Freshwater rock pools: a review of habitat characteristics,faunal diversity and conservation value

1. In the light of the recent surge of interest in small and often temporary wetlands as model systems for ecological and evolutionary research, this article reviews current knowledge on freshwater rock pools and their fauna. 2. Freshwater rock pools occur all over the globe in all major biomes and depend mainly on precipitation for filling. Rock pool clusters are some of the more persistent and oldest freshwater habitats worldwide. Interactions between climate and geology (e.g. limestone, sandstone, granite) generally determine the morphology and hydrology of rock pool habitats, with hydroperiods ranging from several days up to the whole year. Pool volume is usually small, resulting in strongly fluctuating environmental conditions, low conductivity and wide variations in pH (from 4.0 to 11.0) and temperature (from freezing point to 40 °C) often with well‐marked diel cycles. The highly variable environmental conditions, combined with the unpredictability of the flooding regime, require high stress tolerance of the inhabitants, with adaptations for surviving the dry phase such as the production of resistant stages and active emigration followed by recolonisation. 3. About 460 aquatic animal species have been recorded from freshwater rock pools around the world. Approximately 170 of these are passive dispersers, which mainly disperse as resting stages via wind and overflow of water between pools. Successful long distance dispersal seems limited. This group is composed mainly of rock pool specialists with a high degree of endemicity. The remaining taxa can be considered active dispersers, with migration usually restricted to the adult stage. Often these taxa are broadly distributed and occur in a wide range of temporary habitats in addition to rock pools. 4. The inherent characteristics of freshwater rock pools, such as their simple structure and occurrence on similar substrata all over the world, facilitate comparison of research results and promote rock pools as model systems for ecological and evolutionary research. Nevertheless, despite their potential as model systems, the unique fauna and their importance as sources of freshwater in dry countries, the ecology of freshwater rock pools remain virtually unexplored in large parts of the world.     

Breeding habitat selection and larval performance of two anurans in freshwater rock-pools

I studied breeding habitat choice of common toad Bufo bufo and common frog Rana temporaria in 221 freshwater rock-pools on 15 small islands in the southwestern coast of Finland. I monitored tadpole growth rate in a number of rock-pools differing in size, competitors and predator regime. Furthermore, I carried out a short-term field experiment to investigate the effects of different predators on larval survival. Rana bred in pools of virtually all sizes, although the very smallest ones were usually avoided. A logistic regression analysis showed that the amount of aquatic macrophyte vegetation and pool surface area were the most important pool characters for Rana. Bufo preferred the largest pools, and pool surface area was by far the most important habitat variable. Rana avoided pools with the lowest pH. but was more common than expected at pools with pH around 6. In Bufo such an effect was not found, but this may be due to relatively low number of pools occupied by Bufo. In Rana there was a positive correlation between pool area and tadpole body length in early June, but two weeks later this relationship was not significant. In Bufo tadpole body size was not significantly affected by pool area. Presence of predators or presence of the other tadpole species did not affect growth or tadpole body size in either Rana or Bufo. A short-term experiment in wading pools indicated that both species suffered heavy mortality in the presence of a diving beetle larva. In the presence of predatory fish, mortality of Bufo did not differ from controls, whereas mortality was high among Rana tadpoles. It appears that although predators prey heavily on Rana tadpoles, they do not exclude Rana from larger rock-pools. However, it is not evident from this study why Bufo avoids smaller pools.     

Diet of coastal foraging Eurasian otters (<Emphasis Type="Italic">Lutra lutra</Emphasis> L.) in Pembrokeshire south-west Wales

The importance of the marine environment to Eurasian otters is currently poorly understood. Wales is one of the few countries where coastal activity has been recorded and an increase in marine otter sightings could indicate remarkable developments within Welsh populations. The trophic niche of coastal otter populations around Pembrokeshire was investigated over a 12-month period. Marine activity was more widespread than previously thought and marine prey formed the largest component of otter diet, although, otters also consumed freshwater and terrestrial prey throughout the year. Otter diet was very diverse compared to other European coastal populations and a spring contraction in trophic niche width coincided with the estimated timing of breeding activity. Seasonal variation in prey composition was predominantly due to differences in the consumption of alternate prey types. In areas where wetlands are fragmented and populations of freshwater fish are declining, the marine environment may become an increasingly important habitat for otters. It is necessary to define the historical importance of coastal populations to otter conservation. Coastal areas are often subject to pressure from human activities, so the impact of disturbance needs to be assessed. Importantly, there is no verified otter survey method for coastal areas, so the use of marine habitat is likely to be underestimated.     

