Multi-trophic consequences of kelp harvest

Coastal kelp forest ecosystems provide important habitats for a diverse assemblage of invertebrates, fish and marine top-predators such as seabirds and sea mammals. Although kelp is harvested industrially on a worldwide scale little is known about the multi-trophic consequences of this habitat removal. We investigated how kelp fisheries, which remove feeding and nursery grounds of coastal fish, influence local food webs and the availability of food to a marine top predator, the great cormorant (Phalacrocorax carbo). We conducted experimental harvesting of the canopy-forming kelp (Laminaria hyperborea) during a 3 year period (2001-2003) in an area at the coast of Central Norway while synoptically monitoring fish occurrence and cormorant foraging parameters. Our results demonstrate that cormorants preferentially foraged within kelp-forested areas and performed significantly more dives when feeding in harvested versus un-harvested areas suggesting lower foraging yield in the former case. In kelp areas that were newly harvested the number of small (<15 cm) gadid fish was 92% lower than in un-harvested areas. This effect was persistent for at least 1 year following harvest. To our knowledge, this is the first time that the ecological consequences of kelp harvesting have been tested at a multi-trophic level. The results presented strongly suggest that kelp harvesting affects fish abundance and diminishes coastal seabird foraging efficiency. Kelp fisheries are currently managed in order to maximize the net harvest of kelp biomass, and the underlying effects on the ecosystems are partly ignored. This study calls for re-assessment of such management practices.     

Taking it to the next level: Trophic transfer of marker fatty acids from basal resource to predators

Fatty acid (FA) analysis is used increasingly to investigate the trophic structure of soil animal food webs as the technique allows separation of the role of detrital resources such as bacteria, fungi and plant material for consumer nutrition. The applicability of FAs as biomarkers for different diets has been verified for Collembola and Nematoda. However, for the analysis of whole food webs it is crucial to know whether marker FA are valid for different taxa and whether they are transferred along the food chain to higher trophic levels, i.e. predators. Top-predators are integrators of lower level energy fluxes in food webs; therefore analysis of their FAs may allow to identify trophic pathways and to separate bacterial vs. fungal based energy channels. Chilopoda and Arachnida are among the main predators in soil food webs. Our aim was to test the applicability of marker FAs for these two predator taxa and to verify the trophic transfer of marker FAs of different basal resources via first order consumers into predators, i.e. over three trophic levels. Therefore, we investigated the transfer of FAs from different basal resources [fungi (Chaetomium globosum), plant leaf litter (Tilia europaea), Gram-positive (Bacillus amyloliquefaciens) and Gram-negative bacteria (Stenotrophomonas maltophilia)] via Collembola (Heteromurus nitidus) as first order consumers into predators [Lithobius forficatus (Chilopoda) and Pardosa lugubris (Arachnida)]. Fatty acid profiles of predators of food chains with different basal resources differed significantly. Marker FAs of basal resources were clearly detectable in predators, suggesting that FA analysis allows to separate trophic channels of soil food webs. By reflecting basal resources, FAs of predators allow tracking energy/resource fluxes through the food web and thereby clarifying the relative importance of bacterial vs. fungal vs. plant resources for soil animal food webs.     

Plant species richness does not attenuate responses of soil microbial and nematode communities to a flood event

Human activities are causing climatic changes and alter the composition and biodiversity of ecosystems. Climate change has been and will be increasing the frequency and severity of extreme climate events and natural disasters like floods in many ecosystems. Therefore, it is important to investigate the effects of disturbances on ecosystems and identify potential stabilizing features of ecological communities. In this study, soil microbial and nematode communities were investigated in a grassland biodiversity experiment after a natural flood to investigate if plant diversity is able to attenuate or reinforce the magnitude of effects of the disturbance on soil food webs. In addition to community analyses of soil microorganisms and nematodes, the stability indices proportional resilience, proportional recovery, and proportional resistance were calculated. Generally, soil microbial biomass decreased significantly due to the flood with the strongest reduction in gram-negative bacteria, while gram-positive bacteria were less affected by flooding. Fungal biomass increased significantly three months after the flood compared to few days before the flood, reflecting elevated availability of dead plant biomass in response to the flood. Similar to the soil microbial community, nematode community structure changed considerably due to the flood by favoring colonizers (in the broadest sense r-strategists; c–p 1, 2 nematodes), particularly so at high plant diversity. None of the soil microbial community stability indices and few of the nematode stability indices were significantly affected by plant diversity, indicating limited potential of plant diversity to buffer soil food webs against flooding disturbance. However, plant diversity destabilized colonizer populations, while persister populations (in the broadest sense K-strategists; c–p 4 nematodes) were stabilized, suggesting that plant diversity can stabilize and destabilize populations depending on the ecology of the focal taxa. The present study shows that changes in plant diversity and subsequent alterations in resource availability may significantly modify the compositional shifts of soil food webs in response to disturbances.     

