High connectivity and directional gene flow in European Atlantic and Mediterranean populations of Ciona intestinalis sp. A

Understanding the factors that cause population divergence has long been of interest to marine biologists in their attempts to interpret the effect of human‐mediated vectors. Broadcast‐spawning species with limited dispersal capability are excellent candidates to measure the present‐day patterns of genetic diversity. The tunicate Ciona intestinalis (Ascidiacea) is comprised of a complex of morphologically cryptic species that form vigorous aggregates in eutrophic habitats (harbors, gulfs and lagoons) where they can compete with the epibenthic community and cause biofouling problems. This study investigated biogeographic variability and migration patterns of C. intestinalis sp. A along Northeast Atlantic and Mediterranean coasts using microsatellite markers. Data presented here on 371 specimens collected from 17 populations reveal high genetic polymorphism, but with a deficit of heterozygote deficiency. Absence of evidence for isolation by distance suggests that the genetic patterns do not reflect the geographic distribution of sampled populations. Substantial gene flow and artificial potential for dispersal boost high levels of within‐population genetic variability and prevent genetic differentiation within and between seas. A predominant eastward migration pattern was revealed by the data set, with very limited opportunity for C. intestinalis sp. A to travel westward. This directional movement indicates that other properties (e.g. habitat quality, genetic traits, mating system, life cycle) may cause adaptive divergence at a large biogeographic scale.     

The impact of metals on the reproductive mechanisms of the ascidian Ciona intestinalis

Environmental pollution due to anthropogenic activities may exert an adverse impact on the reproductive mechanisms of animals. In particular, environmental chemicals introduced into seawater are able to disrupt the normal development and function of the reproductive system of marine animals. In this study, we have used the whole‐cell voltage clamp technique to examine the effects of four metals – lead, cadmium, mercury, and zinc – on reproductive mechanisms of the marine ascidian Ciona intestinalis (tunicates). In particular, we measured the effect of metals on plasma membrane electrical properties, the steady‐state conductance, the fertilization current in the mature oocyte, and larval development. Results show that oocyte voltage‐gated sodium currents are significantly reduced by all four metals, steady‐state conductance is affected only by zinc, and post‐fertilization contraction is inhibited only by lead. The fertilization current is suppressed in the presence of zinc and mercury. Embryo development up to larval stage is inhibited by zinc and mercury exposure with a reversible effect; however, a long‐term effect on larval morphology was observed. After exposure to cadmium, fertilization occurs but gives rise to abnormal larval development. These findings highlight the point that exposure to metals represents a significant risk factor for the physiology of reproduction of marine species and suggest a possible role of the C. intestinalis as a bioindicator for marine pollution monitoring.     

Changes in life cycle of the Ponto‐Caspian amphipod Pontogammarus robustoides at in the northernmost part of its range

The aim of this study was to investigate the dynamics of abundance, population structure and reproductive variables of the invasive Ponto‐Caspian amphipod Pontogammarus robustoides in its northernmost population, located in the Baltic Sea. Pontogammarus robustoides population variables were studied every month from May to October over 7 years (2002–2008) at two locations in the eastern part of the Gulf of Finland, one site in the north and one in the south. Observations of macrozoobenthos were also conducted once per year in July at 12 sites in this gulf during 2002–2014. This was to monitor the distribution area of P. robustoides and its abundance/biomass in different parts of the Gulf. The results showed that P. robustoides is a widely spread species in the Gulf, preferring to colonize stone‐sandy, vegetated and littoral habitats, from the shore to a depth of 5 m, with water salinity of 0.2–3 ppt. This species co‐exists with other amphipods, such as the Baikalian Gmelinoides fasciatus, the North Atlantic Gammarus tigrinus and the native Gammarus spp. The abundance of P. robustoides varied between the two study sites and among years (2002–2008), reaching a maximum level of 1000 ind.·m^?2 for adults and 3000 ind.·m^?2 for juveniles. The temperature‐dependent duration of egg development (embryogenesis) in the amphipod and the annual number of generations in P. robustoides populations varied among years. Three generations were recorded in most years and two generations in the coldest years. Clutch size (or fecundity) was dependent on the body length of female and averaged between 33 and 43 eggs per clutch for females ranging in body length from 11.2 to 12.2 mm. A maximum of 75 eggs were observed in a female with a body length of 16 mm. This paper concludes that life‐cycle variables change when P. robustoides spreads from the southern (Ponto‐Caspian region) to northern (Baltic Sea) range areas. In the studied northernmost location, the fecundity and number of generations of this amphipod were 1.5–2‐fold lower compared with the more southern locations. In addition, these variables and P. robustoides abundance were different between the coldest and warmest years at study sites that testify about their distinct dependence on local environmental conditions; further changes in life cycle of this species may be expected together with current climate warming.     