Diet of otters (Lutra lutra) in closely associated freshwater, brackish and marine habitats in south-west Portugal

The diet of otters was studied in closely associated freshwater, brackish and marine habitats, from spraints collected on the Portuguese south-west coast over an 18-month period. In areas where marine prey was the only available resource, diet was dominated by blennies, wrasses and gobies, but other prey was taken in areas near coastal lagoons, marshes and estuaries. Eels and amphibians were considered the typical prey of freshwater habitats, and grey mullet the typical prey of brackish water habitats. If the inland habitats near the coast were large enough, otters preferred to forage there rather than in the sea. In one area where otters alternatively used marine and inland habitats, the former were used most extensively in autumn and winter, and the latter in spring and summer. It is suggested that otters prefer to forage inland rather than in the sea.     

The Restoration Gene Pool Concept: Beyond the Native Versus Non-Native Debate

Abstract Restoration practitioners have long been faced with a dichotomous choice of native versus introduced plant material confounded by a general lack of consensus concerning what constitutes being native. The “restoration gene pool” concept assigns plant materials to one of four restoration gene pools (primary to quaternary) in order of declining genetic correspondence to the target population. Adaptation is decoupled from genetic identity because they often do not correspond, particularly if ecosystem function of the disturbed site has been altered. Because use of plant material with highest genetic identity, that is, the primary restoration gene pool, may not be ultimately successful, material of higher order pools may be substituted. This decision can be made individually for each plant species in the restored plant community in the scientific context that ecosystem management demands. The restoration gene pool concept provides a place for cultivars of native species and noninvasive introduced plant material when use of native‐site material is not feasible. The use of metapopulation polycrosses or composites and multiple‐origin polycrosses or composites is encouraged as appropriate. The restoration gene pool concept can be implemented as a hierarchical decision‐support tool within the larger context of planning seedings.     

Effects of freshwater availability on the summer distribution of otters Lutra lutra in the southwest coast of Portugal

The availability of freshwater has been suggested to strongly influence the distribution of coastal otters Lutra lutra The test this hypothesis, a study was undertaken on the relationships between otter distribution and freshwater availability in a coast where freshwater is a very scarce resource during the summer In this area otters occur mostly in a few small coastal streams but feed largely in the sea Twentynine streams were surveyed in the summer of 1990, and the presence/absence of otter signs was related to nine habitat variables Freshwater availability was found to be the most important factor influencing the occurrence of otters in summer It is suggested that otters favour large streams with good vegetation cover, for these are the most likely to maintain frestwater during the dry periods The distribution of otter signs m streams was also analysed, and it was found that signs tend to concentrate particularly near the mouth of the streams This habitat analysis has some conservation implications, indicating that the decrease of freshwater availability or quality of streams can make these unsuitable for otters, severely decreasing the areas suitable for the species in the southwest coast of Portugal     

Genetic structure of the date palm (Phoenix dactylifera) in the Old World reveals a strong differentiation between eastern and western populations

Background and Aims Rock pools are small, geologically stable freshwater ecosystems that are both hydrologically and biologically isolated. They harbour high levels of plant endemism and experience environmental unpredictability driven by the presence of water over variable temporal scales. This study examined the hypothesis that the sediment seed bank in monsoon tropical freshwater rock pools would persist through one or more periods of desiccation, with seed dormancy regulating germination timing in response to rock pool inundation and drying events.Methods Seeds were collected from seven dominant rock pool species, and germination biology and seed dormancy were assessed under laboratory conditions in response to light, temperature and germination stimulators (gibberellic acid, karrikinolide and ethylene). Field surveys of seedling emergence from freshwater rock pools in the Kimberley region of Western Australia were undertaken, and sediment samples were collected from 41 vegetated rock pools. Seedling emergence and seed bank persistence in response to multiple wetting and drying cycles were determined.Key Results The sediment seed bank of individual rock pools was large (13 824 ± 307 to 218 320 ± 42 412 seeds m⁻² for the five species investigated) and spatially variable. Seedling density for these same species in the field ranged from 13 696 to 87 232 seedlings m⁻². Seeds of rock pool taxa were physiologically dormant, with germination promoted by after-ripening and exposure to ethylene or karrikinolide. Patterns of seedling emergence varied between species and were finely tuned to seasonal temperature and moisture conditions, with the proportions of emergent seedlings differing between species through multiple inundation events. A viable seed bank persisted after ten consecutive laboratory inundation events, and seeds retained viability in dry sediments for at least 3 years.Conclusions The persistent seed bank in freshwater rock pools is likely to provide resilience to plant communities against environmental stochasticity. Since rock pool communities are often comprised of highly specialized endemic and range-restricted species, sediment seed banks may represent significant drivers of species persistence and diversification in these ecosystems.     

