The benthic boundary layer approach and its application to Lake Päijänne,Finland

Resuspension of bottom sediments is the net result of a wide variety of different fluid mechanical processes with characteristic time and length scales that extend over six orders of magnitude. The sum of these effects is most heavily concentrated in a layer adjacent to the bottom called the benthic boundary layer (BBL). The physics of BBL must be understood before improved solutions to the resuspension problem are possible. Traditionally in lakes, sedimentation and resuspension have been modelled with the aid of equations which ignore the time and space variations of near bottom processes. This can lead to wrong estimates of material transport. With the exception of few recent studies, benthic boundary layer approach has been mainly applied to marine environments. The instrumentation has been a major problem for development of the theory and its applications, but during recent years some new instruments have been giving promising results. This paper discusses the applicability of the theory in Finnish lakes and presents results from Lake Päijänne.     

Taxonomy of some common Amphidinium species

The taxonomic status of several well known species belonging to the genus Amphidinium (Dinophyceae) has been re-examined. Studies in culture and observations on the micro-anatomy of these organisms suggest that the number of species can be reduced to two, A. klebsii and A. carterae. They may be distinguished on the basis of fundamental differences in chloroplast morphology.     

Changes in dissolved organic material determine exposure of stream benthic communities to UV-B radiation and heavy metals: implications for climate change

Changes in regional climate in the Rocky Mountains over the next 100 years are expected to have significant effects on biogeochemical cycles and hydrological processes. In particular, decreased discharge and lower stream depth during summer when ultraviolet radiation (UVR) is the highest combined with greater photo-oxidation of dissolved organic materials (DOM) will significantly increase exposure of benthic communities to UVR. Communities in many Rocky Mountain streams are simultaneously exposed to elevated metals from abandoned mines, the toxicity and bioavailability of which are also determined by DOM. We integrated field surveys of 19 streams (21 sites) along a gradient of metal contamination with microcosm and field experiments conducted in Colorado, USA, and New Zealand to investigate the influence of DOM on bioavailability of heavy metals and exposure of benthic communities to UVR. Spatial and seasonal variation in DOM were closely related to stream discharge and significantly influenced heavy metal uptake in benthic organisms. Qualitative and quantitative changes in DOM resulting from exposure to sunlight increased UV-B (290–320 nm) penetration and toxicity of heavy metals. Results of microcosm experiments showed that benthic communities from a metal-polluted stream were tolerant of metals, but were more sensitive to UV-B than communities from a reference stream. We speculate that the greater sensitivity of these communities to UV-B resulted from costs associated with metal tolerance. Exclusion of UVR from 12 separate Colorado streams and from outdoor stream microcosms in New Zealand increased the abundance of benthic organisms (mayflies, stoneflies, and caddisflies) by 18% and 54%, respectively. Our findings demonstrate the importance of considering changes in regional climate and UV-B exposure when assessing the effects of local anthropogenic stressors.     

The fish assemblage on a coralligenous shallow shelf off the Mediterranean coast of northern Israel

The fish assemblage on the shallow coralligenous shelf (16-30m depth) off Haifa, Israel was sampled using trammel nets throughout a period of 1 year. Complementary data were obtained via underwater censuses of fish on an artificial reef established later in the sampling area. Fortythree species of fish were sampled by trammel nets, 79% of which were observed also during the underwater censuses. Although fish of Red Sea origin constituted only 11.6% of the species composition in the net samples, they contributed 46.2% of the fish abundance and 40.6% of the biomass in these samples. This was supported by the finding that species of Red Sea origin contributed 64% of the abundance of large fish counted on the artificial reef. Siganus luridas, S. rivulatus and Sargocentron rubrum are the main contributors in number and biomass among fish of Red Sea origin. It is suggested that the biogenic rocky bottom of this area contains several components which are similar to biogenic habitats favoured by these benthic species in the Red Sea; this may explain the high abundance of these species in the studied area.     

Tool use by aquatic animals

Tool-use research has focused primarily on land-based animals, with less consideration given to aquatic animals and the environmental challenges and conditions they face. Here, we review aquatic tool use and examine the contributing ecological, physiological, cognitive and social factors. Tool use among aquatic animals is rare but taxonomically diverse, occurring in fish, cephalopods, mammals, crabs, urchins and possibly gastropods. While additional research is required, the scarcity of tool use can likely be attributable to the characteristics of aquatic habitats, which are generally not conducive to tool use. Nonetheless, studying tool use by aquatic animals provides insights into the conditions that promote and inhibit tool-use behaviour across biomes. Like land-based tool users, aquatic animals tend to find tools on the substrate and use tools during foraging. However, unlike on land, tool users in water often use other animals (and their products) and water itself as a tool. Among sea otters and dolphins, the two aquatic tool users studied in greatest detail, some individuals specialize in tool use, which is vertically socially transmitted possibly because of their long dependency periods. In all, the contrasts between aquatic- and land-based tool users enlighten our understanding of the adaptive value of tool-use behaviour.     

