Prediction of ecological impact of two alien gobiids in habitat structures of differing complexity

Rapid expansion of round goby (Neogobius melanostomus) and western tubenose goby (Proterorhinus semilunaris) beyond their native ranges calls for urgent management action, particularly in localities with high introduction possibility of the species. We used a comparative functional response (FR) approach to forecast invader ecological impact. We compared their foraging efficiency in three habitat structures: sand, coarse gravel, and coarse gravel with an artificial plant. Both Neogobius melanostomus and Proterorhinus semilunaris showed type II FR in all habitats. Interspecific comparison showed similar handling times in both the gravel and gravel with artificial plant habitats, suggesting similar per capita impact. Intraspecific comparison showed significantly lower handling times of both predators on gravel substrates. Therefore, their ecological impact in such an environment could be higher. Neogobius melanostomus showed higher attack rates on sandy substrates compared with Proterorhinus semilunaris, while no significant differences were observed on other substrates. Our results highlight the importance of interacting factors in management of ecosystems with multiple invaders, as the elimination of invasive Neogobius melanostomus may lead to utilization of the empty niche by alien Proterorhinus semilunaris with similar ecological impact.

Bio-Ecological Traits of Western Tubenose Goby Proterorhinus semilunaris (Heckel, 1837): A Key to Understand Its Invasion Success

This study aims to contribute to the limited knowledge on the bio-ecological traits of the native Western tubenose goby, Proterorhinus semilunaris, which is considered to invade many inland waters in Europe and North America. During monthly sampling surveys from March 2012 to June 2013, the species was collected from the four stations in the Istranca River (Turkey) by electrofishing. The standard length and body weight of 310 samples varied between 1.4–6.1 cm and 0.08–7.09 g, respectively. The sex ratio of female to male was found to be 1.7:1.0, with a significant difference. The values of the exponent b in the length–weight relationship were approximately 3 for females, males, and all individuals, indicating an isometric growth. The size at first sexual maturity was 2.44 cm standard length (SL) for females and 2.29 cm SL for males. Absolute fecundity ranged from 56 to 344 eggs with a mean of 164 eggs. The food composition of the species comprised of 8 major groups: Insecta (Diptera, Ephemeroptera, Plecoptera, Odonata, Trichoptera, Coleoptera), Arachnida, Annelida, Gastropoda, Crustacea, Pisces, plant, and detritus. According to the results of modified index of relative importance (MI) and index of relative importance (IRI), insect and Diptera were the most prevalent prey for this fish. The present study has provided baseline information on the basic biological traits of the fish in its natural habitat for further understanding of this species success of invasion.

Plasticity in habitat use of two native Ponto-Caspian gobies, Proterorhinus semilunaris and Neogobius fluviatilis: implications for invasive populations

The Ponto-Caspian region is an important source area for some invasive gobiid fishes. These fishes have colonised several freshwater ecosystems in Europe, as well as in North America. As knowledge on their habitat utilisation in their native range remains limited, the seasonal habitat uses of Western tubenose goby, Proterorhinus semilunaris and monkey goby Neogobius fluviatilis were studied in four natural lakes in the Marmara Region (NW Turkey). Habitat use of both species was highly variable between the lakes and seasons, with P. semilunaris showing higher plasticity. In general, the main habitats used by P. semilunaris were shallow waters in littoral areas that had vegetation cover, whereas N. fluviatilis consistently used sandy substratum in deeper waters that lacked vegetation. These results suggested there was high plasticity in the habitat utilisation of these two gobiids, especially in P. semilunaris, which potentially facilitates their ability to establish and invade novel environments. The habitats that are especially vulnerable to P. semilunaris invasion are medium size substrates which provide individuals with sufficient interstitial space for refuge. Waters providing differing habitats, such as sandy substrata, might inhibit their colonisation, but are potentially more vulnerable to N. fluviatilis invasion.

Plasticity in life history traits of the native Proterorhinus semilunaris suggests high adaptive capacity in its invasive range

Invasion risk assessments are reliant on ecological data that assist the predictions of whether an introduced species will adapt to novel conditions. Data from the native range of potential invaders can thus assist these assessments. Here, the growth and reproductive characteristics of the Western tubenose goby Proterorhinus semilunaris, a Ponto-Caspian gobiid, were assessed in three natural lakes in their native range, as there are few extant data on these traits. Across the three lakes, the gobies were found in varying abundances. Sex ratios varied, with females significantly outnumbering males in only one lake, with equal sex ratios in the other lakes. The fish always showed a positive allometric growth, but had high variability in their somatic growth rates and relative body conditions between the lakes. Scale ageing revealed all populations comprised of individuals to four years old, with one lake having individuals to 5 years old. Reproductive characteristics, including size at maturity, gonado-somatic index and fecundity, did not differ significantly between the lakes. These data suggest that plasticity in aspects of their life history traits provides P. semilunaris with considerable adaptive capacity following their introduction into novel conditions.

The diet of reservoir perch before, during and after establishment of non-native tubenose goby

In recent decades, gobiid species have increased their distribution throughout Europe and now often represent the dominant genus along many rivers and canals. In this study, we assessed the role of tubenose goby (Proterorhinus semilunaris) as a prey species of native perch (Perca fluviatilis) in a lowland reservoir soon after their initial introduction in 1994 (sampling started 1998) and 17 years after establishment (2011–2012). We compare these data with perch diet composition from before introduction (1981–1982). Our data indicate that tubenose gobies quickly became the dominant species along the reservoir bankside, making them an attractive prey for ≥1 + perch. There was a clear increasing trend in the numbers of larger perch caught along the rip-rap, with the largest fish clearly specialising on gobies. As such, introduction of tubenose gobies has had a pronounced effect on food web and population dynamics along the littoral zone. While goby numbers appear to have dropped significantly in recent years, apparently due to predation pressure, further studies are needed to assess whether such changes have had any general impact on population and food web dynamics within the reservoir.