The lake at Llandrindod Wells—a restoration comedy?

• 1. The lake at Llandrindod Wells, Wales, UK, is a typical urban shallow lake. Created in the 19th century for amenity, it has a long history of management for various, often conflicting, purposes. After the 1950s, the once clear water became turbid with phytoplankton, and aquatic plants became very scarce.
• 2. The most likely reason for this was introduction of common carp, for angling, into a fish community that contained no piscivores. Mobilization of phosphorus from the sediments by activities of the fish led to severe internal phosphorus loading, culminating ultimately in a requirement to close the lake, temporarily in summer, to water contact activities, because of a risk of toxic cyanophyte blooms.
• 3. The lake‐owners decided to restore the lake to greater amenity and conservation value by biomanipulation of the fish community and associated works. The restoration was successful in restoring clear water and plant communities, but because of the nature of the plants reintroduced, there were new problems of dense plant growth. Ownership of the lake then changed and, in a somewhat confused situation, the lake has been returned to a carp fishery.
• 4. Documents on the history of management of the lake, and available limnological data, are reviewed in relation to a general strategy for lake restoration and general lessons are drawn for future restoration projects.

Copyright © 2002 John Wiley & Sons, Ltd.     

Habitat associations of invertebrates in reedbeds,with implications for management

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Salinity tolerance during early development of threatened Murray hardyhead (Craterocephalus fluviatilis) to guide environmental watering

1. The worldwide reduction in wetlands has led to the large‐scale decline of wetland‐dependent species. In Australia, to redress some of the decline, partial restoration of the hydrology of a small number of wetlands has been attempted using allocations of environmental water.
2. A common goal of the watering is the maintenance and enhancement of native fish communities, which historically have included populations of the salt tolerant Murray hardyhead (Craterocephalus fluviatilis), a small, short‐lived fish, endemic to the lower Murray–Darling Basin.
3. Despite the addition of environmental water to several sites at which the species is known to persist, populations continue to decline. This decline is, at least in part, suspected to be a consequence of salinities that conflict with the breeding ecology and survival of early life stages.
4. Here the effect of salinity on egg hatch rate and the upper salinity tolerance of larval and juvenile Murray hardyhead was determined under laboratory conditions. It was found that eggs were vulnerable to elevated salinities, whereas juveniles were capable of tolerating salinities up to 105 ppt.
5. Based on the results of the experiment, brackish wetlands managed for Murray hardyhead should be maintained, where possible, between 12 and 45 ppt. Such a salinity regime will necessitate less intensive management of salinity, and a reduced volume of environmental water, providing both environmental and fiscal benefits. The research highlights the benefits of investment in targeted research.

     

Population growth and mass mortality of an estuarine fish,Acanthopagrus butcheri,unlawfully introduced into an inland lake

• 1. In 2006, two periods of hypoxia resulted in the death of approximately 35 tonnes of black bream (Acanthopagrus butcheri) in Lake Indoon, a small inland lake in Western Australia.
• 2. Acanthopagrus butcheri was the first fish species to be recorded in this lake, along with the mosquitofish (Gambusia holbrooki) which was also observed during sampling in 2006. Acanthopagrus butcheri appears to have been introduced to Lake Indoon between 1998 and 2003 and formed a self‐sustaining population. It is believed to have been deliberately introduced for the purpose of creating a recreational fishery, despite the existence of substantial penalties for illegal translocation of fish in Western Australia.
• 3. Recent human‐induced environmental changes, including rising groundwater and salinization, have probably aided the establishment of both species in Lake Indoon. The importance of salinity to recruitment success by A. butcheri was indicated by the presence of only two age classes in 2006, with estimated recruitment dates coinciding with the years of highest recorded salinity in the lake.
• 4. The ‘fish kills’ provided an opportunity to examine aspects of A. butcheri biology in a relatively low salinity environment which is atypical for this estuarine species. In particular, the recruitment period in Lake Indoon was delayed until autumn/winter, rather than spring/summer as seen in other populations. Biological responses in Lake Indoon have implications for natural populations living in estuaries with modified salinity regimes.
• 5. The ecological, social and economic impacts potentially arising from the introduction of fish to Lake Indoon, which is an important migratory bird habitat and a recreational amenity for local residents and tourists, illustrate the complexities of fish translocation and the need for rigorous assessment before stocking to identify potential costs and benefits.

Copyright © 2008 John Wiley & Sons, Ltd.     

