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1.
Excessive macrophytes can cause significant problems in agricultural waterways requiring active management. Conventional control techniques can have a range of adverse effects. We investigated several control tools in two experiments: firstly, we tested eight treatments at a small-scale (2?m?×?2?m). We found intensive hand weeding, weed mat and herbicide spraying to be effective treatments, reducing macrophyte cover to <5%. Hand weeding and weed mat immediately reduced cover, while dieback from herbicide took two months. Weed mat was a novel and effective control mechanism along stream banks. Secondly, we tested the impact of shading on macrophyte growth. Macrophyte growth was enhanced under partially shaded conditions, but with 80% effective shading over the entire channel, cover was reduced to 17%. Once treatments ceased, macrophytes grew back within 3–5 months. Long-term, control methods will require combinations of tools but will need to include optimal shading for the target species.  相似文献   

2.
Abstract

Stomach contents of Gobiomorphus cotidianus,Retropinna retropinna, Gambusia affinis, and Anguilla australis were compared between two shallow lakes in the lower Waikato River basin, to examine the relationship between turbidity and diet. Lake Waahi and the south arm of Lake Whangape had been turbid (20–40 g suspended solids (SS) m?3) and devoid of submerged macrophytes since the late 1970s and early 1980s, respectively. The main basin of Lake Whangape had been generally clearer (5 g SS m?3) with dense beds of submerged macrophytes, but at the time of sampling (1987) water clarity had deteriorated (> c. 10 g SS m3) and submerged macrophytes had declined. The mysid Tenagomysis chiltoni was an important prey for all species of fish from turbid water bodies but was less important in stomachs of fish in the main basin of Lake Whangape. Apparently, mysids were not an important prey in Lake Waahi before it became turbid. Chironomid larvae and pupae dominated the diets of small fish in the main basin of Lake Whangape. Fish and mysids were the most important prey of shortfinned eels in both lakes, with mysids most important in Lake Waahi. High mysid densities in the turbid water bodies provide an alternative food resource apparently compensating for those lost by fish when water clarity declined and submerged macrophytes collapsed.  相似文献   

3.
The effects of riparian manipulation in New Zealand are described for two case studies, one a short‐term study of the effects of the removal of riparian vegetation on fish, and the second, a long‐term study of the effect of re‐establishment of riparian vegetation on fish and benthic macro invertebrates. The first case study was an experiment carried out between November 2001 and May 2002. Overhanging bank vegetation and in‐stream wood were removed from short reaches of a small pastoral stream that had intact riparian margins, resulting in a change in stream structure with the formation of shallow uniform runs rather than pool and riffle structures as in unmodified reaches. The removal of bank cover and consequential instream habitat changes reduced inanga (Galaxias maculatus) densities by a factor of four within months of vegetation removal, showing the importance of instream cover and habitat to inanga. Adult longfin eel (Anguilla dieffenbachii) also became less abundant in the cleared reaches, but elvers (Anguilla spp.) became more abundant. In the second case study, pastoral sections in two small streams draining from native forest catchments were restored in 1995/96 by planting riparian vegetation and preventing stock access. After 10 years, the restoration efforts had more than doubled the numbers of giant kokopu (G. argenteus) and redfin bullies (Gobiomorphus huttoni), slightly increased numbers of banded kokopu (G. fasciatus), and decreased shortfin eel (A. australis) numbers by about 40%. The macroinvertebrate communities changed so that they became more similar to those at upstream native forest reference sites. These two case studies show that riparian margins can influence the composition of the fish and macroinvertebrate communities in small streams through the effects on cover, instream habitat and probably water temperature. Riparian restoration was most effective for the fish species that use cover and pool habitat.  相似文献   

