Research

I am fascinated by the strategies that relatively simple animals use to survive and thrive in complex and variable environments.  As a doctoral student, I initiated a number of investigations related to this topic.  Some of these projects are summarized below.  If you are interested in working or collaborating with me, please contact me at: d.lascala-gruenewald@auckland.ac.nz

The long-term effects of increased temperature on intertidal communities.

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Thermocouples measure temperature on settlement plates in the intertidal zone.  P.C. – Diana LaScala-Gruenewald

Average air and surface temperatures are expected to rise over the coming years, and it is important to understand how organisms and communities will react.  In the intertidal zone, organisms experience moderate average temperatures, with large daily variability, due to the warm, dry conditions that occur during low tide.

In this study, we experimentally increased the average temperature of intertidal communities on rock settlement plates while maintaining the range of daily variation.  After twelve years, we compared the warmed communities to adjacent, unmanipulated communities.  We also used a mechanistic heat-budget model to hindcast the temperatures experienced by the plates and adjacent communities over the twelve year study period.

Using these data, we were able to make concrete, species-specific predictions on how intertidal communities may change with increasing temperatures.  Specifically, we predicted that encrusting green algae will increase, while other major groups of organisms, including barnacles, mussels and filamentous algae, will decrease in abundance and richness.  We also illustrated that using heat budget models to hindcast temperature data can help explain the composition of modern communities.

This research was conducted in collaboration with Mark Denny.  It was supported by the National Science Foundation and Stanford University. 

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

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Epilithic microphytobenthos as visualized by a Scanning Electron Microscope.  PC: Diana LaScala-Gruenewald

The effects of grazers on macroalgal communities in the intertidal zone have been extensively studied.  However, many grazers feed exclusively on epilithic microphytobenthos (MPB), and the spatial distribution and composition of MPB has rarely been described, especially in the context of environmental change.

In this study, we explored the effects of limpet grazing and temperature on the fluorescence, composition and quality of epilithic MPB.  We deployed four plates at each of six sites in the intertidal zone adjacent to Hopkins Marine Station.  One plate was fenced to exclude all grazers, while one lacked a fence and was freely grazed by the natural suite of limpets and littorine snails.  The third plate contained four L. scabra, and the fourth contained four L. austrodigitalis.  The plates were deployed for six months, and temperature and fluorescence (a proxy for chlorophyll a density) were measured throughout that time.  After the plates were collected, the composition of the grazed and ungrazed MPB were assessed using Scanning Electron Microscopy, and the quality of the MPB (as approximated by C:N ratio) was measured.

We found that limpet grazing reduced the percent cover of diatoms and cyanobacteria in the MPB, reduced the fluorescence of the MPB, and increased the C:N ratio of the MPB.  Thus, limpets decreased both the availability and quality of food by grazing.  Additionally, temperature was found to decrease fluorescence, although it did not affect the composition of the MPB.  This suggests that under warmer conditions, the available MPB may decrease and L. scabra and L. austrodigitalis may experience increased competition.  This effect may be exacerbated by the fact that L. scabra and L. austrodigitalis do not appear to partition components of the MPB.

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

The effects of small-scale environmental variability on limpet foraging behavior.

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A waterproof, infrared camera observes limpet foraging regardless of time of day or tidal height.  P.C. – Diana LaScala-Gruenewald

L. austrodigitalis and L. scabra are upper intertidal limpets that forage for epilithic microphytobenthos (MPB) during high tide.  These limpets have relatively limited sensory and neurological capabilities, and yet they perform complex behaviors, such as searching for food sources and returning to a “home scar” after each foraging bout.  Additionally, L. austrodigitalis and L. scabra perform these behaviors under intense and highly variable environmental conditions.

In this study we aimed to describe limpet foraging strategies in situ, and determine whether those strategies appeared to be innate or cued by environmental factors.  To do this, we built four waterproof, infrared cameras (or LimpetCAMs) which could be deployed in the upper intertidal zone adjacent to Hopkins Marine Station.  These cameras recorded limpet movements simultaneously during four, ten-day deployments between June and September of 2015.  During that time period, data on food distributions, small-scale topography, tidal height, time of day, temperature and swell were also collected.

Using the limpet tracks, we characterized foraging behaviors, and tried to determine the search strategies limpets used while foraging.  We also examined the potential roles of trail-following, behavioral plasticity and innate inter-individual variability in limpet foraging behavior.

Results from this study will be posted as they become available.

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.

Perception is paramount: efficient foraging strategies in patchy environments.

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A virtual snail uses a power law foraging strategy with an exponent of -1 to search for food in a simulated patchy environment.

The Levy Flight Foraging Hypothesis (LFFH) states that if 1) a forager is memoryless 2) food is sparse and randomly distributed and 3) the average distance between food patches is much greater than the distance from which the forager can detect food, then the optimal foraging strategy is defined by a power law step length distribution with an exponent of -2 (mu = 2).  Numerous organisms across taxa have been observed using this search strategy over the past two or three decades.  However, the LFFH has a number of limitations.  For example, the optimal exponent of -2 is difficult to identify in empirical data.

The power law exponent of a step length distribution describes how often an organism takes a very long step, where a step is defined as how far that organism moves before changing direction.  A power law distribution with an exponent of -1 describes a relatively high probability of an organism taking very long steps, whereas a power law distribution with an exponent of -3 describes a relatively low probability of an organism taking very long steps.

In this in silico study, we used an agent-based modeling approach to determine foraging success 1) under a range of environmental conditions 2) when the forager’s exponent and range of perception was varied and 3) when the distance traveled in addition to the quantity of food found was taken into account.  We first generated 21 landscapes, which had variable food availabilities and distributions.  Then, we simulated foraging with a variety of exponents and range of perceptions on each landscape.  We measured the quantity of food each forager encountered, and their benefit-cost ratio.

We found that the optimal exponent of -2 never performed best in our simulations.  Additionally, an exponent of -1 was best when considering food found, but an exponent of -3 was best when considering benefit-cost ratios.  Finally, range of perception contributed far more to foraging success than the power law exponent.  These results suggest that foragers will benefit more from improving perception on evolutionary time scales than they will from changing their foraging strategy.

This research was conducted in collaboration with Mark Denny, Rohan Mehta and Ernest Liu.  It was supported by the National Science Foundation and Stanford University.

Snail personality: The trade-off between behavioral traits and behavioral plasticity in an intertidal limpet.

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A limpet forages on an artificial food landscape.  P.C. – Diana LaScala-Gruenewald

In the upper intertidal zone, the limpet Lottia austrodigitalis performs complex and highly individual foraging behaviors.  Some organisms home consistently, while others do not.  The length, tortuosity and large-scale pattern of limpet tracks also differ between individuals.  Sometimes, these features also differ within individuals through time.  But do these features of limpet tracks reflect behavioral plasticity or limpet personality?

In this experiment, we collected 12 L. austrodigitalis from the field and observed their foraging behaviors across a range of artificial food distributions.  These food distributions were created using clean mosaic tiles and mosaic tiles covered in food (microalgae), placed within a 1×1 m enclosure.  We observed each individual foraging for 14 simulated high tides on four food distributions: no food, low patchiness, high patchiness, and all food.  The no food treatment allowed us to quantify the foraging behavior that was innate to each individual observed.  Then, the subsequent treatments allowed us to quantify how that individual adapted its foraging behavior to changes in food distribution.

Results from this study will be posted as they become available.

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.

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Mounting LimpetCAM tripods in the intertidal zone.  P.C. – Tom Hata.