Mark R. Young

Distribution and abundance of small insects and arachnids in relation to structural heterogeneity of grazed, indigenous grasslands

1. The species composition and spatial distribution of small insects (Hemiptera, Coleoptera, Lepidoptera) and arachnids (Araneae, Opiliones, and Pseudoscorpiones) were investigated in three indigenous, upland grasslands identified as the National Vegetation Classification Festuca–Agrostis–Galium typical subcommunity (code U4a), Festuca–Agrostis–Galium, Vaccinium–Deschampsia subcommunity (code U4e), and Nardus stricta species‐poor sub‐community (code U5a), on which grazing management was manipulated experimentally.

The effects of varied grazing management on epigeal spiders, harvestmen and pseudoscorpions of Nardus stricta grassland in upland Scotland

Dennis, P., Young, M. R., Bentley, C. (2001). The effects of varied grazing management on epigeal spiders, harvestmen and pseudoscorpions of Nardus stricta grassland in upland Scotland. Agriculture, Ecosystems and Environment, 86 (1), 39-57.

The effects of a major flood on an endangered freshwater mussel population

During February 1998, a 100-year return flood occurred in the River Kerry, north-western Scotland. A study was undertaken in order to assess the impact of this event on a large, internationally important freshwater pearl mussel (Margaritifera margaritifera L.) population. A conservative estimate of 50,000 mussels killed by the flood was made. This represents 4–8% of the total population. Significant channel reformation and large-scale movements of substrata occurred in some reaches, whereas others appeared to be unchanged. Some mussel beds disappeared or were largely depleted whereas others remained intact. Boulder-dominated substrata appear to have provided the most protection from scouring. The relatively high mussel densities and recruitment levels found in the middle reaches are probably due to the fact that this part of the river is hydrologically stable. It is likely that the intact mussel beds in the middle reaches will be the main source of regeneration in other parts of the river as the population recovers. As a result of recent changes in the hydrological behaviour of Scottish rivers, several M. margaritifera populations may now be more at risk from these catastrophic events. Therefore, it is important that conservation managers are aware of this potential threat.

Freshwater pearl mussel (Margaritifera margaritifera) glochidiosis in wild and farmed salmonid stocks in Scotland

Samples of salmonids were taken from six Scottish rivers and examined for freshwater mussel (Margaritifera margaritifera (L.)) glochidiosis. The prevalence and magnitude of natural infections observed were comparable to those reported elsewhere. In most rivers, older fish seem to be less susceptible than 0+ fish, possibly due to an acquired immunity resulting from previous exposures. Initial infection loads may be greater on older fish due to greater ventilation rates and/or gill surface areas. However, this host size effect appears to be transitory. In a stock of farmed 0+ salmon, an entire parasitic stage was monitored. This took up to 11 months and only 5–10% of the initially attached glochidia managed to metamorphose and excyst as juvenile mussels. There are apparent differences in host utilisation between salmon and trout in certain rivers. Some trout stocks appear to be under-utilised by M. margaritifera, possibly due to differences in behaviour and/or spawning site. 0+ salmon are the most important hosts in several rivers. However, there are a number of mussel populations located in small streams which have no salmon, and these are entirely trout-dependent. This may be important in terms of conservation, with regard to the recent collapse of migratory trout stocks in Scotland.

The status of the freshwater pearl mussel Margaritifera margaritifera Linn. in Scotland

1. One hundred and sixty rivers in Scotland with historical records of freshwater pearl mussel Margaritifera margaritifera were surveyed between 1996 and 1999 for the presence of the species. 2. M. margaritifera populations were classed as either ‘extinct’ (no mussels remaining), ‘not currently viable’ (ranging from only dead shells present to no juveniles present, regardless of the number of adults found), or ‘functional’ (at least one juvenile was found, regardless of the overall numbers of adults present). 3. M. margaritifera populations could be classed as ‘functional’ in only 52 rivers (34% of total surveyed) and in only 17 of these were juveniles below 20 mm (5 yrs old) present. Furthermore, in only 10 of these functional rivers were mussels also still considered either to be common or abundant and these included both large easterly-flowing rivers and small western rivers and streams. 4. In approximately two-thirds (101) of the 155 rivers occupied 100 years ago, M. margaritifera is now extinct or is about to become extinct. Furthermore, analysis indicates that the rate of mussel population extinction has accelerated since 1970, with a recent average of two mussel river extinctions per year. 5. The predominant threat to the mussel populations has undoubtedly been pearl fishing. This has been occurring at every river, even in the most remote northwest areas, where most of the ‘functional’ populations remain. Recent legislation has provided full protection to M. margaritifera, so that all pearl harvesting is now illegal. 6. Locally, river engineering and host salmonid stock decline poses a serious threat and eutrophication has already eliminated populations in southern and eastern Scotland. 7. In every part of its global range, M. margaritifera has declined substantially and is now either threatened with extinction or is highly vulnerable. Based on recent estimates from across the species range, it appears that Scotland now probably holds at least half of the worlds remaining functional M. margaritifera populations. Copyright

The status and conservation of the freshwater pearl mussel Margaritifera margaritifera Linn. in Great Britain

Abstract All available records of the occurrence of the freshwater pearl mussel Margaritifera margaritifera Linn. in Great Britain have been collected. Analysis of these records shows that there has been a recent decline in numbers of the species, which is especially marked in England and Wales. The causes of this decline are thought to be primarily pollution and overfishing in England and Wales, and overfishing in Scotland. Apparently even sparse populations remain fertile, but it is concluded that unless conservation measures can reduce overfishing, pearl mussels will become rare and endangered. It is suggested that the best conservation measures will be to restrict pearl fishing to licensed fishermen, perhaps using non-destructive fishing methods, and to prohibit the use of sub-aqua equipment.