From common to rare: The case of the Mediterranean common dolphin

Although overfishing has been recognized as responsible for the decline of major fish stocks, it has been less easy to demonstrate its indirect and detrimental effects on marine mammals, particularly dolphins. Competition with fisheries for the same food resources has been hypothesized to have led to the decline of several species of dolphins, including the endangered Mediterranean short-beaked common dolphin. Based on an ecosystem model for the Inner Ionian Sea Archipelago, a former hotspot for common dolphins in the Mediterranean Sea, we investigated the effect of increasing fishing effort on common dolphins, its prey and on marine biodiversity and we evaluated the outcomes of different fisheries closures (1 – closure of the purse seine fishery, 2 – closure of purse seine, trawl and beach seine fisheries, 3 – entire area closed to fisheries) ran between the years 2011 and 2030. Our results showed that local fisheries have negatively impacted the marine biodiversity of the ecosystem causing sharp declines of common dolphins and major fish stocks and weakening the robustness of the marine food web. The implementation of fisheries closures would gradually recover fish stocks, while common dolphins would increase more pronouncedly only if the study area was to be closed to all fisheries. As shown in this study, common dolphins have reflected ecosystem changes and degradation over time. Ensuring the survival of dolphin populations is thereby essential to enhance marine ecosystems and ensure sustainable fishing.     

Ecosystem consideration in conservation planning: energy demand of foraging bottlenose whales (Hyperoodon ampullatus) in a marine protected area

The Gully, a submarine canyon off eastern Canada, was nominated as a pilot Marine Protected Area (MPA) in 1998, largely to safeguard the vulnerable population of northern bottlenose whales (Hyperoodon ampullatus) found there. The boundaries and ultimate management regime for the MPA for this area remain under review. We have estimated the energy consumption of bottlenose whales in the Gully based on the number of whales present at any time, their trophic level, the food requirements of each whale, and the rates of energy transfer between trophic levels. These calculations suggest that there must be a substantial spatial subsidy in the underlying foodweb of the submarine canyon to support the bottlenose whales using the Gully. A substantial area beyond the distribution of bottlenose whales in the area will therefore require protection. Conservation priorities to protect such subsidies will primarily involve additional protection at the level of the sea floor. Spatial subsidies are probably common in the marine environment, urging careful ecological analysis in the establishment of marine reserves and suggesting that conservation priorities need to take into account key ecological linkages and processes that are vital for sustaining species and habitats of concern.     

温室土壤食物网静态和动态结构特征

Soil food web structure is fundamental to ecosystem process and function; most studies on soil food web structure have focused on agro-ecosystems under different management practices and natural terrestrial ecosystems, but seldom on greenhouses. This study explored the static and temporal variability of soil food structure in two greenhouses of Shandong Province, North China over a two-year period. The static properties were measured directly by surveying functional group composition and a series of parameters portraying the species properties, link properties, chain properties and omnivory properties of the web, as well as indirectly through calculation of nematode indices, enrichment index （EI）, structure index （SI）, and channel index （CI）. The dynamic variability of greenhouse soil food structure was described by the dynamics of functional groups, Bray-Curtis （BC） similarity and cluster analysis. The results showed that the greenhouse soil food web contained 14 functional groups, with microbes having the highest mean biomass, followed by protozoa. Of the three functional groups of protozoa, flagellates were the dominant group on most sampling dates, amoebae only became the dominant group during the summer, while ciliates were the least prevalent group. All nematodes were assigned into one of the four functional groups, bacterivorous, fungivorous, herbivorous and omnivorous, and the fungivorous nematodes had the lowest mean biomass. Mites were assigned into three functional groups and the omnivorous noncryptostigmatic mites were the dominant group. All the functional groups showed significant seasonal changes. The soil food web connectance was 0.15, the maximum food chain length was 5, and the average food chain length was 3.6. The profiles of the EI and SI showed that the food web was resource- depleted with minimal structure. The results of CI indicated that the bacterial decomposition pathway was the dominant pathway in the food web of the greenhouse soils studied and the results of BC similarity showed that the soil food web had higher variability and instability over time. The cluster analysis showed that the functional groups located at high trophic levels with low biomass were in a cluster, whereas those at low trophic levels with high biomass were closer. Compared with the food web structure of agroecosystem and natural terrestrial ecosystem soils, the structure of greenhouse soil food web was simple and unstable, which was likely driven by high agricultural intensification, particularly over application of fertilizers.     

