Don’t Fight the Site: Three Geomorphic Considerations in Catchment-Scale River Rehabilitation Planning

Three geomorphic considerations that underpin the design and implementation of realistic and strategic river conservation and rehabilitation programs that work with the nature are outlined. First, the importance of appreciating the inherent diversity of river forms and processes is discussed. Second, river dynamics are appraised, framing the contemporary behavioral regime of a reach in relation to system evolution to explain changes to river character and behavior over time. Third, the trajectory of a reach is framed in relation to downstream patterns of river types, analyzing landscape connectivity at the catchment scale to interpret geomorphic river recovery potential. The application of these principles is demonstrated using extensive catchment-scale analyses of geomorphic river responses to human disturbance in the Bega and Upper Hunter catchments in southeastern Australia. Differing implications for reach- and catchment-scale rehabilitation planning prompt the imperative that management practices work with nature rather than strive to ‘fight the site.’     

Potential for long-distance dispersal of Euphausia crystallorophias in fast current jets

The euphausiid Euphausia crystallorophias Holt and Tattersall, 1906 is considered to be a neritic species. It has been found in greatest abundance along the Antarctic continental margins, often in association with regions of pack ice. Although E. crystallorophias has been observed at some islands to the west of the Antarctic Peninsula, the species has not previously been reported from islands of the maritime- or sub-Antarctic further north. During an oceanographic transect in November 1997 from South Georgia to the South Sandwich Islands, acoustic observations revealed a dense, discrete pelagic target at 50 m. The target was fished and was found to be an aggregation of small E. crystallorophias. The fishing location (54.48°S; 30.61°W) was >1500 km from the Antarctic continent, and >250 km from the nearest land, in water of several thousands of metres depth – clearly a non-neritic environment. Examination of hydrographic data revealed that the E. crystallorophias swarm had been located within a fast-flowing band of water that had characteristics of water found near the Antarctic Peninsula. This band was ≃150 km wide, and had a speed ranging from 9 to 22 km d⁻¹ in a north-easterly direction. The possible origins of this E. crystallorophias swarm are explored in the light of the eddy-dominated current patterns prevalent in the Weddell–Scotia Confluence region, and with reference to published growth-rate estimates for the species. We discuss the potential for long-distance dispersal of E. crystallorophias and other neritic species in fast current jets, and examine how such oceanographic features could facilitate long-distance dispersal, colonization, and gene flow. Received: 23 November 1998 / Accepted: 25 March 1999     

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.     

Minute chromatin structures in cells of amniotic fluid—an interpretative dilemma

Single copies of tiny chromosome fragments, appearing either as single or as double minutes, were observed in a high frequency in amniotic fluid cultures of five mothers who underwent prenatal testing because of advanced age. In four cases, the minutes had arisen de novo. The minutes were later confirmed in fetal skin following termination of pregnancy in one case; in another, in cord blood following the birth of a normal boy; and in the third, in peripheral blood of a normal 3-year-old girl. In the fourth case, the minutes were not confirmed in cord blood following the birth of a normal boy. A follow-up chromosome study of the baby boy in the fifth case was not possible but the minutes were maternally transmitted.     

Enhanced survival of 0-group gadoid fish under jellyfish umbrellas

Young (0-group) gadoid fish, which have been observed sheltering beneath jellyfish (Scyphozoa and Hydrozoa) umbrellas, may find refugia from predation by retreating among medusan tentacles. The survival of juvenile gadoids may therefore be improved by high abundances of medusae. Jellyfish (including Cyanea lamarckii and C. capillata) were caught in the North Sea during routine sampling for 0-group gadoids (cod Gadus morhua, haddock Melanogrammus aeglefinus, Norway pout Trisopterus esmarkii and whiting Merlangius merlangus) between 1971 and 1986, and considerable overlaps have been shown between the spatial distributions of these fish and medusae. Here correlations are made between the abundance of medusae in the North Sea and the residual survival of 0-group fish, as quantified by the deviation in 1-group recruitment from the expected Ricker modelled estimate. Significant positive correlations between the residual survival of whiting and medusa abundance are evident for each individual Cyanea sp. and for the combined Cyanea spp. ln(maximum) abundance (all R ≥ 0.60, P < 0.01, N = 15). The abundance of jellyfish may thus be an important factor influencing the mortality of whiting in the North Sea, and as such should be considered in the development of ‘ecosystem-based’ management of whiting stocks.     

