Evaluation of the Egg Bank of Two Small Himalayan Lakes

Hydrobiologia, 2004

We studied the egg banks of Daphnia gr. longispina in four acidified lakes in the Bohemian Forest (Czech Republic, Europe). Daphnia had become extinct in three of the studied lakes due to anthropogenic acidification and we assessed the possibility of autochthonous recovery of the population after recent amelioration of the lake environment. We determined the ephippia distribution in eleven cores 10–30 cm long, and the state of Daphnia resting eggs in over 13 000 ephippia from eight cores. Apparently well-preserved eggs were used for hatching experiments and for DNA amplification. Vertical profiles of ephippia densities in several cores did not agree with historical data on the Daphnia presence in the lakes, as the sediment had been repeatedly disturbed by human activities in the past. Ephippia are present near the surface of the sediment in all lakes, and they might therefore receive hatching cues. We were not able, however, to prove that viable eggs are present in the ephippia banks of the lakes. The percentage of the well-preserved eggs in all but one core was below 1%. In addition, no egg hatched in the hatching experiments and we were not able to amplify DNA from the preserved eggs of lakes where Daphnia is extinct, although amplification from relatively young eggs from the fourth lake was successful in 60% of the cases. We conclude that the recovery of Daphnia populations in studied lakes from autochthonous sources is unlikely.

We report here the results of four scientific expeditions in the Nepalese Himalayas, that were carried out in the period 1992-1997, in the framework of a Project on "The Long Distance transport of micro-pollutants" . Logistic and technical support was given by a laboratory located at 5050 m a.s.l. Phytoplankton, zooplankton and macrozoobenthos were collected from a total of 28 lakes, at altitudes between 4532 and 5580 m a.s.l. Very few phytoplankton species were found in high numbers. As expected, no phytoplankton communities nor algal species characteristic of high altitude sites were found, being in general high mountain environments characterized by a rarefaction of the communities with respect to low altitude sites. We found low chlorophyll-a and biomass values, with a high contribution by small species. Data from the intensive sampling of Lake Piramide Inferiore in late summer 1993, suggest that net phytoplankton was at that time of the year already in a declining phase. An intense growth had probably occurred earlier in the season, possibly just after the icemelting. We identified 9 species of Crustacea and 8 of Rotifera from the 26 lakes sampled for zooplankton. The most widely distributed was an endemic, well-known diaptomid of the palaeoarctic genus Arctodiaptomus (Arctodiaptomus jurisovitchi). Daphniidae were represented by the dark-brown Daphnia tibetana and Simocephalus vetulus, and a pale Daphnia of the longispina group. A melanic Chydorus sphaericus was also widely distributed, with both parthenogenetic and ephippial females, as well as males. Rotifers were found in high numbers in lakes of the western side of the Region, with both genuine high mountain species, (Hexarthra bulgarica var. nepalensis, Filinia maior), as well as the colonial Conochilus unicornis, never reported before. Anostraca, recovered from the littorals of two lakes, were identified as Branchinecta orientalis. We also counted the thecamoebian species occasionally found in some zooplankton samples. Three chironomid genera (Pseudodiamesa, Orthocladius and Micropsectra) and oligochaetes dominated the communities of the nine examined lakes. We found two species of Diamesinae, already reported from the Region, and two larval forms of Micropsectra. All the genera of Orthocladiinae previously recorded in the Region, were present, namely, larvae and pupae of Cricotopus, as well as Acricotopus and Pseudosmittia. In most lakes Oligochaeta were represented by Lumbriculidae. Enchytraeidae and a Tubificid species, probably belonging to Rhyacodrilus cf. stephensoni, were also recovered from the littoral of some lakes.

Journal of Limnology, 2014

We investigated 2500 years of community succession in Cladocera from the sediments of a mountain lake (Lake Piramide Inferiore) located in the Khumbu Valley close to Mt. Everest in the Nepalese Himalayas. Our objective was to determine late Holocene changes in cladoceran species composition and abundance in a biogeographical context and with respect to previous proxy-based paleolimnological data (algal pigments and organic content). The results suggested that cladoceran fauna of Lake Piramide Inferiore was speciespoor and dominated by Chydorus cf. sphaericus throughout the sequence. The sediment profile recorded the occurrence of Alona guttata type individuals, which were attributed to Alona werestschagini Sinev 1999 based on their morphology and the species' current distributional range, and this was the first record of its presence in the Himalayas. In addition, a periodic long-term succession of melanic Daphnia (Ctenodaphnia) fusca Gurney, 1907 and non-melanic D. (Daphnia) dentifera Forbes 1893 was observed in the sediments. The millennia-long cladoceran community changes, although subtle due to the C. cf. sphaericus dominance, were in general agreement with the previous proxy-data of lake productivity following the regional paleoclimatic development and apparently partly driven by bottomup mechanisms. The periodic occurrence and success of D. fusca and D. dentifera throughout the late Holocene in Lake Piramide Inferiore, combined with the knowledge of their phenotypic properties (i.e., carapace melanization) and previous investigations on their contemporary and past distribution in Khumbu Valley, suggested that they may have responded to altered underwater UV radiation regimes. Furthermore, they may have even periodically excluded each other subsequent to changes in the underwater UV environment. The results indicated the usefulness of fossil cladoceran analysis as a tool in biogeographical research, since the occurrence of species in space and time can be observed through sediment records and taxonomic identity of the remains may be resolved with the help of regional faunal distribution.

