Habitat Response Research Articles

Does Wyoming's Core Area Policy Protect Winter Habitats for Greater Sage-Grouse?

Conservation reserves established to protect important habitat for wildlife species are used world-wide as a wildlife conservation measure. Effective reserves must adequately protect year-round habitats to maintain wildlife populations. Wyoming's Sage-Grouse Core Area policy was established to protect breeding habitats for greater sage-grouse (Centrocercus urophasianus). Protecting only one important seasonal habitat could result in loss or degradation of other important habitats and potential declines in local populations. The purpose of our study was to identify the timing of winter habitat use, the extent which individuals breeding in Core Areas used winter habitats, and develop resource selection functions to assess effectiveness of Core Areas in conserving sage-grouse winter habitats in portions of 5 Core Areas in central and north-central Wyoming during winters 2011-2015. We found that use of winter habitats occured over a longer period than current Core Area winter timing stipulations and a substantial amount of winter habitat outside of Core Areas was used by individuals that bred in Core Areas, particularly in smaller Core Areas. Resource selection functions for each study area indicated that sage-grouse were selecting habitats in response to landscapes dominated by big sagebrush and flatter topography similar to other research on sage-grouse winter habitat selection. The substantial portion of sage-grouse locations and predicted probability of selection during winter outside small Core Areas illustrate that winter requirements for sage-grouse are not adequately met by existing Core Areas. Consequently, further considerations for identifying and managing important winter sage-grouse habitats under Wyoming's Core Area Policy are warranted.

Simulating the Effects of Sea Level Rise on the Resilience and Migration of Tidal Wetlands along the Hudson River.

Sea Level Rise (SLR) caused by climate change is impacting coastal wetlands around the globe. Due to their distinctive biophysical characteristics and unique plant communities, freshwater tidal wetlands are expected to exhibit a different response to SLR as compared with the better studied salt marshes. In this study we employed the Sea Level Affecting Marshes Model (SLAMM), which simulates regional- or local-scale changes in tidal wetland habitats in response to SLR, and adapted it for application in a freshwater-dominated tidal river system, the Hudson River Estuary. Using regionally-specific estimated ranges of SLR and accretion rates, we produced simulations for a spectrum of possible future wetland distributions and quantified the projected wetland resilience, migration or loss in the HRE through the end of the 21st century. Projections of total wetland extent and migration were more strongly determined by the rate of SLR than the rate of accretion. Surprisingly, an increase in net tidal wetland area was projected under all scenarios, with newly-formed tidal wetlands expected to comprise at least 33% of the HRE’s wetland area by year 2100. Model simulations with high rates of SLR and/or low rates of accretion resulted in broad shifts in wetland composition with widespread conversion of high marsh habitat to low marsh, tidal flat or permanent inundation. Wetland expansion and resilience were not equally distributed through the estuary, with just three of 48 primary wetland areas encompassing >50% of projected new wetland by the year 2100. Our results open an avenue for improving predictive models of the response of freshwater tidal wetlands to sea level rise, and broadly inform the planning of conservation measures of this critical resource in the Hudson River Estuary.

The trade-off between heat tolerance and metabolic cost drives the bimodal life strategy at the air-water interface.

The principle of oxygen and capacity limitation of thermal tolerance in ectotherms suggests that the long-term upper limits of an organism's thermal niche are equivalent to the upper limits of the organism's functional capacity for oxygen provision to tissues. Air-breathing ectotherms show wider thermal tolerances, since they can take advantage of the higher availability of oxygen in air than in water. Bimodal species move from aquatic to aerial media and switch between habitats in response to environmental variations such as cyclical or anomalous temperature fluctuations. Here we tested the prediction that bimodal species cope better with thermal stress than truly aquatic species using the crab Pachygrapsus marmoratus as a model species. When in water, oxygen consumption rates of P. marmoratus acutely rise during warming. Beyond a temperature threshold of 23 °C the crab's aerobic metabolism in air remains lower than in water. In parallel, the haemolymph oxygen partial pressure of submerged animals progressive decreases during warming, while it remains low but constant during emersion. Our results demonstrate the ability of a bimodal breathing ectotherm to extend its thermal tolerance during air-breathing, suggesting that there are temperature-related physiological benefits during the evolution of the bimodal life style.

