MEPS prepress abstract  -  DOI:

Drought alters the spatial distribution, grazing patterns, and radula morphology of a fungal-farming salt marsh snail

Bridget Chalifour*, Jasper R. H. Hoogveld, Marlous Derksen-Hooijberg, Kathryn L. Harris, Juan M. UrueƱa, W. Gregory Sawyer, Tjisse van der Heide, Christine Angelini


ABSTRACT: Climate change is altering consumer–plant interactions in ecosystems worldwide. How consumers alter their spatial distribution, grazing activities, and functional morphology in response to climate stress can determine whether their effects on plants intensify or relax. Few studies consider multiple consumer response metrics to elucidate the mechanisms underpinning the resulting changes in consumer–plant interactions. Here, we test how drought stress influences the interaction between the dominant consumer, the fungal-farming periwinkle snail Littoraria irrorata, and a foundational plant, cordgrass Spartina alterniflora, in a southeastern US salt marsh. In a four-month field experiment, we maintained moderate snail densities in mesh control chambers and clear plastic climate chambers that simulated drought by elevating temperatures and drying soils. Monitoring revealed that snails more often congregated on cordgrass stems than leaves in climate chambers than controls. Image analyses indicated that this behavioral shift corresponded to snails inflicting shorter, but more numerous, fungal-infested scars on cordgrass leaves, and causing less plant damage in climate chambers than controls. Coincident with their net reduction in grazing, snails maintained longer radulae, whose central teeth were blunter and lateral teeth were sharper in climate chambers compared to controls. These results suggest that under drought, snail radulae may experience less frictional wear and that, at intermediate densities, snail–cordgrass interactions relax. Together with prior research showing that, at high densities, snails can denude cordgrass during drought, we conclude that consumer density, behavior, and morphological responses must be integrated in predictions of how climate change will affect the direction, strength and stability of consumer–plant interactions.