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Trophic interactions between preadult and adult Pomatoschistus minutus and Pomatoschistus microps and young Platichthys flesus occurring in inshore waters of the Gulf of Gdańsk (Southern Baltic)
We intended to estimate if shallow inshore waters of the Gulf of Gdańsk can be considered important feeding grounds for the fishes under investigation. We...
Citations
... Moreover, the lower δ 13 C confirms the dependence on freshwater-derived sources observed from late larval (Dias et al., 2017) to juvenile stages (Pasquaud et al., 2008;Selleslagh et al., 2015) of European flounder. Prey availability (Bos, 1999;Florin & Lavados, 2010;Vasconcelos et al., 2010), and reduced competition for space and food (Beaumont & Mann, 1984;Złoch & Sapota, 2010;Souza et al., 2013) may explain this preference for upstream areas, especially as prey availability and salinity have been previously correlated with the concentration of 0-group flounder in the Lima upper estuary (Ramos et al., 2009;Mendes et al., 2014). Despite this, 0-group flounder feeding was not restricted to the upper estuary, since polychaetes from downstream areas were also identified as prey items. ...
Estuarine habitats are major nurseries for the European flounder Platichthys flesus , with different year classes sharing food and space resources. Hence, an understanding of feeding strategies that optimize resource use and maintain carrying capacity is fundamental for sustainable and successful ecosystem management. The main feeding areas of juvenile European flounder (including 0-group and 1-group age classes) in the Lima estuary (northern Portugal) nursery ground were investigated by integrating stomach content analyses with stable isotopic values (δ ¹³ C and δ ¹⁵ N) and fish condition indices (Fulton K and RNA:DNA ratio). The 0-group flounder that were associated with the upstream section of the estuary presented the lowest δ ¹³ C value (−25.58 ± 1.86‰), while 1-group flounder exhibited a higher δ ¹³ C value (−22.59 ± 2.51‰), indicating use of the more saline areas of the estuary (lower and middle sections). The two age groups did not differ in terms of δ ¹⁵ N (0-group: 13.93 ± 0.29‰; 1-group: 13.50 ± 0.96‰), indicating similar trophic levels. The low salinity upper estuary was the main feeding area of 0-group flounder (74%), while 1-group flounder fed along the estuary both upstream (52%) and downstream (48%). Juvenile flounder showed high individual condition based on the Fulton K index (0-group: 1.05 ± 0.08; 1-group: 1.07 ± 0.05) and RNA:DNA (0-group: 1.70 ± 0.70; 1-group: 1.41 ± 0.47). These indices deal with fish health, and hence indicate nursery habitat quality. It is concluded that in this temperate nursery habitat, different feeding strategies sustained the condition of the European flounder juveniles, compared with other flounder populations.
... Actually, both species are morphologically and ecologically similar, differing mostly on salinity preferences, with P. minutus preferring to inhabit saltier waters compared to P. microps (Leitão et al., 2006;Dolbeth et al., 2007). Also, both species can often compete for food and space (Złoch and Sapota, 2010) and hence, it is reasonable to assume that P. minutus may perhaps be benefited by a decrease in P. microps population, and potentially fulfill the ecological gaps left by the common goby. Notwithstanding, given the uncertainty about the ecological effects that a decrease in P. microps density might trigger, it would be interesting to perform further studies on the interactions between P. microps and P. minutus particularly at different conditions of temperature, salinity and density. ...
A population dynamics model was developed to assess the short and long-term effects of temperature and salinity variations in the common goby Pomatoschistus microps in a Portuguese estuary (Minho estuary, NW Portugal). The population was divided into juveniles, females and males, which constituted the model's state variables. Linear regressions between the observed and the predicted density of juveniles, females and the total population were significant. Parameter's sensitivity and uncertainty analysis were estimated. The model was able to satisfactory describe the P. microps population dynamics, and thus was used to simulate the effects of climatic changes on the fish population. Simulations indicated that the common goby population is sensitive to both temperature and salinity changes. Overall, scenarios of +4 °C increase caused significant population decreases. Similarly, increased salinities led to a population shrinkage, whereas scenarios of salinity decrease generated an opposite variation on the population. According to the IPCC predictions for climatic tendencies, the population of the common goby will tend to decrease in the near future, experiencing marked oscillations (decrease or increase) during climatic extremes, namely droughts and floods, respectively. These results may be a useful tool for future planning and management of estuarine systems given that the common goby is an important species of estuarine food webs in many temperate ecosystems.
