sign of long‐term isolation in the southern species. The Mid‐Atlantic individuals of the northern species were of Eastern Atlantic origin, but Greenland and Iceland showed signs of long‐term isolation. The genetic pattern found in the southern species is not clearly geographical, and can probably be best explained by secondary contact between former isolated populations. Main conclusions North Atlantic intertidal tardigrades from the genus Echiniscoides showed strong geographical differentiation, and the Mid‐Atlantic Islands seemed unimportant as stepping stones across the Atlantic. The geographical variation of the northern species of E. sigismundi suggests post‐glacial recolonization from several refugia.     

Trans‐Pacific and trans‐Arctic pathways of the intertidal macroalga Fucus distichus L. reveal multiple glacial refugia and colonizations from the North Pacific to the North Atlantic

Aim We examined the phylogeography of the cold‐temperate macroalgal species Fucus distichus L., a key foundation species in rocky intertidal shores and the only Fucus species to occur naturally in both the North Pacific and the North Atlantic. Location North Pacific and North Atlantic oceans (42° to 77° N). Methods We genotyped individuals from 23 populations for a mitochondrial DNA (mtDNA) intergenic spacer (IGS) (n = 608) and the cytochrome c oxidase subunit I (COI) region (n = 276), as well as for six nuclear microsatellite loci (n = 592). Phylogeographic structure and connectivity were assessed using population genetic and phylogenetic network analyses. Results IGS mtDNA haplotype diversity was highest in the North Pacific, and divergence between Pacific haplotypes was much older than that of the single cluster of Atlantic haplotypes. Two ancestral Pacific IGS/COI clusters led to a widespread Atlantic cluster. High mtDNA and microsatellite diversities were observed in Prince William Sound, Alaska, 11 years after severe disturbance by the 1989 Exxon Valdez oil spill. Main conclusions At least two colonizations occurred from the older North Pacific populations to the North Atlantic between the opening of the Bering Strait and the onset of the Last Glacial Maximum. One colonization event was from the Japanese Archipelago/eastern Aleutians, and a second was from the Alaskan mainland around the Gulf of Alaska. Japanese populations probably arose from a single recolonization event from the eastern Aleutian Islands before the North Pacific–North Atlantic colonization. In the North Atlantic, the Last Glacial Maximum forced the species into at least two known glacial refugia: the Nova Scotia/Newfoundland (Canada) region and Andøya (northern Norway). The presence of two private haplotypes in the central Atlantic suggests the possibility of colonization from other refugia that are now too warm to support F. distichus. With the continuing decline in Arctic ice cover as a result of global climate change, renewed contact between North Pacific and North Atlantic populations of Fucus species is expected.     

Effects of Soil Properties and Flooding on the Mobility and Transformation of Mercury in a Temperate Riparian Wetland

Three fractions of mercury (mobile, semi-mobile, and non-mobile mercury) were detected in the soil of an estuarine wetland in Nansi Lake, which is on the east route of China's South-to-North Water Transfer Project. The correlations between these mercury fractions and soil properties were examined under different levels of toxicity. Furthermore, the effects of two flooding conditions (permanent flooding and seasonal flooding) on mercury mobility were analyzed. Results showed that soil pH was negatively correlated with mobile mercury, whereas semi-mobile mercury was positively correlated with total aluminum, iron, and manganese. Moreover, free alumina was positively correlated with all three fractions of mercury. Our study suggests that high contents of soil acid and free alumina might promote wetlands as “sinks” for mercury sequestration, along with low concentrations of organic matter and manganese. In addition, seasonally flooded wetland might limit the production of toxic mobile mercury more than permanently flooded wetland. Large areas of seasonally flooded wetlands in the watershed are permanently flooded by the water transfer project, which elevates the water level during the dry season. As a result, the potential toxicity of mercury may increase in the watershed during water transfer, which should gain more attention.     