4.
Temporarily open/closed estuaries typically open to the sea due to freshwater inflow coupled with storm surge events. In September 2008, in the absence of freshwater inflow, the mouth of the East Kleinemonde Estuary breached in response to a storm surge. The mouth of the estuary closed the following day at a high level. Marine overwash events following the breach introduced large volumes of saline water into the estuary and raised the water level by 0.07–0.33 m. Salinity was significantly higher in the 15 month closed phase after the breach (31 ± 0.9) compared to 21.9 ± 0.9 in the closed brackish phase before the breach. The historical average salinity for the estuary during a closed period is 23–25. The increase in salinity has reduced submerged macrophytes Ruppia cirrhosa and Chara vulgaris cover by 38.1%. Macroalgal cover of species such as Dictyota dichotoma, Caulacanthus ustulatus, Codium tenue and Ulva spp. have increased by 7.9%. The saline high water levels have also significantly reduced supratidal salt marsh cover by 15.2%, and reed and sedge cover by 19.7%. Loss of these habitats may result in bank destabilisation and erosion. This is the first record of an extended saline period in the 15 years the estuary has been monitored. Sea level rise in association with climate change, together with localised freshwater inflow reduction is likely to result in an increase in marine overwash events. The frequency and duration of closed saline periods are likely to increase in this type of estuary. A loss of submerged macrophytes may have significant impacts on faunal composition and abundance and on the subsequent functioning of temporarily open/closed estuaries. This has serious ecological implications since these estuaries represent 70% of the different types of estuaries found in South Africa.  相似文献   

5.
A survey was carried out along the shore and adjacent mangrove swamp in the northeast margin of Maputo Bay in Mozambique, east Africa. The study area contained several habitats within close proximity. These were shallow pools in the intertidal muddy sand flats, areas of submerged macrophytes, the swash zone on sandy beaches, primary mangrove channels, secondary mangrove channels, shallow mangrove creeks and a shallow creek with strong freshwater influence at the landward fringe of the swamp. Each station was sampled by means of a small handnet. Data suggest that Penaeus japonicus prefers sandy substrata, while P. semisulcatus chooses areas rich in submerged macrophytes. P. indicus and P. monodon both appear to favour muddy mangrove channels, although P. monodon may require marginal or floating vegetation as nurseries. Metapenaeus stebbingi seems to prefer the swash zone in quiet areas with minimal wave action, while M. monoceros is more widespread and is able to cope with very low salinities. Managers of coastal systems should, therefore, attempt to maintain a diversity of biotopes within larger systems because, even if postlarvae do enter an estuary, juvenile populations with not develop if their specific habitat has been destroyed.  相似文献   

6.
ABSTRACT

National-scale analyses of land cover effects on water quality can aid in directing environmental policy. We compiled a coastal water quality database for New Zealand comprising 320 estuarine and coastal sites with records between 2013 and 2018. Previous literature had shown strong effects of agricultural and urban land cover on the quality of New Zealand’s rivers, so we examined their effects on estuaries, while controlling for marine dilution and freshwater flushing. Sites with greater freshwater influence had higher nutrient and faecal indicator bacteria concentrations, and turbidity, indicating that open coast and estuarine water quality is reduced predominantly via flows from the land. Nitrate, ammonium, total and dissolved reactive phosphorus, and water column chlorophyll-a concentrations were greater in estuaries with higher urban land cover and total phosphorus concentrations were greater with higher agricultural land cover. There was a marginally significant increase in turbidity as agricultural land cover increased. This is the first national-scale compilation and analysis of New Zealand coastal water quality data, and the first national analysis of land cover effects on water quality in New Zealand estuaries.  相似文献   

7.
Sediment resuspension during and after mechanical excavation of macrophytes may have a significant impact on resident fish populations. Unfortunately, little is known about the influence of this sediment on the respiratory performance and feeding abilities of fishes in New Zealand waterways. We examined the effects of suspended sediment (SS) concentrations previously observed after a large-scale macrophyte removal operation on oxygen consumption (MO2) and feeding rates of brown trout (Salmo trutta). MO2 at 0 mg L?1, 150 mg L?1, 300 mg L?1, 450 mg L?1 and 600 mg L?1 of SS was measured using semi-closed respirometry. Feeding rates at the same SS concentrations were also measured using laboratory tank experiments. Results suggest that SS concentrations up to 600 mg L?1 have no effect on MO2. Conversely, feeding rates were significantly reduced at 450 mg L?1 (22% reduction) and 600 mg L?1 (31% reduction), indicating that sediment concentrations above 450 mg L?1 may negatively affect brown trout populations.  相似文献   