Exploring environmental predictors of aquatic macrophytes in water‐dependent Natura 2000 sites of high conservation value: Results from a long‐term study of macrophytes in Greek lakes

1. Aquatic macrophytes play a key role in lake dynamics, but human activities and eutrophication have resulted in macrophyte loss in many lakes throughout Europe. In this study, the relationships between aquatic macrophytes and gradients of environmental factors were explored using an extensive set of data collected from 13 lakes of the Greek mainland that are part of the European network Natura 2000.
2. The main objectives were to assess the importance of key abiotic predictors and estimate possible environmental thresholds of macrophyte richness, diversity, and abundance using boosted regression trees (BRTs), as well as to explore further the distribution of dominant macrophyte taxa along environmental gradients.
3. The results reveal conductivity as a significant predictor of macrophyte total cover and diversity. In addition, orthophosphate and nitrate nitrogen appear to play an important role for several macrophyte species and assemblages, reflecting a major effect of eutrophication on the distribution of taxa. The majority of macrophyte assemblages were found in waters characterized by high nutrient content, although their distribution extends along a wide range of phosphorus and nitrogen concentration. In contrast, charophyte species show the optimum of their distribution in clear, oligotrophic waters.
4. This integrated study can be used for ranking environmental factors that influence macrophyte distribution in the lakes of Greece and for identifying taxa or macrophyte assemblages that can be used as effective indicators of changes in the abiotic environment. In addition, the results can contribute to the conservation of freshwater habitats in the protected areas studied. In particular, measures that aim to improve water quality are expected also to restore oligotrophic habitats that are characterized by benthic charophyte vegetation. Overall, the links between macrophyte assemblages and abiotic factors are critically important in improving freshwater biodiversity management and environmental policies in east Mediterranean lakes.

     

Distribution of aquatic plants in the Northern Vosges rivers: implications for biomonitoring and conservation

• 1. The continual confusion over the definition of the term ‘trophic status’ has led to ambiguous demonstrations of the influence of alkalinity versus inorganic N and P on aquatic plant distribution.
• 2. Data from the Northern Vosges rivers (sandstone geology) were reinvestigated to test whether it was possible to separate the effect of (i) spatial isolation from surface water chemistry, and (ii) alkalinity from inorganic N and P on aquatic macrophyte distribution.
• 3. Alkalinity and pH exerted the strongest influence on plant distribution, soluble reactive phosphorus (SRP) and pCO₂ being subordinate. The effect of spatial isolation between catchments was not significant, which may indicate that aquatic plants dispersed well over the area. The effect of longitudinal connectivity on species distribution was strong, although largely confounded by the effects of water chemistry and possibly other physical factors not recorded. The partial effect of SRP (after removing the effect of pH or alkalinity) was still significant. However this was not the case for NH₄.
• 4. The floristic composition was more likely to indicate the role played by alkalinity than inorganic P, with inorganic N being further subordinate. However, the causality of the significant relationships needs to be investigated further. This study questioned the validity of current macrophyte biomonitoring tools striving to indicate the concentrations of inorganic N and P.
• 5. More work is needed to quantify the role of connected and isolated aquatic habitats in the region, in order to understand how to maintain the species pool and to ensure that recolonization rates compensate for the losses due to disturbances. It is not clear how the vegetation would respond to inorganic P enrichment (or control), based on the individual species response observed here, and river P uptake studies from other rivers. Future monitoring should also include measurements of physical degradation.

Copyright © 2007 John Wiley & Sons, Ltd.     

Identifying optimum locations for new ponds

• 1. Pond ecological quality is influenced by surrounding land uses. Continued intensification of land use has led to a progressive decline in the ecological quality of the pond stock within Britain.
• 2. To reverse this trend new ponds need to be carefully designed and sited using a targeted approach. Consequently, this study uses a Geographical Information System (GIS) to identify optimum locations for new ponds within the Chiltern Hills Area of Outstanding Natural Beauty.
• 3. Multiple regression analysis was used to identify the relationship between macrophyte pond quality indicators and environmental data from 300 ponds to produce models that could predict pond quality.
• 4. These models were tested at 10 locations in the study area by comparing predicted pond qualities with the actual pond qualities, established by identifying all plants in each pond. Aquatic plants successfully predicted pond quality, while emergent plants and total wetland plant species did not.
• 5. The regression model for aquatic plants was used in the GIS to identify locations within the study area where new ponds could be located to obtain maximum ecological quality. Six scenarios were tested and the optimum situation identified.
• 6. The study demonstrated the potential and importance of using GIS in a strategic approach for pond conservation.

