In order to predict which species can successfully cope with global warming and how other environmental stressors modulate their vulnerability to climate‐related environmental factors, an ...understanding of the ecophysiology underpinning thermal limits is essential for both conservation biology and invasion biology.
Heat tolerance and the extent to which heat tolerance differed with oxygen availability were examined for four native and four alien freshwater peracarid crustacean species, with differences in habitat use across species. Three hypotheses were tested: (1) Heat and lack of oxygen synergistically reduce survival of species; (2) patterns in heat tolerance and the modulation thereof by oxygen differ between alien and native species and between species with different habitat use; (3) small animals can better tolerate heat than large animals, and this difference is more pronounced under hypoxia.
To assess heat tolerances under different oxygen levels, animal survival was monitored in experimental chambers in which the water temperature was ramped up (0.25°C min−1). Heat tolerance (CTmax) was scored as the cessation of all pleopod movement, and heating trials were performed under hypoxia (5 kPa oxygen), normoxia (20 kPa) and hyperoxia (60 kPa).
Heat tolerance differed across species as did the extent by which heat tolerance was affected by oxygen conditions. Heat‐tolerant species, for example, Asellus aquaticus and Crangonyx pseudogracilis, showed little response to oxygen conditions in their CTmax, whereas the CTmax of heat‐sensitive species, for example, Dikerogammarus villosus and Gammarus fossarum, was more plastic, being increased by hyperoxia and reduced by hypoxia.
In contrast to other studies on crustaceans, alien species were not more heat‐tolerant than native species. Instead, differences in heat tolerance were best explained by habitat use, with species from standing waters being heat tolerant and species from running waters being heat sensitive. In addition, larger animals displayed lower critical maximum temperature, but only under hypoxia. An analysis of data available in the literature on metabolic responses of the study species to temperature and oxygen conditions suggests that oxygen conformers and species whose oxygen demand rapidly increases with temperature (low activation energy) may be more heat sensitive.
The alien species D. villosus appeared most susceptible to hypoxia and heat stress. This may explain why this species is very successful in colonizing new areas in littoral zones with rocky substrate which are well aerated due to continuous wave action generated by passing ships or prevailing winds. This species is less capable of spreading to other waters which are poorly oxygenated and where C. pseudogracilis is the more likely dominant alien species.
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Nymphaeid macrophytes, rooting in the sediment of water bodies and characterized by floating leaves, play an important role in wetland ecosystems. The present research deals with the effects of ...limited space, limited nutrient availability, water temperature and an unexpected inundation on the production, turnover and plasticity of floating leaves of the globally widespread species
(Fringed waterlily).
The effects of these environmental conditions were studied in two plots in outdoor concrete tanks (CT1, CT2, mesocosms simulating occurrence in small ponds) and in two plots in the floodplain oxbow lake Bemmelse Strang (BS1, BS2). Plot CT1 was situated in a stand coexisting with helophytes, plot CT2 in a monospecific stand, plot BS1 in the center and plot BS2 at the open water border of a monospecific stand. All floating leaf blades within the plots were marked at appearance at the water surface and subsequently length, width and damage of each leaf and maximum and minimum water temperatures were measured bi-weekly. Area and biomass of leaf blades were calculated based on leaf length and width and were used to calculate turnover rates and production.
The growth period started in May and ended mid-October with continuous production of floating leaves during nearly the whole vegetation period. In the tanks the water level was very stable, but the lake underwent an inundation by river water, causing a sudden loss of existing leaves. Considering environmental conditions and based on the assumed ranking from low to high nutrient availability, the ranking of the plots was CT1, CT2, BS1, BS2. This order was found for maximum leaf life span and maximum leaf length, and the reverse order was found for number of leaves, new leaves per day and duration of the vegetation period. Turnover rates appeared to be relatively similar for plots CT1, CT2 and BS1, but for the deeper border plot BS2 lower ratios were found. These results indicate that increased enclosure with expected nutrient limitation causes (1) the production of high numbers of small leaves with larger totals for leaf area and biomass, (2) a shift towards increased sexual reproduction by the production of more flowering stem leaves.