조류 서식지 보전을 위한 친환경적 계획 방안 연구 - 부산 강서지구를 중심으로 -

This study surveys and analyzes the ecology of Gangseo area to be developed near Nakdonggang River and West Nakdonggang River in Busan - before its development. With the result of the surveys as its basis, the study also finds ways to conserve the area's bird habitats in response to the planned development. According to the site surveys over four seasons, West Nakdonggang River which is near the targeted development area is a wintering ground for migratory birds. Some representative bird types in this area are ducks, geese, and other water birds. There are even six legally protected species. The average altitude of their flight is calculated to be and the main purpose for the migration is determined to be for food. According to evalution of the conservation value of the area, Nakdonggang River and West Nakdonggang River turns out to have the highest conservation value. Other areas are developable as long as it was environmentally friendly. Therefore, this study suggests incorporation of ecological parks and biotopes within the targeted development area along with the proposal for spaces in the surroundings where the wintering birds can rest and feed. Especially for the wintering birds that rest at Nakdonggang River and West Nakdonggang River, their flight direction and pattern was examined to determine that their resting ground should be located 50~100m off of the river bank. Furthermore, this study proposes ways to maximize bird habitat by building ecological corridors between the agricultural channel and other small streams in the targeted development area and the habitats in the surroundings. Lastly, the study suggests the construction of low buildings, at most 20m in height, near Nakdonggang River and West Nakdonggang River considering the birds' flight altitude and direction.

Physico-Chemical Characteristics of Culex pipiens sensu lato and Culex torrentium (Diptera: Culicidae) Breeding Sites in Germany.

Culex pipiens sensu lato (L.) and Culex torrentium Martini, 1925 are two widely distributed mosquito species in Europe. Due to difficulties in morphological discrimination, the current knowledge on differences in the breeding ecology is fragmentary. Therefore, this study evaluated the relation between the presence-absence of both species at various types of breeding habitats in response to physico-chemical parameters, using a recently developed molecular assay that allows reliable species-specific typing of larvae and pupae. The results revealed that the two species often occur in sympatry at the studied breeding sites, and there were no substantial differences concerning presence-absence of the two species with regard to the various environmental parameters investigated.

Projecting a spatial shift of Ontario's sugar maple habitat in response to climate change: A GIS approach

Canada is the world's largest producer of maple syrup. Syrup production depends on weather and climatic conditions of the sugarbush. However, forest ecosystems are highly sensitive to climate change. The effect of rapidly changing precipitation and temperature patterns on tree species is of concern as these long‐lived organisms cannot quickly adapt to the new environmental conditions in which they find themselves. As temperatures increase it is expected that there will be a change in species' ranges poleward. This study uses Multi‐Criteria Decision Making (MCDM) and Geographic Information System (GIS) weighted sum analysis to project near future (2050) and distant future (2100) suitability maps of sugar maple (Acer saccharum) habitat in Ontario associated with three different Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) scenarios. Our maps project an overall decrease in the amount of suitable habitat within the current sugar maple range under the scenarios modelled, which intensifies in the later time period. Furthermore there is a projected shift in central and southern Ontario from a region dominated by suitable habitat to one dominated by unsuitable habitat.

