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1.
Ecosystems are fundamentally connected to one another, although empirical documentation of the links between them, especially the links between marine and terrestrial ecosystems, has been limited. This study examined the foraging behavior and ecology of an understudied invertebrate, the hermit crab Coenobita compressus, which is remarkably abundant at the nexus of marine, terrestrial, and freshwater ecosystems. Data collected between 2008 and 2011 in the Osa Peninsula of Costa Rica revealed that C. compressus plays a generalist scavenger role across ecosystems. Beach almond fruits (Terminalia catappa) were a staple of the crabs’ diet, but the crabs also commonly consumed a variety of other fruit species and various parts of plants (nuts, seeds, flowers, husk, stems, buds) as well as algae, fungus, animal feces, and the carcasses of insects, jellyfish, conspecifics, other crustacean species, freshwater and saltwater fish, sea turtles (eggs and adults), and mammals. The crabs fed on these resources in prominent social aggregations, also forming such aggregations as they exchanged the aquatically derived gastropod shells that they use as homes while roaming the land. The size of the crabs’ aggregations around plant versus animal resources and around terrestrial versus aquatic resources did not differ, underscoring the species’ generalist foraging behavior. Broadly, these results suggest that C. compressus has one of the most diverse diets of any crustacean and plays a critical role in recycling organic matter and nutrients. This species might also mediate the passage of resources across different ecosystems, although further research is needed to explore this possibility.  相似文献   

2.
Despite the high number of species and ecological diversity of pandalid shrimps, there has been no previous attempt to resolve evolutionary relationships of several genera using molecular tools. Although mitochondrial DNA cytochrome oxidase I (COI) is widely used in barcoding studies to delimit species boundaries, additional insights into phylogenetic affinities can be obtained, especially when used in combination with data from additional genes. The knowledge of molecular diversity is essential to understand phylogenetic relationships and will help systematic clarifications. Based on partial fragments of the 16S and COI genes, we have focused specifically on addressing the systematic relationships of the economically and ecologically important shrimp genus Plesionika within a framework of five genera from within the Pandalidae. Our results showed that species within Plesionika are substantially divergent when compared with other genera, exhibiting the highest average nucleotide divergence, with 0.1123 and 0.0846 in COI and 16S genes, respectively. In addition, sequence divergence was found to vary greatly within the genus Plesionika (COI/16S): 0.0247/0.0016 between Plesionika antigai and Plesionika heterocarpus and 0.1616/0.098 between Plesionika heterocarpus and Plesionika edwardsii. We did not find amino acid sequence divergence between P. heterocarpus and P. antigai compared with P. heterocarpus and P. edwardsii (8.10%, K2P distance). Three species of Plesionika (P. antigai, P. heterocarpus and Plesionika scopifera) appear well separated from other Plesionika species in both maximum likelihood and Bayesian analyses. The present study confirms the utility of COI over 16S as a genetic marker to resolve relationships between different species of Plesionika from the Northeast Atlantic and Mediterranean Sea, in addition to species delimitation. The findings highlight the need to further review paraphyly within Plesionika in an attempt to recognize a concordance in the evolutionary history of Plesionika with major ecological and geological events.  相似文献   

3.
During the last three decades, population abundances of eastern Bering Sea (EBS) crab stocks fluctuated greatly, driven by highly variable recruitment. In recent years, abundances of these stocks have been very low compared to historical levels. This study aims to understand recruitment variation of six stocks of red king (Paralithodes camtschaticus), blue king (P. platypus), Tanner (Chionoecetes bairdi), and snow (C. opilio) crabs in the EBS. Most crab recruitment time series are not significantly correlated with each other. Spatial distributions of three broadly distributed crab stocks (EBS snow and Tanner crabs and Bristol Bay red king crab) have changed considerably over time, possibly related in part to the regime shift in climate and physical oceanography in 1976–1977. Three climate-forcing hypotheses on larval survival have been proposed to explain crab recruitment variation of Bristol Bay red king crab and EBS Tanner and snow crabs. Some empirical evidence supports speculation that groundfish predation may play an important role in crab recruitment success in the EBS. However, spatial dynamics in the geographic distributions of groundfish and crabs over time make it difficult to relate crab recruitment strength to groundfish biomass. Comprehensive field and spatially explicit modeling studies are needed to test the hypotheses and better understand the relative importance and compound effects of bottom-up and top-down controls on crab recruitment.  相似文献   

