Experiencing the salt marsh environment through the foot of Littoraria irrorata: Behavioral responses to thermal and desiccation stresses Josephine C. Iacarella ⁎, Brian Helmuth University of South Carolina, Department of Biological Sciences and Marine Science Program, Columbia, SC 29208, United States abstract article info Article history: Received 27 November 2010 Received in revised form 16 August 2011 Accepted 17 August 2011 Available online 8 September 2011 Keywords: Behavior Desiccation stress Evaporative cooling Littoraria irrorata Salt marsh Thermal stress Behavioral responses to environmental conditions can determine both the microclimate surrounding an or- ganism, as well as how an organism experiences that microclimate. The salt marsh snail Littoraria irrorata (Say) employs two types of behaviors that potentially affect its likelihood of experiencing thermal and/or desiccation stress: 1) retracting its foot into its shell and 2) vertically migrating on the marsh grass Spartina alterniflora. One aim of our study was to determine how the use of retracting behaviors by L. irrorata modifies its ability to tolerate thermal and desiccation stresses, and the interactions between these stresses. A related goal was to elucidate whether the snails move vertically on the stalks of S. alterniflora to avoid thermal and/or desiccation stresses. In the laboratory, snails were kept in 10 biomimic (~ potential body) temperature (25– 45 °C in 5 °C increments) and vapor density (VD) deficit (~ 3 g/m 3 and ~ 17 g/m 3 ) treatments to determine how they use retracting behaviors to avoid thermal and desiccation stresses. Performance measurements of water loss, body temperature, and mortality were made in relation to behavioral responses, with indepen- dent measures from 1.5 to 9 h. In the South Carolina salt marsh, snails' movements and retracting behaviors were monitored and compared to their body temperatures and microclimate conditions. Measurements were made in the high and low marsh (characterized by the height of S. alterniflora) as a function of height in the canopy. We found that the snails used retracting behaviors to shift their ability to tolerate thermal and des- iccation stresses by changing their capacity for evaporative cooling through mantle exposure. L. irrorata con- sistently responded to emersion, or potential desiccation stress, by retracting into its shell, and continued to avoid water loss even under high thermal stress. Both field and laboratory experiments indicated that the snails' behavioral avoidance of thermal stress was severely limited by simultaneous avoidance of desiccation stress. Furthermore, snail movement was largely restricted to periods of tidal inundation in the low marsh and did not reflect behavioral avoidance of abiotic stresses. The use of retracting behaviors by L. irrorata to manipulate its tolerance to temperature and humidity levels exemplifies the importance of behavior as a functional trait that determines its climate space. Viewing behavior at a mechanistic level provides a more accurate picture of how organisms experience their environment and how these impacts translate to interac- tions at the community level. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Mechanistic approaches to measuring an organism's fundamental niche generally focus on physiological tolerance to environmental pa- rameters, but including the effects of an organism's behavior can be challenging (McGill et al., 2006). For example, many studies of desert ectotherms have modeled behavioral responses of reptiles in response to changing environmental conditions, allowing animals to move be- tween microhabitats in a heterogeneous landscape as a means of main- taining a preferred body temperature (eg. Huey et al., 1989; Huey, 1991). However, few studies have considered the role of behaviors other than movement, especially in marine invertebrates. The fundamental niche (Hutchinson, 1957) has traditionally been defined as an organism's physiological tolerance to environmental pa- rameters (Porter et al., 1973) and has been used to correlate environ- mental variables and performance measurements (Kearney et al., 2010). However, this method does not account for the fact that ambi- ent environmental measurements are often poor predictors of an organism's physiological condition and that they do not necessarily reflect physiological and behavioral responses (Kearney et al., 2010). For example, body temperatures often differ from air temperature as a result of changes in parameters such as solar radiation and wind speed (Broitman et al., 2009; Davies, 1970; Edney, 1953; Etter, 1988; Gates, 1980; Lewis, 1963; Southward, 1958; Vermeij, 1971). There- fore, defining the axis of a fundamental niche space with a few envi- ronmental parameters, and no direct connection to the organism's physiological condition, may yield little or no correlation to survival, growth, or reproduction (Kearney, 2006). Journal of Experimental Marine Biology and Ecology 409 (2011) 143–153 ⁎ Corresponding author. Tel.: + 1 803 777 3931. E-mail address: josephine.iacarella@mail.mcgill.ca (J.C. Iacarella). 0022-0981/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jembe.2011.08.011 Contents lists available at SciVerse ScienceDirect Journal of Experimental Marine Biology and Ecology journal homepage: www.elsevier.com/locate/jembe