Biodiversity in soil ecosystems: the role of energy flow and community stability

In a series of community food webs from native and agricultural soils, we modeled energetics and stability, and evaluated the role of the various groups of organisms and their interactions in energy flow and community stability. Species were aggregated into functional groups based on their trophic position in the food webs. Energy flow rates among the groups were calculated by a model using observations on population sizes, death rates, specific feeding preferences and energy conversion efficiencies. From the energetic organization of the communities we derived the strengths of the mutual effects among the populations. These interaction strengths were found to be patterned in a way that is important to community stability. The patterning consisted of the simultaneous occurrence of strong top down effects at lower trophic levels and strong bottom up effects at higher trophic levels. These patterns resulted directly from the empirical data we used to parameterize the model, as we found no stabilizing patterns with random but plausible parameter values. Also, the impact of each individual interaction on community stability was established. This analysis showed that some interactions had a relatively strong impact on stability, whereas other interactions had only a small impact. These impacts on stability were neither correlated with energy flow nor with interaction strength. Comparison of the seven food webs showed that these impacts were sometimes connected to particular groups of organisms involved in the interaction, but sometimes they were not, which might be due to different trophic positions in the food webs. We argue that future research should be directed to answer the question which energetic properties of the organisms form the basis of the patterning of the interaction strengths, as this would improve our understanding of the interrelationships between energetics, community stability, and hence the maintenance of biological diversity.     

Behavior of Cd,Pb, and Cu in the marine deltaic area of the Po River (North Adriatic Sea)

An analysis of the spatial trend of concentrations and of the correlation between heavy metals and total suspended matter was performed in a multidisciplinary study of transport of pollutants in the marine coastal area involving in situ investigations, remote sensing techniques and modeling. This paper presents results concerning the chemical behavior of heavy metals (Cu, Cd, Pb) in the North Adriatic Sea and in particular in the marine deltaic area of the Po river. The samples were collected during the JRC Remote Sensing Campaigns ADRIA 84 and ADRIA 85, carried out in the entire North Adriatic Sea and in the selected area in front of the Po when passing from the fluvial to the marine environment. In the dissolved phase, Cu undergoes a dilution process consistent with the mixing theory, while there is a tenfold increase in Pb concentrations. A pronounced tendency to augment the level in the dissolved phase is observed for all three elements in the pelagic waters. In the particulate phase, Cd and Cu, after a diminution in the nearshore stations, their concentration increases as the pelagic area is approached. The total amount of heavy metals in solid phase of the water decreases according to the dispersion and the sedimentation processes of the fluvial load in the marine water. A satisfactory correlation was found between the Cu and Pb with the total suspended matter (TSS). An attempt was made to characterize sediments and suspended matter in order to assess the role of the organic and mineralogical components on heavy metal behavior.     

Spatial variations in the trophic structure of soil animal communities in boreal forests of Pechora-Ilych Nature Reserve

Soil animal communities and detrital food webs are spatially compartmentalized. In old-growth boreal forests the dynamics of dominating plant species forms a considerable heterogeneity of edaphic conditions in the soil layer. We demonstrate a strong difference in total and relative abundance of main trophic groups of soil macrofauna in four microsites, i.e. under tree crowns, in gaps, in mounds and in pits created by fallen spruce trees. The variation in the functional structure of soil animal communities is likely related to different availability of key energy resources (leaf litter, roots and root deposits) in the microsites studied. However, results of the stable isotope analysis suggest that mobile litter-dwelling predators occupy very similar trophic positions in different microsites. The compartmentalization of soil invertebrate communities caused by the vegetation-induced mosaic of edaphic conditions seemingly does not lead to spatial isolation of local food webs that are integrated at the top trophic levels.     

