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John S Gray

Publications and source records attributed to John S Gray.

9 recordsLinked to original sources
PubMed2006

On effects of trawling, benthos and sampling design.

The evidence for the wider effects of fishing on the marine ecosystem demands that we incorporate these considerations into our management of human activities. The consequences of the direct physical disturbance of the seabed caused by towed bottom-fishing gear have been studied extensively with over 100 manipulations reported in the peer-reviewed literature. The outcome of these studies varies according to the gear used and the habitat in which it was deployed. This variability in the response of different benthic systems concurs with established theoretical models of the response of community metrics to disturbance. Despite this powerful evidence, a recent FAO report wrongly concludes that the variability in the reported responses to fishing disturbance mean that no firm conclusion as to the effects of fishing disturbance can be made. This thesis is further supported (incorrectly) by the supposition that current benthic sampling methodologies are inadequate to demonstrate the effects of fishing disturbance on benthic systems. The present article addresses these two erroneous conclusions which may confuse non-experts and in particular policy-makers.

Animals↗
PubMed2006

On plotting species abundance distributions.

1. There has been a revival of interest in species abundance distribution (SAD) models, stimulated by the claim that the log-normal distribution gave an underestimate of the observed numbers of rare species in species-rich assemblages. This led to the development of the neutral Zero Sum Multinomial distribution (ZSM) to better fit the observed data. 2. Yet plots of SADs, purportedly of the same data, showed differences in frequencies of species and of statistical fits to the ZSM and log-normal models due to the use of different binning methods. 3. We plot six different binning methods for the Barro Colorado Island (BCI) tropical tree data. The appearances of the curves are very different for the different binning methods. Consequently, the fits to different models may vary depending on the binning system used. 4. There is no agreed binning method for SAD plots. Our analysis suggests that a simple doubling of the number of individuals per species in each bin is perhaps the most practical one for illustrative purposes. Alternatively rank-abundance plots should be used. 5. For fitting and testing models exact methods have been developed and application of these does not require binning of data. Errors are introduced unnecessarily if data are binned before testing goodness-of-fit to models.

Animals↗
PubMed2006

Predicting the effects of habitat homogenization on marine biodiversity.

Seafloor habitats throughout the world's oceans are being homogenized by physical disturbance. Even though seafloor sediments are commonly considered to be simple and unstructured ecosystems, the negative impacts of habitat homogenization are widespread because resident organisms create much of their habitat's structure. We combine the insight gained from remote sensing of seafloor habitats with recently developed analytical techniques to estimate species richness and assess the potential for change with habitat homogenization. Using habitat-dependent species-area relationships we show that realistic scenarios of habitat homogenization predict biodiversity losses when biogenic habitats in soft sediments are homogenized. We develop a simple model that highlights the degree to which the reductions in the number of species and functional diversity are related to the distribution across habitats of habitat-specific and generalist species. Our results suggest that, by using habitat-dependent species-area relationships, we can better predict variation in biodiversity across seafloor landscapes and contribute to improved management and conservation.

Biodiversity↗
PubMed2006

Minimizing environmental impacts of a major construction: the Øresund link.

The Øresund Link is a 4-lane motorway with a 2-line rail link between Copenhagen, Denmark, and Malmö, Sweden, built across the Øresund Sound between the 2 countries. The environmental concerns associated with construction of the Link were that that it might affect the water and salt flow through the Sound and into and out of the Baltic Sea, lead to destruction of the cod fishery, and affect other biological systems. An International Expert Panel was formed to design mitigation strategies to avoid negative environmental impacts. The Panel designed stringent environmental controls for the construction, of which the most significant was to limit sediment discharges to 5% of the dredged material. This was one-fifth of the discharge limit construction companies usually accept as normal for such a large-scale project. An environmental monitoring program was instituted to monitor compliance with the environmental control measures. As a result of the imposition of tough environmental requirements, the Link was built with little environmental impact and 3 y after it was completed, environmental conditions have returned to normal.

Conservation of Natural Resources↗
PubMed2005

Deriving sediment quality guidelines from field-based species sensitivity distributions.

The determination of predicted no-effect concentrations (PNECs) and sediment quality guidelines (SQGs) of toxic chemicals in marine sediment is extremely important in ecological risk assessment. However, current methods of deriving sediment PNECs or threshold effect levels (TELs) are primarily based on laboratory ecotoxicity bioassays that may not be ecologically and environmentally relevant. This study explores the possibility of utilizing field data of benthic communities and contaminant loadings concurrently measured in sediment samples collected from the Norwegian continental shelf to derive SQGs. This unique dataset contains abundance data for ca. 2200 benthic species measured at over 4200 sampling stations, along with co-occurring concentration data for >25 chemical species. Using barium, cadmium, and total polycyclic aromatic hydrocarbons (PAHs) as examples, this paper describes a novel approach that makes use of the above data set for constructing field-based species sensitivity distributions (f-SSDs). Field-based SQGs are then derived based on the f-SSDs and HCx values [hazardous concentration for x% of species or the (100-x)% protection level] by the nonparametric bootstrap method. Our results for Cd and total PAHs indicate that there are some discrepancies between the SQGs currently in use in various countries and our field-data-derived SQGs. The field-data-derived criteria appear to be more environmentally relevant and realistic. Here, we suggest that the f-SSDs can be directly used as benchmarks for probabilistic risk assessment, while the field-data-derived SQGs can be used as site-specific guidelines or integrated into current SQGs.

Animals↗
PubMed2003

The use of biomarkers in environmental monitoring programmes.

The monitoring of biological effects has recently become an integral component of environmental monitoring programmes as a supplement to the commonly used contaminant monitoring. Over the years, many biomarkers have been developed that are claimed to be efficient at providing an early warning of deleterious effects on biological systems and for estimating biological effects due to contaminants. Although biomarkers are potentially useful, they have a number of important limitations. In this paper, we examine some of the key assumptions behind the theory and practice of use of biomarkers, and propose a scheme, which may facilitate decisions by environmental managers as to how and when to use biomarkers in their monitoring programmes.

Animals↗
PubMed2002

Biomagnification in marine systems: the perspective of an ecologist.

Biomagnification is the process where xenobiotic substances are transferred from food to an organism resulting in higher concentrations compared with the source. It is Widely believed that this is a general phenomenon for marine food webs. An analysis of 148 papers with biomagnification in the title shows that under half show biomagnification. Of studies on metals only organic mercury shows biomagnification and most metals are regulated and excreted and do not biomagnify. Of the studies on organic compounds 67% claimed to show biomagnification. However, bioconcentration (uptake from the surrounding water) is the most usual way that organic compounds are accumulated in organisms from invertebrates to and including fish. Only in sea-birds and marine mammals is food intake the major route and where biomagnification can be clearly shown. Body concentrations of organic compounds vary with lipid content and thus in order to compare across species normalisation to uniform lipid content should be done. Yet often this is not done so data purporting to show biomagnification merely relate to differing lipid content in the different species studied. Finally suggestions are made as to how data can be collected to better interpret the process of biomagnification in marine food webs.

Animals↗