8.
Submerged rooted macrophytes and drift algae were studied in shallow (0–1 m) brackish soft-bottom bays in the Åland Islands, N Baltic Sea, in 1997–2000. The study was performed by aerial photography and ground-truth sampling and the compatibility of the methods was evaluated. The study provided quantitative results on seasonal and inter-annual variation in growth, distribution and biomass of submerged macrophytes and drift algae.On an average, 18 submerged macrophyte species occurred in the studied bays. The most common species, by weight and occurrence, were Chara aspera, Cladophora glomerata, Pilayella littoralis and Potamogeton pectinatus. Filamentous green algae constituted 45–70% of the biomass, charophytes 25–40% and vascular plants 3–18%. A seasonal pattern with a peak in biomass in July–August was found and the mean biomass was negatively correlated with exposure. There were statistically significant differences in coverage among years, and among levels of exposure. The coverage was highest when exposure was low. Both sheltered and exposed bays were influenced by drift algae (30 and 60% occurrence in July–August) and there was a positive correlation between exposure and occurrence of algal accumulations. At exposed sites, most of the algae had drifted in from other areas, while at sheltered ones they were mainly of local origin.Data obtained by aerial photography and ground-truth sampling showed a high concordance, but aerial photography gave a 9% higher estimate than the ground-truth samples. The results can be applied in planning of monitoring and management strategies for shallow soft-bottom areas under potential threat of drift algae.  相似文献   

9.
Extensive artificial waterways have replaced natural wetlands and created new estuarine habitats on the southern Queensland coast, Australia. Economically important fish species found in adjacent natural wetlands of mangrove, saltmarsh and seagrass also occur in the artificial waterways. Stable isotope analyses (δ13C, δ15N) were used to test whether the relative importance of basal sources of energy varied for foodwebs found in artificial (canals and tidal lakes) and natural waterways. None of the fish species differed in their isotope values between artificial waterways. In contrast, isotopic signatures of snub-nosed garfish (Arrhamphus sclerolepis; Hemiramphidae) varied greatly between natural and artificial waterways, having highly enriched δ13C values (−10.5‰) in natural wetlands, demonstrating reliance on seagrass (−11.4‰), and significantly less enriched values (−19.0‰) in artificial waterways, consistent with either local algal sources (−19.8 to −20.4‰) or a mixture of seagrass and other less enriched autotrophs from adjacent natural wetlands. Isotopic signatures of sand whiting (Sillago ciliata; Sillaginidae) were also significantly more enriched in natural (−18.2‰) than artificial (−21.0‰) habitats, but means were not far enough apart to distinguish between different sources of nutrition. δ13C values of yellowfin bream (Acanthopagrus australis; Sparidae) did not differ between artificial and natural habitats (about −20‰ in both). δ15N values of fish varied among habitats only for A. sclerolepis, which in artificial waterways had values enriched by 2‰ over those in natural waterways. This was consistent with a shift from seagrass (relatively depleted δ15N) as a source in natural habitat to algal sources (relatively enriched δ15N) in artificial habitats. This study provides some of the first evidence that at least some fish species rely on different autotrophs in artificial waterways than in adjacent natural wetlands.  相似文献   

10.
The fauna associated with sea-bed accumulations of decomposing Laminaria saccharina has been studied by year-round SCUBA diving at two sites in the Clyde Sea area. Seasonal changes in density of 64 species are reported. In the autumn, large quantities of kelp are detached by storms. This weed carries with it to the sea bed a large part of its normal fauna. Additional species settle onto the weed from the plankton whilst others migrate onto it from the surrounding sea bed. Peak densities of associated species were recorded in autumn. Litter bag experiments in situ showed that, except during the summer, weed is lost from sea-bed accumulations at a faster rate when macrofaunal animals are excluded. The macrofauna therefore inhibits decomposition. The relative importance of interactive cropping by three macrodetritivores, Psammechinus miliaris (Echinodermata), Platynereis dumerilii (Polychaeta) and Gammarus locusta (Amphipoda) was studied by in situ containment of different species combinations. The presence of Gammarus with Psammechinus resulted in less weed being lost than when Psammechinus was isolated. This is because Gammarus selectively crops rotting weed, retarding frond disintegration by microbes. Platynereis retards microbial colonization of frond tissues ruptured during its feeding by repeated cropping of the same region. Weed would decompose very rapidly were it not for macrofaunal cropping. Macroalgal decay thus differs profoundly from that of vascular plants.  相似文献   