Sizes, densities and age structures of ScottishMargaritifera margaritifera (L.) populations

1. Populations of freshwater pearl mussels (Margaritifera margaritifera (L.)) were surveyed in 12 Scottish rivers (selected from those known to contain viable populations). Overall mussel densities in different rivers ranged from 0.27 to 30.01 m−2. Median densities ranged from 2.5 to 14.5 m−2 and a maximum of 398 mussels m−2 was observed in one river. 2. Total population estimates in different rivers ranged from 2000 to 0.9–3.7 million. One population is particularly dense, with an estimated 0.6–1.2 million mussels in a 4-km stretch of river. 3. Samples from nine populations were taken in order to provide mussel size/age data. Marked differences between size profiles and their corresponding age profiles were observed. It is difficult to interpret the former in terms of recruitment. 4. There were signs of recent recruitment in all of the populations investigated. Large numbers of young mussels (aged ≤20 years) were found in four rivers. The largest proportions at any particular site were 67/219 (30.6%) aged ≤10 years and 191/219 (87.2%) aged ≤20 years, both values being recorded in the same river. 5. The expected predominance of young mussels was not achieved in any population. Presumably, there is considerable underestimation of the youngest age classes owing to biased sampling techniques. However, several populations are thought to be recruiting at levels that are high enough to maintain viability. 6. One population (River F) is the best example of a ‘healthy’, moderately fished, recruiting population and its age profile could be used as a benchmark for future comparisons. 7. The results of this study emphasize the international importance of Scotland in terms of M. margaritifera conservation. However, the small numbers of juveniles found in some Scottish rivers indicates that many populations are vulnerable to decline and, therefore, their conservation status may be threatened in the long term. Copyright

The microhabitat of Culicoides impunctatus (Diptera: Ceratopogonidae) larvae in Scotland

Soil samples were taken from two transects (total 63 sampling points; 25 cm quadrats) representing the Betula pubescens (Betulaceae) woodland, rush-pasture and peat-based mire vegetation of the west coast and Highlands of Scotland, in an attempt to relate soil and vegetation features to the occurrence of Culicoides impunctatus Goetghebuer larvae. The covers of vegetation groups were recorded at each sample site and soil wetness was assessed on an arbitrary scale. Culicoides spp. larvae were extracted from half of each sample and stored for subsequent identification of C. impunctatus larvae, while the remaining half was used for analysis of soil pH and organic content (loss on ignition, LOI). Correspondence analysis (using DECORANA) separated the sample sites and vegetation groups and the ordination axes were significantly correlated with the density of C. impunctatus larvae, soil organic content and soil wetness index. Simple regression analyses revealed that the density of Juncus acutiflorus/J. articulatus (Juncaceae) and soil wetness index were positively related to the overall variation in C. impunctatus larval density. The wetness index had the strongest relationship and this remained the case in step-wise multiple regression. There was no relationship between larval density and soil pH. This information on the specific microhabitat preferences of the larvae could aid colonization attempts of this dominantly important species of biting midge in the UK.

Saprolegnia strains isolated from river insects and amphipods are broad spectrum pathogens

Saprolegnia species are destructive pathogens to many aquatic organisms and are found in most parts of the world. Reports based on phylogenetic analysis suggest that Saprolegnia strains isolated from aquatic animals such as crustaceans and frogs are close to Saprolegnia strains isolated from infected fish or fish eggs and vice versa. However, it has often been assumed that host specificity occurs for each individual isolate or strain. Here we demonstrate that Saprolegnia spp. can have multiple hosts and are thus capable of infecting different aquatic organisms. Saprolegnia delica, Saprolegnia hypogyna, and 2 strains of Saprolegnia diclina were isolated from aquatic insects and amphipods while S. delica, Saprolegnia ferax, Pythium pachycaule, and a Pythium sp. were isolated from the water of a medium to fast flowing river. The ITS region of the rRNA gene was sequenced for all isolates. In challenge experiments, all four isolates from insects were found to be highly pathogenic to eggs of Atlantic salmon (Salmo salar) and embryos of the African clawed frog (Xenopus laevis). We found that Saprolegnia spp. isolated from salmon eggs were also able to successfully establish infection in nymphs of stonefly (Perla bipunctata) and embryos of X. laevis). These results suggest that Saprolegnia spp. are capable of infecting multiple hosts, which may give them an advantage during seasonal variation in their natural environments.

Bryophyte use by an insect herbivore: does the crane‐fly Tipula montana select food to maximise growth?

1. Growth rates of immature invertebrates can be of profound importance to subsequent reproductive success in the adult stage. If diet selection in herbivores is a principal means of maximising growth and rate of development, individuals should select food of the highest quality.