Warming favours small-bodied organisms through enhanced reproduction and compositional shifts in belowground systems

The increased prevalence of smaller-bodied species under warmer conditions (community downsizing) is hypothesized as an ecologically critical consequence of climate change, leading to changes in trophic transfer efficiency, and rates of nutrient and energy flux within ecosystems. This study used 100 intact peat-soil mescosms to measure changes in belowground biodiversity under three manipulated climate variables: elevated temperature, elevated CO₂, and altered water table. Changes in species richness, abundance, community composition and body size spectra were used to determine whether climate change factors led to community downsizing, and elucidate any underlying mechanisms. Warming was the primary driver of compositional shifts in belowground fauna communities with the strongest effect among the smaller-bodied, non-sexually reproducing species. Increases in abundance driven by enhanced reproduction in small-bodied species rather than an increased extinction-rate among large-bodied predators was the basis of the observed downsizing. The overall consequences of warming-induced changes in belowground systems on ecosystem function are still unclear. However, as body size is intricately linked to metabolism, observed community downsizing suggests reductions in food web trophic transfer efficiency with consequences for nutrient and energy dynamics in belowground systems.     

Incidental capture of marine turtles by the Italian trawl fishery in the north Adriatic Sea

In the north Adriatic Sea on-board observations on midwater and bottom trawlers were carried out during years 1999 and 2000. Results indicate that the north Adriatic Sea, and especially the north-east part, is a very important foraging and overwintering habitat for loggerhead turtles (Caretta caretta). Since the distribution of fishing effort in the area is not known, the total turtle catch by the Italian bottom trawl fleet was conservatively estimated from the lower catch rate observed in the south-west sub-area: 4273 turtle captures/year (95% C.I.=2186-8546). The actual total catch in the whole north Adriatic is likely to be much higher, due both to an unknown Italian trawling effort in the south-west part with multi-gear vessels and to the Italian and Croatian trawling efforts in the north-east part, where catch rate was 15 times greater than in the south-west part. In the south-west sub-area 9.4% of captured turtles were dead and potential mortality (assuming that all comatose turtles would die too) was 43.8%. Hence, trawling in the north Adriatic is likely to represent a serious threat to the populations, and possible conservation measures are discussed.     

Long-term trends in lobster populations in a partially protected vs. no-take Marine Park

Increasing the level of protection afforded to the marine environment requires assessment of the efficacy of existing marine protected areas (MPAs) in protecting exploited species. Long-term data from before and after the establishment of MPAs provide a rare but valuable opportunity to assess these effects. In this study we present long-term data (1977-2005) from before and after park establishment, on the abundance of spiny lobster Jasus edwardsii from fixed sites in a no-take marine park and a recreationally fished marine park, to assess the efficacy of no-take vs. partial protection. Lobster densities were comparable between both marine parks prior to park establishment, but the response of lobster populations differed markedly following protection. On average, legal-sized lobster were eleven times more abundant and biomass 25 times higher in the no-take marine park following park establishment, while in the partially protected marine park there has been no significant change in lobster numbers. Furthermore, no difference was found in densities of legal-sized lobster between the partially protected marine park and nearby fully-fished sites (<1 per 500 m²). Long-term data from fully fished and partially protected sites suggest long-term declines in lobster populations and reflect regional patterns in catch per unit effort estimates for the fishery. The long-term patterns presented provide an unequivocal example of the recovery of lobster populations in no-take MPAs, but clearly demonstrate that allowing recreational fishing in MPAs has little benefit to populations of exploited species such as J. edwardsii.     

