Assessment of space utilisation in a subtidal temperate bryozoan community

On subtidal hard substrata, Bryozoa are often very abundant, both in terms of numbers of colonies and numbers of species. To investigate how so many species are able to co-exist, often in close proximity to each other, subtidal material was dredged from an area of bryozoan-rich coarse shelly sea-bed off the south-west of the Isle of Man (British Isles) in autumn 1984 and 1985. A survey was performed on the distribution of colonies of eight common, encrusting cheilostome bryozoan species across the surfaces of four types of empty, disarticulated bivalve shells. Each species was found to be significantly commoner on certain substratum types such as rough surfaces or inner concave surfaces. Fenestrulina malusii (Audouin) showed a further, more specific, tendency to be signficantly more abundant on the grooves of the corrugated inner surfaces of left valves of Pecten maximus (L.). In general however there was much overlap in distribution and it is proposed that such large numbers of species are able to co-exist because of the evolution of different life-history strategies ensuring that each species uses the available temporally and spatially heterogenous substrata in subtly different ways; some species, for example, occupying substrata that are optimal to bryozoan growth and other species, by reaching maturity earlier, being able to inhabit more ephemeral suboptimal substrata.     

A biochemical genetic study of population structure in queen scallop (Chlamys opercularis) stocks in the Northern Irish Sea

Electrophoresis was used to survey a number of enzymes for loci of potential value as stock markers in Chlamys opercularis (L.). Two loci, Pgi and Pgd, were then studied in larger samples from each of two localities around the Isle of Man. One Pgi allele was found to be restricted to a particular year-class in both populations. This was confirmed by subsequent studies of three further populations, in each of which the same allele occurred only in the one year-class. Otherwise, no significant differences in allele frequencies were found between year-classes or between populations in any of the samples used. From the results it is concluded that there is temporal variation in the sources of recruitment of C. opercularis stocks around the Isle of Man. Possible origins of larvae contributing to these stocks are discussed in the light of what is known of current circulation patterns in the northern Irish Sea.     

Genetic evidence of population heterogeneity and cryptic speciation in the ommastrephid squid Martialia hyadesi from the Patagonian Shelf and Antarctic Polar Frontal Zone

Horizontal starch gel electrophoresis was used to investigate levels of genetic differentiation between four samples of the nominate squid species Martialia hyadesi Rochbrune and Mabille, 1889, obtained from regions of the Patagonian Shelf and Antarctic Polar Fron-tal Zone over 1000 km apart. M. hyadesi is an ecologically important South Atlantic ommastrephid squid and it is probable that, in the future, fishing effort will be increasingly directed towards this species. Details regarding the population structure of the species are therefore required. In comparison with the other three samples of M. hyadesi, one of the samples from the Patagonian Shelf (PAT 89II) exhibited fixed allelic differences at 16 of the 39 enzyme loci which were resolved (genetic identity, I=0.51). This high level of genetic differentiation contradicts the apparent morphological similarity between samples, indicating the presence of a cryptic or sibling congeneric species. Deviations from Hardy-Weinberg equilibrium and significant differences in allele distribution were also detected within and between the other three putative M. hyadesi samples, suggesting that the species fails to maintain effective panmixia across its geographical range. The occurrence of both temporal (1986 cf. 1989) and geographic structuring within the species complex is consequently indicated, caused possibly by an overlap of reproductively isolated stocks (stock mixing) outside their respective breeding areas. Low levels of genetic variability were detected throughout the samples examined, estimates of average heterozygosity per locus within the two species detected being in the order of 0.01 and 0.002. These values are discussed in relation to levels of genetic variability reported for other squid species, and in comparison with values typically expected for marine invertebrates.     

Population structure and genetic variation in two tropical sea anemones (Cnidaria,Actinidae) with different reproductive strategies

Genetic variation and population structure of two tropical sea anemones, Bunodosoma caissarum Correa and Actinia bermudensis McMurrich were related to their different dispersal capabilities and reproductive modes. B. caissarum reproduces sexually and has a long-lived planktotrophic larva; A. bermudensis can reproduce both sexually and asexually, supposedly with short-range dispersal. Both species were sampled along 1150 km of Brazilian coastline between 1990 and 1991 and analyzed by horizontal starch gel electrophoresis for 16 enzyme loci in B. caissarum and 19 in A. bermudensis. B. caissarum had higher levels of heterozygosity (H=0.35) and lower levels of population structuring (F _ST=0.042) than A. bermudensis (H=0.17; F _ST=0.262). At one locality large genetic differences between two sympatric colour morphs of A. bermudensis provide evidence of possible cryptic speciation. Overall levels of genetic variation and heterozygosity in the two species are compatible with their known modes of reproduction.     

