Annual variations in the reproductive traits of Pomatoschistus microps in a Mediterranean lagoon undergoing environmental changes: evidence of phenotypic plasticity

The spawning period of the common goby Pomatoschistus microps from 1993 to 1997 in the Vaccarès lagoon did not vary, except in 1997 when it was longer due to the reproduction of the young-of-the-year. Egg size and number, and reproductive allocation varied greatly with one year to another. Female common gobies increased both their fecundity per spawning act and their egg size from 1993 to 1995. The annual variation in the reproductive effort suggests a high phenotypic plasticity of reproductive traits in P. microps , in the face of environmental perturbations. In winter 1993–1994, a centennial flood of the Rhône River caused major hydrological changes in the lagoon in less than 1 week, affecting many invertebrates and fish for several years. The reproductive investment of the common goby increased, possibly as a consequence of those environmental changes.     

Life-history variation within a three-spined stickleback population in the Camargue

Among individuals of female three-spined sticklebacks Gasterosteus aculeatus from a population in the Camargue, southern France, studied in 12 successive years, adult L _T ranged from 31–64 mm, clutch size ranged from 33–660 eggs, and mean egg diameter per clutch ranged from 1.15–1.67 mm. Because the population was strictly annual, inter-annual variation corresponded to variation among generations having experienced different environmental conditions. Body mass varied significantly among years, suggesting an effect of varying environmental conditions. Gonad mass and clutch size increased with body mass, but mean egg diameter was not correlated to body mass. Body mass-adjusted gonad mass, interpreted as reproductive effort per clutch, did not vary significantly among years, suggesting that this trait was not influenced by environmental conditions. Body mass-adjusted clutch size and egg size varied significantly among years. Inter-annual variation in body length at breeding, clutch size and egg size was of the same order of magnitude as inter-population variation reported by other authors for this species. During the breeding season, reproductive effort and clutch size tended to increase. Egg size tended to decrease during the breeding season but this seasonal pattern varied among years. Observed life-history variation is discussed both in terms of its evolutionary significance and methodological implications in the study of life-history variation among populations.     

Host death: a necessary condition for the transmission of Aphalloides coelomicola Dollfus, Chabaud, and Golvan, 1957 (Digenea, Cryptogonimidae)?

Eggs of the trematode Aphalloides coelomicola were observed free in the abdominal cavity of Pomatoschistus microps from March 1993 to October 1995 (Pisces, Gobiidae) in the Vaccares lagoon (delta du Rhone, France). The eggs were contained in a fine membrane of parasitic origin as no immunological reaction of the fish was noted. The alternatively high prevalence of adults and low prevalence of free eggs, and vice versa, suggest that P. microps is both the second intermediate and final hosts of the trematode Aphalloides coelomicola and that the mechanism of transfer to the first intermediate host is through death of the definitive host.     

Long-term monitoring on the occurrence of a myxosporean parasite Kudoa camarguensis (Myxosporean) on the common goby (Teleostei, pisces) Pomatoschistus microps.

The evolution of a host-parasite system composed of Pomatoschistus microps-Kudoa camarguensis was investigated in the Vaccarès lagoon (Rh?ne river Delta, France) from 1993 to 1997. During this long-term monitoring, centennial flooding of the Rh?ne river occurred, leading to an inrush of about 110 million m3 of freshwater in the Vaccarès lagoon. The salinity drastically dropped from 14 to 5 g l(-1) in 1 wk. We observed that the annual prevalence and abundance of the myxosporean parasite decreased from 12.18 in 1993 to 3.7% in 1997 and from 1.10 in 1993 to 0.27 in 1997, respectively. Here, we discuss the possible reasons for the rapid decline of this host-parasite system following the flood.     

Uselessness and indirect negative effects of an insecticide on rice field invertebrates

Macro-invertebrate assemblages on organic and conventional rice fields were quantitatively compared in the Camargue (Rhone delta, France). There was no major difference in family richness, but significant differences as regard to abundance. Fipronil, the insecticide used to control chironomid larvae, was one of the main factors explaining those differences. Its negative impact on predatory invertebrates appears to explain the paradoxical lack of difference in chironomid abundance between organic and conventional fields, observed during the study. Macro-invertebrate biomass estimation showed that, for some birds such as herons, conventional rice fields offered a lower value as foraging habitats than organic ones.     