4.
The determination of costs and benefits experienced by crustaceans as a result of occupation by their symbionts has received increased attention from marine ecologists. However, the interactions between some important species and their associates remain unclear. We examined the distribution of amphipods in the genus Ischyrocerus on the red king crab Paralithodes camtschaticus, a commercially important species, in two areas of the Barents Sea. Ischyrocerus commensalis was found on 30.5% of crabs in Dalnezelenetskaya Bay (DZB) with the mean number per crab being 55.1, in Dolgaya Bay (DLB) these rates were 28.6% with 19.3 specimens per crab. Sympatric species Ischyrocerus anguipes was found on 13.5% of crabs in DZB with a mean of 7.3 individuals per host, in DLB it had much lower occurrence (1.3% and 1.5 specimens per host). There were no significant differences between proportions of male and female crabs infested by amphipods in both areas examined. Prevalence of amphipods was similar among years examined except for I. commensalis on small crabs (carapace length CL <90 mm) and I. anguipes on large crabs (CL >90 mm) in DZB. We found that I. commensalis and I. anguipes are not egg predators of P. camtschaticus in the Barents Sea, at least in summer. High numbers of I. commensalis occur in crab gills, and both mean intensity of the amphipods and their empty tubes increased with crab size. In the gills, I. commensalis predominated in the section nearest the mouth parts. Possible negative impacts for the hosts due to gills infestation are discussed. In contrast, I. anguipes were predominately found on the carapace and limbs of crabs and appears to be a less specific symbiont of P. camtschaticus. Both amphipod species seem to be commensals, however possible negative impacts for the host could not be excluded.  相似文献   

5.
The spatial and temporal biomass distribution of Chaceon affinis and its vulnerability to fishing activity in Gran Canaria (Canary Islands) were investigated. The first goal was to assess the influence of the slope steepness and substrate on the size of crab patches, size of the crabs, and crab biomass. The second goal was to evaluate spatial and temporal variation in the biomass over a 15‐month period. The last goal was to assess the influence of fishing activity upon the reduction in the biomass over the same 15‐month period. Only two or three locations in the sampling area generated high‐biomass contour patches. When these patches were superimposed on the isobath lines, they were coincident with the main depth range described for the species in the area. The map of the biomass values clearly showed three structures with cores of the highest biomass in both muddy and rocky‐muddy areas. The biomass was higher on muddy than on rocky‐muddy bottoms. Biomass was twice as high when steepness was reduced to one third between isobaths of 500 and 900 m. The size of crab patches increases linearly with the decrease in slope steepness. The spatial structure of crabs remained fairly stable over time, showing that biomass changes with depth over time. Maps of the estimated biomass values over the 15‐month period showed the same two main patches over time with the cores of highest biomass separated by a distance of between 4.2 and 4.5 km. Although the bathymetric distribution by sexes showed temporal changes, with a displacement to deeper areas made by both sexes over the studied period, only a partial temporal segregation between males and females was observed. During the study period, crabs underwent a significant decline in biomass and this was consistent with the combined catches of both commercial and experimental fishing in the area. Due to its low mobility, C. affinis is highly vulnerable to local depletion by intensive fishing efforts.  相似文献   