Impact of land cover homogenization on the Corncrake (Crex crex) in traditional farmland

The loss of landscape heterogeneity is causing declines of farmland biodiversity around the world. Traditional farmland regions are often highly heterogeneous and harbor high biodiversity, but are under threat of land cover homogenization due to changing agricultural practices. One species potentially affected by landscape homogenization is the Corncrake (Crex crex), which is threatened in Western Europe but remains widespread in the traditional farmland regions of Eastern Europe. In this study we present a case study aiming to assess the potential threat of landscape homogenization for the Corncrake in Romania. We first examined current Corncrake distribution in relation to woody vegetation cover, landscape heterogeneity, and topography (measured at three different spatial scales), as well as human disturbance, throughout the existing agricultural mosaic. Second, we predicted potential future distribution of suitable Corncrake habitat in response to land cover homogenization by simulating a reduction in land cover diversity. Corncrakes were present in grassland and arable fields, and preferentially occupied remote areas that were wet and flat, and had high land cover diversity at the 100 ha scale. The simulation of land cover diversity loss revealed that even a moderate reduction of land cover diversity could drastically reduce the extent of suitable Corncrake habitat. Our findings show the high conservation value of traditional heterogeneous farmland for the Corncrake. Therefore, to protect the Corncrake in traditional farmland, pro-active policy measures should encourage the continuation of mixed farming practices to maintain a diversity of land covers.

Shelterbelts in agricultural landscapes enhance ladybeetle abundance in spillover from cropland to adjacent habitats

The natural enemies of herbivorous pests in cropping systems may relocate to adjacent habitats in response to declining habitat quality in heterogeneous landscapes. In this study, we measured the cross-edge spillover of ladybeetles from wheat fields to shelterbelts, and tested how landscape variables at various spatial scales influence ladybeetle populations. We conducted a large-scale sampling study of agricultural landscapes differing in structural complexity during 2012 and 2013. The effects of landscape variables (i.e., landscape diversity and the percentage of woody habitats) on the ladybeetle abundance were investigated. Propylea japonica (Thunberg) and Harmonia axyridis (Pallas) were the dominant ladybeetle species. The abundances of ladybeetles in spillover were positively correlated with the percentage of woody area, and negatively correlated with landscape diversity and edge density of crop habitats. It indicates that a low diversity landscape with a large area of shelterbelts supports larger ladybeetle abundance in spillover compared with a high diversity landscape with a limited area of shelterbelts. By contrast, greater numbers of within-field ladybeetles were associated with landscape diversity increase. Landscape features at the spatial scale of 2.5–3 km could best predict the abundance of ladybeetles in spillover, whereas the best prediction model for ladybeetle abundance within field was at the 1.5 km scale. These results suggest that the landscape variables influence ladybeetle abundance differently in spillover and within fields. The introduction of shelterbelts in the agricultural landscape could enhance the conservation of ladybeetle populations.

A transferability study of the kernel-based reclassification algorithm for habitat delineation

Wetland mapping using Earth observation (EO) data has proved to be a challenging task for practitioners due to the complexity in the spatial structure and composition, the wide within-class spectral variability and the absence of easily distinguishable boundaries between habitat types. Furthermore, the inherent temporal water instability of these landscapes poses an obstacle to the integration of field data with remote sensing data, which also are not acquired simultaneously at all times.To cope with these limitations we tested the applicability of the Kernel-based reclassification (KRC) algorithm on very high spatial resolution (VHR) satellite imagery over a wetland. A composite multi-temporal (i.e. dual-date) VHR WorldView-2 image consisting of spectral bands and indices derived from two images acquired during flooded and dry water conditions were employed. This dataset stresses the seasonal variations of the habitat in response to environmental changes (i.e. flooding) occurring between the two acquisition dates. Multi-temporal imagery is an important information source for fine mapping of wetlands such are river deltas. A multi-temporal approach could reveal even more specific information during the phenology of these habitats.The methodology was applied firstly to Axios and then to Aliakmonas river deltas in Northern Greece. The results revealed an overall accuracy of 53% in the first and more complex site, and 86% in the second site.

