Diel variation in egg-laying by the freshwater fish louse Argulus foliaceus (Crustacea : Branchiura)

Removal of deposited eggs could be a useful control strategy for the damaging fish ectoparasite Argulus foliaceus, but focused control requires knowledge of egg-laying patterns. Here, we investigated diel changes in the egg-laying behaviour of a natural population of A. foliaceus. Data were collected from 17-28 May 2004. Days were divided into 3 time periods: 06:00-14:00, 14:00-22:00 and 22:00-06:00 h. Significantly more egg clutches were laid from 06:00-14:00 h than during the other 2 time periods, which were not significantly different from each other. Significantly more egg clutches per hour were laid during hours of daylight as compared to hours of darkness. Significantly more egg clutches were laid in the top 1 m of the water column than at the bottom, and this was consistent throughout all 3 time periods. It is suggested that the increase in egg-laying activity during daylight hours may be due to a higher motivation to search for hosts during the night and an increased ability to locate silhouetted egg-laying sites during the day. These data can provide information useful for egg removal and control strategies.

Invasion by the amphipod Gammarus pulex alters community composition of native freshwater macroinvertebrates

Assessing the effects of invading species on native community structure is often confounded by environmental factors and weakened by lack of replicated, long-term pre- and post-invasion monitoring. Here, we uncouple the community effects of a freshwater amphipod invader from environmental differences. In Irish rivers, the introduced Gammarus pulex replaces the native Gammarus duebeni celticus. However, the River Lissan in Northern Ireland is dissected by a weir that has slowed the upstream invasion by G. pulex. This allowed us in 2000 to sample three contiguous 150-m reaches that were (1) G. pulex dominated; (2) mixed Gammarus spp.; and (3) G. duebeni celticus only. In 2003, we resampled these reaches and one additional of mixed Gammarus species and one with only G. duebeni celticus further upstream. In temperature, conductivity, and pH, there were statistically significant but no biologically relevant differences among the five reaches of 2003, and between the three reaches surveyed in both years. Although there was evidence of recovery in macroinvertebrate diversity and richness in invaded reaches between years, continued upstream invasion was associated with sustained reductions in these community metrics as compared to un-invaded sites. Community ordination indicated (1) different associations of community composition attributed to the distribution, abundance, and biomass of the invader; and (2) increasing similarity of invaded communities over time. The impact mechanisms of G. pulex on macroinvertebrate community composition may include predation and competition. The consequences of the observed community changes for ecosystem functioning require further investigation.

Suitability of Crangonyx pseudogracilis (Crustacea : Amphipoda) as an early warning indicator in the multispecies freshwater biomonitor

Background. Biological monitors are increasingly important in 'Biological Early Warning Systems' (BEWS) for monitoring water quality. This study examines the freshwater amphipod Crangonyx pseudogracilis as a potential new indicator species when used in the Multispecies Freshwater Biomonitor (MFB). The MFB is an online continuous biomonitor which uses impedance conversion to record behavioural responses of vertebrates and invertebrates.

Use of the multispecies freshwater biomonitor to assess behavioral changes of Corophium volutator (Pallas, 1766) (Crustacea, Amphipoda) in response to toxicant exposure in sediment

Automated sediment toxicity testing and biomonitoring has grown rapidly. This study tested the suitability of the marine amphipod Corophium volutator (Pallas, 1766) for sediment biomonitoring using the Multispecies Freshwater Biomonitor (MFB). Two experiments were undertaken to (1) characterize individual behaviors of C. volutator using the MFB and (2) examine behavioral changes in response to sediment spiked with the pesticide Bioban. Four behaviors were visually identified (walking, swimming, grooming and falling) and characterized in the MFB as different patterns of locomotor activity (0-2 Hz range). Ventilation was not visually observed but was detected by the MFB (2-8 Hz). No clear diel activity patterns were detected. The MFB detected an overall increase in C. volutator locomotor activity after Bioban addition to the sediments (56, 100, 121 mg kg(-1)). C. volutator was more active (both locomotion and ventilation) in the water column than the spiked sediment. C. volutator appears a sensitive and appropriate species for behavioral sediment toxicity assessment and biomonitoring. (c) 2005 Elsevier Inc. All rights reserved.

