Abstract
The microphytobenthos (MPB) - Hydrobia ulvae trophic interaction is one of the main channels of material transfer to higher trophic levels in intertidal mudflats. A new non-invasive approach to evaluate the grazing activity of H. ulvae on microphytobenthos is proposed. The effects of season and period (combination of tide and day/night) on ingestion rates of H. ulvae (using 14 C- labeled MPB) and egested pheopigments a (using HPLC pigment analysis) were also investigated. H. ulvae ingestion rate was found to vary significantly over season and period, being higher in summer and during diurnal low tide periods. This is possibly related to higher growth rates of H. ulvae in sum- mer, as well as to an increase in surface MPB biomass during diurnal low tides. A highly significant relationship was found between ingested chl a and egested pheophorbide a, allowing the estimation of ingestion rate from the amount of egested pheophorbide a on H. ulvae faecal pellets. This new non-invasive methodology may allow the improvement of long-term studies of consumption rates and the evaluation of grazing of H. ulvae on MPB.
Highlights
The mud snail Hydrobia ulvae (Pennant) is one of the most abundant deposit feeders in intertidal mudflats of the North Atlantic coast, forming large populations that can reach densities of up to 106 ind. m–2 (Barnes 1999)
Samples of sediment surface containing MPB and Hydrobia ulvae were collected from intertidal mudflats in Ria de Aveiro (40° 38’ N, 8° 44’ W), which is a shallow coastal lagoon located on the northwest coast of Portugal
The major aim of this study was to investigate the possibility of establishing a new non-invasive methodology to estimate the ingestion rate as chl a flux from benthic microalgae to Hydrobia ulvae, based on the relationship between ingested chl a and egested degradation products
Summary
The mud snail Hydrobia ulvae (Pennant) is one of the most abundant deposit feeders in intertidal mudflats of the North Atlantic coast, forming large populations that can reach densities of up to 106 ind. m–2 (Barnes 1999). Top-down controls include erosion and several studies have already demonstrated that MPB erosion is controlled by physical variables as well as biological ones, such as bioturbation (Blanchard et al 1997, Orvain et al 2003, 2004, 2006, Orvain 2005) In this context, H. ulvae play a role in the dynamics of MBP biomass, facilitating MPB erodability through snail biouturbation activities that occur simultaneously with grazing. H. ulvae play a role in the dynamics of MBP biomass, facilitating MPB erodability through snail biouturbation activities that occur simultaneously with grazing This trophic link is one of the main channels of material transfer to higher trophic levels in estuarine food webs since H. ulvae is an important prey item for fish, birds and other estuarine invertebrates (Piersma et al 1993, Aarnio & Mattila 2000)
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