6.
Vulnerability to predation may be high for many megafaunal taxa in deep‐sea sedimentary habitats where physical heterogeneity is low. During ROV observations in a bathyal sediment plain off Central California, juveniles of the lithodid crab Neolithodes diomedeae were frequently observed on or under the holothurian (sea cucumber) Scotoplanes sp. A, and are hypothesized to benefit from this association as a nursery or refugium from predation. Ninety‐six percent (n = 574 of 599) of the juvenile N. diomedeae observed (density varied from 0.02–0.75/m2 among sites and seasons) in the study area were associated with Scotoplanes sp. A. Of the 2596 Scotoplanes sp. A observed (density varied from 0.48 to 25.90/m2), 22% were attended by at least one juvenile crab, and rarely two crabs (n = 4). Solitary N. diomedeae were rarely observed. This decapod–holothurian symbiosis appears to be largely commensal, with juvenile crabs (carapace width = 0.03–0.31 ×  holothurian length) observed on or beneath Scotoplanes sp. A in a habitat with few refugia from epibenthic predators. Other hypotheses may explain or enhance the potential benefits of the association for N. diomedeae, such as elevated food availability due to the activities of Scotoplanes sp. A. The relationship may be mutualistic if there is a benefit for the holothurian, including the removal of epizoic parasites. Ultimately, the nursery or other effects on the population dynamics of N. diomedeae may be minimal in low‐relief, sediment‐dominated habitats, as very few sub‐adult crabs were observed in the study area and were likely consumed upon outgrowing their refugia. While sedimentary habitats may be a sink for N. diomedeae populations, growth of juvenile crabs during their association with Scotoplanes sp. A should increase energy flow to its predator populations. This association has not been reported previously but may be expected in sediment‐dominated habitats where these species overlap.  相似文献   

7.
Crabs are important predators of inter‐tidal ecosystems, controlling the abundance and distribution of their prey populations. Often the same crab species occupies several habitats and, although their effects on prey have been quantified across habitats, crabs’ dietary and morphological responses to differing environmental influences have been overlooked. Here, we used the crabs Eriphia verrucosa and Pachygrapsus marmoratus as model species to examine differences in claw morphometry – size and wear – and diet between rocky shore and heterogeneous sand flat habitats. We predicted that, intra‐specifically, crabs from rocky shores would consume more hard‐shelled prey owing to their high availability and consequently, would display chelipeds with the following claw characteristics: a higher degree of claw damage, stronger musculature (higher propel height) and increased mechanical advantage (defined as the ratio of input lever length to output lever length) than crabs in the heterogeneous sand flat habitats. Sampling was performed in heterogeneous sand flat habitats and rocky shores of the Central Portuguese coast. For each crab species, carapace width, diet composition and several claw morphometric measures were recorded, revealing significant intra‐specific differences (using multivariate analysis) between shore types. We found that E. verrucosa and P. marmoratus consumed more hard prey on rocky shore than on sand flat habitats, which resulted in rocky shore crabs having more accentuated dentition wear and larger musculature than their sand flat habitat counterparts. We suggest that the strong response of crab claw morphometry to environmentally induced diet variations is an important mechanism in the successful adaptation of crab species to inhabit differing habitats. A major implication is that the impact of the same species on prey may vary largely with habitat type as a result of predation efficiency varying with claw condition.  相似文献   

8.
作者根据2012年5月和2013年11月对日照近岸海域进行的底拖网调查资料,分析了该海域虾蟹类的种类组成、优势种和生物多样性。调查海域共捕获虾蟹类25种,根据相对重要性指数计算优势种为8种,其中经济价值较高的中大型虾蟹类5种,分别为:口虾蛄(Oratosquilla oratoria)、戴氏赤虾(Meraenaeopsis dalei)、鹰爪虾(Trachypenaeus curvirostris)、日本[虫寻](Charybdis japonica)和三疣梭子蟹(Portunus trituberculatus)。分别计算了日照近岸海域春、秋季虾蟹类群落的多样性指数(H')、丰富度指数(D)和均匀度指数(J)。该海域虾蟹类群落多样性整体处在较低的水平,在生物量和丰度上经济较高的中大型虾蟹类物种占据优势。  相似文献   