Protistan diversity estimates based on 18S rDNA from seawater incubations in the Western North Atlantic

Cloning/sequencing and fragment analysis of ribosomal RNA genes (rDNA) are becoming increasingly common methods for the identification of microbial taxa. Sequences of these genes provide many additional taxonomic characters for species that otherwise have few distinctive morphological features, or that require involved microscopy or laboratory culture and testing. These same approaches are now being applied with great success in ecological studies of natural communities of microorganisms. Extensive information on the composition of natural microbial assemblages is being amassed at a rapid pace through genetic analyses of environmental samples and comparison of the resulting genetic information with well-established (and rapidly growing) public databases. We examined microbial eukaryote diversity in a natural seawater sample from the coastal western North Atlantic Ocean using two molecular biological approaches: the cloning and sequencing of rRNA genes and by fragment analysis of these genes using the terminal restriction fragment length polymorphism (T-RFLP) method. A simple experiment was carried out to examine changes in the overall eukaryote (largely protistan) diversity and species composition (phylotype diversity) of a natural microbial assemblage when a seawater sample is placed in a container and incubated at ambient light and temperature for 72 h. Containment of the natural seawater sample resulted in relatively minor changes in the overall eukaryote diversity (species richness) obtained by either molecular method at three time points (time-zero, time-24 h, time-72 h). However, substantial changes in the dominance of particular eukaryote phylotypes took place between the three sampling times. Only 18% of the total number of phylotypes observed in the study were observed at all three time points, while 65% (108 of 165) phylotypes were observed only at a single time point (54 unique phylotypes initially, 37 more unique phylotypes at 24 h, and 17 more at 72 h). The results of this study indicate that a high diversity of protistan taxa existed in the original seawater sample at very low abundance, and thus were not observed in the initial characterization of community structure. Containment resulted in significant shifts in the dominance of these taxa, enabling the presence of previously unobserved phylotypes to be documented after 24 or 72 h of incubation.     

基于贝叶斯Schaefer模型的阿根廷滑柔鱼资源评估与管理

利用基于贝叶斯统计方法的Schaefer模型对西南大西洋阿根廷滑柔鱼资源量进行评估,并对评估结果进行风险分析.结果表明:正态分布方案和基准方案两个模型参数的预测值及估算的生物学参考点接近,但均大于对数正态分布方案.3种方案下,2001-2010年的捕捞死亡率都远低于限制参考点F0.1,2001-2010年的渔获量也小于最大可持续产量(MSY),表明西南大西洋阿根廷滑柔鱼资源目前处于良好开发状况,没有遭受过度捕捞.决策分析表明,在相同的收获率情况下,对数正态分布方案得到的2025年资源量最低、资源崩溃的概率最大.3种方案下2025年渔获量最大时的收获率均为0.6,但是若将管理策略定为收获率0.6,则2025年以后资源量存在一定风险,因此较为保守的管理策略应将收获率控制在0.4左右,渔获量在55万t左右.     

Effects of Pleistocene climate changes on species ranges and evolutionary processes in the Neotropical Atlantic Forest

The effects of global glaciations on the distribution of organisms is an essential element of many diversification models. However, the empirical evidence supporting this idea is mixed, in particular with respect to explaining tropical forest evolution. In the present study, we evaluated the impacts of range shifts associated with Pleistocene global glacial cycles on the evolution of tropical forests. In particular, we tested the predictions: (1) that population genetic structure increases with fragmentation variation between the present and the Last Glacial Maximum (LGM) and also (2) with geographical range instability; and (3) that genetic diversity increases with range stability and (4) decreases with fragmentation variation between periods. To address our predictions, we studied population genetic structures and modelled present and past distributions of 15 Atlantic Forest (AF) endemic birds. Afterwards, we evaluated the relationship of population genetic parameters with metrics of species range shifts between the present and the LGM. We found that geographical ranges of AF birds changed in concert with Pleistocene glacial cycles but, unexpectedly, our findings suggest the novel idea that ranges during glacial maxima were slightly larger on average, as well as equally fragmented and displaced from the interglacial ranges. Our findings suggest that range shifts over the late Pleistocene impacted on the diversification of forest organisms, although they did not show that those range shifts had a strong effect. We found that a combination of fragmentation variation across time, small current range size, and range stability increased population genetic structure. However, neither fragmentation, nor range stability affected genetic diversity. Our study showed that evolutionary responses to range shifts across AF birds have a high variance, which could explain the mixed support given by single‐species studies to the action of Pleistocene range shifts on population evolution.     