Life history traits of Pomatoschistus minutus in the Rhône Delta, France

Life history traits and migratory status of the Sand goby Pomatoschistus minutus were investigated in a brackish lagoon of the Rhône river Delta (Mediterranean Sea, south of France).     

Is the brown shrimp Crangon crangon (L.) population of the Vaccarès lagoon (Camargue, France, Rhône delta) an annual population?

To study the population dynamics of Crangon crangon in the Vaccarès lagoon in the Camargue (Rh?ne delta), the age of brown shrimp was determined using the method of Tiews (1954). This method consists in counting the number of segments of the outer branch of the first antenna. This number is correlated with the number of moults already accomplished by the shrimp. The duration of the intermoult depends on water temperature. Adapting this model to our environmental data, we determined the age of the brown shrimp. Hatching of larvae occurs in the sea in May, and juveniles enter the lagoon from June to September. Our results showed that Crangon crangon in the Vaccarès lagoon reached sexual maturity between 6 and 11 months, and individuals are 1 year old when they leave the lagoon. A few adults from the previous year (1+) migrate back to the lagoon the following year, but these older individuals represent only a very small part of the population, and have only been observed occasionally. The Vaccarès brown shrimp population can therefore be considered as annual, in contrast to northern European populations.     

First record of Kudoa (Myxosporea) in Pomatoschistus microps in the Rhône Delta, France

Myxosporidiosis due to Kudoa sp. has been recorded in gobies Pomatoschistus microps , collected from the Etang du Vaccarès (Rhône Delta, France).     

Can life‐history traits predict the fate of introduced species? A case study on two cyprinid fish in southern France

1. The ecological and economic costs of introduced species can be high. Ecologists try to predict the probability of success and potential risk of the establishment of recently introduced species, given their biological characteristics.
2. In 1990 gudgeon, Gobio gobio , were released in a drainage canal of the Rhône delta of southern France. The Asian topmouth gudgeon, Pseudorasbora parva, was found for the first time in the same canal in 1993. Those introductions offered a unique opportunity to compare in situ the fate of two closely related fish in the same habitat.
3. Our major aims were to assess whether G. gobio was able to establish in what seemed an unlikely environment, to compare populations trends and life-history traits of both species and to assess whether we could explain or could have predicted our results, by considering their life-history strategies.
4. Data show that both species have established in the canal and have spread. Catches of P. parva have increased strongly and are now higher than those of G. gobio .
5. The two cyprinids have the same breeding season and comparable traits (such as short generation time, small body, high reproductive effort), so both could be classified as opportunists. The observed difference in their success (in terms of population growth and colonization rate) could be explained by the wider ecological and physiological tolerance of P. parva .
6. In conclusion, our field study seems to suggest that invasive vigour also results from the ability to tolerate environmental changes through phenotypic plasticity, rather than from particular life-history features pre-adapted to invasion. It thus remains difficult to define a good invader simply on the basis of its life-history features.     

Environmental factors influencing the gobiid assemblage of a Mediterranean Lagoon: Empirical evidence from a long-term study

A severe freshwater inflow during our long-term ichthyological study of the brackish Vaccarès lagoon (1993–1998) helped us to assess the impact of sudden environmental changes on the specific biomass composition of the gobiid population and the catches per unit effort of the black goby Gobius niger, the common goby Pomatoschistus microps and the sand goby P. minutus. In 1993, the composition of the Gobiid fish assemblage of the Vaccarès lagoon was dominated by the black goby (63%) and finally evolved to an assemblage dominated by the common goby (80%). The black goby disappeared from the Vaccarès lagoon 2 years after the inflow, whereas catches of the common goby increased significantly after the environmental changes and reached maximum values in 1998. Catches of sand goby did not seem to be affected by environmental changes and depended on the communication between sea and lagoon. This study showed that evolution of an ecosystem after environmental changes is linked to the reaction that species developed to face perturbations.