Journal of Experimental Marine Biology and Ecology, 2006

Here we present a quantitative study on the density, age and viability of the diapausing egg banks of the rotifer species complex Brachionus plicatilis in the sediments of 15 water bodies from Eastern Spain. Sampled ponds, located in coastal and inland areas, varied in salinity and ranged in size, depth and permanence. By identifying 'hatched', 'deteriorated' and 'viable' diapausing eggs in the sediment samples, we estimated production, hatching and deterioration in relation to the habitat properties of each pond. Our results indicate the presence of large numbers of diapausing eggs in the sediments of almost all of the ponds studied (2-115 eggs cm − 2 ). Inland ponds tended to have higher densities than coastal lagoons. The vertical distribution of eggs in the sediments frequently showed a non-decreasing pattern, which suggested a high among-year variation in egg production. Despite maximum age of eggs of 60-80 years, the median age (3-30 years) suggests that rotifer egg banks are young in the studied ponds. Egg senescence is suggested by the declining abundance of 'healthy-looking' eggs with depth. The proportion of 'deteriorated' eggs ranged 75-99% suggesting that deterioration rates in the sediments are high and vary among habitats. Hatching and deterioration rates, as estimated from the counts of 'hatched', 'deteriorated' and 'healthy-looking' eggs in the sediments, largely varied among ponds. An association between hatching and deterioration rates is suggested by our data. This is in agreement with the hypothesis that hatching rates of diapausing eggs depended not only on the risks associated with the water column, as initially expected by the general theory on diapause, but they are also related to the incidence of deterioration processes in the sediment.

CHIRONOMUS Journal of Chironomidae Research, 2012

Chironomid head capsules were identified from sediment cores taken from Lake Gokyo (4750 m) and Lake Gosaikunda (4350 m) in the east-central Himalaya, to determine taxonomic composition of chironomid assemblages over time. The sedimentation rate of Lake Gosaikunda was estimated at 0.05 cm/yr and that of Gokyo was estimated at 0.07 cm/yr by 210 Pb and 137 Cs dating. Micropsectra sp. was dominant in the sediments of both lakes. Lake Gokyo sediments also contained Pseudodiamesa sp., Eukiefferiella/Tvetenia sp., Orthocladius/Cricotopus sp. and Rheocricotopus sp. The concentration of headcapsules was nearly an order of magnitude greater in the Lake Gosaikunda core, which contained mostly Micropsectra sp. and Pseudodiamesa sp. These taxa are typical of cold oligotrophic lakes. Differences in lake depth, dissolved minerals, plus epi-and hypolimnetic temperature and dissolved oxygen suggest that stratification and temperature-induced increases in primary production may affect chironomid assemblages in these pristine lakes. Palaeolimnological studies of Himalayan lakes should include replicate cores within lake, to increase headcapsule sample sizes given potentially high rates of sedimentation from glacial runoff.

Hydrobiologia

Global environmental change has affected aquatic ecosystems of the southeast Tibetan Plateau during the past 200 years, altering the composition and biomass of primary producers (e.g. algae). However, the response of primary consumers (e.g. cladocerans) to this recent environmental forcing is not well documented. Cladoceran remains from a small, remote alpine lake (Moon Lake) in Sichuan Province (SW China). Samples from sediment traps (1-yr deployment), surface sediments covering a range of water depths and a short 22.5-cm sediment core were analysed. Littoral forms, notably Chydorus sphaericus and Acroperus harpae, together with Daphnia pulex dominated the cladoceran community. Remains of these cladocerans were well represented in the sediment core assemblages as indicated by their relative abundance in the surface sample. There was a marked increase in the abundance of D. pulex and total cladoceran fluxes in the sediment core from ca. 1880 AD, coinciding with the changes in diatom assemblages and pigments. Analysis of the multi-proxy data (cladocerans, diatom, pigment, total organic carbon, C/N ratio, air temperature and atmospheric NO 3 records) suggest that both direct and indirect climatic forcing, coupled with enhanced nutrient supply (e.g. NO 3 deposition) effects on primary producers have changed cladoceran community dynamics in Moon Lake over the last ~200 years.