Preliminary assessment of crustacean distribution patterns in New Zealand groundwater aquifers

Crustaceans were sampled in 17 groundwater wells at five locations in North and South Islands of New Zealand. Three sampling locations were associated with unconfined aquifers adjacent to gravel‐bed rivers, whereas the other two locations were distant from rivers, but associated with land‐based sewage effluent disposal sites. Crustaceans and basic physico‐chemical parameters were sampled in summer and winter. Total abundance varied from 1 to 1064 individuals/250 litre sample. Copepods dominated the fauna at four of the five locations, and were most abundant immediately downstream of a sewage effluent disposal area. Paraleptamphopus spp. (Amphipoda) was found at all five locations, and abundance was also greatest downstream of sewage effluent disposal areas. Several crustacean taxa were rare or limited in distribution, including the gammarid Paracrangonyx sp. and the anthurid isopod Cruregens sp. Syncarids were widely distributed, but found in low numbers, and no specimens were found immediately below sewage effluent disposal areas. We suggest that groundwater ecology in New Zealand is restricted by lack of knowledge of taxonomy and ecology of key groups, particularly the Copepoda.     

Seasonal abundance and reproductive strategy of Tetrastemma fozensis (Hoplonemertea, Nemertea) in the Villaviciosa estuary (Asturias, Northern Spain)

The seasonal occurrence and reproductive strategy of the nemertean Tetrastemma fozensis, which inhabits the mantle cavity of the bivalve Scrobicularia plana, was studied through the analysis of the temporal diversity of a T. fozensis population. Bimonthly sampling was carried out from February 2001 to January 2002 at mudflats of Villaviciosa estuary (Asturias, Northern Spain). Nemerteans were found throughout the study period, but variations in their abundance were detected, with a maximum during winter months and a minimum during summer months. Moreover, variations in mean size of nemerteans were found, with maximal sizes at the end of the spring and the beginning of the summer and minimum size at early autumn. The annual variations in population parameters (decrease in abundance and complete disappearance of large individuals in summer) suggest that T. fozensis has a distinct reproductive season and a semelparous reproductive strategy.     

Catastrophic reduction of the oyster,Tiostrea chilensis (Bivalvia: Ostreidae), in Foveaux Strait,New Zealand,due to infestation by the protistan Bonamia sp.

Between 1985 and 1992, mortality due to infestation by the protistan Bonamia sp. severely reduced the numbers of the oyster, Tiostrea chilensis in Foveaux Strait, New Zealand. In 1990, two dredge surveys gave relative estimates, and a dive survey an absolute estimate, of the size of this oyster population; this allowed us to estimate dredge efficiency precisely. This estimate was used to re‐evaluate the dredge survey of 1975–76 and relate the size of the population in 1990 to that in 1975. By 1990 the population density had declined by 67% while a dredge survey in 1992 showed that the population density had declined by 91% from 1975. A dredge survey in 1993 showed that the population had increased slightly (but not significantly) over the 1992 level. By 1992 the population had probably been reduced below 10% of the virgin level. The fishery was closed in 1993 to allow the population to rebuild. The population surveys have followed stratified random and grid pattern sampling designs and the merits of the designs and methodology are discussed.     

Reproductive biology of spiny lobster Panulirus regius from the north-western Cape Verde Islands

Green (spiny) lobsters Panulirus regius were obtained by diving at Cape Verde, West Africa, during three sampling periods: May–November 2001, April–December 2002 and April–June 2003. Totals of 429 male lobsters and 423 females (852 in all) were caught. Half the females were ovigerous throughout the sampling periods. Female estimated size-at-50% maturity was 87.9mm carapace length (CL). Brood size and egg developmental stage were examined in 68 ovigerous females. The relationship between brood size (BS, thousands of eggs) and CL (mm) was BS = 1.59CL^2.77. Females in the size-class 100–105mm and 115–120mm CL produced half the eggs in the population. Based on these results, an increase in the minimum landing size is proposed. The potential implementation of a maximum landing size is discussed.     