Predicting territory density of Dusky Orange-crowned Warblers Oreothlypis celata sordida breeding on Santa Catalina Island, California

Capsule Territory density of the Dusky Orange-crowned Warbler Oreothlypis celata sordida, endemic to the California Channel Islands, USA, varied with vegetation greenness and oak coverage on Santa Catalina Island.Aims To model factors affecting territory density of warblers on Santa Catalina Island.Methods Breeding warblers were monitored in a dry and a more mesic habitat on the island in 2006–2008 and modelled using a GIS tool to predict territory density. Data of three-year territory boundaries with ecological covariates were used to develop a regression tree and project the distribution of territory density on an island-wide scale. The fitted model was indirectly evaluated using the island-wide point counts.Results The territory density of warblers differed between mesic and xeric habitats in response to oak coverage and food abundance in oaks. In the model, Normalized Difference Vegetation Index and oak coverage were the best predictors. Individual density estimates from distance sampling were comparable with the model prediction.Conclusion Plot-based surveying and statistical modelling provided an insight on how breeding warblers responded to resource abundance. This approach may facilitate the management of these insular birds that are highly dependent on oak habitats on the island where habitat loss has been occurring due to anthropogenic fire.

Biogeography and Phylogenetic Position of a Warm-stenotherm Centric Diatom, Skeletonema potamos (C.I. Weber) Hasle and its Long-term Dynamics in the River Danube

Skeletonema potamos is a poorly known freshwater species in the ancestrally and predominantly marine genus Skeletonema. With phylogenetic analysis of two nuclear {partial SSU (18S) and partial LSU (28S) rDNA)} and two chloroplast (rbcL and psbC) genes, we verified its placement within the genus Skeletonema and identified the mostly brackish species, Skeletonema subsalsum, as its closest known relative. Comparisons of SSU and LSU rRNA genes from S. potamos populations from Europe and North America revealed no intraspecific variation. Skeletonema potamos can be a dominant element of the phytoplankton community in various ecosystems, including the River Danube. We tracked phytoplankton composition in the River Danube weekly from 1979 to 2 012, and throughout this period, S. potamos exhibited a strong increase in proportion of total phytoplankton abundance and biomass - an increase that was correlated with increasing water temperature over the same time period. Current records indicate a temperate distribution of S. potamos, but ecological data predict possible expansion of its geographic range and increase in seasonal duration within existing habitats in response to the warming of surface waters.

Climate change and Southern Ocean ecosystems I: how changes in physical habitats directly affect marine biota.

Antarctic and Southern Ocean (ASO) marine ecosystems have been changing for at least the last 30 years, including in response to increasing ocean temperatures and changes in the extent and seasonality of sea ice; the magnitude and direction of these changes differ between regions around Antarctica that could see populations of the same species changing differently in different regions. This article reviews current and expected changes in ASO physical habitats in response to climate change. It then reviews how these changes may impact the autecology of marine biota of this polar region: microbes, zooplankton, salps, Antarctic krill, fish, cephalopods, marine mammals, seabirds, and benthos. The general prognosis for ASO marine habitats is for an overall warming and freshening, strengthening of westerly winds, with a potential pole-ward movement of those winds and the frontal systems, and an increase in ocean eddy activity. Many habitat parameters will have regionally specific changes, particularly relating to sea ice characteristics and seasonal dynamics. Lower trophic levels are expected to move south as the ocean conditions in which they are currently found move pole-ward. For Antarctic krill and finfish, the latitudinal breadth of their range will depend on their tolerance of warming oceans and changes to productivity. Ocean acidification is a concern not only for calcifying organisms but also for crustaceans such as Antarctic krill; it is also likely to be the most important change in benthic habitats over the coming century. For marine mammals and birds, the expected changes primarily relate to their flexibility in moving to alternative locations for food and the energetic cost of longer or more complex foraging trips for those that are bound to breeding colonies. Few species are sufficiently well studied to make comprehensive species-specific vulnerability assessments possible. Priorities for future work are discussed.