Hydrobiologia

Using a sediment core covering the last 3,500 years, we analysed photosynthetic pigments' concentrations in lake sediments and carbon stable isotopic composition of chironomid (Diptera, Chironomidae) remains (d 13 C HC). We aimed to reconstruct temporal changes in aquatic primary productivity and carbon resources sustaining chironomid larvae in a high mountain lake (Lake Pyramid Inferior; 5,067 m a.s.l.) located in the Nepalese Himalayas. Both pigments and d 13 C HC trends followed a similar fluctuating pattern over time, and we found significant positive relationships between these proxies, suggesting the strong reliance of benthic consumers on the aquatic primary production. Temporal trends matched well with main known climatic phases in the Eastern part of the Himalayan Mountains. Past glacier dynamics and associated in-lake solute concentrations appeared to be the main driver of autochthonous primary productivity, suggesting then the indirect impact of climate change on carbon processing in the benthic food web. During warm periods, the glacier retreat induced a rise in in-lake solute concentrations leading to an increasing primary productivity. Complementary investigations are still needed to strengthen our understanding about the response of past aquatic carbon cycling in CO 2-limiting environments.

Journal of Limnology, 2016

Despite their ecological importance and rapid response to environmental changes, rotifers are rarely included in palaeolimnological studies. Here, we describe changes in abundance (ABD) and morphotype (MTs) diversity of rotifer resting eggs in the sediments of deep subalpine Lake Orta, Italy, covering a period prior to (pre-) 1926, during long-term ammonia and metal pollution from a rayon factory, and subsequent recovery of water quality. Following the pollution and bacterial oxidation of the ammonia, Lake Orta became the largest and deepest acid lake in Europe. Recovery of water quality followed both a ban on the discharge of industrial wastes, and a liming intervention in 1989 and 1990. We sectioned a sediment core collected from the deepest part of the lake (ORTA 07/2A) to provide a high time resolution, given the ca. 3-4 y cm-1 of sediment accumulation. Rotifer resting egg abundance and morphotypes were examined from the sediments and compared to limnological variables indicating the pollution. Rotifer resting egg abundance significantly increased with lake contamination (r=0.609 and-0.624 for copper and pH, respectively; P<0.001; n=27). A lake-water copper concentration threshold of ca. 40 µg L-1 discriminated among pre-, during-, and post-pollution compositions of the rotifer morphotype assemblages. Diversity and morphotype richness increased during the recovery from copper pollution and with complete restoration from acidity, while abundance increased during pollution. The persistence of presumably viable Brachionus resting eggs and of hatched egg cases during the heavy pollution phase suggests that, unlike most other organisms, which were extirpated by the pollution of the lake, rotifers survived producing resting eggs, which secured future generations.

Saline Systems, 2009

The cyst banks of 6 coastal hypersaline lakes of South-East Europe have been investigated. The study concerned the bottom sediments of Khersonesskoe and Koyashskoe lakes in the Crimea (Ukraine), Nartë saltworks (Albania), Vecchia Salina at Torre Colimena (Apulia, Italy), Pantano Grande and Pantano Roveto at Vendicari (Sicily, Italy). A total of 19 cyst types were recognised. The cyst banks of lakes were found to be well separated in the representation derived from a statistical multivariate data analysis. For all the lakes examined a comparison was possible between the resting community in sediments (cyst bank) and the active one in the water. The cyst banks contained more species than those recorded over a multi-year sampling effort in the water column. The study of cyst hatching, performed on 5 cyst types under lab conditions, demonstrated that cysts do not hatch under the same conditions. Furthermore, each cyst type shows a wide range of preferential hatching conditions, which allow us to confirm the ecological generalism of salt lake species.

Freshwater Biology, 2006

1. Planktonic rotifers inhabiting variable environments produce diapausing eggs that accumulate in the sediment of lakes and ponds, forming egg banks that may withstand adverse periods. A common assumption in zooplankton diapausing egg bank studies is to count as viable all eggs in the sediment that look healthy. This assumption should be challenged by asking how effectively ‘healthy-looking’ eggs represent viable eggs.2. In this study, viability of more than 1100 ‘healthy-looking’ diapausing eggs belonging to the Brachionus plicatilis species complex was assessed in a laboratory hatching experiment. Eggs were collected at different depths from sediment cores obtained from 15 ponds located in coastal and inland areas of Eastern Spain.3. Only approximately one half of the ‘healthy-looking’ diapausing eggs hatched after incubation in experimental conditions. Almost all the hatchlings (99.4%) survived to maturity. The proportion of ‘healthy-looking’ diapausing eggs that hatched varied among areas and among ponds within area, and substantially declined with sediment depth. Most of the hatchlings (88%) were obtained from the uppermost 2 cm of sediment. ‘Healthy-looking’ eggs from upper sediment layers hatched after significantly shorter incubation times than eggs recovered from deeper layers.4. Both decreased hatching success and increased incubation time for hatching with sediment depth suggest that older ‘healthy-looking’ eggs are less responsive to hatching stimuli and could become unviable. However, the strong correlation found between the number of ‘healthy-looking’ eggs and the number of hatchlings indicates that the abundance of ‘healthy-looking’ eggs is a good index of egg bank viability.