Spatio-temporal variations in reproductive patterns and population structure of Pasiphaea multidentata (Decapoda: Caridea) in the Blanes canyon and adjacent margin, North-western Mediterranean Sea

Pasiphaea multidentata is a deep‐water caridean shrimp fished in the Mediterranean in association with the commercially exploited red‐shrimp Aristeus antennatus. A previous study describes seasonality in the reproductive pattern of P. multidentata using external morphological parametres. This study assesses the spatio‐temporal variations in the population structure, sex ratio, ovary cycle and gametogenesis of P. multidentata from three different fishing grounds in the Blanes canyon and adjacent margin (North‐western Mediterranean) over an annual cycle. The oogenetic pattern of this species is typical of a caridean shrimp. There is a pool of previtellogenic oocytes at all times that develop from the periphery of the gonad towards the centre during maturation. Previtellogenic oocytes grow to approximately 200 μm before undergoing vitellogenesis. The vitellogenic oocytes are surrounded by a monolayer of accessory cells. The maximum size observed for a mature oocyte was 1420 μm. The oocyte‐size distribution confirmed the seasonal reproductive pattern of this species; in winter, the ovaries contained mainly previtellogenic oocytes, some of which start maturing in spring, resulting in a slightly bimodal distribution. In summer, the vitellogenic oocytes reach approximately 1000 μm and in late autumn the ovaries are fully mature and ready to spawn. There were no significant differences in the reproductive and population structure patterns of P. multidentata among the three sites, suggesting that the population’s distribution is not affected by the geomorphology of the area, in particular the presence of the canyon. The populations are dominated by females at all sites and all seasons, with the arrival of juveniles in spring. The seasonal variations in the reproduction and recruitment of P. multidentata and the lack of spatial segregation within the population are discussed in terms of the species’ known biology, the effects of canyons in energy supply to the deep‐sea floor and the relationships of this species with the red‐shrimp A. antennatus.     

First record of mosquitofish,Gambusia holbrooki,in Tasmania,Australia: Stock structure and reproductive biology

The first population of mosquitofish, Gambusia holbrooki, was discovered in a wetland area of the upper Tamar Estuary, northern Tasmania, Australia, in November 2000. We report aspects of the structure and reproductive biology of this population, based on 1567 fish collected between August 2001 and January 2002. Females dominated most catches. Maximum lengths were 48.9 and 23.6 mm standard length (SL) for females and males, respectively. Growth of the over‐wintered cohort was evident from October, when temperatures reached >19°C; growth rates in the young‐of‐season cohort from length frequency plots were 0.38 mm/ day for females and 0.19 mm/day for males. Estimated SL at 50% maturity for females (25.0 mm) and males (17.4 mm) were attained within 7 weeks of birth. Developing embryos were present from mid October and offspring from mid November; average number of stage III embryos was 55.5 (3–144). Given their rapid reproductive turnover (c. 34‐day gestation period) and resilience to broad environmental conditions, it is likely that this exotic pest will spread to other Tasmanian localities, as it has already been discovered in areas near the wetlands since the completion of this study.     

Atlantic humpback dolphins Sousa teuszii in the Saloum Delta (Senegal): distribution,relative abundance and photo-identification

During October and November 2015, the first systematic survey of Sousa teuszii was carried out in the Saloum Delta (Senegal, West Africa), comprising 1 617.5 km of boat-based survey coverage. Thirty sightings were recorded in the Saloum and Diomboss rivers, and along the southern coastline. Dolphins were also observed entering the Bandiala and Djinack channels, and travelling across the border into Gambia. The initial sighting locations were 0.043–1.192 km from shore, and tracked dolphins did not move more than 2.082 km from shore. Groups comprised 1–29 animals (mean 9.3 animals), and at least three neonate calves were observed during November. The overall relative abundance was 0.018 sight. km^?1 and 0.175 ind. km^?1. Sightings were concentrated in the Diomboss where relative abundance reached 0.037 sight. km^?1 and 0.331 ind. km^?1. Non-intensive photo-identification produced a minimum population size of 103 animals, the highest recorded for S. teuszii anywhere in its range. Photo-identification also confirmed a movement of individuals between different parts of the Saloum Delta. Combined travel–forage dominated the behaviour. Dolphins were photographed capturing mullet (Mugil sp.) on three occasions. The distribution, population size and movements of S. teuszii are discussed in relation to management.     