► We investigated how macrophytes influence macroinvertebrate communities, which is useful for predicting overall biodiversity. ► The data presented show interesting results with respect to presence ...and growth form of the macrophytes within a single aquatic system. ► Previous studies often used artificial structures/plants in waters with different physic-chemical conditions making comparisons difficult. ► This study employed an alternative approach to minimise variation due to season, physico-chemical conditions and spatial variation.
Multivariate analysis demonstrated that macroinvertebrate assemblages of macrophyte-dominated sub-habitats within a small eutrophic pond differed markedly from those of Bottom substrate and Open water habitats. Certain habitats (e.g. Nymphaea and Phragmites) appeared to be quite similar in their macroinvertebrate communities, whereas others appeared to be very distinct in terms of the species composition (e.g. Open water habitat). Analysis of functional feeding groups also revealed differences between habitats in terms of the community structure. Again, the Open water habitat exhibiting the most marked difference. Macrophyte growth form does not cause significant differences in macroinvertebrate species richness and diversity but it has a significant effect on macroinvertebrate abundance. Habitats consisting of highly branched and dissected macrophyte growth forms provide more food resources and microhabitats supporting larger numbers of macroinvertebrates than macrophytes with firm undissected stalks and leaves. This study highlights the importance of maintaining the ecological quality of small freshwater habitats in order to promote macrophyte growth and thus maintain a high level of species richness within such ecosystems.
Aim: Patterns of high biodiversity among less mobile organisms throughout isolated locations suggest that passive dispersal importantly contributes to biodiversity. We examined the contribution of ...waterbirds to the dispersal of plant seeds and macroinvertebrates between aquatic wetlands. Birds are renowned vectors for seeds of terrestrial plants, but less is known about their role in more dispersal-dependent aquatic systems. We therefore performed a meta-analysis on bird-mediated endozoochorous dispersal of aquatic species. Location: Our review included studies that collected data world-wide. Methods: We analysed data from 81 peer-reviewed publications on endozoochorous dispersal of aquatic plant seeds and macroinvertebrates by waterbirds. Results: In total, 36% of 1581 waterbird droppings collected in the field contained one or more intact propagules, with macroinvertebrates found almost as frequently as plant seeds. Positive droppings contained on average 3.3 intact propagules, of which one-third were viable. In 728 trials from 17 published feeding experiments 24% of the ingested propagules were retrieved intact, with c. 6.5% both viable and intact. As many as 17 species of Anatidae and Rallidae were involved in the dispersal of at least 39 species of macroinvertebrates and seeds from 97 species of plants across a wide taxonomic range. Smaller propagules seemed less affected by digestion than larger ones. We provide a first quantitative model that can be used to estimate waterbird-mediated dispersal of propagules between wetlands. This model indicates that an average waterbird has the potential to disperse five viable propagules after flying more than 100 km, and one additional propagule after flying 300 km. Main conclusions: We demonstrate that waterbirds have the potential to transport a wide variety of aquatic plants and animals over several hundreds of kilometres. High survival of propagules might be explained by propagule adaptations or by the digestive adaptations of birds, whereby energy absorption is thought to be maximized rather than assimilation efficiency. Our meta-analysis suggests that waterbirds might contribute significantly to wetland biodiversity around the world, despite several limitations to our current knowledge. We outline avenues for future research to address these knowledge gaps.
The Asian cyprinid
Pseudorasbora parva
is considered to be a major threat to native fish communities and listed as an invasive alien species of European Union concern. Our study aims to gain ...evidence-based knowledge on the impact of both
P. parva
and its parasite
Sphaerothecum destruens
on native fish populations by analysing fish assemblages and body condition of individuals of native fish species in floodplain water bodies that were invaded and uninvaded by
P
.
parva
. We explored the use of environmental DNA (eDNA) techniques to detect
S. destruens
. Prevalence of
S. destruens
in native fish species was assessed. Fish samplings showed significantly negative correlations between the abundance of
P. parva
and the native
Leucaspius delineatus
, and
Pungitius pungitius
and three biodiversity indices of the fish assemblages (Simpson’s diversity index, Shannon–Wiener index and evenness). Contrastingly, the abundances of the native
Gasterosteus aculeatus
and
P. parva
were positively related. In nearly all isolated water bodies with
P. parva
, this species is outnumbering native fish species. No effect of
P. parva
presence was found on body condition of native fish species.