Copyright © 2003 John Wiley & Sons, Ltd.     

Fishless shallow lakes of Southern Patagonia as habitat for waterbirds at the onset of trout aquaculture

• 1. The Strobel Meseta, a basaltic plateau of Patagonia (Santa Cruz Province, Argentina), holds thousands of shallow fishless lakes that are prime habitat for many species of waterbirds, including some considered ‘near threatened’. In recent years, several lakes have been stocked with trout which has created uncertainty about the potential effects on the recipient ecosystem.
• 2. Limnological and topographical analyses were performed in a group of 32 lakes of the Strobel Meseta in order to characterize and classify individual lakes of the meseta based on their limnological and topographic features, analyze the association between lake type and use by aquatic birds in general and by the endemic hooded grebe (Podiceps gallardoi) in particular, and evaluate the overlap between trout aquaculture and critical habitat for waterbirds.
• 3. The lakes were classified by multivariate analyses into four characteristic types: turbid, high conductivity lakes (T), small vegetated lakes (SV) and larger lakes which were subdivided into either vegetated (LV) or unvegetated (LU). In general, macrophyte cover was the main classificatory variable, whereas conductivity, pH, surface, and depth contributed moderately. Large vegetated lakes were generally found to be important for waterbirds and provided critical habitat for the hooded grebe, whereas trout farmers largely favoured large unvegetated lakes. However, since some large vegetated lakes have already been stocked, there is some level of geographical overlap between waterbird habitat and trout farming.
• 4. The existence of some level of spatial segregation between production and critical waterbird habitat affords opportunities for designing a spatially‐based management system for trout aquaculture.

Copyright © 2008 John Wiley & Sons Ltd.     

Salinity tolerance of non‐native suckermouth armoured catfish (Loricariidae: Pterygoplichthys) in south‐eastern Mexico: implications for invasion and dispersal

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Conservation of a permanent hypersaline lake: management options evaluated from decadal variability of Coleofasciculus chthonoplastes microbial mats

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The use of littoral mesohabitats and their macroinvertebrate assemblages in the ecological assessment of lakes

• 1. Historically, ecological assessment of lakes has depended on open‐water chemical and phytoplankton analysis, with trophic status determined by chlorophyll a and total phosphorus following the general protocol of the OECD lake classification scheme. This has been accompanied by a prevailing opinion that the littoral zone of lakes is too heterogeneous to allow meaningful inter‐lake comparisons.
• 2. Council of the European Communities Directive 2000/60/EC establishing a framework in the field of water policy (the Water Framework Directive) requires a broader approach to ecological assessment, including the need to incorporate a range of biotic variables. This paper describes the results of a monitoring programme designed to determine within‐ and among‐lake variation of macroinvertebrate communities found in defined mesohabitats of 22 lakes incorporating a range of lake types. Three sampling approaches were applied to the study.
• 3. Triplicate macroinvertebrate samples from a cobble/pebble mesohabitat of 11 lakes showed that community composition from a standard habitat was robust.
• 4. Twinned samples from contrasting habitats of pebble/cobble and macrophyte dominated mesohabitats of 21 lakes had greater similarity within than among lakes. This showed that even across contrasting habitat structure, macroinvertebrate assemblages can provide a reliable lake‐specific indicator.
• 5. Multivariate analysis of replicate samples from 15 visually distinct mesohabitats in one lake showed that within‐lake variation could, nevertheless, be identified as distinct clusters of invertebrate assemblages.
• 6. Conclusions from the work are that variations within lakes were nested in among‐lake variation across a range of lake types, and that macroinvertebrate assemblages can provide meaningful assessment of ecological differences across lakes. Monitoring can, however, produce a substantial amount of ‘noise’ from the data that reflects the complexity of macroinvertebrate community structure in littoral zones. It is recommended that incorporation of macroinvertebrates in ecological assessment is most useful when confined to well defined mesohabitats rather than attempt to incorporate a complete range of mesohabitats within a single lake.

Copyright © 2003 John Wiley & Sons, Ltd.     

Ornamental lakes — an overlooked conservation resource?

