Field temperatures from Tegula Intertidal marine snail habitats in San Diego, California

Climate change-induced population declines of highly abundant intertidal invertebrates will affect ecosystem function and stability, but it is not fully understood which species are most vulnerable to these declines. Rocky intertidal Tegula snails live at different tidal heights and exhibit variability in heat tolerance, but the temperatures these different species experience in the field, and thus which species are most susceptible to climate change, remains unknown. Here, we use HOBO data loggers to record field temperatures in the unique thermal habitats of Tegula eiseni, Tegula funebralis, and Tegula gallina in San Diego, California. Determining the maximum temperatures each Tegula species is exposed to in the field will ultimately inform conservation efforts by identifying which Tegula species are most threatened by heat stress.

Methods
HOBO Pendant MX Water Temperature Data Loggers (Onset) set to record temperature every 10 minutes were deployed at two different study sites in San Diego, CA: La Jolla (LJ; 32°52’N, 117°15’W) and Bird Rock (BR; 32°48’N, 117°15’W) for 12.5 weeks. At La Jolla, only Tegula gallina were abundant, so two loggers were deployed to assess field temperatures experienced by this species. At Bird Rock, all three Tegula species (Tegula eiseni, Tegula funebralis, and Tegula gallina) were abundant, so six total loggers were deployed with two set to assess field temperatures experienced by each species. Loggers were attached to the horizontal surface of rocks next to live individuals of each respective species in the intertidal using Z-spar epoxy (A-788 Splash Zone Compound; Lima & Wethey 2009). This placement ensured temperatures were recorded from habitat the Tegula individuals utilize. 

Loggers were deployed for 12.5 weeks from July to October 2024. Bird Rock suffered high loss of instrumentation, losing one T. eiseni logger, one T. funebralis logger, and both T. gallina loggers. T. gallina data presented here are from the La Jolla loggers placed ~ +0.5 m and ~ +1.0 m above mean lower low water (MLLW). The T. funebralis and T. eiseni data are from Bird Rock loggers, placed at ~+0.76 m and ~+0.12 m, respectively. During deployment, the T. funebralis logger at Bird Rock was turned upside down and submerged in a tidepool which prevented it from logging air temperatures. To estimate when this occurred, we used the temperature data, in conjunction with the high and low tide times and predictions of temperature fluctuations that would occur if the logger was exposed to air, and thus removed any data after September 18, 2024.