Inventory and comparison of abundance of parasitic copepods on fish hosts in the western Wadden Sea (North Sea) between 1968 and 2010

A conspicuous part of the parasite fauna of marine fish are ectoparasites, which attach mainly to the fins or gills. The abundant copepods have received much interest due to their negative effects on hosts. However, for many localities the copepod fauna of fish is still poorly known, and we know little about their temporal stability as long-term observations are largely absent. Our study provides the first inventory of ectoparasitic copepods on fish from the western Wadden Sea (North Sea) based on field data from 1968 and 2010 and additional unpublished notes. In total, 47 copepod parasite species have been recorded on 52 fish host species to date. For two copepod species parasitizing the European flounder (Platichthys flesus), a quantitative comparison of infection levels between 1968 and 2010 was possible. Whereas Acanthochondria cornuta did not show a change in the relationship between host size and infection levels, Lepeophtheirus pectoralis shifted towards the infection of smaller hosts, with higher infection levels in 2010 compared to 1968. These differences probably reflect the biology of the species and the observed decrease in abundance and size of flounders during the last decades. The skin-infecting L. pectoralis can probably compensate for dwindling host abundance by infecting smaller fish and increasing its abundance per given host size. In contrast, the gill cavity inhabiting A. cornuta probably faces a spatial constraint (fixed number of gill arches), thus limiting its abundance and setting a minimum for the host size necessary for infections

Comparison of the stable carbon and nitrogen isotopic values of gill and white muscle tissue of fish

The potential use of stable carbon and nitrogen isotope ratios (d13C, d15N) of fish gills for studies on fish feeding ecology was evaluated by comparing the d13C and d15N of gill tissue with the more commonly used white muscle tissue. To account for the effect of lipid content on the d13C signatures, a study-specific lipid correction model based on C:N ratios was developed and applied to the bulk d13C data. For the majority of species in the study, we found no significant difference in d13C values between gill and muscle tissue after correction, but several species showed a small (0.3–1.4‰) depletion of 13C in white muscle compared to gill tissue. The average species difference in d15N between muscle and gill tissue ranged from - 0.2 to 1.6‰ for the different fish species with muscle tissue generally more enriched in 15N. The d13C values of muscle and gill were strongly linearly correlated (R2 = 0.85) over a large isotopic range (13‰), suggesting that both tissues can be used to determine long-term feeding or migratory habits of fish. Muscle and gill tissue bulk d15N values were also strongly positively correlated (R2 = 0.76) but with a small difference between muscle and gill tissue. This difference indicates that the bulk d15N of the two tissue types may be influenced by different isotopic turnover rates or a different composition of amino acids

Movement, connectivity and population structure of the intertidal fish <i>Lipophrys pholis</i> as revealed by otolith oxygen and carbon stable

The shanny Lipophrys pholis is an intertidal fish commonly found in Portuguese coastalwaters. Spawning takes place from early autumn to mid spring, after which demersal eggshatch and larvae disperse along the coast. Two to three months later, young juvenilesreturn to the tide pools to settle. However, information on fish movement, habitatconnectivity and population structure is scarce for this species. One hundred and twentyearly juveniles (16–35 mm) were collected in April 2014 from six rocky beaches along thewestern and south Portuguese coasts (Agudela, Cabo do Mundo, Boa Nova, Peniche, Sinesand Olhos de Água). δ18O and δ13C were determined by isotope-ratio mass spectrometry.Data were analysed to determine whether isotopic signatures could be used to assess thedegree of separation between individuals collected from different locations. Mean δ13Cand δ18O values ranged from −0.02‰ to 1.14‰ and −7.77‰ to −6.62‰, respectively.Both seawater temperature and salinity caused differences in otolith δ18O among the fourmain sampling areas. The variation among areas in δ13C was most likely related toslight differences in the diet, growth and metabolism of fish. The distinct isotopicsignatures, at least for the northern and central areas, suggested low levels of connectivityacross large spatial scales during the juvenile stage. Furthermore, similar isotopicsignatures within the same area indicated some degree of larval oceanic retention at shortspatial scales. This study suggests that stable isotope records in otoliths could provideinformation about the home residency, movements and habitat connectivity of intertidalfishes