11.
ABSTRACT

This study investigated the impact of pastoral land use and nutrient and fine sediment inputs on Microcoleus autumnalis and filamentous algae-dominated mats, and benthic chlorophyll-a in streams (lower North Island, New Zealand). Surveying and sampling was undertaken monthly at 61 sites spanning a wide gradient in catchment cover and environmental conditions. Two boosted regression tree models were built. The first models included pastoral land cover and five environmental variables as predictors. In the second model pastoral land cover was replaced by nutrient/sediment data. The abundance of the two mat types and chlorophyll-a increased when pastoral land cover was between 20% and 70% (model 1). Replacement of pastoral land cover by nutrient/sediment data (model 2) slightly improved the model fit for all three periphyton variables. Microcoleus autumnalis-dominant mats increased with dissolved inorganic nitrogen concentrations up to ca. 0.6?mg?L?1, and in streams with more frequent flushes. In contrast, filamentous algal-dominated mats increased with turbidity, and in streams with less frequent flushes. Chlorophyll-a generally followed the response of the dominant periphyton type. Increased knowledge on responses of specific periphyton types, rather than total biomass, to environmental variables is essential to guide effective management strategies.  相似文献   

12.
In the submerged aquatic CAM plant, Isoetes kirkii A. Braun, light was shown to be the environmental factor having the major influence on daily did malic acid/titratable acid fluctuations. In Lake Taupo (New Zealand), a large oligotrophic lake, seasonal variation in the level of did fluctuations was demonstrated and this corresponded to changes in temperature, light, and daylength while Total Inorganic Carbon (TIC) remained relatively constant. However, in situ shading experiments demonstrated that, at any one time, the diel acid fluctuations were controlled by the ambient light levels as the other variables were constant. Laboratory experiments supported this and also showed that there was a close relationship between photosynthetic rates and de‐acidification when related to light intensity.  相似文献   

13.
Seagrass beds serve as nursery grounds for many fish species and often play an important role in the juvenile stages of economically and recreationally important fishes. The eelgrass Zostera capensis is the dominant submerged macrophyte in permanently open South African estuaries and occupies large intertidal and subtidal areas within the Knysna system. The primary objective of this study was to compare the occurrence of sparids and mugilids in eelgrass and nearby bare sediment areas using sampling with seine nets. The hypothesis that was tested is that mugilids are dominant in unvegetated areas of the Knysna Estuary littoral whereas sparids predominate within eelgrass beds located in the same zone. The results indicate that the family Mugilidae is better represented at unvegetated sites when compared to members of the family Sparidae, with the exception of Lithognathus lithognathus, but that the dominant three sparids and dominant two mugilids were most abundant in sparse eelgrass beds that included both bare and vegetated areas within this habitat type. The main fish species responsible for the separation of fish assemblages associated with unvegetated sites versus those associated with vegetated areas were Rhabdosargus holubi, Liza dumerili, Liza richardsonii, Lithognathus lithognathus, Sarpa salpa and Diplodus capensis, with R. holubi, S. salpa and D. capensis being mainly attracted to eelgrass habitats and L. dumerili, L. richardsonii and L. lithognathus having a stronger affinity for bare areas. This finding confirms a previous estuarine study in the nearby Swartvlei lake littoral, which found that sparids dominated areas where aquatic macrophytes were extensive and that mugilids became more prevalent at those same sites when the macrophytes underwent complete senescence. The length-frequency distributions of some sparid and mugilid species differed considerably between eelgrass and bare sediment areas, whereas those of other species showed little or no difference between these two habitat types.  相似文献   