• 1. Shallow lakes excavated for ornamental purposes during the 18th and 19th centuries are abundant in lowland Europe. However, relative to older man‐made and/or natural lakes, these lakes may have been undervalued from the perspective of nature conservation.
• 2. To evaluate this idea a comparison was made between the aquatic macrophyte communities (submerged and floating‐leaved vegetation) of 66 shallow, English lakes including 34 ornamental lakes and 32 flooded medieval peat workings (the Norfolk and Suffolk Broads system), the latter being widely protected by conservation legislation.
• 3. Some 47%, 38% and 15% of the lakes studied were phytoplankton‐dominated, macrophyte‐dominated or deemed too shallow (<50 cm water depth), respectively, to support a macrophyte vegetation. A higher proportion of the ornamental lakes were macrophyte‐dominated (51%) by comparison with the broads (34%). In addition, many of the ornamental lakes contained diverse plant communities including abundant populations of Characeae, a common feature of lakes in the region before the major onset of eutrophication.
• 4. From the perspectives of macrophyte species richness, charophyte communities and indeed ‘reference condition macrophyte assemblages’, many of the studied ornamental lakes can be considered to be of high conservation value. Yet, in contrast to the broads, the vast majority of ornamental lakes have little conservation protection and are rarely subject to biological monitoring and/or surveying, thus leaving them vulnerable to eutrophication and inappropriate management. This study suggests that ornamental lakes are worthy of much greater attention from conservation organizations.

Copyright © 2008 John Wiley & Sons, Ltd.     

Niche specialization and functional traits regulate the rarity of charophytes in the Nordic countries

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Phytoplankton biomass and environmental factors over a gradient of clear to turbid peri‐urban ponds

• 1. Small lakes and ponds with high nutrient loadings can be clear, turbid or intermediate, with low, high and intermediate phytoplankton biomass, respectively.
• 2. A combination of biotic and abiotic factors, such as hydraulic retention time, presence of submerged vegetation, depth, top‐down phytoplankton control, and cascading effects of fish community structure, play an important role in phytoplankton biomass control when nutrients are not limiting. Different combinations of these factors lead to different levels of phytoplankton biomass.
• 3. Identification of the main factors controlling phytoplankton biomass in a particular pond or a small lake is essential for choosing an appropriate management strategy for the maintenance of a desired ecosystem state.
• 4. When a pond or a small lake ecosystem is impaired by eutrophication, a considerable degree of its ecological quality can be restored through the modification of some environmental factors when a sufficient reduction in nutrient input is not feasible.

Copyright © 2006 John Wiley & Sons, Ltd.     

Climate variability and trends in the reproductive habitat of the critically endangered hooded grebe

1. The population of the critically endangered hooded grebe (Podiceps gallardoi) has decreased drastically during recent decades. The effects of climate change on their reproductive area (Southern Patagonia) have been proposed as one of the potential causes of their critical situation. However, there is much uncertainty about climate variability and climate trends at local scales in Patagonia, and their effects on the hooded grebe habitat.
2. Variability and trends in temperature, precipitation, and wind from 1960 to 2016 in one of the most important reproductive areas of hooded grebe – the Lake Strobel plateau – were analysed. A Landsat satellite image series (1973–2016) was used to evaluate changes in lake area in the region.
3. Generalized linear models were used to analyse the relationship between the variation in lake area and climatic variables, including the Antarctic Oscillation Mode (AAO) index, which is the most important year to year pattern in climate variability at high latitudes of the Southern Hemisphere.
4. High inter‐annual variability and increasing coefficients of variation in precipitation and wind were found, as well as a significant positive trend in temperature. Total lake area, as well as the area specifically used by hooded grebe to reproduce, decreased significantly over time, with high inter‐annual variability. Variation in lake area was significantly correlated with variation in precipitation, and with the AAO index.
5. The loss of reproductive habitat may force the hooded grebe to use sub‐optimal environments, such as lakes with lower food supply, lower macrophyte cover, and less protection from wind – a potential major handicap for this declining species.
6. Information on lake variation in response to climatic variability could be used to guide hooded grebe conservation strategies, directing more resources and special efforts to those reproductive lakes that are more resilient to the effects of climate fluctuations.