Variation in stream organic matter processing among years and benthic habitats in response to forest clearfelling

We assessed rates of organic matter (OM) processing in coarse gravel and fine benthic sediment, along with water temperature, in four clearfell harvested and two undisturbed headwater streams flowing through wet eucalypt forest in southern Tasmania, Australia. Clearfell forestry in Tasmanian wet eucalypt forest involves felling of all timber followed by a high intensity regeneration burn to provide a receptive mineral seedbed for seedling growth. Bacterial carbon production and cellulose decomposition potential (together referred to as OM processing) were measured seasonally 3–5years before and 2–4years after harvesting in each stream. We employed a staircase design (staggered harvesting treatments) within a multiple before–after control–impact design to distinguish harvesting effects from natural variation. Clearfell harvesting raised the yearly mean water temperature by between 0.25°C and 0.94°C, and raised the maximum water temperature by between 0.84 and 1.6°C. Rates of cellulose decomposition were not significantly correlated with sediment temperature but bacterial carbon production showed weak, significant correlations with temperature in fine (r=0.20, P=0.01, n=137) and coarse gravel sediment (r=0.39, P<0.001, n=137). The response in OM processing to clearfell harvesting differed between years and among benthic habitats. In coarse gravel habitat, there was a significant decrease in rates of cellulose decomposition potential in the 2nd and 4th year after harvesting, and a significant decrease in bacterial carbon production in the 3rd year after harvesting. However, we found a significant increase in rates of bacterial carbon production of fine sediment habitat in the 2nd and 4th year after harvesting. The contrasting response of OM processing between habitats indicates that habitat-specific changes occur after clearfell harvesting, which inhibit attempts to quantitatively predict downstream cumulative effects. Scaling up the habitat-specific responses will not only require estimates of the relative abundances of the distinct habitats, but may also require research into how different spatial configurations of habitats may affect reach- and catchment-scale estimates of OM processing.

Relationship between Diet and Microhabitat Use of Red-legged Salamanders (Plethodon shermani) in Southwestern North Carolina

The selection of a foraging habitat may be driven by food availability or by the cost associated with the use of that habitat. This basic tradeoff can lead individuals in the same population to occupy different habitats in response to perceived risk levels. In the southeastern United States, plethodontid salamanders are often observed climbing vegetation, which represents a potential foraging habitat. We examined whether diet composition of the Red-legged Salamander, Plethodon shermani, differed between salamanders found on vegetation and on the ground surface. Contrary to the results of a previous study, we found that the overall number and mass of prey items did not differ between salamanders in these two microhabitats. Furthermore, we found no evidence that the relative use of different prey categories varied in relation to a salamander's selected microhabitat. Although salamanders of all body sizes had consumed a diverse range of prey items, we found evidence of an ontogenetic shift in prey utilizatio...

Predator avoidance during reproduction: diel movements by spawning sockeye salmon between stream and lake habitats