9.
In the culture of mud crab Scylla serrata, cannibalism is often the greatest cause of mortality. A laboratory study was conducted to compare the influence of size class differences and shelter on cannibalism and limb loss in juvenile mud crabs (20–70 mm internal carapace width; ICW). Four size classes of juvenile crab (A: 21–30 mm, B: 31–40 mm, C: 41–50 mm and D: 51–70 mm ICW) were tested in all possible combinations using four different substrata with varying degree of shelter (seaweed, plastic strings, bamboo tubes and open sand substratum) in 48 h trials. Results suggest that cannibalistic interactions are heavily influenced both by size differences of crabs and the availability of shelter. Cannibalism on the smallest size class (20–30 mm ICW) increased about 10 times in the presence of the largest crab (51–70 mm ICW) compared with treatment with only same-size crabs (control treatment). Shelter provided little refuge for the smallest crabs, whereas cannibalism in larger size classes decreased by >50% in all the shelters compared with the sand substratum. The findings suggest that both size-grading and provision of shelter could minimise cannibalism in the culture of mud crabs.  相似文献   

10.
Mud crab (Scylla serrata) is a delicacy for subsistence consumption in fisher communities and tourist hotels in the coast of Kenya while export demand to markets in China and Japan is expanding and provides competitively higher prices. Crab exploitation and degradation of the mangrove forests have increased over the last decades therefore threatening the capture fishery. The preferred market size crab has consistently decreased from more than 1 kg two decades ago to the current size of 0.5 kg therefore posing both management and livelihood threat to the critical ecosystem (mangrove) and coastal populations. To meet the increased tourist and export demand and provide surplus for the local community while conserving the critical crab ecosystem, small-scale aquaculture has been initiated in the concept of silvofisheries. Initial culture methods have targeted sub-adult crabs of 150–350 g for culture to market size (>0.5 kg) in drive-in cages and pens (mud crab fattening). These technology attained survival of between 50 and 70% and a market price of 5 dollars per kilogram. However, research is ongoing to assess viability of stocking juvenile seed crabs directly in ponds as practised in South East Asia (SEA) as opposed to stocking of sub-adults in drive-in cages. In comparison with other areas, crab capture fisheries in East Africa have limited management and enforcement frameworks/capabilities within the wider regional fisheries policies. Also there is limited understanding of wild mud crab resources and suitable management options to avoid over-exploitation as observed in SEA. The double-edged demand (wild market size capture and juvenile capture for aquaculture) for mud crabs in addition to mangrove degradation are likely to cause great challenges to stock exploitation and livelihoods of the coastal people dependent on the resource. This review paper provides an inside onto the tradition, trends and options for development of mud crab capture and culture in Kenya.  相似文献   

11.
The alien Asian date mussel Arcuatula senhousia inhabits several coastal environments worldwide. This species can form dense mats where individuals attach through byssus threads, thus altering the structure, functioning and biodiversity of the native communities. We investigated the feeding preference of different predators on this alien species in a Mediterranean coastal lagoon. To do this, a mesocosm experiment was conducted using two crab species (the Mediterranean green crab Carcinus aestuarii) and the Say mud crab Dyspanopeus sayi, and one gastropod, the banded dye-murex Hexaplex trunculus as predators of A. senhousia with or without byssus mats. Our data suggest that C. aestuarii is a more effective predator against A. senhousia than D. sayi, and that H. trunculus is almost ineffective. A possible implication of this result is the potential use of the native crab C. aestuarii for limit the formation of the byssus mats, thus mitigating their potential negative effects on the native communities.  相似文献   

