Mar Torralva

Understanding of the impact of chemicals on amphibians: a meta-analytic review

Many studies have assessed the impact of different pollutants on amphibians across a variety of experimental venues (laboratory, mesocosm, and enclosure conditions). Past reviews, using vote-counting methods, have described pollution as one of the major threats faced by amphibians. However, vote-counting methods lack strong statistical power, do not permit one to determine the magnitudes of effects, and do not compare responses among predefined groups. To address these challenges, we conducted a meta-analysis of experimental studies that measured the effects of different chemical pollutants (nitrogenous and phosphorous compounds, pesticides, road deicers, heavy metals, and other wastewater contaminants) at environmentally relevant concentrations on amphibian survival, mass, time to hatching, time to metamorphosis, and frequency of abnormalities. The overall effect size of pollutant exposure was a medium decrease in amphibian survival and mass and a large increase in abnormality frequency. This translates to a 14.3% decrease in survival, a 7.5% decrease in mass, and a 535% increase in abnormality frequency across all studies. In contrast, we found no overall effect of pollutants on time to hatching and time to metamorphosis. We also found that effect sizes differed among experimental venues and among types of pollutants, but we only detected weak differences among amphibian families. These results suggest that variation in sensitivity to contaminants is generally independent of phylogeny. Some publication bias (i.e., selective reporting) was detected, but only for mass and the interaction effect size among stressors. We conclude that the overall impact of pollution on amphibians is moderately to largely negative. This implies that pollutants at environmentally relevant concentrations pose an important threat to amphibians and may play a role in their present global decline.

Populational divergence in the impact of three nitrogenous compounds and their combination on larvae of the frog Pelophylax perezi (Seoane, 1885)

Pollution by nitrogenous compounds is a putative stressful factor that may be causally linked to the decline of amphibians. One way to understand the potentially detrimental consequences of eutrophication on amphibian populations is to investigate variation among populations differing in exposure to nitrogen, this variation potentially indicating evolutionary potential to cope with this stressor. We have examined the effect of nitrogenous compounds (NH(4)(+); NO(2)(-); NO(3)(-), both alone and in combination) on fitness-related larval traits in four populations of Pelophylax perezi naturally exposed to different degrees of eutrophication. The results indicate that both survival and larval final size decrease at higher concentrations of these compounds, either singly or in combination. Additionally, the nitrogenous compounds were more lethal and larval food consumption and final mass were significantly reduced when they were exposed to combinations of compounds. Populations inhabiting highly polluted aquatic environments tolerated higher levels of nitrogenous compounds and showed higher survival rates and larger final size than the populations of less polluted environments, suggesting the potential to adapt to increased nitrogenous contamination in this species.

Behavioral responses of the Iberian waterfrog, Pelophylax perezi (Seoane, 1885), to three nitrogenous compounds in laboratory conditions

Several studies have assessed the effects of nitrogenous compounds on amphibian behavior. However, few have focused on the effects of their combination with other stressors or on the variation of the response to pollutants among populations. We analyzed the effect of nitrogenous compounds (NH4+; NO2−; NO3−, both alone and in combination) on larval behavior (activity level and location in the water column) in four populations of Pelophylax perezi naturally exposed to different levels of eutrophication. Larval activity was highest and use of the bottom of the experimental beaker was lowest at lower concentrations of nitrogenous compounds acting singly, these responses being minimal and maximal, respectively, at both control and higher concentrations. This pattern appears to fit to an hormetic reponse. Additionally, the combination of nitrogenous compounds affected more severely the response variables than when ammonium or nitrite acted singly according to an additive model. Populations inhabiting highly polluted aquatic habitats marginally showed higher activity level than the populations from less polluted environments, especially when larvae were exposed to ammonium or when nitrite appeared in combination with other nitrogen forms. Levels of activity correlated positively with larval final mass. Moreover, for similar levels of activity, larvae from polluted populations had higher growth rates than those coming from reference populations which suggests interdemic differences in behavioral sensitivity to nitrogenous pollutants.