Morphology, reproduction, ecology and isoenzyme electrophoresis of Capitella complex in Qingdao

-Morphology, reproduction, ecology and isoenzyme electrophoresis of a Capitella complex in Qingdao were examined from 1983 to 1984. We determined that the Capitella complex in Qingdao was composed of at least three sibling species: Capitella cf capitata, Capitella sp. I and Capitella sp. IT. Although these three species are very similar in morphology, they differ in: three kinds of isoenzyme electrophoresis, staining reactions, developmental pattern, larval morphology and dispersal, reproductive strategies, breeding season and population ecology. In addition, they show a series of minor quantitative variations in adult morphology, especially in number and morphology of setae. Such differences can be detected only at the population level. Some ecological data such as density, growth rate, mortality and sex distribution are also provided in this paper.     

Distribution,Population Structure, ­Population Biomass and Morphological Characteristics of the Tunicate Pyura stoloniferain the Bay of Antofagasta,Chile

Abstract. The present study analyzes the distribution, population structure, population biomass and morphological characteristics of the intertidal tunicate Pyura stolonifera (Heller, 1878) in the Bay of Antofagasta, Chile, where the species shows a reduced geographical range extending around 60 – 70 km. Three sites along its distribution were studied. At the central site the tunicate presents the widest intertidal belts, reaching nearly 11 m (the mid‐intertidal‐Pyura‐zone shows the higher percent cover). Population dry biomass here averaged up to 20.45 kg·m^–2, representing one of the highest intertidal specific biomasses reported in the literature. Lower values occur towards the borders of its distribution. Population densities were over 1800 indiv.·m^–2 at mid‐intertidal‐Pyura‐belts. Crowding and competition potentially affect morphological characteristics and the energy/tissue allocation along the intertidal and geographical gradient of P. stolonifera.     

Sexual reproduction and early life‐history traits of the Mediterranean soft coral Alcyonium acaule

Understanding processes that contribute to a better comprehension of the population dynamics of long‐lived species is critical for the maintenance and potential recovery of such species. Despite the abundance of soft corals in Mediterranean rocky reefs, little information exists on their life histories and reproductive patterns. In this study, we assessed the main reproductive characteristics and early life‐history traits of the long‐lived soft coral Alcyonium acaule. The sex ratio was 1:1; the smallest fertile colonies were one finger in size (2.1 ± 0.6 cm in height), and both colony and polyp fertility increased with colony size. Likewise, the number of eggs and spermary sacs per polyp increased significantly with colony size, whereas the diameter of the female and male sexual products did not. Over 6 years of observations (2007–2012), spawning occurred primarily in July, after the seawater reached 20 °C, in a single spawning episode per year. Approximately 80% of female colonies released eggs, which were retained on the surface of the mother colony by mucous strings for up to a few days. High fertilization rates were observed during spawning in 2008 and 2009 (94.9% and 87.0%, respectively). The timing of development was ~24 h for the blastulae, ~48–72 h for the planulae and 8–22 days for metamorphosis into primary polyps. Survivorship of planulae was relatively high (~50% at 45 days after release), but only 24% of larvae metamorphosed into primary polyps, and their survivorship was moderate after 2 months (65% in 2008 and 74% in 2009). Asexual reproduction was negligible, indicating that sexual reproduction is the main mechanism supporting the maintenance and recovery of populations.     

Reproductive resilience of ice‐dependent Antarctic silverfish in a rapidly changing system along the Western Antarctic Peninsula

The Western Antarctic Peninsula (wAP) is globally one of the systems most heavily impacted by climate change, notably steep declines in sea ice extent. In forage species, reproductive resilience to change is particularly important because population fluctuations are rapidly communicated through the system via trophic interactions. The reproductive traits of the ice‐dependent forage species Antarctic silverfish (Pleuragramma antarctica) from different areas along the wAP and at the tip of the Antarctic Peninsula were investigated through macroscopic and histological analyses of gonads, with the aim to assess its reproductive potential and to test for spatial differences in fecundity and spawning season. Fish samples were collected in late summer off Charcot Island, in Marguerite Bay and off Joinville Island; no fish were caught in the central wAP. Samples from Charcot Island and Marguerite Bay consisted of adults in developing gonad stage, whereas those from Joinville consisted almost exclusively of juveniles. Mean GSI was relatively low (2–3%) and similar in both sexes, as specimens were still far from being actively reproducing. Developing females exhibited two discrete, though partially overlapping modes of oocytes of different size, with vitellogenic oocytes measuring 0.5–1.0 mm. Absolute and relative fecundity ranged between 3000 and 12,000 eggs per female and between 80 and 190 eggs·g^?1, with a strong relationship between absolute fecundity and body size. These results were consistent with a single population at Charcot Island and Marguerite Bay and indicated substantial reproductive potential, which may mitigate population isolation and reductions in habitat availability but cannot ultimately offset catastrophic loss of spawning habitat linked to sea‐ice retreat.     