Diet composition of the Eurasian otter Lutra lutra in different freshwater habitats of temperate Europe: a review and meta‐analysis

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Richness and structure of plant communities in temporary pools from western Morocco: influence of human activities

Temporary pools are numerous in coastal plains of Atlantic Morocco and have a rich and diverse flora. These habitats are increasingly under pressure by man impact through grazing by domestic livestock and the development of annual crops in their catchments. The objectives of this work were to evaluate the species richness and the species composition of the vegetation of a sample of 30 pools in this region, in order to assess the structure of the vegetation within pools and to evaluate the role of environmental and anthropogenic factors in their richness and species composition. The results highlighted the species richness of the pools with 300 species found among which annual species were heavily dominant. The structure of the vegetation varied within pools according to a topographical/flooding gradient and between pools in relation with the land use in the surrounding areas. Three vegetation belts were recognized from the centre to the periphery of the pool. The total species richness per pool was not found significantly related to environmental or anthropogenic factors. The species characteristics of the pools were found mostly in the centre and their number affected by hydrological factors and land use in the pool and in the surrounding areas. The species characteristics of woodland habitats and of agriculture crops were found mostly in the peripheral zone. Temporary pools maintain specific communities of both aquatic and amphibious species, probably because of the selection induced by water level variations. The peripheral zone, although often dominated by terrestrial species, is clearly interpreted as part of the pool. It contains amphibious species highly characteristic of the pool for which the irregular flooding is a key environmental factor which decreases competition.     

Early life histories of three sympatric sticklebacks in a salt-marsh

The effects of abiotic factors (water level, temperature, dissolved oxygen and salinity) and interspecific competition on the survival and growth of early life stages of three sympatric sticklebacks, Gasterosteus aculeatus , G. wheallandi and Pungitius pungitius , were studied in salt-marsh tide pools near Isle Verte, Quebec. Significant year-to-year variation was observed in the percentage of live eggs per nest, egg incubation times, and the growth and condition of juveniles for all three species. These differences were associated with variations in temperature, oxygen and salinity in the pools. Comparisons of egg survival and juvenile growth rates were also made for G. aculeatus living in two contrasting habitats of the salt-marsh, the harsh and variable tide pools, and a less harsh, less variable freshwater site. Egg incubation times were longer, and the percentage of live eggs per nest lower, in the river than in the pools. However, river juveniles had higher growth rates and condition factors than pool juveniles. Results of experiments to study interspecific competition between juvenile G. aculaetus and juvenile G. wheatlandi were inconsistent, and it is suggested that the effects of abiotic factors on the survival and growth of early life stages in sticklebacks are more important than competition at this site.     

Evidence for a Novel Marine Harmful Algal Bloom: Cyanotoxin (Microcystin) Transfer from Land to Sea Otters