... By virtue of adults spawning at cold temperatures (2-5°C), pelagic larvae benefit from reduced competition with other species (Jeffries and Terceiro, 1985). After metamorphosis, however, inter-and intraspecific competition among juvenile winter flounder may be greatly enhanced (Karlson et al., 2007;Nissling et al., 2007;Złoch and Sapota, 2010;Ustups et al., 2016). For example, juvenile winter flounder are often confined to specific depth ranges, have relatively low mobility, and possess more ob-vious habitat requirements than pelagic fish (Bailey, 1994). ...
... The IRI index was selected as a descriptor of the diet of winter and summer flounder in this study for 2 principal reasons: 1) to minimize biases associated with individual component indices (Hyslop, 1980;Cortés, 1997;Liao et al., 2001;Hart et al., 2002), although others have noted that compound indices may exacerbate the error term and are affected by the taxonomic resolution of prey (Hyslop 1980;Hansson, 1998), and 2) to facilitate comparisons with other studies of juvenile flounder diet that have a similar approach (Burke, 1995;Carlson et al., 1997;Grover, 1998;Złoch and Sapota, 2010;Sagarese et al., 2011). Lastly, each seine haul yielded a cluster of winter and summer flounder, and these individuals likely have increased similarities in diet relative to conspecifics sampled at different sites or dates (Bogstad et al., 1995). ...
... Ontogenetic dietary shifts exhibited by winter and summer flounder then resulted in notable deviations in their food habits, although amphipods remained a common prey among larger individuals (up to 85 mm TL). Multiple species of flatfish often coexist in nursery habitats as juveniles (Burke, 1995;Rooper et al., 2006;Nissling et al., 2007;Mariani et al., 2011), leading to potential interspecific competition (Złoch and Sapota, 2010). Niche overlap is typically minimized, however, because of differences in prey preferences (i.e., biological or diet segregation) or fine-scale distribution patterns within the nursery (i.e., physical or spatiotemporal segregation), the latter in response to heterogeneous environmental conditions (Burke, 1995;Rooper et al., 2006;Mariani et al., 2011). ...
Age-0 winter flounder (Pseudopleuronectes americanus; 20-90 mm in total length [TL]) and summer flounder (Paralichthys dentatus; 19-172 mm TL) were collected from the Seekonk and Taunton Rivers (in Rhode Island and Massachusetts, respectively) from May through September during 2009-2015, and stomach content analysis was used to assess diet composition and resource overlap for these species. Winter and summer flounder underwent ontogenetic dietary shifts. Winter flounder <40 mm TL predominantly fed on copepods, transitioning to amphipods, isopods, and bivalves with increasing size. Polychaetes also were consumed frequently by winter flounder, irrespective of size. The principal prey of summer flounder <60 mm TL were mysid shrimp and copepods, whereas sand shrimp (Crangon septemspinosa), amphipods, and fish were the dominant prey of larger conspecifics. There was minimal dietary overlap for the flounder species when comparisons were made independent of body size, indicating food niche segregation. For winter and summer flounder of equivalent sizes, however, dietary overlap was inversely related to TL. Moderate to high resource overlap occurred for small winter and summer flounder (<40 mm TL) and was attributed to their mutual reliance on copepods and amphipods. Despite evidence of dietary overlap, it is unlikely that shared prey resources were diminished enough to negatively affect either flounder species. © 2017, National Marine Fisheries Service. All rights reserved.
... Alternatively, larger eggs in BW may be evolved in response to predator pressure from small fish like Gobiidae that are absent in FW. Common goby Pomatoschistus minutus and sand goby Pomatoschistus microps have been shown to feed on small fish eggs and larvae (Ojaveer 2003;Zloch and Sapota 2010), but larger eggs and larger larvae hatched from them may be out of the threat due to small gape size of the gobies. ...