     

Precautionary rules for exotic trout aquaculture in fishless shallow lakes of Patagonia: minimizing impacts on the threatened hooded grebe (Podiceps gallardoi)

• 1. Conflicts between habitat use and conservation are inherent to the management of wetlands. A major challenge for their management is to preserve habitat while addressing the demands from multiple users. In southern Patagonia (Argentina), a growing aquaculture activity based on rainbow trout introductions in shallow lakes is generating concerns about the effects on the waterbird fauna, including some endemic species.
• 2. Generalized linear models (GLM) were used to analyse data on the endemic hooded grebe (Podiceps gallardoi) collected over a diverse set of lakes to: (1) build presence‐absence models as a function of environmental variables; (2) assess current and potential overlap with trout aquaculture; (3) explore the power of alternative lake assignment algorithms based on habitat variables to segregate critical habitat and aquaculture activities; and (4) explore the correlation between the probability of grebe presence and their abundance in given lakes.
• 3. Hooded grebe presence is clearly correlated with macrophyte cover, lake area, and water conductivity. Medium size lakes, with a combination of emerging macrophytes, adjacent to open water areas had the highest probability of both hooded grebe presence and abundance.
• 4. Different lake allocation scenarios are identified that could grant significant protection to hooded grebes without substantial losses for trout producers. The a priori probability to hold hooded grebe, assigned by the model based on lake characteristics, provides a tool that can be used by managing authorities to derive precautionary management rules to regulate aquaculture and to preserve primary hooded grebe habitat. Copyright © 2009 John Wiley & Sons, Ltd.

     

Effect of salinity on growth, survival and oxygen consumption of juvenile brown shrimp, Farfantepenaeus californiensis (Holmes)

The brown shrimp, Farfantepenaeus californiensis (Holmes), is a species native to north‐west Mexico, where its culture potential is presently being addressed. Because of the climatic conditions prevailing in the region, salinities over 40 g L^?1 is a commonly encountered problem. In the present study, the effect of salinity on the growth and mortality of juvenile F. californiensis is described. The change in short‐term routine metabolism at different salinities was also evaluated in order to define the adaptive capacity of the shrimp and to provide insight into the changes in the pathways of energy distribution. Groups of shrimp were exposed to increasing salinity (25, 35, 45 and 55 g L^?1), and growth and survival rates after 75 days were determined in duplicate 1.8‐m³ tanks for each salinity level. Significant differences were found in final weight, growth rate and mortality of shrimp as a result of salinity level. Final mean shrimp weights at increasing salinity levels were 10.0, 9.4, 8.6 and 7.8 g. Corresponding mortality was 24.4%, 15.1%, 33.6% and 55.7%. Oxygen consumption was found to depend significantly on salinity and was equivalent to 0.0027, 0.0037, 0.0043 and 0.0053 mg g^?1 min^?1 respectively for the increasing salinities. The increased rate of oxygen consumption at high salinities reflects the response of the organism to osmoregulatory and ionic imbalances. Increased energy requirements to fulfil basic metabolic function as salinity increased resulted in a reduction in the energy that could be diverted to growth. Consequently, the culture of the brown shrimp at salinities over 35 g L^?1 would probably result in reduced yields.     

Declines in the tuber‐feeding waterbird guild at Shengjin Lake National Nature Reserve,China – a barometer of submerged macrophyte collapse

• 1. The Yangtze floodplain is globally unique for its extensive ephemeral wetlands, recharged by summer monsoon precipitation. The annual cycle of inundation and water table recession favours submerged macrophytes, including Vallisneria that overwinters in desiccated substrates as tubers, which provide high‐energy winter food for tuber‐feeding waterbirds that were formerly abundant in the region.
• 2. Large declines among the tuber‐feeding waterbirds swan goose Anser cygnoides (L.), tundra swan Cygnus columbianus (Ord) and hooded crane Grus monacha Temminck between 2004/2005 and 2009/2010 at Shengjin Lake, Anhui Province, suggest that major changes in food availability have occurred there.
• 3. Based on observations of feeding behaviour and energy budgets of these species, it was calculated that at least 5.0 and 8.9 km² of Vallisneria beds in 2004 and 2005, respectively, would be needed to support observed numbers of these species, compared with less than 1.5 km² found in 2009 and 2010.
• 4. An incomplete macrophyte survey in summer 2000 located at least 7.7 km² of Vallisneria beds in the Upper Lake, where none was present during resurveys in 2008 and 2009. Declines in tuber‐feeding waterbirds at Shengjin Lake coincide with the disappearance of their submerged macrophyte food plants, possibly as a result of eutrophication since the mid‐2000s.
• 5. Widespread declines and concentration of tuber‐eating wintering waterbirds at other sites elsewhere in the Yangtze floodplain may also reflect the local collapse of submerged macrophytes and of ecosystem services that these wetlands provide to the human communities. Copyright © 2010 John Wiley & Sons, Ltd.