DOI: 10.5061/dryad.9s4mw6mg9
title: Microhabitat temperature variation combines with physiological variation to enhance thermal resilience of the intertidal mussel Mytilisepta virgata

description: 1. Predicting the effects of rising temperature entails measuring both
 habitat thermal characteristics and the physiological variation of the
 species as it relates to this microhabitat variation; these two types of
 measurements can generate what is termed a “physiological landscape” for
 the species. Mapping the micro-scale physiological landscape across space
 and time, rather than relying on large-scale averages of temperature and
 means of thermal limits in a species, can allow more accurate estimates of
 an organism’s sensitivity to temperature change and support development of
 more refined models of the impacts of anthropogenic climate change that
 have higher predictive power. 2. We thus continually monitored the body
 (operative) temperature of the intertidal mussel Mytilisepta virgata in
 both sun-exposed and shaded microhabitats and determined the seasonal
 variations of cardiac performance of field-acclimatized and
 laboratory-acclimated mussels from different microhabitats for calculating
 the thermal sensitivity, as indicated by the difference between the
 maximum ambient temperature and an individual’s upper thermal limit
 (thermal safety margin, TSM), in each microhabitat and each month. 3. The
 mussels experienced divergent thermal stress, in average temperature,
 acute and chronic thermal stress, and thermal predictivity among different
 microhabitats, and presented high spatial-temporal variations of cardiac
 function as results of seasonal acclimatization and inter-individual
 variations. Results of TSMs indicated that the thermal sensitivities of
 the mussels to high temperature were season- and microhabitat-specific,
 and the mussels in the shaded microhabitats were predicted to survive the
 hottest summer temperatures; however, some individuals in the sun-exposed
 microhabitats experienced temperatures above their sublethal temperature.
 4. With the large, high-resolution dataset of thermal environmental
 characteristics and the cardiac performances with high variations, we were
 able to integrate the effects of synchronized changes in
 microenvironmental temperatures and cardiac thermal responses and thereby
 characterize the physiological landscape of thermal sensitivity. The
 complex physiological landscape that exists in the intertidal zone must be
 taken into account when predicting effects of changes in environmental
 temperature, such as those occurring with global climate change.
description: The operative temperature of the mussels was continuously
 recorded using biomimetic thermal loggers, Robo-mussels. For preparing a
 Robo-mussel, a data logger iButton (DS1922L, Maxim Integrated, CA, USA)
 was inserted into a shell of a mussel (shell length, 4-5 cm) filled with
 3M Scotchcast 2130 Flame Retardant Compound as described in the previous
 study. A total of 12 Robo-mussels were deployed at six microhabitats at
 the Dongshan Swire Marine Station (D-SMART), Fujian Province, China
 (23.65°N, 117.49°E). In each microhabitat, two Robo-mussels were deployed
 between 1.80 and 2.50 meters above chart datum (CD, the level from which
 depths displayed on a nautical chart are measured) where the black mussel
 normally occurs. Among the six microhabitats, three were south-facing
 (sun-exposed) and three were north-facing (shaded) microhabitats. After
 May 2019, due to the low density of the mussel in the shaded #3
 microhabitat, another shaded microhabitat (shaded #4) was added as a
 substitute. Temperature was recorded at an interval of 1 hour and an
 accuracy of 0.5°C from May 2018 to September 2019. A
 non-invasive method was used to measure individual heart rates. An
 infrared sensor (IR-EX, Newshift, Portugal) for heart rate measurement was
 directly attached above the mussel's peripheral heart cavity using
 Blu-Tack (Bostik, Wauwatosa, Wisconsin). The mussel was heated in air
 using a water bath (TXF 200, Grant, UK) from 25°C at a rate of 6°C h-1
 until a temperature was reached where the heart rate fells to zero (Flat
 line temperature, FLT) as described in our previous study. Body
 temperature was measured simultaneously during heating using thermocouple
 thermometers inserted inside the shell (Fluke 54II, Fluke, WA). The
 infrared heartbeat signal was amplified (AMP03, Newshift, Leiria,
 Portugal), filtered, smoothed, and recorded with a PowerLab unit (16/30,
 ADInstruments, March-Hugstetten, Germany). Data were viewed and analyzed
 using LabChart (v. 7.2) (ADInstruments, Germany). Arrhenius break
 temperature (ABT) values were calculated by using linear regression in
 Origin ver. 9 (OriginLab Corporation, MA, USA).