Geographic variation in Loligo forbesi in the Northeast Atlantic Ocean: analysis of morphometric data and tests of causal hypotheses

Geographic variation in the squid Loligo forbesi was investigated using multivariate analysis of morphometric and meristic characters in samples of squid taken from 13 localities in the Northeast Atlantic Ocean. Two character sets, body morphometrics and beak morphometrics, indicated similar patterns of variation, with squid from the Azores differing markedly from those on the continental shelf. No consistent pattern was apparent in meristic data. Partial Mantel tests indicated that similarity matrices for morphological data were significantly correlated with distance matrices for (a) geographic proximity, (b) whether the capture site was on the continental shelf or the Azorean bank, and (c) (beak data only) average seasurface temperature at site of capture. Partial Mantel tests on allozyme data for the same individuals support hypothesis (b). The results suggest that L. forbesi in the Azores may reasonably be regarded as a distinct stock, differing significantly from L. forbesi on the continental shelf.     

Identification of brake wear particles and derivation of a quantitative tracer for brake dust at a major road

Traffic-generated air pollutant emissions can be classified into exhaust and non-exhaust emissions. Increased attention is focussing on non-exhaust emissions as exhaust emissions are progressively limited by regulations. To characterise metal-rich emission from abrasion processes, size-segregated analysis of atmospheric aerosol particles sampled with micro-orifice uniform deposit impactors (MOUDI) in March 2007 in London was performed. The samples were collected at a roadside and a background site and were analysed for Al, Ba, Cu, Fe, Sb, Ti, V, Zn, Ca²⁺, K⁺, Mg²⁺, Na⁺, and NH₄⁺. Most components showed a clear roadside increment, which was evident as a higher mass concentration and a change in the size distribution. In particular, Fe, Cu, Ba, and Sb correlated highly, indicative of a common traffic-related source. Using complementary information on the fleet composition, vehicle number and average speed, the brake wear emission was calculated using the EMEP/CORINAIR emission database. The total PM₁₀ and barium emission of the traffic was determined by ratio to NO_x whose source strength was estimated from published emission factors. Barium was found to comprise 1.1% of brake wear (PM₁₀) particles from the traffic fleet as a whole, allowing its use as a quantitative tracer of brake wear emissions at other traffic-influenced sites.     

Crop–livestock interactions along agro-ecological gradients: a meso-level analysis in the Indo-Gangetic Plains, India

Although conceptually simple and often idealized, disentangling crop–livestock interactions typically proves more complex in practice. Part of the complexity arises from their changing nature along agricultural intensification gradients. Such interactions increase in scope when extensive systems intensify, but decline in importance as already intermediate systems intensify further. This changing nature of crop–livestock interactions in relation to the system’s developmental stage implies that these exchanges can both contribute but also undermine system sustainability. We examine crop–livestock interactions in the Indo-Gangetic Plains as an empirical case, drawing from village surveys to explore and illustrate these relations and implications along the agro-ecological gradient of this vast and important eco-region. Such an understanding is increasingly needed as adapting crop residue management practices is recognized as the key to address sustainability concerns in the prevailing rice–wheat systems and as a stepping stone towards conservation agriculture. The agricultural R&D community needs to incorporate this understanding more proactively into its R&D agenda if it is to succeed in sustaining productivity gains, improving rural livelihoods equitably, and securing environmental sustainability.     

Distribution of encrusting bryozoans and other epifauna on the subtidal bivalveChlamys opercularis

The shells of living queen scallops,Chlamys opercularis (L.), are often completely colonised with epifauna. In this study, the distribution of the major epifaunal groups across the surfaces of left (upper) and right (lower) valves is examined using samples from two commercial queen scallop beds off the Isle of Man. The composition of the epifauna differs across and between the valves and also varies with the age of the scallop. YoungerC. opercularis are commonly encrusted by sponges, but on older shells other epifauna colonise the surfaces. The encrusting bryozoan assemblage found on livingC. opercularis is not as abundant or speciose as on some other substrata such as stones and dead shell. This may be a result of intense competition from other phyla. The distribution of different bryozoan species between the surfaces is examined. Most species are more abundant on the lower valves.     

Restricted gene flow and evolutionary divergence between geographically separated populations of the Antarctic octopus Pareledone turqueti

Samples of the Antarctic octopus Pareledone turqueti were taken from three locations on the Scotia Ridge in the Southern Ocean. The genetic homogeneity of these populations was investigated using isozyme electrophoresis. Whilst panmixia appeared to be maintained around South Georgia (F _ST = 0) gene flow between this island and Shag Rocks, an island only 150 km away but separated by great depths, was extremely limited (F _ST = 0.74). These results are examined with respect to the discontinuous distribution of P. turqueti throughout Antarctica. An estimate of effective population size was also calculated (N _e = 3600). Received: 7 March 1997 / Accepted: 27 March 1997