12.
根据2013年11月、2014年2月、5月、9月在南麂列岛国家海洋自然保护区海域进行生物资源调查所获得的资料,分析了南麂列岛海域蟹类种类组成、优势种、生物多样性等群落结构特征,并定量分析了群落结构与水文环境因子之间的关系。结果表明,周年4个季度月调查共鉴定出蟹类21种,隶属7科、12属,其中优势种为三疣梭子蟹（Portunus trituberculatus）、日本蟳（Charybdis bimaculata）和双斑蟳（Charybdis bimaculata）3种。不同季节的蟹类种类组成差异较大,而优势种类组成变化较少,其中,以秋季的蟹类种类数最多,冬季最少。从不同水深区域的渔获种类分布趋势来看,蟹类种类以20~30 m水深带较多,30~40 m水深带较少。夏季多样性指数低于其他季节,以水深来看,多样性指数在10~20 m水深带较高,30~40 m水深带较低,蟹类多样性指数与水深呈反比。根据冗余分析认为,水深、水温和盐度是影响调查海域蟹类种类组成和群落结构特征的主要环境因子。  相似文献   

13.
There is little information on the movement and connectivity patterns for many species. The movement by shells occupied by the hermit crab Pagurus bernhardus and the organisms encrusting these shells was investigated on the south coast of Wales (UK). Hermit crabs shells moved considerable distances along the shore over 1 month periods, moving a minimum mean distance (±SE) of 148 (±8) and 174 (±9) m from release sites in the January and August respectively. Hermit crab-inhabited shells were also found to travel across habitats (sandy areas) that are unsuitable for both hermit crabs and epibionts. Through the examination of 150 of the most abundant shells used by P. bernhardus (Nucella lapillus), twelve epibiont species were found (10 animal and 2 algal species) and choice experiments demonstrated that hermit crabs preferred epibiont covered shells (84%), compared with bare shells (16%). The distance that shells were moved and the preference of hermit crabs for epibiont encrusted shells, coupled with the ability for epibionts to cross unsuitable habitats, may provide a dispersal advantage for epibiont species.  相似文献   

14.
The sea anemones Calliactis conchicola Parry, 1952 and Paracalliactis rosea n.sp. are described. This is the first report of the hormathiid genus Paracalliactis for New Zealand. Calliactis conchicola occurs with living gastropods, hermit crabs, and a true crab, and Paracalliactis rosea occurs with hermit crabs and a true crab. Certain characteristics of each of the two anemones suggest that the genera Calliactis and Paracalliactis may not be as discrete as was indicated by earlier reports.  相似文献   

15.
The burrowing behaviour of Ovalipes catharus (White, 1843) is described and compared with that of some other burrowing crabs. O. catharus is a fast, back burrowing crab which makes temporary burrows in soft sand. The average time from initiation of burrowing to complete submergence was 6.5 s, there was no difference between males and females but burrowing time increased significantly with crab size. Similar morphological adaptations are required for burrowing and swimming: streamlined body shape, smooth lightly constructed exoskeleton, and flattened legs. O. catharus has a reversed respiratory current like O. guadulpensis but it differs in its burrowing behaviour. Compared to some other crabs, burrowing in O. catharus is rapid.  相似文献   

16.
《Journal of Sea Research》2009,61(4):303-309
Collection of marine invertebrates for use as fishing bait is a substantial activity in many parts of the world, often with unknown ecological consequences. As new fisheries develop, it is critical for environmental managers to have high quality ecological information regarding the potential impacts, in order to develop sound management strategies. Crab-tiling is a largely unregulated and un-researched fishery, which operates commercially in the south-west UK. The target species is the green crab Carcinus maenas. Those crabs which are pre-ecdysis and have a carapace width greater than 40 mm are collected to be sold to recreational anglers as bait. Collection involves laying artificial structures on intertidal sandflats and mudflats in estuaries. Crabs use these structures as refugia and are collected during low tide. However, the effect that this fishery has on populations of C. maenas is not known. The impact of crab-tiling on C. maenas population structure was determined by sampling crabs from tiled estuaries and non-tiled estuaries using baited drop-nets. A spatially and temporarily replicated, balanced design was used to compare crab abundance, sizes and sex ratios between estuaries. Typically, fisheries are associated with a reduction in the abundance of the target species. Crab-tiling, however, significantly increased C. maenas abundance. This was thought to be a result of the extra habitat in tiled estuaries, which probably provides protection from natural predators, such as birds and fish. Although crabs were more abundant in tiled estuaries than non-tiled estuaries, the overall percentage of reproductively active crabs in non-tiled estuaries was greater than in tiled estuaries. As with most exploited fisheries stocks, crabs in exploited (tiled) estuaries tended to be smaller, with a modal carapace width of 20–29 mm rather than 30–39 mm in non-tiled estuaries. The sex ratio of crabs however; was not significantly different between tiled and non-tiled estuaries. These results illustrate the potential to manage fished populations using habitat provision to mitigate the effects of fishing pressure.  相似文献   

