Selective grazing by the mud snail Ilyanassa obsoleta

Abstract

Mud snails (Ilyanassa obsoleta) starved for 48 h were allowed to feed on sediments in laboratory microcosms. Sediment cores sliced at 2 mm intervals were compared to snail stomach contents for per cent carbon and nitrogen, plant pigment contents and species composition of benthic diatoms. Concentrations of carbon, nitrogen, phaeopigments, phycocyanin and chlorophyll were enriched in the top 2 mm of the sediments compared to 7-10 mm depth by a factor of 2-10. In turn, these materials were 20-40 times more concentrated in snail guts than in the surface sediments. Snail feces were enriched for carbon and nitrogen by 5-7 times over the surface sediments. Bacterial chlorophyll peaked at about 3-4 mm in the sediments and was not detectable in the snail stomach contents. The C/N ratio of the snail stomach contents was only 6 compared to a ratio of 8.5 for their feces and 12 for the surface sediments.The percentage of migratory diatoms (e.g. Nitzschia and Navicula) decreased with depth where non-migratory species, such as Fragilaria pinnata, dominated. These migratory species were more common in the snails than in the sediments on which they were feeding.A comparison of daily ingestion rates to the animal's energy budget shows that this selective ingestion is sufficient to meet Ilyanassa's energy needs.

Field and laboratory experiments on interference between Hydrobia totteni and llyanassa obsoleta (Gastropoda) and its possible relation to seasonal shifts in vertical mudflat zonation

“…Its diet can be varied, but probably is mainly confined to deposit feeding (e.g. Curtis & Hurd 1981, Connor & Edgar 1982. The genus Hydrobia has a similar main diet (Newel1 1965, Lopez & Kofoed 1980 and is occasionally as abundant as in the European Atlantic and North Sea region (e.g.…”

“…Hydrobia populations are commonly at densities where resource limitation by food availability is likely (Fenchel & Kofoed 1976, Levinton & Lopez 1977. I. obsoleta is efficient at grazing and digestion of diatoms (Pace et al 1979, Connor & Edgar 1982, the principal source of food for Hydrobia (Fenchel & Kofoed 1976, and seems to be far more effective at reducing microalgal standing stocks than H, totteni . However, significant as it may seem, this effect may be minor relative to interference effects.…”

Comparative Study on Microphytobenthic Pigments and Total Microbial Biomass by ATP in Intertidal Sediments

“…갯벌 내 대표적인 생산자로 저서미세조류는 퇴적물 섭 식자의 직접적인 먹이원일 뿐만 아니라 (Connor and Edgar 1982;Hughes and Sherr 1983), 재부유되어 부유 섭식자에게도 중요한 먹이원이 된다 (Baillie and Welsh 1980). 또한 재부유된 저서미세조류의 생체량과 생산력이 수층 내 식물플랑크톤보다 높게 나타나는 경우도 있다 (Varela and Penas 1985;Lukatelich and McComb 1986;de Jonge and van Beusekom 1995).…”

Concepts and Controversies in Tidal Marsh Ecology

“…He suggested that detritus-feeders augment their C uptake when detritus supply is low by eating benthic algae. The relative importance of microphytobenthos may be much greater for at least a few of the key marsh invertebrates, such as gastropods (Pace et al 1979, Lopez and Kofoed 1980, Conner and Edgar 1982, Lopez-Figueroa and Neill 1987, shrimp (R.I.E. Newell and B. Bebout, unpublished data) and mussels (D.A.…”

“…Observational studies have shown that gastropods, such Melampus bidentatus, Littorina irrorata, Ilyanassa obsoleta, and Hydrobia ulvae do feed on epiphytic and epibenthic algae (Wetzel 1976, Barnes 1989. A variety of reports suggest that these snails preferentially select and digest surface-associated algae, which often comprise the bulk of material in their guts (Pace et al 1979, Lopez and Kofoed 1980, Conner and Edgar 1982, Lopez-Figueroa and Neill 1987. Recent work by and Newell and Porter (this volume) indicate that 3 to 28% of the biomass of senescent cordgrass is composed of fungi and that this fungal component is efficiently utilized by gastropods (Newell and Bärlocher 1993, Newell and Porter, this volume).…”