The roles of competition, behavioural plasticity and personality in limpet foraging

 

Biotic and abiotic drivers of limpet foraging movements in the intertidal zone

Determining how animals move, and why they move where they do, can be challenging, especially for large organisms that inhabit and travel across relatively large spaces. In the intertidal zone, the region of the ocean exposed during low tide, organisms are small, and their habitats are relatively small in extent. As a result, accurate, detailed data can be collected, and used to determine the movement ecology of intertidal organisms. In this study, we examined foraging movements in the intertidal limpet, Lottia austrodigitalis, which is a centimeter-long, dome-shelled snail that clings to vertical rock surfaces with a large, muscular foot, and forages for microscopic algae (microalgae) approximately twice per day, usually during high tides. To observe L. austrodigitalis foraging, we deployed infrared-sensitive waterproof cameras that photographed labeled individuals once per minute at two field sites in the intertidal zone adjacent to Hopkins Marine Station in Monterey Bay, CA. We used Generalized Linear Mixed Modeling to determine whether the initiation of foraging behaviour, and the duration and velocity of foraging movements were correlated with tidal height, significant wave height, sea surface temperature or time of day. Then, we used a variety of statistical techniques to determine whether L. austrodigitalis individuals moved optimally while foraging, chose to forage in areas of higher food density, and changed their movement behaviour upon encountering food patches. We found that the abiotic drivers of L. austrodigitalis foraging movements differed between sites, and that L. austrodigitalis generally does not change its movement behaviour in response to food in its environment.

This research was conducted in collaboration with Mark Denny.  It was supported by the National Science Foundation, Stanford University, the Eugene and Aileen Haderlie Award, the Earl and Ethel Myers Oceanographic and Marine Biology Trust Award, the Esther M. Zimmer Graduate Fellowship and the Melbourne R. Carriker Student Research Award in Malacology.

 

Behavioural plasticity is limited by an exploratory behavioural syndrome in foraging intertidal limpets

Many animals move as they forage for food, and are able to alter their movement behaviours in response to complex and variable environmental conditions. However, recent evidence suggests that this ability, known as behavioural plasticity, can be limited by animal personality, or the tendency for individuals to behave consistently across a range of scenarios or conditions. Here, we examine the trade-offs between behavioural plasticity and animal personality in an intertidal limpet, Lottia austrodigitalis. L. austrodigitalis forages for epilithic, microscopic algae approximately twice per day during high tides. We manipulated food availability and distribution in an outdoor seawater table, observed and quantified L. austrodigitalis foraging behavior, and determined the effects of food treatment and individual on our foraging parameters. We found that limpets are behaviourally plastic with respect to food in their environment, and that limpet movement in a uniform, plentiful food environment best approximates foraging behaviour previously described in the field. In addition, we provide the first preliminary evidence of animal personality in a marine snail.

This research was conducted in collaboration with Mark Denny.  It was supported by the National Science Foundation, Stanford University and the Melbourne R. Carriker Student Research Award in Malacology.

 

Quantifying the top-down effects of grazers on a rocky shore: selective grazing and the potential for competition

The effect of grazers on the diversity, distribution, and composition of their principal food source has rarely been described for the high intertidal zone of rocky shores, a model system for studying the potential effects of climate change. Along rocky, wave-swept shores in central California, the microphytobenthos (MPB) supports diverse assemblages of limpets and littorine snails, which, at current benign temperatures, could potentially partition food resources in a complementary fashion, thereby enhancing secondary productivity. Two limpet species in particular, Lottia scabra and L. austrodigitalis, may partition components of the MPB, and are likely to affect the composition of the MPB on which they graze. In this study, we describe the composition, nutritional value (C:N ratio), and fluorescence (an index of chlorophyll density) of ungrazed, L. scabra-grazed and L. austrodigitalis-grazed MPB, each as a function of temperature. Fluorescence decreased with increased average daily maximum temperature for ungrazed MPB, but temperature had no discernible effects on either fluorescence or the composition of the MPB of grazed assemblages. L. austrodigitalis and L. scabra did not partition the MPB, and did not exhibit complementarity. Both species exhibited an ordered grazing scheme, in which limpets grazed down certain components of the MPB before others, and grazing increased the C:N ratio of the MPB, decreasing its nutritional value. Taken together, these results suggest that L. austrodigitalis and L. scabra may experience increased competition as warming temperatures reduce the available MPB.

This research was published in MEPS in 2016.  It was conducted in collaboration with Luke Miller, Matthew Bracken, Bengt Allen and Mark Denny.  It was supported by the National Science Foundation and Stanford University.

 

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