|Utilisation of sandy beaches by larval and early postlarval fish|
Beyst, B.; Dewicke, A.; Mees, J. (1998). Utilisation of sandy beaches by larval and early postlarval fish. Biol. Jb. Dodonaea 65: 107-108
In: Biologisch Jaarboek (Dodonaea). Koninklijk Natuurwetenschappelijk Genootschap Dodonaea: Gent. ISSN 0366-0818, more
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|Document type: Project report|
Beaches; Conferences; Fish; Juveniles; Larvae; Marine
Larval and early postlarval fish seem to utilise intertidal and very shallow subtidal areas as nurseries. In this study, the utilisation of sandy beaches by these organisms was investigated. Since specific larval and early postlarval stages of several fish species seem to have a hyperbenthic life style (i.e. living in the water layer close to the sea bed), sampling was dolle by means of a hyperbenthic sledge that samples the hyperbentha from 5 to 45 cm above the bottom. The sledge consisted of two nets placed one above the other (3 m long with a mesh size of 1 x 1 mm). The results are only based on the contellts of the lower net. The total area sampled per station was 450 m2. Samples were taken around ebb tide in 12 stations along the Belgian coast in spring 1996 (April/May). In each station, environmental variables (temperature, salinity, oxygen content, nutrients and pigments in the water column and grain size distribution of the sediment) were measured. Species composition, distribution patterns, densities and length-frequency distributions are described. Correlations with environmental variables measured are analysed with multivariate statistical techniques. Larval and postlarval fish represented a considerable part of the hyperbenthic fauna of the sandy beaches (21,6 % of the total community and 69,8% of the temporary hyperbenthos). Densities varied between 20 and 200 ind./100 m2, but maxima of 426 (Bray-Dunes) and 365 ind./100 m2 (Bredene) were recorded. In total 12 (post)larval fish species were found. The most important species were flounder Pleuronectes flesus (81,4% ), Clupeidae species larvae (12,3 %), whiting Merlangius merlangus (2,5%) and plaice Pleuronectes platessa (2,4 %). P. flesus was the dominant species in most stations (> 65 %), but in De Haan, Blankenberge and especially in Knokke 't Zoute, Clupeidae species larvae - probably a mixture of herring Clupea harengus and sprat Sprattus sprattus - were most abundant (> 40%). Only in Bredene did M. merlangus contribute for more than 9%' and the species was absent in Bray-Dunes, De Panne, Lombardsijde, De Haan, Zeebrugge and Knokke 't Zoute. P. platessa occurred in all stations, but only in Blankenberge it represented more than 5% of the community. The hyperbenthic sledge obviously sampled specific pre-settlement stages of all three flatfish species: individuals just before or at the onset of asymmetry were clearly over-represented in the hyperbenthos. Hardly any post-settlement demersal larvae nor yolk-sac larvae were caught. Merlangius merlangus was mainly found at a length between 10 and 12 mm and Clupeidae species larvae around 29,5 mm. Multivariate analyses (TWINSPAN and CA) allowed for the identification of 2 distinct communities which occurred discontinuously along the coast: a first group of stations had Nilsson 's pipefish Syngnathus rostellatus as indicator species (the preferentials also included sole Solea solea), while the second group was characterised by Clupeidae larvae, sandeel Ammodytes tobianus and Merlangius merlangus. Ongoing research includes the monthly sampling of hyperbenthic stages of fish in 4 stations along the Belgian coast and 24-hours cycles in 1 station in spring 1997. The feeding ecology of these hyperbenthic larvae and postlarvae will be investigated by means of stomach content analyses.