Frode Olsgard

Surrogates in marine benthic investigations ‐ which taxonomic unit to target?

Although the identification of organisms to the levelof species is the ideal in studies of marinemacrobenthos, there are situations where such a finelevel of taxonomic discrimination may be eitherimpossible or unwarranted, for example when much thefauna is undescribed, or if the task for which samplesare collected does not require them to be identifiedto the species level. The idea that abundances ofhigher taxa, or particular groups of organisms, may beused as surrogates for the total fauna in such studiesis explored in this paper using data from theNorwegian sector of the North Sea. The generalconclusion is that, in surveys of soft sedimentmacrofauna in disturbed areas of the North Sea wherepollution imposes simple spatial gradients on thebenthic communities, little information aboutinter-sample relationships is lost using data based onfamily, polychaete species, or polychaete familyabundances, rather than species abundances. In morepristine areas where spatial patterns are determinedby a number of processes, correlations betweencalculated diversity indices and similarity in faunalpatterns between species and family abundances arestill very high, but less so for polychaete species orpolychaete family abundances. This suggests thatidentification to the level of family may besatisfactory in many routine monitoring surveys,andidentification of only the polychaetes, either to thelevel of species or family, may also be a possiblealternative if there are clear disturbance gradientsin the survey area. Polychaetes are of importance indisturbed areas because the group contains tolerantand intolerant species, and in undisturbed areasbecause within the taxon species have a greater rangeof trophic and reproductive strategies than withinother taxa. Ultimately it is the distribution ofspecies, their identities, and their interactions witheach other and with the environment, that are ofinterest. The use of surrogates is likely to be mostadvantageous if it is only the extent of pollutioneffects from a discrete source that matters, andspecies level baseline studies have already beencompleted.

Impact of waste from titanium mining on benthic fauna

Abstract The Jossingfjord area, Norway has been used since 1960 for sea disposal of finely ground, inert tailings from a titanium mine. The discharged quantity was about 2 million tonnes · year−1 in the 1980s. The submarine outfall was in 1984 relocated from the shallow Jossingfjord to a deep basin outside the fjord entrance. Results reported here are from yearly monitoring surveys in the period 1983–1988. The aim of the study was to examine the structure of the soft bottom communities, and describe effects of mine tailings disposal after relocation. The spreading of mine tailings has generally remained constant after 1984. The relocation resulted in increased accumulation within 2–3 km from the new outfall. The accumulated material decreases rapidly with distance, from several metres · year−1 in the outfall basin, to 4–5 cm · year−1 within 1 km from the outfall site, and is in the order of 1 mm · year−1 at distances > 2–3 km from the outfall. Changes in the benthic fauna at varying distances from the outfall were followed. Despite complicated bottom topography and large variations in depth and sediment types it has been possible to identify the biological impact of mine tailings. For example, one year after relocation a clear increase in numbers of the typical opportunistic species Heteromastus filiformis, Chaetozone setosa and Cossura longocirrata was found. In the following years a significant reduction in diversity was observed at sites most disturbed by sedimentation, while diversity at sites > 2–3 km from the outlet remained unaltered. Multivariate analysis of the faunal data (classification, MDS and DCA ordination) revealed clear site-group differences, and two site-groups were related to tailings content in the sediment. Multivariate methods combining fauna and environmental variables identified depth and sediment content of tailings and organic matter as the most important factors influencing the structure of the benthic communities in the area. A sedimentation of 4–5 cm of tailings · year−1 resulted in changes in fauna composition, while at rate of 1 mm · year−1 no impact was observed on the fauna. Recolonization on the old tailings deposits inside Jossingfjord commenced within one year after cessation of discharge, and within 4 years all the main macrobenthic phyla were represented.

Effects of copper contamination on recolonisation of subtidal marine soft sediments : an experimental field study

Abstract Recolonisation patterns of soft-bottom macrofauna on defaunated Cu-spiked sediments were studied in a field experiment at 63 m depth in the Oslofjord, Norway. Field experiments studying colonisation patterns of contaminated sediments are ecologically relevant since settling and metamorphosis of pelagic larvae are generally considered the most critical phases in the development of marine benthic assemblages. Total faunal abundance and the density of the polychaetes Pectinaria koreni and Prionospio cirrifera decreased significantly at sediment Cu-concentrations of 300 mg kg−1. Also the polychaetes Pseudopolydora paucibranchiata, Capitella capitata, Chaetozone setosa, Harmothoe spp., the bivalve Thyasira sarsi and the brittlestar Ophiura affinis were significantly negative correlated to increased sediment Cu-content. Although these species were affected negatively, most of the 116 taxa within the experimental trays showed no response over the entire range of Cu sediment concentrations. Most field studies on recolonisation have been performed in the intertidal or shallow subtidal. These environments are often dominated by robust organisms while animals living in deeper waters are more sensitive to disturbance. The experimental system developed could easily be used at depths between 20 and 100 m to study effects of toxic compounds separately or as mixtures, or colonisation and succession processes of uncontaminated sediments in general.