Fecundity and spawning of the Atlantic horseshoe crab, Limulus polyphemus, in Pleasant Bay, Cape Cod, Massachusetts, USA

This study provided the first comprehensive analysis of Atlantic horseshoe crab (Limulus polyphemus) fecundity. Limulus appear to be a determinate spawner, maturing all eggs for the breeding season before spawning begins. On average, larger females held a larger number of eggs (63,500) than smaller females (14,500). By the end of the breeding season there was an average of 11,600 mature eggs per female left undeposited, regardless of female size. Larger females laid a higher percentage of the eggs they contained. Thus they not only contain more eggs, but are more effective at laying them as well. Size of spawning females ranged from about 185–300 mm prosomal width, with by far the highest concentration in the mid‐size ranges. Although on an individual basis large females carry and lay the greatest number of eggs, mid‐size crabs as a group contributed more to the horseshoe crab population in Pleasant Bay because they were more plentiful (net fecundity was highest for mid‐size crabs). These results have implications for the management of this important species, which is harvested for bait, scientific, and biomedical uses. Incorporation of these results into models and other management tools can help predict growth rates, effects of size‐selective harvest, reproductive value, and stable stage distribution of populations.     

Oceanographic influences on the distribution and relative abundance of market squid paralarvae (Doryteuthis opalescens) off the Southern and Central California coast

Market squid (Doryteuthis opalescens) are ecologically and economically important to the California Current Ecosystem, but populations undergo dramatic fluctuations that greatly affect food web dynamics and fishing communities. These population fluctuations are broadly attributed to 5–7‐years trends that can affect the oceanography across 1,000 km areas; however, monthly patterns over kilometer scales remain elusive. To investigate the population dynamics of market squid, we analysed the density and distribution of paralarvae in coastal waters from San Diego to Half Moon Bay, California, from 2011 to 2016. Warming local ocean conditions and a strong El Niño event drove a dramatic decline in relative paralarval abundance during the study period. Paralarval abundance was high during cool and productive La Niña conditions from 2011 to 2013, and extraordinarily low during warm and eutrophic El Niño conditions from 2015 to 2016 over the traditional spawning grounds in Southern and Central California. Market squid spawned earlier in the season and shifted northward during the transition from cool to warm ocean conditions. We used a general additive model to assess the variability in paralarval density and found that sea surface temperature (SST), zooplankton displacement volume, the log of surface chlorophyll‐a, and spatial and temporal predictor variables explained >40% of the deviance (adjusted r² of .29). Greatest paralarval densities were associated with cool SST, moderate zooplankton concentrations and low chlorophyll‐a concentrations. In this paper we explore yearly and monthly trends in nearshore spawning for an economically important squid species and identify the major environmental influences that control their population variability.     

Distribution and relative density of cetaceans in the Hauraki Gulf,New Zealand

Understanding species distributions, and how they change in space and time, is vital when prioritising conservation or management initiatives. We assessed the distribution and density patterns of common dolphins (Delphinus sp.), bottlenose dolphins (Tursiops truncatus) and Bryde’s whales (Balaenoptera edeni) in the Hauraki Gulf, New Zealand. Dedicated boat-based surveys were conducted in the inner Hauraki Gulf (IHG) and off Great Barrier Island (GBI) during 2010–2012. Generalised linear models were used to investigate temporal changes in relative densities and kernel density estimation was implemented to examine spatial trends. Common dolphins were widely distributed during all seasons, with higher densities observed during winter and spring in the IHG but during autumn off GBI. There was inter-annual variation in Bryde’s whale distribution, with high densities recorded off GBI in 2011. Bottlenose dolphins were infrequently sighted in the IHG but regularly encountered off GBI, with the highest densities during spring and summer.     

