Impacts of Off-Road Vehicles (ORVs) on Burrow Architecture of Ghost Crabs (Genus Ocypode) on Sandy Beaches

Recreational beach use with off-road vehicles is popular, but potentially harmful from an environmental perspective. Beaches are important habitats to invertebrates such as ghost crabs of the genus Ocyopde, which excavate extensive and elaborate burrows. Ghost crabs are sensitive to human pressures and changes in burrow architecture may thus be a consequence of disturbance by vehicles—the predictive hypothesis of this article. This was tested during the austral spring and summer by comparing 305 burrow casts between beaches open and closed to vehicles in Eastern Australia. Traffic influenced burrow architecture: there were smaller crabs on vehicle-impacted beaches, and after the peak traffic period (Christmas and New Year holidays), these crabs had tunnelled deeper into the sediment on shores rutted by cars. Crabs constructed all types of previously described burrows, but, significantly, smaller crabs from vehicle-impacted beaches simplified their shapes following heavy traffic disturbance from four (I, J, Y, M) to only two types (I, Y). These data support a model of active behavioural responses to disturbance from vehicles, extending the known effects of beach traffic to impacts on behavioural traits of the beach fauna.     

Soil heavy metal contamination in an industrial area: analysis of the data collected during a decade

Soil contamination by heavy metals has become a serious problem mainly because, above certain concentrations, all metals have adverse effects on human health. In particular, the accumulation of heavy metals in agricultural soils leads to elevated uptake by crops and affects food quality and safety. In this paper, we present the results of a study carried out over a decade for evaluating the impact of a new industrial settlement in an area geared to agriculture and livestock and far from urban sites. We focus our study on the bioavailable fraction of Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn in soil samples. Heavy metal concentrations in soil are analysed with both univariate and multivariate statistical procedures. The main goal of this paper is the development of a statistical procedure, based on a mix of multivariate analysis, able to compare field surveys carried out during different years and to characterize spatial and temporal changes in soil heavy metals concentrations.     

Shell acquisition by hermit crabs: which tactic is more efficient?

Gastropod shells are limited resources for most hermit crab species, acting as primary factors in various aspects of their biology. To investigate the efficacy of different behavioral tactics adopted for their acquisition (locomotion, attendance at shell-supplying sites, interactions with conspecifics in aggregation) we conducted observations and experiments at a salt marsh in New England (USA). Locomotion, fast and meandering, significantly increased the chances of encountering empty shells and conspecifics. However, shell exchanges were rare. Simulated gastropod predation sites quickly attracted a larger number of hermit crabs than the other shell-supplying sites tested (live and dead conspecifics, live snails) and induced the rapid occupancy of all the empty shells offered, usually by the first crabs arriving at the site. Aggregations seemed not to function as shell exchange markets, as previously suggested for several other species. In the short run, exploitation seems to be more efficient for the acquisition of new shells by Pagurus longicarpus. In the long run, it is the density of nondestructive gastropod predators that regulates the availability of new shells of good quality in the pool available to this hermit crab species.     

Health and environmental impacts of a fertilizer plant--Part I: assessment of radioactive pollution

The aim of the first part of this investigation is to assess the radioactive pollution caused by a production plant of complex fertilizers (that is to say containing nitrogen, phosphorus and, in some cases, potassium). Firstly, the authors determine the concentrations of natural radioactivity present in raw materials, end products and wastes of the industrial plant. Then, they carry out an assessment of radioactive releases into the atmosphere, hydrosphere and lithosphere as well as of their significance from the environmental point of view. The second part of the investigation will be aimed at assessing the annual effective doses to plant workers and to members of the population surrounding the industrial site.     

