Parasites of the flounder Platichthys flesus (L.) from the German Bight, North Sea, and their potential use in ecosystem monitoring

Abstract

As part of integrated biological-effect monitoring, the parasite fauna of the flounder Platichthys flesus (L.) was investigated at five locations in the German Bight, with a view to using parasite species as bioindicators. Over a period of 6 years, parasites from 30 different taxa were identified, but only 7 taxa of the parasite community occurred regularly at all locations and in sufficient abundance that they could be considered as potential indicator species. These species were the ciliophoran Trichodina spp., the copepods Acanthochondria cornuta, Lepeophtheirus pectoralis and Lernaeocera branchialis, the helminths Zoogonoides viviparus and Cucullanus heterochrous and metacercaria of an unidentified digenean species. Infection characteristics of these parasites are presented, with a comparison of the results from individual sampling periods and those of the longterm data set. Natural influences on the infection levels, such as temporal variations, habitat conditions and hostrelated factors, were evaluated. All of these parasite species showed significant differences in their infection levels between the Elbe estuary, as the most polluted site, and the less polluted coastal and marine locations: Helgoland, Outer Eider estuary and Spiekeroog, especially in the long-term data set. Gradual differences between the Elbe, the Outer Eider and Helgoland, which were not detected in individual sampling periods, also became evident in the pooled-data set. These were found in the prevalence of Trichodina spp., A. cornuta, Z. viviparus and C. heterochrous. Although salinity is considered as the most important natural factor, influencing the distribution pattern of the majority of the potential indicator species, infection levels of most of these species differed between locations with similar salinity conditions. Infection levels corresponded to a contamination gradient (Elbe > Inner Eider, Outer Eider > Helgoland) established across the locations. Seasonal variation in the infection parameters affected the spatial distribution of the copepod species Lepeophtheirus pectoralis and Lernaeocera branchialis. Annual variations are considered to occur in the range of natural variability, so no trend of increasing or decreasing infection levels of the parasites was found during the course of the study. This study underlined the idea that an analysis of fish-parasite fauna is very useful in ecosystem monitoring.

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

“…This first inventory of parasitic copepods of fish in the western Wadden Sea to date revealed a rich parasite fauna, with 47 copepod parasite species found on 52 examined fish species. The observations in this study expand our knowledge from previous surveys in the North Sea region (Groenewold et al, 1996;Palm et al, 1999;Schmidt et al, 2003;Boxshall, 2009). In these reports, another 37 fish species were investigated that were not examined in our study, including the orders Syngnathiformes (five species, all without copepods) and Perciformes (15 species, only a few with copepods).…”

“…Data based on Table 1. The 23 copepod species found in our study area but not mentioned in previous publications from the North Sea region (Groenewold et al, 1996;Palm et al, 1999;Schmidt et al, 2003;Boxshall, 2009) are indicated with an asterisk.…”

“…Host names are in accordance with www.fishbase.org; parasite names follow Kabata (2003). The eight host species not investigated in other studies from the North Sea region (Groenewold et al, 1996;Palm et al, 1999;Schmidt et al, 2003;Boxshall, 2009) are indicated with an asterisk. Name changes compared to the 1968 study due to taxonomic changes are as follows (1968 Table 2.…”

“…However, local inventories and quantitative data sets remain rare and are usually restricted to limited numbers of host species (e.g. Causey, 1960;Groenewold et al, 1996;Schmidt et al, 2003;Kleinertz et al, 2011). In addition, long-term time-series on parasitic copepod faunas are scarce.…”

Salinity gradient shapes distance decay of similarity among parasite communities in three marine fishes

“…To calculate distances among localities, the co‐ordinates of the sampling stations were obtained either from the original source (Schmidt et al , 2003) or from maps in the original publications. Scans of these maps were imported into a geographic information system (GIS) and georeferenced using the ESRI software ArcGIS 9.2, ArcMap (http://www.esri.com).…”