First record of Polyprion oxygeneios(Perciformes: Polyprionidae) for the south‐west Atlantic and a northernmost range extension

The occurrence of Polyprion oxygeneios (Perciformes: Polyprionidae) is recorded for the first in the south‐west Atlantic. Twenty specimens were caught off Rio Grande do Sul (33°41·8'–34° 15·3' S, 370–854 m depth) during winter cruises of the commercial fishing fleet.     

2013年北太平洋公海渔场柔鱼体内典型放射性核素分析及风险评估

为了解福岛核泄漏放射性核素对北太平洋公海渔场的后续性污染影响情况,于2013年8—11月在北太平洋公海渔场(40°—44° N、145°—160° E)采集柔鱼样品,利用超低本底HPGe γ 谱仪分析5种放射性核素.结果表明: ¹³⁴Cs和^110mAg未检测出高于本底值的比活度,而²¹⁰Pb、¹³⁷Cs和⁴⁰K均有检出.其中²¹⁰Pb在柔鱼体的比活度范围为0.99～7.60 Bq·kg^-1,¹³⁷Cs的比活度范围为最低检测限～0.37 Bq·kg^-1,⁴⁰K的比活度范围为46.00～107.00 Bq·kg^-1.²¹⁰Pb核素含量在柔鱼250～300 mm胴长组分布最高;在200～250和>400 mm胴长组中最低.¹³⁷Cs含量在柔鱼200～250 mm胴长组中最高;在250～300和350～400 mm胴长组较低.⁴⁰K核素含量在柔鱼250～300 mm胴长组中最高,在150～200 mm胴长组最低,总体分布比较均匀.3种核素在柔鱼的不同组织中含量不同,但均在内脏中含量最高.通过风险评估发现,北太平洋公海渔场所有检测的海洋生物的放射性核素含量值与基准值的熵值均未超过1,说明目前核辐射对该海域渔业资源的影响暂无大风险.研究可为福岛核事故对海洋环境生态影响及公众健康危害评估提供理论依据.     

Visual and acoustic surveys for North Atlantic right whales,Eubalaena glacialis,in Cape Cod Bay,Massachusetts, 2001–2005: Management implications

North Atlantic right whales, Eubalaena glacialis, remain endangered, primarily due to excessive anthropogenic mortality. Current management protocols in US waters are triggered by identifying the presence of at least one right whale in a management area. We assessed whether acoustic detection of right whale contact calls can work as an alternative to visual aerial surveys for establishing their presence. Aerial survey and acoustic monitoring were conducted in Cape Cod Bay, Massachusetts, in 2001–2005 and used to evaluate and compare right whale detections. Over the 58 d with simultaneous aerial and acoustic coverage, aerial surveys saw whales on approximately two-thirds of the days during which acoustic monitoring heard whales. There was no strong relationship between numbers of whales seen during aerial surveys and numbers of contact calls detected on survey days. Results indicate acoustic monitoring is a more reliable mechanism than aerial survey for detecting right whales. Because simple detection is sufficient to trigger current management protocols, continuous, autonomous acoustic monitoring provides information of immediate management utility more reliably than aerial surveillance. Aerial surveys are still required to provide data for estimating population parameters and for visually assessing the frequency and severity of injuries from shipping and fishing and detecting injured and entangled right whales.