Mosaic Patterns of Thermal Stress in the Rocky Intertidal Zone: Implications for Climate Change

Abstract

Abstract. We explicitly quantified spatial and temporal patterns in the body temperature of an ecologically important species of intertidal invertebrate, the mussel Mytilus californianus, along the majority of its latitudinal range from Washington to southern California, USA. Using long-term (five years), high-frequency temperature records recorded at multiple sites, we tested the hypothesis that local ''modifying factors'' such as the timing of low tide in summer can lead to large-scale geographic mosaics of body temperature. Our results show that patterns of body temperature during aerial exposure at low tide vary in physiologically meaningful and often counterintuitive ways over large sections of this species' geographic range. We evaluated the spatial correlations among sites to explore how body temperatures change along the latitudinal gradient, and these analyses show that ''hot spots'' and ''cold spots'' exist where temperatures are hotter or colder than expected based on latitude. We identified four major hot spots and four cold spots along the entire geographic gradient with at least one hot spot and one cold spot in each of the three regions examined (WashingtonOregon, Central California, and Southern California). Temporal autocorrelation analysis of year-to-year consistency and temporal predictability in the mussel body temperatures revealed that southern animals experience higher levels of predictability in thermal signals than northern animals. We also explored the role of wave splash at a subset of sites and found that, while average daily temperature extremes varied between sites with different levels of wave splash, yearly extreme temperatures were often similar, as were patterns of predictability. Our results suggest that regional patterns of tidal regime and local pattern of wave splash can overwhelm those of large-scale climate in driving patterns of body temperature, leading to complex thermal mosaics of temperature rather than simple latitudinal gradients. A narrow focus on population changes only at range margins may overlook climatically forced local extinctions and other population changes at sites well within a species range. Our results emphasize the importance of quantitatively examining biogeographic patterns in environmental variables at scales relevant to organisms, and in forecasting the impacts of changes in climate across species ranges.

Contingencies and compounded rare perturbations dictate sudden distributional shifts during periods of gradual climate change

“…Thus, the M. parksii zone may eventually collapse to zero (a local extinction event) as conditions warm through time, as has been observed across local and regional scale temperature gradients in space (8). Furthermore, in the southern portions of its range, or at localized ''hotspots'' (23,24), site-scale local extinctions should become more frequent, resulting in step-like range contractions that reflect the stochastic occurrence of lethal stress events. Although the ''tipping point'' and the mechanisms underlying the responses of this high intertidal alga may seem minor on a global scale, they clearly identify the challenge to managers of anticipating, let alone reacting to more catastrophic events.…”

Supply-side biogeography: geographic patterns of settlement and early mortality for a barnacle approaching its range limit

“…This is perhaps surprising because studies have shown that such differences in seawater temperatures can influence the reproductive ability of benthic marine invertebrates (Brey 1995, Vilchis et al 2005, and field investigations have detected reduced fecundity at range limits due to changes in seawater temperature (Barber & Blake 1983, Amaro et al 2005). However, Helmuth et al (2006) assessed body temperatures of the intertidal mussel Mytilus californianus across a latitudinal gradient in sea-surface temperatures and found that body temperatures were often hotter or colder than was predicted from sea-surface temperatures. Consequently, the lack of a latitudinal decline in larval production within the present study may reflect complex interactions between air and seasurface temperatures.…”

Thermal tolerance of the hermit crab <i>Pagurus samuelis</i> subjected to shallow burial events

“…Northward range shifts in the distribution of marine organisms, such as the Zebra perch fish, Hermosilla azurea (Sturm & Horn, 2001), and the Kellet s whelk, Kelletia kelletii (Zacherl et al, 2003), have already been measured in California. Other studies have identified the presence of hotspots and coldspots where maximal and minimal daily temperatures are relatively higher and lower, respectively, than expected at their latitudes (Helmuth et al, 2006). Intertidal organisms in these regions are susceptible to temperatures outside their normal physiological range which may result in lethal alterations of biological and physiological processes (Stillman, 2002), since almost all biological structures and processes are affected by temperature (Hochachka & Somero, 2002).…”