Spatial Variation in Thermal Stress Experienced by Barnacles on Rocky Shores: The Interplay Between Geographic Variation, Tidal Cycles and Microhabitat Temperatures

Hui-Yu Wang,Rui Seabra,Monthon Ganmanee,Ling Ming Tsang,Benny K K Chan,Gray A Williams,Fernando P Lima

doi:10.3389/fmars.2020.00553

Abstract

Thermal stress is an important driver of species’ distribution in the intertidal zone and, with the forecasted increasing frequency of extreme high temperatures associated with climate change, is likely to play an even greater role in the future. To better understand the scales at which thermal stress impacts organisms, we used biomimetic temperature loggers (robobarnacles) to measure latitudinal variation in estimated barnacle body temperatures (Tetraclita spp.) and evaluated the influences of large, geographic, and smaller scale, microhabitat variation on temperatures experienced. Robobarnacles were deployed at nine sites along the West Pacific and South China Sea coast (five sites in Taiwan, three in Hong Kong and one in Thailand, spanning 13-25 N) from May to September 2013. Estimated body temperatures did not follow a latitudinal gradient; instead, they revealed a mosaic of hot (e.g., NE Taiwan and Thailand) and cooler sites (e.g., two sites in Hong Kong). The hot sites were characterized by frequent occurrences of ‘heat stress’ events (estimated body temperatures  40C for  2 hours which would result in  50% Tetraclita entering coma). There was a correlation between hourly air temperatures and robo-temperatures, suggesting that air temperature together with solar radiation and thermal radiation re-emited by the rocky substrate drove the observed spatial robo-temperature variation. Air temperature is, therefore, an important contributor in affecting the body temperature of sessile intertidal species in the tropical and subtropical W Pacific and South China Sea and can be a good predictor for body temperature and thermal stress of intertidal barnacles.

Highlights

Global climate change has been predicted to severely impact marine ecosystems, driving mass mortality, altering selection pressures and the geographic distribution of species (Helmuth et al, 2006a; Hawkins et al, 2008)
Biomimetic loggers collecting long-term, high-resolution temperature data can provide a direct measure of temperature variability and extremes experienced by intertidal organisms during periods of high thermal stress such as in the summer/hot season (Helmuth et al, 2006b; Dong et al, 2015; Lathlean et al, 2015; Judge et al, 2018; this study)
Based on such temperature data from robobarnacles, our analyses revealed a mosaic pattern of hot (e.g., NE of Taiwan and Thailand) and cool sites or “spots” along locations of the W Pacific and South China Sea, which did not match a simple latitudinal pattern

Summary

Introduction

Global climate change has been predicted to severely impact marine ecosystems, driving mass mortality, altering selection pressures and the geographic distribution of species (Helmuth et al, 2006a; Hawkins et al, 2008). A common prediction of the impacts of increasing temperature is a latitudinal, poleward shift of species with the assumption that thermal stress will be more intense toward the equator (Southward et al, 1995; Broitman et al, 2001; Helmuth et al, 2006a; Parmesan, 2006; Sanda et al, 2019). Helmuth et al (2002), showed that estimates of the “body” temperature of the intertidal mussel, Mytilus californianus, using biomimetic robomussels, did not increase monotonically with decreasing latitude along the west coast of United States, but rather reflected a mosaic of sites with different thermal environments. A further study on heat stress of limpets along the Atlantic coast of Europe, based on thermal profiles recorded by biomimetic loggers (robolimpets), demonstrated that the degree of exposure to solar radiation may override large-scale latitudinal gradients in thermal stress, resulting in a mosaic pattern of hot and cold sites (Seabra et al, 2011)

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