14.
《Coastal Engineering》2006,53(7):589-611
The results of a series of 2DH numerical and 3D scaled physical modelling tests indicate that processes governing shoreline response to submerged structures, such as artificial surfing reefs, are different from those associated with emergent offshore breakwaters. Unlike the case of emergent offshore breakwaters, where shoreline accretion (salient development) is expected under all structural/environmental conditions, the principal mode of shoreline response to submerged structures can vary between erosive and accretive, depending on the offshore distance to the structure. The predominant wave incidence angle and structure crest level also have important implications on the magnitude of shoreline response, but not on the mode of shoreline response (i.e. erosion vs. accretion). Based on the results obtained here, a predictive empirical relationship is proposed as a preliminary engineering tool to assess shoreline response to submerged structures.  相似文献   

15.
The submerged vegetation of Lakes Sumner, Marion, Katrine, Taylor, and Sheppard was surveyed in May 1987. These high‐altitude lakes lie at c. 600 m a.s.l., within the largely unmodified upper Hurunui catchment. Submerged vegetation was diverse and included numerous short shallow‐water species, dense swards of Isoetes alpinus, low covers of taller native vascular plants, and charophyte meadows beyond the depth limit of vascular plants to a maximum of 15 m. A sparse deepwater bryophyte community was observed from 11 to 32 m depth in Lake Sumner. Displacement of native vegetation by dense growths of the adventive oxygen weed Elodea canadensis over mid‐depths of 3–6 m was noted in all lakes, except Lake Marion.  相似文献   

16.
Stable carbon isotopes were used to determine the contribution of emergent demersal zooplankton to the diet of the scyphozoan jellyfish Catostylus mosaicus at Smiths Lake, New South Wales, Australia. A preliminary study in 2004 indicated that there was no difference in the δ13C of ectodermal tissue and mesoglea of the medusae. In 2005, medusae and zooplankton present during the day and night were sampled and isotopic signatures were modelled using IsoSource. Modelling indicated that: (1) mollusc veligers and copepods sampled during the day contributed <13% of the carbon to the jellyfish; (2) copepods sampled at night contributed up to 25%; and (3) the large, emergent decapod Lucifer sp. contributed 88–94%. We hypothesised, therefore, that medusae derive most of their carbon from emergent species of zooplankton. In 2006, sampling done in 2005 was repeated three times over a period of 4 weeks to measure short-term temporal variation in isotopic signatures of medusae and zooplankton, and emergent demersal zooplankton was specifically sampled using emergence traps. Short-term temporal variation in isotopic signatures was observed for some taxa, however, actual variations were small (<1.5‰) and the values of medusae and zooplankton remained consistent relative to each other. IsoSource modelling revealed that mysid shrimp and emergent copepods together contributed 79–100% of the carbon to the jellyfish, and that the maximum possible contribution of daytime copepods and molluscs was only 22%. Jellyfish apparently derive most of their carbon from emergent zooplankton and by capturing small numbers of relatively large taxa, such as Lucifer sp. or mysid shrimp. Small but abundantly captured zooplankton (such as mollusc veligers) contribute only minor amounts of carbon. Jellyfish have a major role in the transfer of carbon between benthic and pelagic food webs in coastal systems.  相似文献   

17.
The aim of this work is to study the temporal dynamics of rhizome epiphytes and sessile animals living on the rhizomes of the seagrass Posidonia oceanica in the east of Tunisia. Surveys were conducted in October 2009, and in January, April and August 2010 on a fringing reef located in Chebba. Rhizomes were sampled by SCUBA diving at three stations. Samples were examined with a microscope to estimate the cover of macroinvertebrate and macroalgal organisms on the top 10 cm of each rhizome. Results revealed a high diversity of epiphytes on P. oceanica rhizomes with a dominance of red and brown algae, ascidians, and bryozoans. Distinct temporal changes were observed in Oued Lafrann, with a high January cover (winter period) for all groups. These winter increases can be attributed to: (i) the low phenological parameters of P. oceanica in winter that reduce the effects of shading, (ii) life cycles of the epiphytes and invertebrates, (iii) water motion and (iv) grazing.  相似文献   