Seasonal and vertical patterns of egg-laying by the freshwater fish louse Argulus foliaceus (Crustacea : Branchiura)

Argulus foliaceus is a damaging fish ectoparasite for which new control measures are being developed based on egg-removal, In an attempt to develop further understanding of seasonal and vertical egg-laying patterns in this parasite, egg-laying activity was monitored over the period 14 April to 17 November 2003 in 2 rainbow trout Oncorhynchus mykiss fisheries in Northern Ireland, UK. At Site 1, egg-laying was continuous from 21 April to 17 November, when water temperature was above 8 to 10 degrees C. At Site 2, egg-laying was continuous from 4 June to 29 October. In the early months of the season, egg-laying was recorded mainly within the top 1 m of the water column; however, a significant shift to deep water egg-laying was recorded between 7 July and 17 November at Site 1 and between 20 August and 29 October at Site 2. Egg clutches were preferentially laid at depths of up to 8.5 m during this time (Site 2), a feature of egg-laying hitherto unappreciated. Temperature and dissolved oxygen did not differ significantly among depths, but there was an increase in water clarity over time. However, the precise environmental triggers for deep water egg-laying are still unclear. These new insights into the reproductive behaviour of this species will be useful in developing control methods based on egg-removal.

A freshwater-feeding Lampetra fluviatilis L. Population in Lough Neagh, Northern Ireland

Pollan Coregonus autumnalis, caught in the fresh waters of Lough Neagh, Northern Ireland, were scarred by river lamprey Lampetra fluviatilis and adult river lamprey were found for much of the year with full guts, indicating a freshwater-feeding population.

Ecological impacts of the microsporidian parasite Pleistophora mulleri on its freshwater amphipod host Gammarus duebeni celticus

The microsporidian parasite, Pleistophora mulleri, infects the abdominal muscle of the freshwater amphipod Gammarus duebeni celticus. We recently showed that P. mulleri infection was associated with G. d. celticus hosts being more vulnerable to predation by the invasive amphipod Gammarus pulex. Parasitized G. d. celticus also had a reduced ability to prey upon other co-occurring amphipods. We suggested the parasite may have pervasive influences on host ecology and behaviour. Here, we examine the association between P. mulleri parasitism and parameters influencing individual host fitness, behaviour and interspecific interactions. We also investigate the relationship between parasite prevalence and host population structure in the field. In our G. d. celticus study population, P. mulleri prevalence was strongly seasonal, ranging from 8.5% in summer to 44.9% in winter. The relative abundance of hosts with the heaviest parasite burden increased during summer, which coincided with high host mortality, suggesting that parasitism may regulate host abundance to some degree. Females were more likely to be parasitized than males and parasitized males were paired with smaller females than unparasitized males. Parasitism was associated with reduction in the host's activity level and reduced both its predation on the isopod Asellus aquaticus and aggression towards precopula pairs of the invasive G. pulex. We discuss the pervasive influence of this parasite on the ecology of its host.

Coexistence among native and introduced freshwater amphipods (Crustacea); habitat utilization patterns in littoral habitats