“Super-blooms” of cyanobacteria that produce potent and environmentally persistent biotoxins (microcystins) are an emerging global health issue in freshwater habitats. Monitoring of the marine environment for secondary impacts has been minimal, although microcystin-contaminated freshwater is known to be entering marine ecosystems. Here we confirm deaths of marine mammals from microcystin intoxication and provide evidence implicating land-sea flow with trophic transfer through marine invertebrates as the most likely route of exposure. This hypothesis was evaluated through environmental detection of potential freshwater and marine microcystin sources, sea otter necropsy with biochemical analysis of tissues and evaluation of bioaccumulation of freshwater microcystins by marine invertebrates. Ocean discharge of freshwater microcystins was confirmed for three nutrient-impaired rivers flowing into the Monterey Bay National Marine Sanctuary, and microcystin concentrations up to 2,900 ppm (2.9 million ppb) were detected in a freshwater lake and downstream tributaries to within 1 km of the ocean. Deaths of 21 southern sea otters, a federally listed threatened species, were linked to microcystin intoxication. Finally, farmed and free-living marine clams, mussels and oysters of species that are often consumed by sea otters and humans exhibited significant biomagnification (to 107 times ambient water levels) and slow depuration of freshwater cyanotoxins, suggesting a potentially serious environmental and public health threat that extends from the lowest trophic levels of nutrient-impaired freshwater habitat to apex marine predators. Microcystin-poisoned sea otters were commonly recovered near river mouths and harbors and contaminated marine bivalves were implicated as the most likely source of this potent hepatotoxin for wild otters. This is the first report of deaths of marine mammals due to cyanotoxins and confirms the existence of a novel class of marine “harmful algal bloom” in the Pacific coastal environment; that of hepatotoxic shellfish poisoning (HSP), suggesting that animals and humans are at risk from microcystin poisoning when consuming shellfish harvested at the land-sea interface.     

Divergence in parental care, habitat selection and larval life history between two species of Peruvian poison frogs: an experimental analysis

Changes in the nature of the ecological resources exploited by a species can lead to the evolution of novel suites of behaviours. We identified a case in which the transition from large pool use to the use of very small breeding pools in neotropical poison frogs (family Dendrobatidae) is associated with the evolution of a suite of behaviours, including biparental care (from uniparental care) and social monogamy (from promiscuity). We manipulated breeding pool size in order to demonstrate experimentally that breeding habitat selection strategy has evolved in concert with changes in parental care and mating system. We also manipulated intra- and interspecific larval interactions to demonstrate that larval adaptation to the use of very small pools for breeding affected the evolution of larval competition and cannibalism. Our results illustrate the intimate connection between breeding pool ecology, parental care and mating strategies in Peruvian poison frogs.     

Physical characteristics influencing the utilization of pools by brown trout in an afforested catchment in Southern Ireland

Seasonal and spatial variation in brown trout Salmo trutta L. abundance, density and biomass were studied in 29 pools of varying size in an afforested catchment together with the physical characteristics of those pools. A movement of 0+ trout towards the pools as the year progresses was detected. Water volume of the pool accounted for a significant amount of the variation in metrics across all seasons. Cover provided by overhanging vegetation also explained a significant amount of variation, especially during the summer. Water velocity, percentage of undercut bank and substrate composition had little explanatory power in the distribution of trout in the pools. In all seasons significant relationships between both fish biomass (g m⁻²) and fish number and water volume in the pool were found. However, in summer and autumn there was also a significant correlation between both fish density (fish m⁻²) and biomass and water volume in the pool described by a power function with a coefficient >1. These relationships were consistent across the subset of pools studied over a 2-year period. Thus there was a proportionally greater number of fish in deeper pools than in the shallower ones in summer and autumn, suggesting that trout use the available habitat (i.e. the pool) as a three dimensional space in which an increase in the third dimension (depth) leads to a proportionally greater number of fish per unit area.     

A captive behavioral enrichment study with Asian small-clawed river otters (Aonyx cinerea)

Asian small-clawed river otters (Aonyx cinerea) were given the opportunity to hunt for and capture live crickets (Acheta domestica) in a public interactive display. The otters learned the experimental routine during the first day of exposure. Different response levels were recorded at each of three capture sites, A, B, and C. The animals showed continued motivation for hunting despite the fact that there was no deprivation and the crickets represented an insignificant part of the diet. Besides live crickets, other items—cat food, dead crickets, and gelatin capsules—were introduced for five days each. The otters made the most captures per opportunity for live crickets, followed, in order of preference, by dead crickets, cat food, and gelatin capsules. Although gelatin capsules were found to be the least motivating prey item, the otters hunted for them whenever they were offered. Thus, any active opportunity to produce a change in their environment was rewarding to the otters.     

