Since 1975, juvenile flatfish (plaice and flounder) populations have been monitored at the Balgzand intertidal and, based on this data series , the interannual patterns in predation pressure were quantified. Temporal patterns in abundance have changed greatly, especially for plaice. Up to the early 1980s, 3 year classes (0-, I-and II-group) were present and growing up in the area, but from the late 1980s onwards, densities of the I-and II-group plaice dropped from a few hundred individuals per 1000 m 2 to levels close to zero. It appears that the Balgzand intertidal has lost its nursery function for I-and II-group plaice, although feeding conditions have remained the same or even slightly increased since the late 1970s. The absence of I-and II-group flatfish in the intertidal cannot be explained at present; however, processes operating offshore are most likely involved. As a consequence, the annual predation pressure by juvenile flatfish upon the intertidal macrozoobenthos dropped by 94%, declining from an average of approximately 5 to 0.25 g ash free dry mass m -2. Such a decline in top-down predation may not only have directly influenced the macrozoobenthic community, but may also have indirectly affected food availability and accessibility for other top predators (e.g. shorebirds).

The Balgzand intertidal is an important nursery area for early life stages of various epibenthic crustacean and fish species. Especially in summer, extremely high numbers of individuals occur. This study analyses whether these high densities in summer lead to food limitation using 0-group plaice Pleuronectes platessa L. as a model species. Between 1975 and, this species was quantitatively monitored during 20 yr. The aim of this study is twofold: (1) a statistical analysis of field growth in relation to density, whereby negative density-dependent growth is considered as an indication of intraspecific competition, and (2) a comparison of observed field growth with predicted maximum growth according to the dynamic energy budget (DEB) model, to detect whether growth reduction occurs during the growing season as an indication of interspecies competition. The statistical analysis indicated no negative density-dependent growth during the whole growing season, suggesting the absence of intraspecies competition for food. The comparison of observed growth with DEB-predicted maximum growth showed that field growth was lower than the possible maximum, and that the difference increased over time until about the end of July, suggesting interspecies competition for food in summer. The stabilization in growth rate from July onwards might be related to a change in food quality: a shift from small bivalve siphons as main food items to larger tail tips of the lugworm Arenicola marina. These findings illustrate that not only food quantity but also food quality affects growth rates, at least in 0-group plaice.KEY WORDS: Plaice · Pleuronectes platessa · Wadden Sea · Growth · Dynamic energy budget · Intertidal · Food quantity · Food quality · Food limitation Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 416: [215][216][217][218][219][220][221][222][223][224][225][226][227] 2010 P. microps, and the juvenile flatfishes Pleuronectes platessa, Platichthys flesus, Limanda limanda and Solea solea (Zijlstra 1972, Jensen & Jensen 1985, Pihl 1985, Ansell et al. 1999, Amara 2003, Amara & Paul 2003, Freitas et al. 2010a.For those species, shallow coastal areas are typically important habitats as nursery grounds for early life stages due to presumed favourable conditions for growth and survival (Zijlstra 1972, Bergman et al. 1988. In general, juveniles arrive and settle in the intertidal with rising temperatures in spring and disappear with decreasing temperatures at the end of the growing season, emigrating to deeper waters. As a result, high densities (10s to 1000s of ind. m -2 ) of epibenthic consumers build up in these shallow areas in the course of the season. Since the various species have overlapping food spectra, these high numbers, and hence high biomass, have raised questions about their growth conditions, suggesting that food might be limited by either intra-and/or interspecies competition (Pihl 1985). For most species, growth is difficult to monitor due to more or less co...