17.
The sea anemones Calliactis conchicola Parry, 1952 and Paracalliactis rosea Hand, 1975, which live associated with gastropods, hermit crabs, and true crabs, possess mounting responses similar to those known for several species of Calliactis. In some areas of New Zealand Calliactis conchicola occurs most abundantly on living gastropods and in others on gastropod shells occupied by hermit crabs. No behaviour by either the gastropod or the hermit crabs was observed which explains this differential distribution. One hermit crab stimulates Paracalliactis rosea to mount its shell by a regular tapping of the anemone with its chelae or dactyls, but ignores Calliactis conchicola. Several other hermit crabs, which may be found carrying these anemones, do not stimulate them to mount. The spider crab Leptomithrax longipes may be found in nature carrying specimens of four kinds of anemones: Calliactis conchicola, Paracalliactis rosea, Bunodactis chrysobathys, and Phellia aucklandica. This crab prises these anemones from most substrates with its chelae, cleans them with its mouth parts, and places them on its legs and carapace with its chelae. From observation, Calliactis conchicola apparently protects this crab from octopus predatiori, but not from other predators such as small sharks. Though associations of anemones with hermit crabs and other invertebrates are usually considered to be commensal, it seems likely that these associations may be mutualistic.  相似文献   

18.
The community structure of the decapod crustaceans inhabiting Le Danois Bank (Cantabrian Sea, NE Atlantic Ocean) was studied on two cruises performed in October 2003 and April 2004. Otter and beam-trawls were used to collect this fauna. At depths ranging between 455 and 1048 m, we found distinct decapod assemblages on the bank summit and deeper in the inner basin (between the bank and the continental shelf). The faunal discontinuity between these groups appeared at around 600 m (e.g. between 612 and 642 m in the basis of species replacement). The summit assemblage was characterized by low diversity (in terms of number and relative abundances of species) and by the dominance of hermit crabs (Pagurus alatus, Anapagurus laevis, Pagurus excavatus), the crangonid Pontophilus spinosus and the squat lobster Munida sarsi. Species characterizing the deeper assemblage, which was richer in terms of diversity, were Munida tenuimana, Parapagurus pilosimanus, Pontophilus norvegicus, the crab Geryon trispinosus and a number of bathypelagic shrimps (Sergia robusta, Acanthephyra pelagica and Pasiphaea tarda). Changes in decapod composition characterized by multidimensional scaling analyses were correlated with different variables, e.g. %mud and %organic matter (OM), temperature and salinity close to the bottom. Among those the %OM and %mud in sediments affected decapod distributions the most. The summit of the bank was covered by fine sediments with low proportion of mud (13.9–29.3%) and OM (2.55–3.50%). By contrast, sediment of the inner basin had a higher proportion of OM and mud (64.1–84.2%; 6.26–7.00%, respectively). The low proportion of mud at the summit of Le Danois Bank may explain the absence or scarcity of burrowing species (e.g. the lobster Nephrops norvegicus, the shrimps Calocaris macandreae and Alpheus glaber and the crab Goneplax rhomboides), that are dominant at similar depths (400–500 m) in the upper muddy assemblage on the mainland-continental slope in the Bay of Biscay (44–46°N). The dominance of certain species on the summit of submarine mounts can probably be related to their biology and feeding ecology. For example, pagurids are deposit feeders, even consuming marine snow (e.g. Chl-a identified in guts of Pagurus alatus), and they have low gut fullness (probably indicating a capacity to withstand long periods under starvation), that would favour their adaptability to a rather unpredictable habitat such as Le Danois Bank summit. Regarding prey availability, zooplankton/micronekton and infauna distributed around Le Danois Bank showed different depth-related patterns. Among zooplankton, mesopelagic decapods, mysids, and fishes were absent at the bank summit, while euphausiids exhibited high abundances over the summit. No significant trends with depth were found for infauna abundance, and for instance polychaete densities were similar both at the summit and the inner basin. Therefore, prey availability was lower for summit assemblages regarding zooplankton/micronekton. Patterns in mean size vs. depth were species specific for decapods, and the possible role of the bank summit as a recruitment area was not general for the whole decapod assemblage.  相似文献   