Transmission of Toxoplasma: clues from the study of sea otters as sentinels of Toxoplasma gondii flow into the marine environment

Toxoplasma gondii affects a wide variety of hosts including threatened southern sea otters (Enhydra lutris nereis) which serve as sentinels for the detection of the parasite's transmission into marine ecosystems. Toxoplasmosis is a major cause of mortality and contributor to the slow rate of population recovery for southern sea otters in California. An updated seroprevalence analysis showed that 52% of 305 freshly dead, beachcast sea otters and 38% of 257 live sea otters sampled along the California coast from 1998 to 2004 were infected with T. gondii. Areas with high T. gondii exposure were predominantly sandy bays near urban centres with freshwater runoff. Genotypic characterisation of 15 new T. gondii isolates obtained from otters in 2004 identified only X alleles at B1 and SAG1. A total of 38/50 or 72% of all otter isolates so far examined have been infected with a Type X strain. Type X isolates were also obtained from a Pacific harbor seal (Phoca vitulina) and California sea lion (Zalophus californianus). Molecular analysis using the C8 RAPD marker showed that the X isolates were more genetically heterogeneous than archetypal Type I, II and III genotypes of T. gondii. The origin and transmission of the Type X T. gondii genotype are not yet clear. Sea otters do not prey on known intermediate hosts for T. gondii and vertical transmission appears to play a minor role in maintaining infection in the populations. Therefore, the most likely source of infection is by infectious, environmentally resistant oocysts that are shed in the feces of felids and transported via freshwater runoff into the marine ecosystem. As nearshore predators, otters serve as sentinels of protozoal pathogen flow into the marine environment since they share the same environment and consume some of the same foods as humans. Investigation into the processes promoting T. gondii infections in sea otters will provide a better understanding of terrestrial parasite flow and the emergence of disease at the interface between wildlife, domestic animals and humans.     

A whole genome scan for quantitative trait loci affecting milk protein percentage in Israeli-Holstein cattle, by means of selective milk DNA pooling in a daughter design, using an adjusted false discovery rate criterion

Selective DNA pooling was employed in a daughter design to screen all bovine autosomes for quantitative trait loci (QTL) affecting estimated breeding value for milk protein percentage (EBVP%). Milk pools prepared from high and low daughters of each of seven sires were genotyped for 138 dinucleotide microsatellites. Shadow-corrected estimates of sire allele frequencies were compared between high and low pools. An adjusted false discovery rate (FDR) method was employed to calculate experimentwise significance levels and empirical power. Significant associations with milk protein percentage were found for 61 of the markers (adjusted FDR = 0.10; estimated power, 0.68). The significant markers appear to be linked to 19--28 QTL. Mean allele substitution effects of the putative QTL averaged 0.016 (0.009--0.028) in units of the within-sire family standard deviation of EBVP% and summed to 0.460 EBVP%. Overall QTL heterozygosity was 0.40. The identified QTL appear to account for all of the variation in EBVP% in the population. Through use of selective DNA pooling, 4400 pool data points provided the statistical power of 600,000 individual data points.     

Species richness and the proportion of predatory animal species in temporary freshwater pools: relationships with habitat size and permanence

The proportion of predatory animal species is often believed not to vary systematically across communities. However, we predict that larger temporary freshwater pools, and pools that are more permanent, will contain a higher proportion of predatory animal species. In 24 temporary rockpools in Northern Israel (supporting communities dominated by ostracods, copepods, cladocerans, flatworms, dipterans and amphibians), the mean proportion of macroscopic predatory species (averaged over a series of samples) increased with increasing pool area. For the highest possible proportion of predatory species (including microscopic species with uncertain diets), the relationship with pool area was not statistically significant. We did not find significant relationships between permanence and the proportion of either macroscopic or all possible predatory species. Larger pools and pools that were more permanent had more species. Species richness and the proportion of macroscopic predators were positively correlated. These patterns imply that species-poor ecosystems are likely to be functionally different from species-rich systems.     

Diet diversity and breeding of top predators are determined by habitat stability and structure: a case study with the Eurasian otter (<Emphasis Type="Italic">Lutra lutra</Emphasis> L.)

A study on Eurasian otter was conducted in order to establish if feeding ecology and breeding of this European freshwater top predator were affected by the habitat complexity or stability. The work was based on the comparison of contrasting environmental settings. Significant gradients were found for otter diet parameters and breeding, both also changing according to habitat gradient patterns (water capacity and permanence during droughts, habitat stability, and habitat complexity). The otter diet was less diverse in the most stable (and complex) habitats, eating more fish. Otters also breed more regularly in such more stable courses, with more suitable fish availability. The step toward lower habitat stability can put otters in a less advantageous position in front of generalist predators, foraging more frequently outside or in the edge of aquatic ecosystems. Implications for otters and other similar top predator’s conservation are discussed.