Frontiers in Marine Science (Nov 2015)
Determination of interannual variability in early life history of Pleuronectes platessa (L.) using otolith microstructure
Abstract
Plaice, Pleuronectes platessa, is a commercially exploited flatfish species in northern European waters. Despite numerous studies on plaice early life history, information for its northern range of distribution is still scarce. Here we present data on juvenile plaice from a cold-water estuary in northern Norway. Otolith microstructure can be used to understand recruitment processes namely their interannual variability which is assumed to be generated in the early life stage. Therefore, the main objectives of this study were to examine differences in age, time of hatching and settlement, larval duration, and growth rates among years and to relate observed patterns with seawater temperature. Plaice 0-group juveniles were sampled from an inshore nursery ground (Valosen, Bodø, Norway) between 2005 and 2006, and otolith microstructure was examined. For that, sagitta otoliths were mounted in microscope slides using a thermoplastic cement (crystalbond™), with the concave side down. Otoliths were then hand-ground to the otolith core using sandpaper (3, 1 µm) and examined under transmitted light in a microscope linked to an image analysis system. This technique exposed the daily increments in the otoliths that once counted allowed to determine hatch dates, larval duration, settlement dates and total age of the fish. A one-month difference in hatching and settlement times was found between 2005 and 2006, occurring later in 2006, but larval stage duration was similar in both years. Compared to other areas located further south, hatching and settlement occurred earlier showing a latitudinal cline. Interannual differences in growth were also detected, with higher rates in 2006 which could be related to warmer temperatures during plaice first summer of life. Yet, growth rates were similar to other locations across the species distributional range which suggest the existence of a countergradient growth compensation mechanism in this northern population. This means that despite the lower environmental temperature at high latitudes, other factors such as productivity and photoperiod may play a key role during the growing season. Nevertheless, further work needs to be done in order to fully understand temporal variation in plaice early life dynamics.
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