Sphaerothecum destruens
was demonstrated to occur in both
P. parva
and
G. aculeatus
.
Gasterosteus aculeatus
is suggested to be an asymptomatic carrier that can aid the further spread of
S. destruens.
Analysis of eDNA proved to be a promising method for early detection of
S. destruens
, here showing that
S. destruens
presence coincided with
P. parva
presence. The ongoing invasion of both
P. parva
and
S. destruens
is predicted to pose a significant risk to native fish communities.
The initial decomposition of large floating-leaved macrophytes, such as waterlilies, can be studied by following changes in leaf damage and area loss of leaf blades tagged in their natural ...environment. This approach was taken in the present study to examine the initial decomposition patterns of floating leaf blades of
(L.) Sm.,
L. and
C. Presl at three freshwater sites differing in nutrient status, alkalinity and pH. Floating leaf blades of the three plant species were tagged and numbered within established replicate plots and the leaf length, percentages and types of damage and decay of all tagged leaves were recorded weekly during the growing season. Microbial decay, infection by phytopathogenic fungi (
) and oomycetes (
sp.), consumption by pond snails, and mechanical factors were the most important causes of leaf damage. Several types of succession comprising different causes of damage were distinguished during the season. For example, young floating leaves are affected by more or less specialized invertebrate species consuming leaf tissue, followed by non-specialized invertebrate species feeding on the damaged floating leaves. In the two investigated hardwater lakes the seasonal patterns of initial decomposition differed between
and
.
Floating leaf blades of waterlilies fulfill several functions in wetland ecosystems by production, decomposition and turnover as well as exchange processes. Production and turnover rates of floating ...leaf blades of three waterlily species,
(L.) Sm.,
L. and
Presl, were studied in three freshwater bodies, differing in trophic status, pH and alkalinity. Length and percentages of leaf loss of marked leaf blades were measured weekly during the growing season. Area and biomass were calculated based on leaf length and were used to calculate the turnover rate of floating leaf blades. Seasonal changes in floating leaf production showed that values decreased in the order:
,
,
. The highest production was reached for
and
in alkaline, eutrophic water bodies. The production per leaf was relatively high for both species in the acid water body.
showed a very short vegetation period and low turnover rates. The ratio Total potential leaf biomass/Maximum potential leaf biomass (P/B
) of the three species ranged from 1.35-2.25. The ratio Vegetation period (Period with floating leaves)/Mean leaf life span ranged from 2.94-4.63, the ratio Growth period (Period with appearance of new floating leaves)/Vegetation period from 0.53-0.73. The clear differences between
versus
and
, may be due to adaptations of
to an Euro-Siberic climate with short-lasting summer conditions.
Stable isotope analysis of soft bodies of the shipworm Teredo navalis demonstrated that this species is mainly feeding on seston by filter feeding in contrast to wood consumption. T. navalis showed ...similar stable isotope values (δ13C, δ15N) as Mytilus edulis and Crassostrea gigas, which species were attached to the wood instead of boring into.
•We compared δ13C and δ15N values of shipworm, Blue mussel, Pacific oyster and wood.•Values of shipworm, mussel, oyster were much higher than those of wood.•Values of the shipworm closely resembled the values of mussel and oyster.•Food obtained by filter feeding is the main source of C and N for the shipworm.•Teredo navalis drills in wood for shelter rather than food.
Kees den Hartog, born in Den Helder (The Netherlands), with artistic bow tie, was a versatile aquatic ecologist. He became appointed in 1970 as extra ordinary professor in botany and general ecology ...at the Vrije Universiteit Brussel (Belgium) and in 1973 as professor in the aquatic ecology at the Universities of Nijmegen and Wageningen (The Netherlands). Kees den Hartog and his Laboratory of Aquatic Ecology made important and famous contributions to the knowledge of aquatic ecosystems dominated by macrophytes. According to Kees den Hartog, the study of these macrophyte-dominated ecosystems was incomplete if it did not include other organisms such as macroinvertebrates and fish.
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