18.
Linking habitat distributions of prey to the probability of predation is important to understanding consumptive effects of predators on prey populations. This study reports how within-reach spatial variability of two snails, the hydrobiid Potamopyrgus antipodarum and the physid Physella acuta, was linked to habitat-based predation risk by young brown trout (Salmo trutta) of different age classes. Potamopyrgus is endemic to New Zealand streams and lakes, where it commonly co-exists with the invader P. acuta, but both snails are worldwide invaders to many freshwater systems. Examination of egested snails revealed Potamopyrgus and Physella were consumed in similar numbers within age classes. However, 10-month-old trout consumed, on average, fewer snails than 20-month-old trout, and 8-month-old trout ate essentially no snails, suggesting snails were a more important prey item for larger age-1 fish than smaller age-0 fish. No Physella were egested alive by any trout age class. However, 38% and 16% of the Potamopyrgus consumed were egested alive by 10- and 20-month-old trout, respectively, with some passing live after ~70 h in digestive tracts. Physella and the spiny-shell form of Potamopyrgus were significantly denser on macrophytes than on stony sediments in midchannel, and these habitat distributions affected their odds of consumption. Risk of consumption by trout was ~10 times greater for Physella than Potamopyrgus on stones, but their risk was similar in protective macrophytes. Odds of consumption were similar for spiny and smooth shell forms of Potamopyrgus on stones, suggesting spines do not provide protection from large predators like trout. My results suggest that brown trout can potentially exert stronger population regulatory effects on Physella than on Potamopyrgus and that these effects are partly mediated by macrophyte cover.  相似文献   

19.
The role of submerged macrophytes as refugia from fish predation and as possible food sources for the estuarine isopod Exosphaeroma hylocoetes ( Barnard, K.H., 1940) was investigated. Laboratory experiments tested the effectiveness of artificial vegetation, replicating submerged vegetation, in enabling isopods to elude selected fish predators Rhabdosargus holubi, Glossogobius callidus, Monodactylus falciformis and Clinus cottoides. Isopods preferentially hid in the vegetation (>90%), even in absence of fish. The predatory fish had varying success in finding isopods within the vegetation. Isopod mortality ranged from 2% (R. holubi) to a maximum of 87% (C. cottoides) within vegetation, depending on the fish predator present. Stable isotope and fatty acid analyses ruled out the submerged macrophyte Ruppia maritima and inundated fringing grasses as direct food sources, but highlighted the epiphytic biota (mainly diatoms) found on the submerged vegetation and sediments as more likely food sources. These findings are consistent with gut content analyses. The results suggest that the close association of E. hylocoetes with R. maritima is the result of the vegetation providing the isopod with a refuge against fish predation as well as areas of increased food availability.  相似文献   

20.
Spatial and seasonal variations of fish assemblage composition were studied in three non-estuarine mangrove creeks of Zanzibar (Tanzania). Fish were collected monthly for one year at three sites (lower, intermediate and upper reaches) in each creek using a seine net (each haul covering 170 m2). Density, species number and diversity of fish were all higher at sites with dense cover of macrophytes (seagrass and macroalgae) than over unvegetated sandy sites. In general, fish assemblages mainly comprised juveniles of a few abundant taxa, e.g. Mugil cephalus, Mugilidae spp. and Leiognathus equulus at sites with mud substratum and Gerres oyena, Lethrinus harak and Sillago sihama at sites dominated by macrophytes. Multivariate analyses revealed significant separations in fish assemblage composition within the two creeks where the bottom substratum differed among sites. Overall, season seemed to have little effect on density, species number, diversity index (H′) and assemblage structure of fish. Water condition variables were also relatively stable across the season, although a short-term fluctuation primarily induced by decreased salinity, occurred during the heavy rains in April and May. Fish assemblage structure was not significantly affected by any of the abiotic factors tested. However, significant regressions were found between the other fish variables and environmental variables, but since these associations were mostly species-specific and generally inconsistent, we suggest that the overall distribution patterns of fish were mainly an effect of particular substrate preferences of fish species rather than contemporary water conditions.  相似文献   

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