Soil macroinvertebrate fauna of a Mediterranean arid system: Composition and temporal changes in the assemblage

Temporal variability is a key factor to understand the structure of belowground communities. Seasonal and annual variations are especially relevant in unpredictable desert ecosystems, where macroinvertebrates are poorly known, despite constituting an important group of soil organisms. In the present study, we analyse the composition and temporal (seasonal and annual) variations of soil macroinvertebrates in an arid area of southern Spain. During two years, macroinvertebrates were sampled in litter and belowground levels by means of soil cores. Results show that the assemblage was dominated by arthropods, especially Formicidae and Coleoptera. The assemblage differed between litter and belowground levels. In litter, detritivores dominated the community, while belowground fauna showed a similar proportion of detritivores and herbivores and a low percentage of predators. Litter and belowground assemblages showed seasonal variations in richness, abundance, biomass and composition, although variations were more marked in litter than belowground. Patterns of seasonal variation also differed between the two study years for both litter and belowground invertebrates. The seasonal and annual variability of the assemblage has potentially important implications for community dynamics in the study system, since the changes in species composition and trophic structure of soil invertebrate assemblages may affect species interactions and food web dynamics over time. Therefore, integrating temporal variability is likely to be crucial to understand soil community dynamics and food webs, especially in heterogeneous, variable systems as deserts.     

Trophic interactions in centipedes (Chilopoda,Myriapoda) as indicated by fatty acid patterns: Variations with life stage,forest age and season

Fatty acid (FA) analysis investigates changes in the relative contribution of prey from major energy channels in decomposer food webs for predator nutrition. Adopting this approach we investigated whether the trophic niche of centipedes, as major invertebrate predators in forest soil food webs, changes with maturation, season or forest age. Generally, each of the four centipede species studied differed significantly in their FA composition suggesting trophic niche differentiation. FA profiles differed more strongly in the two geophilomorph (Strigamia acuminata and Geophilus ribauti) than in the two lithobiomorph species (Lithobius crassipes and Lithobius mutabilis) suggesting that in particular the former feed on markedly different prey. FA profiles changed during post-embryonic development in each of the four centipede species. Differences were most pronounced in the two lithobiomorph species shifting to predominantly fungal feeding prey. Further, FA profiles varied with season indicating that centipedes exploit more prey out of the bacterial channel in autumn. FA profiles of centipedes varied little with forest age suggesting that soil food webs are remarkably invariant across different forest ecosystems. The results indicate that FA composition of second order consumers closely reflects changes in diet of prey species and composition of basal resources. The study proved FA profiles as powerful tool to gain insight into critical characteristics of soil food web stability, i.e., compartmentalisation and the relative importance and variability of energy channels.     

A phototrophy-driven microbial food web in a rice soil

Purpose  

Light is a major driver of primary productivity in most ecosystems on Earth. Phototrophic microorganisms harvest light to synthesize organic biomass for sustaining the global energy and carbon flow. However, the bottom-up model of phototrophic microorganisms as primary production and food source for higher trophic levels remains unclear in the terrestrial environment.     

The formation of terrestrial food webs in glacier foreland: Evidence for the pivotal role of decomposer prey and intraguild predation

We investigated the structure of invertebrate food webs at three glacier foreland sites of an age of 2-34, ca. 60 and ca. 120 years in the European Alps at 2250-2450 m asl. The trophic structure was investigated by analyzing stable isotope ratios of ¹⁵N/¹⁴N and ¹³C/¹²C. The results suggest that the formation of terrestrial food webs during early primary succession heavily relies on prey out of the decomposer system with Collembola being most important. The diet of decomposers likely is based predominantly on allochthonous humus material blown in by wind and deposited by the retreating glacier. Irrespective of the successional stage the animal community consisted mainly of generalist predators with a number of species occurring at each of the successional stages. The results suggest that terrestrial food web formation is associated with a prolongation of food chains caused mainly by predator species switching their diet to include other predators, i.e. by intraguild predation. This suggests that generalist predators, such as cursorial spiders, carabid beetles, harvestman and centipedes, switch prey and include other predators if these are becoming more abundant, i.e. if ecosystems become more productive. Intraguild predation results in complex food webs with high linkage density which likely affects food web functioning and stability.     