Food and energy in the diet of brown and rainbow trout from Lake Benmore,New Zealand

The diet of brown trout (Salmo trutta) and rainbow trout (S. gairdnerii) was studied in specimens from Lake Benmore, a deep, oligo‐trophic lake in South Island, New Zealand. Between November and July, both species fed mainly on small molluscs (Potamopyrgus antipodarum, Physa sp., and Gyraulus corinna) gleaned from the littoral weed beds. Energy values for the three species of mollusc were determined: P. antipodarum, 6000 J g^‐1; G. corinna, 5500 J g^‐1; Physa sp., 9800 J g^‐1. Potamopyrgus antipodarum yielded little energy to the fish, unless its shell broke during passage through the gut. Physa sp. was the most profitable mollusc, irrespective of shell breakage and Potamopyrgus antipodanim the least profitable. The mean energy value per snail for G. corinna and Physa sp. eaten by rainbow trout was 25–30% less than for snails eaten by brown trout, possibly because rainbow trout ingested empty shells from the sediment surface. Rainbow trout extracted about 20% more energy than brown trout from unbroken shells. In July, 84% of the brown trout switched to predation of common bullies, Gobio‐morphus cotidianus, probably as a result of bully reproductive behaviour. Rainbow trout did not show the same change, apparently because they were feeding in deeper water where few bullies were available. The low‐energy diet and its possible connection with growth rate are discussed.     

莱州湾拟哲水蚤Paracalanus sp.发育期丰度组成和个体大小季节变化

拟哲水蚤是莱州湾桡足类中周年出现的优势种;是上层鱼类幼鱼早期开口饵料的重要贡献者;掌握其种群动态分布特点;有利于了解湾内生物环境状况、次级生产力生产水平。基于2011年5月至20 12年4月采集的浮游生物资料的分析结果显示;莱州湾拟哲水蚤的发育期丰度组成和个体大小均表现了明显的季节变化。调查季节中;4-6月以成体居多;其他季节以桡足幼体CⅢ-CⅤ较多;其中10-11月和3月主要由后期桡足幼体CⅣ和CⅤ期构成。成体中以雌体为主导;雌/雄比介于1.46~9.62;该比值在3-4月最低;10-11月最高。拟哲水蚤各期桡足幼体和成体个体大小以4-5月最大、8月最小;并与水温表现出明显的负相关。拟哲水蚤桡足幼体和成体的总生物量月变化与丰度变化相同;即以8月值最高;3-5月值最低;月均值为2.69 mg/m3（以碳计）;日生产力估算值为0.74 mg/（m3·d）（以碳计）。由上述结果;推测莱州湾拟哲水蚤的种群结构周年变化主要可分3个阶段;4-6月是莱州湾拟哲水蚤开始繁殖期;7-8月为种群数量快速增长期;9月之后为种群增长相对停滞期。     

Temporal correlation of population composition and environmental variables in the marine invader Ciona robusta

The capacity for ascidians to inhabit coastal sea floor worldwide relies on their peculiar tolerance to environmental variables and pollution, which is considered, together with high levels of genetic diversity, among the main drivers of their invasive potential. In spite of the continued interest in the genetics of invasive species, little attention has been paid toward the microevolutionary processes that drive structure and fate of ascidian populations over time under chemically polluted conditions. Understanding the interplay between environmental and population dynamics is critical to predict the biodiversity of marine coastal ecosystems. In the present study, a local population of the ascidian Ciona robusta living in the Fusaro Lagoon has been monitored over a 13‐month period of sampling. Physico‐chemical parameters (temperature, salinity, turbidity, dissolved oxygen, heavy metals), genetic composition (microsatellites, ITS‐2), abundance and biomass (wet and dry weight) were assessed with the aim to infer fine‐scale temporal variation of population structure with respect to rapid environmental change. Analysis of biomass showed that C. robusta is highly sensitive to salinity and oxygen concentrations. Further, genetic analysis suggested a highly dynamic population structure, likely due to the strong clustering of temporal samples and distinct responses to environmental conditions, including bioaccumulation of heavy metals. Here, we hypothesize that rapid variation in allele frequencies of neutral markers in C. robusta populations may increase the ability of the species to colonize habitats that are subject to strong variation and are under heavy human pressure.