Breeding habitat selection of Salamandra salamandra (Linnaeus, 1758) in the most arid zone of its European distribution range: application to conservation management

The influence of environmental variables on the selection of a water body as breeding habitat by Salamandra salamandra was studied in an arid zone located in the southwestern part of its distribution range. From November 2002 to October 2003, 50 water bodies were monitored in the south east of the Iberian Peninsula. Environmental data were submitted to a stepwise logistic regression analysis at macrohabitat, water body typology and microhabitat scales in order to establish the main factors influencing the use of a given water body as breeding habitat by this species. A significant degree of dependence between the reproduction of Salamandra salamandra and environmental variables was observed at all of these levels. These results should be taken into account when populations of this species are subjected to management and/or recovery programmes in arid areas.

Assessing the nursery role for marine fish species in a hypersaline coastal lagoon (Mar Menor, Mediterranean Sea)

Abstract The shallow inshore areas of coastal lagoons function as nursery grounds for the early life stages of marine fish. Multi-species approaches and the assessment of several population variables are of great value in studies focused upon the ecological importance of estuarine systems as fish nursery areas. Therefore, the objective of this study was to analyse the spatial differences in the abundance, biomass, growth and condition indexes of juveniles from three marine species: Sparus aurata, Liza aurata and Liza ramada, in order to assess the nursery role of the Mar Menor coastal lagoon for these species. Results showed high spatial variability of the studied variables, with higher abundance and biomass values at those sites closest to the inlet connecting the lagoon with the Mediterranean Sea. Moreover, there were significant relationships between the growth and condition of the fish with hydrographical circulation patterns within the lagoon, indicating the suitability of the Mar Menor as a nursery area for the three studied fish species.

Biology of the endangered cyprinodontid Aphanius iberus in a saline wetland (SE Iberian Peninsula)

For the last few decades, Aphanius iberus, an endemic cyprinodontid from the Iberian Peninsula and included in international red lists, has been declining despite several management efforts. In this study we present the biology of the species in an isolated wetland managed for salt exploitation (its most common habitat type in the southeastern Iberian Peninsula). The population studied is found under conditions of extreme high salinity and water temperature. We have examined the effects of extractive management on catchability, population structure, growth and reproduction traits. The stock was characterized by significant differences in abundance between seasons (higher values: end of summer and early autumn). Drastic changes in salinity and water level have negatively affected the species abundance. The population structure was characterized by three age groups (0+, 1+ and 2+ in both sexes), a high degree of group‐size overlapping into the 0+ (>2 groups), a short life span and a long reproductive period (April/May to September). Gonadal mass represented a maximum of 19.6±0.5% of the total mass in females. We detected changes in life‐history traits which could be related to the management of the salt extraction, variations in water level that increase the salinity should be indirect effects on fish population by reducing vegetation mats.

Removal control of the highly invasive fish Gambusia holbrooki and effects on its population biology: learning by doing

Abstract Context. For the success of future conservation and management programs, it is necessary to better understand the resilience mechanisms of invasive species and their invasive potential. In this sense, the study of the effects that management actions have on their biological traits is essential. Aims. The present study aimed to assess the effects of removal control on the abundance and biology of an isolated population of the top invasive fish Gambusia holbrooki (eastern mosquitofish). Methods. Experimental removal control with traps and handnets was carried out on a population of mosquitofish inhabiting a small semiarid stream in south-eastern Spain. Mosquitofish were periodically captured for more than 3 years. Temporal variations in abundance, fish somatic condition and reproductive investment, percentage of mature females, size at maturity and population recruitment were analysed. Key results. Individuals of the 1+ age class increased their reproductive investment when population abundance was lower, thus increasing recruitment rate during the first months of the recruitment period. Individuals of the 0+ age class were responsible for expanding the reproductive period in conditions of low fish abundance. Conclusions. The mosquitofish population showed variations of reproductive parameters that could indicate a compensatory density-dependent phenotypic response under diminished abundance conditions. However, its removal by the constant use of a combination of active and passive capture methods, reinforced by increased extraction effort according to its local biology, has led to an eradication of the population. The target mosquitofish population showed distinct ecological features that may have contributed to the effectiveness of local control, namely, low initial fish density, isolation in a headwater stretch and the prevalence of individuals in sunlit shallow ponds. Implications. The compensatory mechanisms of this invasive species in low-density conditions should be considered in the design of management programs. Moreover, further research into removal control methods for mosquitofish or similar species is also needed.