The effects of including marine ecological values in terrestrial reserve planning for a forest-nesting seabird

Theoretical advances in systematic reserve design aim to promote the efficient use of limited conservation resources and to increase the likelihood that reserve networks enhance the persistence of valued species and ecosystems. However, these methods have rarely been applied to species that rely on spatially disjunct habitats. We used the marbled murrelet, a seabird that requires old-growth forest in which to nest and high quality marine habitats in which to forage, as a case study to explore methods of incorporating multiple ecological values into single species spatial reserve design. Specifically, we used the cost function in MARXAN to include the ecological value of marine habitats while identifying spatial solutions for terrestrial nesting habitat reserves. Including marine values influenced terrestrial reserve designs most when terrestrial habitat targets were low and little or none of the target was represented in pre-existing protected areas. Our results suggest that including marine values in the planning process will influence marbled murrelet terrestrial reserve designs most where substantial terrestrial nesting habitat still exists, where new reserves are relatively unconstrained by pre-existing reserves, or when conservation resources only allow the protection of a small fraction of available habitat. This paper presents a novel framework for incorporating multiple measures of ecological value in the spatial reserve design process and should be particularly useful for species that rely on multiple habitats during their life cycle.     

Extinction risk assessment of the world’s seagrass species

Seagrasses, a functional group of marine flowering plants rooted in the world’s coastal oceans, support marine food webs and provide essential habitat for many coastal species, playing a critical role in the equilibrium of coastal ecosystems and human livelihoods. For the first time, the probability of extinction is determined for the world’s seagrass species under the Categories and Criteria of the International Union for the Conservation of Nature (IUCN) Red List of Threatened Species. Several studies have indicated that seagrass habitat is declining worldwide. Our focus is to determine the risk of extinction for individual seagrass species, a 4-year process involving seagrass experts internationally, compilation of data on species’ status, populations, and distribution, and review of the biology and ecology of each of the world’s seagrass species. Ten seagrass species are at elevated risk of extinction (14% of all seagrass species), with three species qualifying as Endangered. Seagrass species loss and degradation of seagrass biodiversity will have serious repercussions for marine biodiversity and the human populations that depend upon the resources and ecosystem services that seagrasses provide.     

Do we protect biological originality in protected areas? A new index and an application to the Bonifacio Strait Natural Reserve

Changes in biodiversity may disrupt the ecological functions performed by species assemblages. Hence, we urgently need to examine the implications of biodiversity loss not only in terms of species conservation but also in terms of sustainability of ecosystem services. The ability of protected areas to maintain local species richness has been clearly demonstrated. However, preserving goods and services provided by ecosystems requires not only the conservation of species richness but also the conservation of the most ‘original’ species, i.e. the ones with the highest average rarity of their attributes which are likely to perform some unique functions in ecosystems. We proposed a new conservation of biological originality (CBO) index as well as associated randomization tests to quantify the ability of protected areas to maintain viable populations for the most original species. As an application, we used long-term fisheries data collected in the Bonifacio Strait Natural Reserve (BSNR) to determine the species which benefited from the protection reinforcement in 1999. We also estimated a set of 14 ecomorphological functional traits on the 37 fish species caught in the BSNR and we obtained a functional originality value for each species. As a result, we found that functional originality was significantly protected in the fish assemblage of the BSNR: species with the most original functional trait combinations became more abundant after 1999. Our finding suggests that protecting most original species is an insurance against functional diversity erosion in the BSNR. More generally, our new index can be used to test whether protected areas may protect preferentially the most original species and whether restorative management promotes the reestablishment of the most original species with particular habitat requirements.     

A comparison of soil food webs beneath C<Subscript>3</Subscript>- and C<Subscript>4</Subscript>-dominated grasslands

Soil food webs influence organic matter mineralization and plant nutrient availability, but the potential for plants to capitalize on these processes by altering soil food webs has received little attention. We compared soil food webs beneath C₃- and C₄-grass plantings by measuring bacterial and fungal biomass and protozoan and nematode abundance repeatedly over 2 years. We tested published expectations that C₃ detritus and root chemistry (low lignin/N) favor bacterial-based food webs and root-feeding nematodes, whereas C₄ detritus (high lignin/N) and greater production favor fungal decomposers and predatory nematodes. We also hypothesized that seasonal differences in plant growth between the two grassland types would generate season-specific differences in soil food webs. In contrast to our expectations, bacterial biomass and ciliate abundance were greater beneath C₄ grasses, and we found no differences in fungi, amoebae, flagellates, or nematodes. Soil food webs varied significantly among sample dates, but differences were unrelated to aboveground plant growth. Our findings, in combination with previous work, suggest that preexisting soil properties moderate the effect of plant inputs on soil food webs. We hypothesize that high levels of soil organic matter provide a stable environment and energy source for soil organisms and thus buffer soil food webs from short-term dynamics of plant communities.