Fighting behavior in hermit crabs: the combined effect of resource-holding potential and resource value in Pagurus longicarpus

A study was conducted to determine whether asymmetries in both resource-holding potential (RHP) and resource value (RV) influence dominance and fighting behavior in the hermit crab Pagurus longicarpus. A total of 120 groups of three crabs were observed for 10 min in four experiments that tested all diverse combinations of equal/different RHP (i.e. ‘body size’) and equal/different RV (i.e. ‘shell size’ and ‘shell quality’). In a fifth experiment, dominant and subordinate individuals of the same size category (26 groups) were forced to enter shells of opposite quality than those previously occupied, and then the behavior of the reconstituted original groups was observed for additional 10 min. As expected, crabs in lower quality shells were more willing to initiate and to escalate fights. However, their attacks were directed to any crab of the group, independently of the defender's shell quality, and the fight duration did not vary with the different value of the resources at stake. This may indicate that P. longicarpus is unable to assess the quality of the shells available in its social environment but bases its tactical decisions during fights solely on its own resource. This suggestion was confirmed by the change in the fighting behavior of crabs whose shell quality was experimentally altered. This manipulation induced an overall increase in the intensity of aggression, drastic modification of crab behavior, and inversion of the hierarchy even though these crabs have had previous experiences of wins/losses and were familiar to the other members of the group. In this species, large crab size and/or the occupancy of adequate (and oversized) shells appeared to be the most likely determinant of contest resolution. Individuals seemed to retain a memory of the previously held resource and behaved accordingly.     

Hermit crabsin a mangrove swamp: the structure of Clibanarius laevimanus clusters

To address the question of hermit crab clustering, 11 clumps composed of Clibanarius laevimanus were studied in the mangal of Mida Creek, Kenya in 1988. Hermit size and sex were analyzed, as well as the type, dimensions, and status of their shells. Empty gastropod shells constituted a limiting factor on the population studied; the architectural traits which seemed to be favored by the hermits were those associated with a defence against crab predators (high weight and narrow apertures). Differences in either the availability of adequate shells or in the services provided by the housing in question explained the observed diversity in both the type and the mass of shells occupied among the examined population categories. Furthermore, each clump showed homogeneity with respect to the dimensions of the hermits participating in it, and immature and adult specimens were partitioned among three cluster types. It is suggested that clustering might be classified as a social phenomenon, becaus hermits are attracted by similarly sized conspecifics, interact through an elaborate communication system, and because most benefit from a chain process in shell exchange.     

Conceptual Frameworks and Methods for Advancing Invasion Ecology

Invasion ecology has much advanced since its early beginnings. Nevertheless, explanation, prediction, and management of biological invasions remain difficult. We argue that progress in invasion research can be accelerated by, first, pointing out difficulties this field is currently facing and, second, looking for measures to overcome them. We see basic and applied research in invasion ecology confronted with difficulties arising from (A) societal issues, e.g., disparate perceptions of invasive species; (B) the peculiarity of the invasion process, e.g., its complexity and context dependency; and (C) the scientific methodology, e.g., imprecise hypotheses. To overcome these difficulties, we propose three key measures: (1) a checklist for definitions to encourage explicit definitions; (2) implementation of a hierarchy of hypotheses (HoH), where general hypotheses branch into specific and precisely testable hypotheses; and (3) platforms for improved communication. These measures may significantly increase conceptual clarity and enhance communication, thus advancing invasion ecology.     

Past ownership makes crayfish more aggressive

There is plenty of evidence that resource value is one of the most important non-strategic variables in animal fighting behavior. Here, we tested whether the past ownership of a shelter might modify the agonistic behavior of the crayfish Austropotamobius pallipes, eventually increasing its probability to win when it reencounters a previously met conspecific away from that resource. The agonistic behavior of familiar pairs composed of size-matched males was observed for an hour; after that, the two contestants had been kept in isolation for 2 days, either in the presence or in the absence of a shelter. Specifically, in the isolation phase, a shelter was offered to (1) both crayfish, (2) no crayfish, (3) the dominant crayfish only, and (4) the subordinate crayfish only. The following combat was conducted in the absence of any refuge. The crayfish that previously owned a shelter showed a higher aggressive motivation to fight than the individuals kept without a shelter. Particularly, in the pairs (4), subordinate crayfish were even more aggressive than dominants but were never able to invert hierarchies. Taken together, our results confirm the role played by shelters as determinants of agonism and also show, for the first time, how the behavior of crayfish and their internal state may be affected by their past ownership of a resource.