Daily movements of mobile organisms between habitats in response to changing trade-offs between predation risk and foraging gains are well established; however, less in known about whether similar tactics are used during reproduction, a time period when many organisms are particularly vulnerable to predators. We investigated the reproductive behaviour of adult sockeye salmon (Oncorhynchus nerka) and the activity of their principal predator, brown bears (Ursus arctos), on streams in south-western Alaska. Specifically, we continuously monitored movements of salmon between lake habitat, where salmon are invulnerable to bears, and three small streams, where salmon spawn and are highly vulnerable to bears. We conducted our study across 2 years that offered a distinct contrast in bear activity and predation rates. Diel movements by adult sockeye salmon between stream and lake habitat were observed in 51.3% ± 17.7% (mean ± SD) of individuals among years and sites. Fish that moved tended to hold in the lake for most of the day and then migrated into spawning streams during the night, coincident with when bear activity on streams tended to be lowest. Additionally, cyclic movements between lakes and spawning streams were concentrated earlier in the spawning season. Individuals that exhibited diel movements had longer average reproductive life spans than those who made only one directed movement into a stream. However, the relative effect was dependent on the timing of bear predation, which varied between years. When predation pressure primarily occurred early in the spawning run (i.e., during the height of the diel movements), movers lived 120-310% longer than non-movers. If predation pressure was concentrated later in the spawning run (i.e. when most movements had ceased), movers only lived 10-60% longer. Our results suggest a dynamic trade-off in reproductive strategies of sockeye salmon; adults must be in the stream to reproduce, but must also avoid predation long enough to spawn. Given the interannual variation in the timing and intensity of predation pressure, the advantages of a particular movement strategy will likely vary among years. Regardless, movements by salmon allowed individuals to exploit fine-scale habitat heterogeneity during reproduction, which appears to be a strategy to reduce predation risk on the spawning grounds.

From non-static vignettes to unprecedented change: The U.S. National Park System, climate impacts and animal dispersal

US Federal land management agencies and the public are currently facing a challenge unlike any other in history: climate change. In the case of the US National Park Service (NPS), agency action to cope with the problem began in earnest in January 2009. The objective of this review is to provide an assessment of NPS policy statements, plans and on-ground activity for the purpose of reducing the future biological impacts of climate change on US National Park System biota. I looked at Presidential initiatives, Secretarial orders, and agency planning documents, policy statements, reports, and Web sites. I also reviewed the scientific literature. Based on my work experience with the agency, I also illustrate how values influenced NPS natural resources policy evolution. One critical piece of the initiatives toolbox is not being given adequate emphasis: land use planning. Without effective land use planning, some terrestrial park biota will find it difficult or impossible to move to higher latitude and cooler habitat in response to changes in atmospheric temperature and moisture. One technical problem is predicting where to provide corridors and of what dimensions, or preferably a more permeable regional landscape, so certain species can navigate around or through developed land. In many cases, the choices remaining are few since much adjacent natural land is so developed as to be realistically beyond reclamation. The implications of not planning for landscape permeability is that many terrestrial, non-volant park species will likely vanish in a developed, human-dominated mortality sink. Unfortunately, land use planning is a politically volatile topic that federal agencies avoid. American society nevertheless will be forced to deal with the inevitable tension between private land rights and the need to allow protected area biota to move.

Preference induction and the benefits of floral resources for a facultative florivore

The causes and consequences of flower feeding for facultative florivores are poorly understood. Several factors can influence host selection and may, by extension, influence host part selection. Two such factors cited for the facultative florivore, Liriomyza trifolii (Burgess), are the optimisation of adult performance and natal habitat preference induction (NHPI) – a change in preference for a habitat in response to cues associated with the natal habitat. In this study we compared the nutritive and physical qualities of leaves and petals of Gerbera jamesonii, measured the survival and fitness of adults flies reared on leaves, flowers or a mixed diet, and investigated the influence of NHPI on adult host part choice. Liriomyza trifolii exhibited more than 50% higher lifetime fecundity on a mixed diet than on strict diets of leaves or flowers. Newly emerged adult flies exposed to leaves for 24 h showed a significant preference towards leaves, while flower‐exposed flies showed no significant preference; flower‐exposed flies were thus more than twice as likely as leaf‐exposed flies to feed and oviposit on flowers. These results suggest that the optimisation of adult performance may be driving facultative florivory for L. trifolii in general, but the degree of florivory expressed is influenced by early adult experience, as NHPI explained 33% and 39% of feeding and oviposition host part choice, respectively. The potential for NHPI to influence the spatiotemporal occurrence of florivory is discussed.

