Biology. 9 Springer-Verlag 1984. Predation on meiofauna by juvenile fish in a Western Mediterranean flatfish nursery ground. L. Tito de Morais and J. Y. Bodiou.
Marine Biology
Marine Biology82, 209-215 (1984)
............
9 Springer-Verlag1984
Predation on meiofauna by juvenile fish in a Western Mediterranean flatfish nursery ground L. Tito de Morais and J. Y. Bodiou Laboratoire Arago; F-66650 Banyuls-sur-Mer, France
Abstract
The authors investigated the gut contents of juveniles of three flatfish species (Buglossidium Iuteum, Arnoglossus thori and A. laterna) collected from Banyuls Bay, Western Mediterranean, from January 1981 through June 1982. Young solenettes, B. luteum, appear to be dependent on meiofauna, particularly harpacticoid copepods, as prey during their first year of benthic fife. By comparison, the scaldfish, especially A. laterna, prey primarily upon peracarids from the beginning of their benthic fife. Evidence of prey selection exists for the genera Photis (amphipod) and Longipedia (harpacticoid copepod). By regrouping these results with those of Bodiou and Villiers (1978/1979) on the goby Deltentosteus quadrimaeulatus, and comparing them with other data from the literature, it appears that the impact of predation by juvenile fish is significant for some meiofaunal species, providing that they are actively selected by the predators, as is Longipedia scotti. Generally, however, predation impact on the meiofauna as a whole is weak.
Introduction
The Bay of Banyuls sur Mer, with its area of well-sorted fine sands is a well documented region from faunistic and bionomic aspects. Recent research has been directed towards defining and quantifying trophic webs in this homogenous biotope, mainly regarding potential predators such as juvenile benthic fish (Bodiou and Villiers, 1978/ 1979; Morais, 1983). It is now known that meiofauna and small macrofauna are preyed upon by the juveniles of a large number of fish species (Bregnballe, 1961; Arndt and Nehls, 1964; MacIntyre and Murison, 1973; Elmgren, 1978; Bodiou and Villiers, 1978/1979; Carle and Hastings, 1982; Evans, 1983; etc.), even by those with pelagic adult forms, such as
salmonids (Sibert et al., 1977). Precise evaluation of this trophic relationship is still a point of debate (see reviews by P6rbs 1980; and Hicks and Coull, 1983). The latter authors pointed out the importance of harpacticoids as food for higher trophic levels, and that fundamental questions remain: How much of the larval juvenile fish energy requirements do they provide? How much biomass is transferred into the water column by this mechanism? How does this apparent significant removal affect the population biology and community structure of the harpacticoid assemblage? The present study on food of juvenile fish revealed trophic relationships in the fine sands area, feeding selectivity, and, by comparing closely related benthic species, allows us to examine the problems of interspecific competition and regulation of benthic populations.
Materials and methods
The sediment in the sampling area (the Banyuls Bay, Western Mediterranean: 3~ 42~ at 20 m depth) consists of well-sorted fine sand (median grain diameter about 120/~m), this area belongs to the macrofaunal "Spisula subtruncata community" of Guille (1970), corresponding to the meiofaunal "Halectinosoma herdmani and Harpaeticusflexus community" of Soyer (1971) (see Guille and Soyer, 1974). Juvenile fish caught by trawling were: gobies (Deltentosteus quadrimaeulatus), callionymes (Callionymus spp.), and the Pleuronectiformes Buglossidium luteum (the solenette) and Arnoglossus thori, and A. laterna (scaldfish). These last three species form the subjects of the present study. Fish juveniles were caught with a small trawl with a 1 m mouth opening (Labat, 1977), from January 1981 through June 1982. According to Kuipers (1975), escape underneath and over a small beam trawl is negligible for
210
L. Tito de Morais and J. Y. Bodiou: Predation on meiofauna by juvenile fish
0-group flatfish (Pleuronectes ylatessa in Kuipers' experiment), the net takes 100% o f the fish in front o f it's central part whereas the fish in front o f the side parts all m a n a g e to escape laterally. S C U B A observations o f the trawl used in our experiments confirmed this (J. P. Labat, personal c o m m u n i c a tion) a n d r e v e a l e d that the effective trawl width is app r o x i m a t e l y 0.5 m. The distance covered b y each trawling event (ca. 309 m), the average effective area covered by the trawl (309 • 0.5 m 2= 154 m 2) a n d the m e a n n u m b e r o f fish caught allowed us to estimate the average density o f fish juveniles on the bottom. This estimate is the "low hypothesis". A "high hypothesis" has also been calculated from in situ s e d i m e n t - p u m p i n g samplings using 0.25 m s box cores. I m m e d i a t e l y after capture, fish were fixed using 10% formalin to stop digestive processes a n d total length (TL) was m e a s u r e d to the nearest ram. After lens dissection, p r e y from. the stomach contents were identified. Percentage occurrence (% oc), percentage n u m b e r (% nb) a n d percentage volume (% vol) (points m e t h o d : Swynnerton a n d Worthington, 1940) were calculated (see Hyslop, 1980, for review). These values were used to calculate the " a l i m e n t a r y index" (AI) (Lauzanne, 1975) for each food item:
AI-
% o c • % vol 100
0 10 25 50
< < <