19.
Indirect interactions are among the many important factors that influence the community structure of the rocky intertidal zone. Trait‐mediated indirect interactions, in which the presence of a predator or competitor can influence the relationship between two other species, have emerged as vital for understanding community dynamics. This study examined the effect of different crab species on the feeding habits of an intertidal snail, Nucella lapillus. Crab species were defined as being sympatric predatory (Carcinus maenas and Cancer irroratus), sympatric non‐predatory (Uca pugnax and Pagurus longicarpus), or allopatric predatory (Mithrax sculptus and Percnon gibbesi). Nucella lapillus were potentially exposed to risk cues from each of the crab species. Crabs were kept in perforated boxes, which allowed any chemical cues to be emitted but prevented direct contact. Nucella lapillus had significantly lower feeding rates in the presence of sympatric predatory crab species than N. lapillus exposed to either sympatric non‐predatory crabs or allopatric predatory crabs. There was no difference in feeding rate between N. lapillus exposed to the sympatric non‐predatory crabs and to the allopatric predatory crabs. Nucella lapillus in the presence of sympatric predatory crabs had a feeding rate of only 0.07 barnacles per snail per day, whereas N. lapillus housed with non‐predatory crabs and allopatric predatory crabs had rates of 0.11 and 0.12, respectively, suggesting that N. lapillus alter their behavior in response to chemical risk cues from local predators. These results suggest that the ability to detect and respond to risk cues is a selectively evolved trait.  相似文献   

20.
Collection of marine invertebrates for use as fishing bait is a substantial activity in many parts of the world, often with unknown ecological consequences. As new fisheries develop, it is critical for environmental managers to have high quality ecological information regarding the potential impacts, in order to develop sound management strategies. Crab-tiling is a largely unregulated and un-researched fishery, which operates commercially in the south-west UK. The target species is the green crab Carcinus maenas. Those crabs which are pre-ecdysis and have a carapace width greater than 40 mm are collected to be sold to recreational anglers as bait. Collection involves laying artificial structures on intertidal sandflats and mudflats in estuaries. Crabs use these structures as refugia and are collected during low tide. However, the effect that this fishery has on populations of C. maenas is not known. The impact of crab-tiling on C. maenas population structure was determined by sampling crabs from tiled estuaries and non-tiled estuaries using baited drop-nets. A spatially and temporarily replicated, balanced design was used to compare crab abundance, sizes and sex ratios between estuaries. Typically, fisheries are associated with a reduction in the abundance of the target species. Crab-tiling, however, significantly increased C. maenas abundance. This was thought to be a result of the extra habitat in tiled estuaries, which probably provides protection from natural predators, such as birds and fish. Although crabs were more abundant in tiled estuaries than non-tiled estuaries, the overall percentage of reproductively active crabs in non-tiled estuaries was greater than in tiled estuaries. As with most exploited fisheries stocks, crabs in exploited (tiled) estuaries tended to be smaller, with a modal carapace width of 20–29 mm rather than 30–39 mm in non-tiled estuaries. The sex ratio of crabs however; was not significantly different between tiled and non-tiled estuaries. These results illustrate the potential to manage fished populations using habitat provision to mitigate the effects of fishing pressure.  相似文献   

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