Resource Availability and Spatial Heterogeneity Control Bacterial Community Response to Nutrient Enrichment in Lakes

The diversity and composition of ecological communities often co-vary with ecosystem productivity. However, the relative importance of productivity, or resource abundance, versus the spatial distribution of resources in shaping those ecological patterns is not well understood, particularly for the bacterial communities that underlie most important ecosystem functions. Increasing ecosystem productivity in lakes has been shown to influence the composition and ecology of bacterial communities, but existing work has only evaluated the effect of increasing resource supply and not heterogeneity in how those resources are distributed. We quantified how bacterial communities varied with the trophic status of lakes and whether community responses differed in surface and deep habitats in response to heterogeneity in nutrient resources. Using ARISA fingerprinting, we found that bacterial communities were more abundant, richer, and more distinct among habitats as lake trophic state and vertical heterogeneity in nutrients increased, and that spatial resource variation produced habitat specific responses of bacteria in response to increased productivity. Furthermore, changes in communities in high nutrient lakes were not produced by turnover in community composition but from additional taxa augmenting core bacterial communities found in lower productivity lakes. These data suggests that bacterial community responses to nutrient enrichment in lakes vary spatially and are likely influenced disproportionately by rare taxa.

Biogeography and spatio-temporal diversification of Selenidera and Andigena Toucans (Aves: Ramphastidae)

Andean uplift, Plio-Pleistocene climatic fluctuation, and river dynamics in the Amazon basin have all been implicated in the diversification of the South American avifauna. We reconstructed phylogenetic relationships in the genus Selenidera, which has served as a classic case of putative refugial speciation, and the closely related genus Andigena, to better understand the processes driving their diversification. Using mitochondrial and nuclear DNA sequences, we constructed a phylogeny to estimate the pattern and timing of divergence within and between seven lowland Selenidera toucanets and the five species of Andigena mountain-toucans, which together form a single clade. All phylogenetic analyses supported the monophyly of the montane genus Andigena, but indicated that the genus Selenidera is likely paraphyletic with respect to Andigena. Our time tree analysis is consistent with the orogenic uplift of the northern Andean range having initiated the divergence between Selenidera and Andigena, and that the movement and fragmentation of montane habitats in response to Pleistocene climatic oscillations likely influenced diversification within Andigena. Estimated divergence times for lowland Amazonian Selenidera did not support the Last Glacial Maximum (LGM) refuge hypothesis as an important biogeographic factor for the diversification of lineages studied here. The timing of divergence within Selenidera is consistent with the hypothesis that geographic isolation of areas of endemism generated by Amazonian river dynamics during the Plio-Pleistocene contributed to Selenidera speciation and current species distributions.

Effects of sympatric predatory crabs Romaleon polyodon and Cancer plebejus (Decapoda, Brachyura, Cancridae) on sublittoral macrobenthic communities

Although large crabs are recognized as important sediment disturbers influencing the structure of benthic communities, the role of dominant predatory crabs in soft-bottom habitats along the Humboldt Current Ecosystem, remains largely unknown. A field study was conducted, hypothesizing that the digging activity of these predators disturbs the habitat thereby leading to a reduction in individual abundance, biomass and species richness; these changes result in a modified structure of macrobenthic communities. A directed sampling (crab pits vs. reference areas) showed significant reductions in total abundances in pits compared to reference areas, but no differences were observed in taxonomic richness or benthic biomass. Short-term cage experiment showed significant decreases in total abundance and biomass of macroinvertebrates in predator inclusion treatments compared to exclusions and controls. In consequence, our results confirmed that burrowing activities and the generation of small disturbed sediment patches influence the community structure. These results highlight the importance of large cancrid crabs in soft-bottom habitats, where their modification of the physical configuration of the sediment affects community structure over small spatial scales. Crabs are thus an important source of spatial heterogeneity of the sea-floor landscape. This ecological role must be considered in management strategies of the extensive artisanal fishery for these crabs, as current evidence is showing increasing populations of intermediate predators (like cancrid crabs) in many benthic habitats in response to the depletion of top predators.