Studies of biological invasions predominantly stress threats to biodiversity through the elimination and replacement of native species. However, we must realise that resident communities may often be capable of integrating invaders, leading to patterns of coexistence. Within the past ninety years, three freshwater amphipod species have invaded Northern Ireland the North American Gammarus tigrinus and Crangonyx pseudogracilis, plus the European G. pulex. These species have come into contact with the ubiquitous native species, G. duebeni celticus. This study examined spatiotemporal patterns of stability of single and mixed species assemblages in an invaded lake. Lough Beg and its associated rivers were surveyed in summer 1994 and winter 1995, and a selection of stations re-sampled in summer one and five years later. All possible combinations of the four amphipod species were found. Although species presence/absence was stable between seasons at the scale of the whole lough, it was extremely fluid at the scale of individual sites, 82% of which changed in species composition between seasons. Overall mean amphipod abundance was similar across 5 distinguishable habitat types, but there were differences in species compositions among these habitats. In addition, although co-occurrences of Gammarus species did not differ from random, there was a strong negative association between Gammarus spp. and C. pseudogracilis. This latter pattern was at least in part generated by the better tolerance of C. pseudogracilis to lower water quality. A review of previous studies indicates that the exclusion of C. pseudogracilis by Gammarus species from high water quality areas is likely to involve biotic interaction. Thus, overall, co-existence of the four species, which is clearly dynamic and scale-dependent, appears promoted by spatial and temporal habitat heterogeneity. However, biotic interactions may also play a role in local exclusions. Since the three introduced species have not eliminated the native species, and each successive invasion has not replaced the previous invader, this study demonstrates that freshwater invaders may integrate with native communities leading to coexistence and increased species diversity.

‘Doing it with men’: feminist research practice and patriarchal inheritance practices in Welsh family farming

Internationally, the gender relations of the family farming ‘way of life’ have beenshown to be stubbornly persistent in their adherence to patriarchal inheritancepractices. This article demonstrates how such ‘agri-cultural’ practices are situated bothwithin the subjective sphere of farming individuals’ and within global agri-economics,bringing new challenges to patrilineal farm survival. It is suggested here that the recenttendency for post-structuralist theorisation in rural studies has underestimated theexistence and impact of patrilineal patterns in family farming. Such patterns mean thatwomen are shown to largely occupy relational gender identities as the ‘helper’, whilstmen are strongly identified as the ‘farmer’. Drawing on repeated life-history interviewsconducted with farming men and women from Powys, Mid Wales, the aim of thisarticle is to generate debate as to the extent to which men can be brought into feministresearch practice in order to reveal patriarchy to a greater degree. The article begins bysituating the near-exclusion of men from feminist research practice within theoreticaldevelopments in feminist geography. This discussion also assists in deriving issues ofresearch methods, positionality and interpretive power which focus the integration ofempirical material in the methodological reflections provided in section three. In sectiontwo, the rationale for the epistemological stance taken in the research is provided. Thearticle provides an example of the successful integration of men into a feminist researchframe, suggests avenues for theoretical development and identifies future researchdirections which can be informed by ‘doing it with men’.

Keywords: epistemology; family farming; feminist res

From stress to distress: Conceptualizing the British family farming patriarchal way of life

‘Rural stress’ and ‘farming stress’ are terms that have become commonly appropriated by British health-based academic disciplines, the medical profession and social support networks, especially since the agricultural ‘crises’ of B.S.E. and Foot and Mouth Disease. Looking beyond the media headlines, it is apparent that the terms in fact are colloquial catch-alls for visible psychological and physiological outcomes shown by individuals. Seldom have the underlying causes and origins of presentable medical outcomes been probed, particularly within the context of the patriarchal and traditionally patrilineal way of life which family forms of farming business activity in Britain encapsulate. Thus, this paper argues that insufficient attention has been paid to the conceptualization of the terms. They have become both over-used and ill-defined in their application to British family farm individuals and their life situations. A conceptual framework is outlined that attempts to shift the stress research agenda into the unilluminated spaces of the family farming ‘way of life’ and focus instead on ‘distress’. Drawing upon theorization from agricultural and feminist geography together with cultural approaches from rural geography, four distinct clusters of distress originate from the thoughts of individuals and the social practices now required to enact patriarchal family farming gender identities. These are explored using case study evidence from ethnographic repeated life history interviews with members of seven farming families in Powys, Mid Wales, an area dominated by family forms of farming business. Future research agendas need to be based firmly on the distressing reality of patriarchal family farming and also be inclusive of those who, having rejected the associated way of life, now lie beyond the farm gate.