Snail grazing effects on the composition and metabolism of benthic diatom communities and subsequent effects on fish growth

Connor, Michael S.

doi:10.1575/1912/1613

Cited by 8 publications

(4 citation statements)

References 23 publications

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“…Yet, the primary mechanism by which these species benefited from I. obsoleta differed: U. compressa growth was primarily facilitated by I. obsoleta nitrogenous wastes, while the primary mechanism facilitating U. rigida growth was the removal of fouling microalgae by I. obsoleta , thus indicating physiological differences between these species. Individual I. obsoleta excrete ammonium at an average rate of 0.6 mg per day (Connor ). As U. compressa readily responded to snail nitrogenous wastes, it may be superior at ammonium utilization; this may also account for U. compressa 's superior ability to tolerate microalgal fouling.…”

Section: Discussionmentioning

confidence: 99%

Snail grazing facilitates growth of two morphologically similar bloom‐forming Ulva species through different mechanisms

2012

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Summary1. Herbivores can facilitate macrophyte growth through stimulation of overcompensation pathways, removal of neighbouring or fouling competitors or increasing nutrient availability via nitrogenous waste inputs. 2. We examined the facilitative relationship between the mud snail Ilyanassa obsoleta and two morphologically similar bloom-forming Ulva species, Ulva compressa and Ulva rigida. Through mesocosm experiments, we determined the occurrence and underlying mechanisms responsible for facilitating Ulva growth. In situ snail enclosure experiments determined the occurrence of this facilitative pathway under natural conditions. 3. We found that both U. compressa and U. rigida are facilitated by I. obsoleta, but despite their morphological similarity, the primary facilitative mechanism differed for each species. Ulva compressa experienced increased growth via snail nitrogenous waste inputs, while U. rigida was facilitated by the removal of fouling microalgae. These results suggest that physiological differences exist between these two species, potentially sustaining their coexistence within blooms. 4. Ground tissue assays showed I. obsoleta preference for microalgal foulers in whole-tissue assays was driven by Ulva blade morphology rather than chemical or nutritive properties. This indicates that the underlying mechanism for I. obsoleta's facilitation via grazing is an inability of the snail's radula to effectively puncture Ulva blades, confining their grazing activities to fouling organisms on the blade surface. 5. In contrast to our mesocosm results, in situ experiments failed to find a positive impact of mud snail presence on Ulva blade growth. However, Ulva blades within these experiments were located at a highly eutrophic site and isolated from potential competitors. Consequently, this may have created an environment where I. obsoleta facilitation was not required for maximum Ulva growth. 6. Synthesis. We demonstrated two mechanisms by which top-down forces can facilitate macroalgal growth: herbivore nitrogenous waste inputs and removal of microalgal fouling organisms. This facilitation may occur within the large mats of macroalgae that form during bloom events, exacerbating bloom conditions.

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Section: Discussionmentioning

confidence: 99%

Snail grazing facilitates growth of two morphologically similar bloom‐forming Ulva species through different mechanisms

2012

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“…This idea is further developed by the enhancement of benthic microalgae in the presence of low densities of snails, i.e. densities high enough to stimulate growth through fertilization, but low enough not to decimate microbial populations by grazing (Connor, 1980;Premo and Tyler, submitted for publication). Where we observed senescence of macroalgae, rather than growth, both in the laboratory and in the South Harbor in July, nutrients released from decomposing tissue would also have been available to support new growth.…”

Section: Discussionmentioning

confidence: 99%

“…We conducted the first experiment in June 2010 to determine urea, nitrate (NO 3 − ), ammonium (NH 4 + ) and total dissolved nitrogen (TDN) excretion rates using a modification of Connor (1980) that involves placing snails in sealed containers and measuring the change in solute concentration over time. Because snails from the IH tended to be larger than snails from the SH and potentially had different diets, we conducted the experiment separately with snails from each basin.…”

Section: Control Of Nutrient Availability By Snails In the Laboratorymentioning

confidence: 99%

Do snails facilitate bloom-forming macroalgae in a eutrophic estuary?

Yarrington

Tyler

Altieri

2013

Journal of Experimental Marine Biology and Ecology

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“…At low densities (< 80 ind. m −2 ), I. obsoleta may stimulate microalgal growth, through either fertilization effects or increased nutrient regeneration (Connor 1980) and inhibit growth of BMA at higher densities due to increased grazing pressures (McLenaghan et al 2011). Our results suggest that grazing had a balanced effect on BMA through the effect of consumption, which possibly reduced self-shading, and the facilitative effect of nutrient provision, with a net effect of higher photosynthetic efficiency (as GPP: chl a) in I. obsoleta treatments.…”

Section: Ilyanassa Obsoletamentioning

confidence: 99%

Threat of predation alters the ability of benthic invertebrates to modify sediment biogeochemistry and benthic microalgal abundance

Premo¹,

Tyler²

2013

Mar. Ecol. Prog. Ser.

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Benthic invertebrates alter estuarine ecosystem function by moderating benthic microalgal production and sediment biogeochemistry. While lethal predation eliminates the effect of invertebrates, non-consumptive effects of predation through trait-mediated indirect effects on behavior may reduce prey control of ecosystem function. Using microcosms, we investigated how chemical cues from the predatory mud crab Panopeus herbstii changed prey behavior and thereby affected the ability of the grazing-deposit feeding gastropod Ilyanassa obsoleta and filter-feeding bivalve Mercenaria mercenaria to regulate benthic ecosystem function. Sediment−water column fluxes of oxygen and nutrients, microscale profiles of sediment oxygen, benthic chlorophyll a, porewater ammonium and organic matter were measured after exposure to predator effluent. Both species had significant effects on sediment processes, with higher sediment oxygen consumption and release of ammonium to the water column, and lower porewater ammonium. However, individual effects were altered in the presence of chemical cues from P. herbstii. The negative effect of M. mercenaria on porewater ammonium was diminished by 26% in predator treatments, suggesting less movement and therefore less sediment oxidation and nitrogen removal. For I. obsoleta, there was a 30% increase in microalgal biomass and a 35% decrease in sediment ammonium release in the predator treatments, possibly associated with decreased foraging activity. In these experiments, non-consumptive predator effects indirectly altered benthic biogeochemistry, benthic microalgae and nutrient fluxes. These results suggest that experiments conducted without predators may overestimate the impact of benthic fauna on ecosystem processes and that changes in community structure resulting in loss of predators may have indirect effects on benthic ecosystem function, leading to faster nitrogen turnover and release to the water column.

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Snail grazing effects on the composition and metabolism of benthic diatom communities and subsequent effects on fish growth

Cited by 8 publications

References 23 publications

Snail grazing facilitates growth of two morphologically similar bloom‐forming Ulva species through different mechanisms

Snail grazing facilitates growth of two morphologically similar bloom‐forming Ulva species through different mechanisms

Do snails facilitate bloom-forming macroalgae in a eutrophic estuary?

Threat of predation alters the ability of benthic invertebrates to modify sediment biogeochemistry and benthic microalgal abundance

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