Rainfall and Temperature Modulate Heart Rates in the Intertidal Limpet Siphonaria javanica (Lamarck, 1819) (Gastropoda: Heterobranchia: Siphonariidae)

This study investigated the heart rate (HR) patterns of Siphonaria javanica on a rocky shore in west central Philippines. Five individuals (shell lengths: 2.8–15.6 mm) were monitored noninvasively using a heart rate monitor (ElectricBlue PULSE V2) while exposed to occasional rainfall without seawater immersion. Results revealed a significant inverse relationship between limpet size and HR, with smaller limpets exhibiting higher baseline heart rates (100–122 bpm) compared to the largest individual (~70 bpm). A midday rainfall event led to transient bradycardia, correlating with sudden declines in air and rock temperatures. Cross-correlation analysis further indicated a strong delayed metabolic response to rock temperature fluctuations. This study is the first to examine heart rate in a marine organism, specifically S. javanica, in the Philippines. Our findings support the size dependence of HR and highlight the effects of hypo-osmotic stress. Future studies should increase the sample size and replicates, capture varying environmental conditions such as clear, high-irradiance periods, and include other intertidal species. These efforts will be crucial for further elucidating the range of metabolic responses of intertidal species in the Philippines.