Egg characteristics of teleost fishes are affected by various abiotic and biotic factors. In order to reproduce successfully, freshwater fishes inhabiting brackish environments must alter their reproductive characteristics, including egg properties, to increased osmotic pressure. Ruffe Gymnocephalus cernua was used as a model species to compare egg characteristics between fish populations inhabiting brackish and freshwater environments. Fish from the brackish environment had larger eggs with higher energy content than the individuals originating from freshwater. In freshwater, eggs from the first batch were larger than from the second. Female size correlated positively with egg size in the brackish water population. In freshwater, this correlation was evident only with eggs from the first batch. Only a weak positive correlation was found between fish condition and egg size in females from the brackish water population. Egg size variation did not differ between sites, nor was it correlated with mean egg size or any other maternal traits within populations. These results indicate significant modifications in reproductive strategies between brackish and freshwater ruffe populations. Additionally, results show that at least in freshwater, the first batch of eggs is of the highest quality and therefore more important for reproduction.
... On the other hand, the densities recorded in the Minho estuary were much higher than elsewhere, suggesting that in this system, P. microps might find a combination of factors which helps it to achieve higher densities than would be expected, given the latitude of this estuary. The common goby is sympatric with the sand goby P. minutus in several estuaries, and presents some degree of habitat and diet overlap (Leitão et al. 2006;Złoch and Sapota 2010). Nevertheless, the sand goby is less tolerant to salinity and temperature fluctuations than the common goby, preferring to inhabit estuarine zones with higher salinities or the sea, whereas P. microps is preferentially found in brackish waters (Fonds and Van Buurt 1974;Pampoulie et al. 1999). ...
The common goby, Pomatoschistus microps, is a relevant species from estuarine food webs, playing important roles as predator of polychaetes and crustaceans and as prey for larger fishes and crustaceans. The Minho estuary (NW Portugal) is a relatively well preserved and productive system. To assess the population structure and production of P. microps in this estuary, monthly samples were undertaken in three different areas along an estuarine gradient in the lower estuary. The density of P. microps varied considerably among seasons and sampling stations, with higher densities occurring in summer and autumn. The lowest densities were found closer to the sea. In general, the density of females was higher than the density of males in all sampling stations, while juveniles were more abundant within a salt marsh area. Compared with other European estuaries, our data showed a remarkable higher density and production values of P. microps. This may be related to the high freshwater input and the low salinities found in this estuary. In addition, we hypothesize that the lower density of the sympatric species P. minutus and the high availability of bivalve shells observed in the Minho estuary may have also contributed to the present results, once P. minutus and P. microps often display a diet overlap and the bivalve shells are crucial for the common goby reproduction.
... All P. minutus individuals were counted, measured to the nearest 0.01 mm (total length -TL), wet weighted to the nearest 0.001 g in a precision scale and observed under a stereomicroscope for sex distinction based upon dimorphic features on their morphology and gonads (Whitehead et al. 1986). Individuals smaller than 26 mm of TL did not show clear morphological signs of their genders and thus were considered sexually immature and classified as juveniles. ...
... The competition theory states that similar sympatric species compete for similar resources and, therefore, tend to avoid each other by fine-scale niche partitioning (Dobzhansky 1950;Colwell 1973). In fact, these species are known to present some degree of niche and diet overlap (Leitão et al. 2006;Złoch and Sapota 2010). Therefore, the two species might occupy different estuarine zones, thus avoiding the negative impacts of competition for space and/or food. ...
Estuaries are highly productive and heterogeneous ecosystems, and hence they provide an excellent opportunity to study the population structure and feeding patterns of euryhaline species like the sand goby Pomatoschistus minutus. In this context the population dynamics of the sand goby was investigated during 18 months in the Minho estuary (NW Iberian Peninsula). The fish density varied significantly among estuarine areas and seasons, with most of the individuals being caught near the river mouth during the autumn (38 % of the total). Males, females and juveniles were not spatially segregated, as well as fishes belonging to different size classes. The sand goby fed mostly on crustaceans (Frequency of Occurrence - FO) = 35 %; Relative Abundance - RA = 40 %), detritus (FO = 27 %; RA = 23 %) and annelids (FO = 15 %; RA = 14 %), with no obvious difference between the diet of males and females. The density (up to 20 times) and the secondary production (up to 16 times) of the sand goby were substantially higher than in other southern European estuaries. Our results highlighted that the population dynamics of the sand goby can vary considerably among nearby systems and that the Minho estuary, probably due to the lower temperature and salinity values and also the different water circulation regime found in this system when compared to other Iberian estuaries, promotes noticeable differences on the P. minutus population dynamics.