Effects of Shoreline Urban Modification on Habitat Structure and Fish Community in Littoral Areas of a Mediterranean Coastal Lagoon (Mar Menor, Spain)

The shallow habitats of coastal lagoons play an invaluable role for fish communities as nursery areas and provide essential habitats for threatened fish species. Shoreline modification is an anthropogenic coastal stressor that can negatively affect aquatic communities through the modification of nearshore habitats. The aim of the present study was to quantify the effects of two types of shoreline conditions on habitat structure and fish community of littoral habitats. Unmodified shorelines adjacent to saltmarshes and recreational beaches in urbanised areas of the Mar Menor coastal lagoon were compared. The results showed that there were significant differences in habitat structure, fish community structure and fish species abundance by shoreline type. Recreational beaches were characterised by higher water depth and homogeneous substrata, while unmodified shorelines showed high substrata heterogeneity and supported well developed meadows of submerged vegetation. The latter shoreline type provided an important nursery habitat for marine species such as Sparus aurata and Liza saliens, and represented critical habitats for species of conservation concern such as Aphanius iberus and Syngnathus abaster. Littoral areas adjacent to modified shorelines were dominated by Pomatoschistus marmoratus. We suggest that urbanisation has impacted fish assemblages through degradation of habitat structure (loss of complexity and refuge areas).

Fish assemblages in different littoral habitat types of a hypersaline coastal lagoon (Mar Menor, Mediterranean Sea)

Abstract The fish community that inhabits shallow littoral areas of the Mar Menor coastal lagoon was studied seasonally. Three different habitat types were compared: deep sandy habitats, vegetated habitats and shallow muddy habitats. The results indicated that the dominant fish families in the lagoon were Mugilidae, Gobiidae, Sparidae and Atherinidae. In general, vegetated habitats and shallow muddy habitats showed higher fish abundance, biomass and fish diversity than deep sandy habitats. Moreover, fish community structure differed significantly among habitats. Vegetated habitats and shallow muddy habitats seems to play an important nursery role, mainly for marine migrant species of the Mugilidae and Sparidae families, and constituted essential habitats for species of conservationist interest such Aphanius iberus and Syngnathus abaster. Deep sandy habitats were dominated by the resident goby Pomatoschistus marmoratus. These habitat-related differences are probably related to variations in structural complexity.

The effects of competitors on fitness of marbled goby Pomatoschistus marmoratus (Pisces, Gobiidae) in the Mar Menor coastal lagoon (SE Iberian Peninsula)

We investigated the relationship, at local level, between fitness (measured as fish condition) of Pomastoschistus marmoratus and environmental variables of shallow areas in the Mar Menor lagoon (Spain, Mediterranean Sea): water temperature (°C), water salinity (‰), depth (cm), submerged vegetation cover (%), submerged vegetation volume, substrate size, substrate heterogeneity, fish species richness, potential competitor fish species abundance, potential competitor fish species biomass, P. marmoratus abundance and P. marmoratus biomass. The mass–length relationships were used to test differences in fish condition between nine sampling sites. The ecological variable that accounted for most of the variation in condition was the abundance of potential competitor fish species, wich was related to interspecific fish interactions. The condition of P. marmoratus populations may be a good indicator of fish density interactions in coastal lagoons and could be considered when such populations are subjected to recovery plans or any other management programmes.