Response of three lotic assemblages to riparian and catchment‐scale land use: implications for designing catchment monitoring programmes

1. Although many studies have focussed on the effects of catchment land use on lotic systems, the importance of broad (catchment) and fine (segment/reach) scale effects on stream assemblages remain poorly understood. 2. Nine biological metrics for macrophytes (498 sites), benthic macroinvertebrates (491) and fish (478) of lowland and mountain streams in four ecoregions of France and Germany were related to catchment and riparian buffer land use using partial Redundancy Analysis and Boosted Regression Trees (BRTs). 3. Lotic fauna was better correlated (mean max., r = 0.450) than flora (r = 0.277) to both scales of land use: the strongest correlations were noted for mountain streams. BRTs revealed strong non‐linear relationships between mountain assemblage metrics and land use. Correlations increased with increasing buffer lengths, suggesting the importance of near‐stream land use on biotic assemblages. 4. Several metrics changed markedly between 10–20% (mountain ecoregions) and 40–45% (lowland) of arable land use, irrespective of the buffer size. At mountain sites with >10% catchment arable land use, metric values differed between sites with <30% and sites with >30% forest in the near‐stream riparian area. 5. These findings support the role of riparian land use in catchment management; however, differences between mountain and lowland ecoregions support the need for ecoregion‐specific management.     

Mass loss and macroinvertebrate colonisation of fish carcasses in riffles and pools of a NW Italian stream

In this study, we analysed the decomposition of trout carcasses in a low-order Apennine stream, with the aim to investigate the mass loss rate in a Mediterranean lotic system, and to examine the influence of microhabitats on the invertebrates colonising fish carcasses. In May 2003, we put 56 dead rainbow trout (Oncorhynchus mykiss) in the stream, placing seven sets (four trout each) in both riffle and pool habitats. At four dates, we removed one trout per set to measure its dry mass and determine the associated macroinvertebrate assemblage. Fifty-eight macroinvertebrate taxa colonised the carcasses, with significant differences between the erosive and depositional microhabitats. Riffle trouts hosted richer and denser colonist communities than pool trouts. Chironomidae, Serratella ignita, Habrophlebia sp., Dugesia sp. and Protonemura sp. were the five most abundant taxa. Decomposition was initially very rapid in both environments and then tapered off over time. The mass loss rate was higher (k= –0.057 day^–1) than that found in other studies. Higher Mediterranean temperatures probably increase the process. Although we found no significant difference between riffles and pools, mass loss was more regular in erosive habitats, underlining the importance of local, small-scale conditions. In small, low-order, heterotrophic streams, fish carcasses represent an important resource and shelter for rich and diversified invertebrate assemblages.     

Effects of harvesting callianassid (ghost) shrimps on subtropical benthic communities

The effects of harvesting of callianassid shrimp (Trypaea australiensis) on the abundance and composition of macrobenthic assemblages in unvegetated sediments of a subtropical coastal embayment in Queensland, Australia were examined using a combination of sampling and manipulative experiments. First, the abundance and composition of the benthic infauna in an area regularly used for the collection of shrimp for bait by recreational anglers was compared with multiple reference areas. Second, a BACI design, with multiple reference areas, was used to examine the short-term effects of harvesting on the benthic assemblages from an intensive commercialised fishing competition. Third, a large-scale, controlled manipulative experiment, where shrimp were harvested from 10,000 m² plots at intensities commensurate with those from recreational and commercial operators, was done to determine the impacts on different components of the infaunal assemblage.

Only a few benthic taxa showed significant declines in abundance in response to the removal of ghost shrimp from the unvegetated sediments. There was evidence, however, of more subtle effects with changes in the degree of spatial variation (patchiness) of several taxa as a result of harvesting. Groups such as capitellid polychaetes, gammarid amphipods and some bivalves were significantly more patchy in their distribution in areas subjected to harvesting than reference areas, at a scale of tens of metres. This scale corresponds to the patterns of movement and activity of recreational harvesters working in these areas. In contrast, patchiness in the abundance of ghost shrimp decreased significantly under harvesting at scales of hundreds of metres, in response to harvesters focussing their efforts on areas with greater numbers of burrow entrances, leading to a more even distribution of the animals. Controlled experimental harvesting caused declines in the abundance of soldier crabs (Mictyris longicarpus), polychaetes and amphipods and an increase in the spatial patchiness of polychaetes. Populations of ghost shrimp were, however, resilient to harvesting over extended periods of time. In conclusion, harvesting of ghost shrimp for bait by recreational and commercial fishers causes significant but localised impacts on a limited range of benthic fauna in unvegetated sediments, including changes in the degree of spatial patchiness in their distribution.     

Relationship between Riparian Vegetation and Stream Benthic Communities at Three Spatial Scales

We examined the influence of riparian vegetation on macroinvertebrate community structure in streams of the Upper Thames River watershed in southwestern Ontario. Thirty-three μ-basins (129–1458 ha) were used to identify land cover variables that influenced stream macroinvertebrates. Micro-basins represented the entire drainage area of study streams and were similar in stream order (first, second) and land cover (agricultural or forest; no urban). We described the structure and composition of riparian vegetation and benthic macroinvertebrate communities at the outflow reach. The nature of the land cover was quantified for the stream network buffer (30 m) and the whole μ-basin. The objective of this study was to measure the magnitude and nature of the relationship between the riparian vegetation and benthic macroinvertebrate community at the outflow reach, stream network buffer, and whole μ-basin scales. Taxon richness (including total number of Ephemeroptera, Plecoptera, and Trichoptera taxa) and Simpson’s diversity of the macroinvertebrate community all increased with increased tree cover in the riparian zone at the outflow reach scale. Simpson’s equitability was lower with greater agricultural land cover in the stream network buffer. No relationship between the macroinvertebrate community and land cover was found at the whole μ-basin scale. Analysis of the influence of land cover on stream communities within a spatial hierarchy is important for understanding the interactions of stream ecosystems with their adjacent landscapes.