Concordance of interannual fluctuations in acoustically estimated densities of Antarctic krill around South Georgia and Elephant Island: biological evidence of same-year teleconnections across the Scotia Sea

Acoustic estimates of the densities of Antarctic krill, Euphausia superba, in areas around South Georgia (SG) and Elephant Island (EI) were compared for seven austral summers between 1981 and 1997. Estimated densities of krill at SG were most often lower than at EI, although this may simply have been a function of differences in the survey and data-analysis techniques used at each site. More interestingly, the magnitudes of density and between-year gradients of density at each site were mirrored by those at the other location; for example 1991 and 1994 were years of very low krill density at both SG and EI. There was no apparent lag in changes in density between sites, and ranked between-year gradients in density at both locations were closely correlated. These pronounced similarities suggest that densities of krill at both locations are linked directly, and may be impacted by the same gross physical and biological factors (e.g. recruitment, dispersal and environmental variability) acting over the same temporal and spatial scales. The observed concordance also implies that the pelagic ecosystems at these widely separated sites (≃1500 km distant at opposite sides of the Scotia Sea) are not operating in isolation. Fluctuations in krill density were investigated with reference to cyclical variations in sea ice extent, and in air and sea-surface temperature. The resulting model suggests that the 1999/2000 austral summer will be one of low krill density. Received: 8 October 1998 / Accepted: 12 April 1999     

River Styles, a Geomorphic Approach to Catchment Characterization: Implications for River Rehabilitation in Bega Catchment, New South Wales, Australia

Analysis of the character and condition of each river style in Bega catchment, and their downstream patterns, are used to provide a biophysical basis to prioritorize river management strategies. These reach-scale strategies are prioritorized within an integrative catchment framework. Conserving near-intact sections of the catchment is the first priority. Second, those parts of the catchment that have natural recovery potential are targeted. Finally, rehabilitation priorities are considered for highly degraded reaches. At these sites, erosion and sedimentation problems may reflect irreversible changes to river structure.     

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.     

Drivers of euphausiid species abundance and numerical abundance in the Atlantic Ocean

Mid-ocean ridges are common features of the world’s oceans but there is a lack of understanding as to how their presence affects overlying pelagic biota. The Mid-Atlantic Ridge (MAR) is a dominant feature of the Atlantic Ocean. Here, we examined data on euphausiid distribution and abundance arising from several international research programmes and from the continuous plankton recorder. We used a generalized additive model (GAM) framework to explore spatial patterns of variability in euphausiid distribution on, and at either side of, the MAR from 60°N to 55°S in conjunction with variability in a suite of biological, physical and environmental parameters. Euphausiid species abundance peaked in mid-latitudes and was significantly higher on the ridge than in adjacent waters, but the ridge did not influence numerical abundance significantly. Sea surface temperature (SST) was the most important single factor influencing both euphausiid numerical abundance and species abundance. Increases in sea surface height variance, a proxy for mixing, increased the numerical abundance of euphausiids. GAM predictions of variability in species abundance as a function of SST and depth of the mixed layer were consistent with present theories, which suggest that pelagic niche availability is related to the thermal structure of the near surface water: more deeply-mixed water contained higher euphausiid biodiversity. In addition to exposing present distributional patterns, the GAM framework enables responses to potential future and past environmental variability including temperature change to be explored.     

Preliminary observations on the effect of heavy metals from mining and smelting on nitrogen-fixing bacteria in some British soils

Nitrogen fixation by free-living non-symbiotic bacteria has been qualitatively estimated in several surface soils and mine wastes from mineralised areas in Derbyshire and Cornwall, using a technique based on acetylene reduction. Fresh samples contaminated with varying amounts of one or more of the metals lead, zinc, cadmium and copper, together with appropriate controls, showed no ability to reduce acetylene, indicating an absence of nitrogen fixation. Addition of activeAzotobacter chroococcum resulted in acetylene reduction in the majority but not all of the samples. The effects of varying concentrations of lead, zinc, cadmium and copper on the growth ofAzotobacter chroococcum andBeijerinckia lactogenes were tested in laboratory culture.