Factorial field manipulation reveals multi-stressor effects on a critical habitat-forming shellfish

Ocean acidification and warming are expected to have negative impacts on marine organisms, and particularly on shell-building species. Acidification and warming may operate independently or interactively, amplifying or mitigating impacts on individuals. Previous results have primarily come from lab studies of single species, yet these climate stressors are occurring within naturally dynamic systems with high abiotic and biotic variability. As a result, the impacts of these stressors in situ remains poorly understood. We conducted a 6-month field manipulation to determine the effects of ocean acidification and warming on a habitat-forming shellfish, the Pacific blue mussel (Mytilus trossulus), in a dynamic coastal system. Twenty tide pools were factorially manipulated, including unmanipulated control, CO2 added, warmed, and combined CO2 added and warmed treatments. We measured mussel shell thickness, strength, and corrosion at 0, 3, and 6 months of exposure to treatment conditions. CO2 a..., Temperature Data:
Temperature data was collected at the tide pool level using Onset ® HOBO TidbiT temperature loggers (±0.2 accuracy) that recorded temperature consecutively every 5 min from March to September 2019. Temperature data were summarized for the 28-day periods preceding each collection period (March, July, and September). For each tidepool, we calculated the following thermal parameters: minimum, mean daily minimum, 10th percentile, median, average, range, mean daily range, mean daily average, maximum, mean daily maximum, 90th percentile, mean daily 90th percentile, 95th percentile, 99th percentile, mean daily 90th percentile temperatures, mean daily 95th percentile temperatures, mean daily 99th percentile temperatures. All temperature data was separated into low day and nighttime tides based on known shore heights and observed tide data from  Sitka Harbor, Baranof Island, Sitka, Alaska (tbone tides; https://tide.arthroinfo.org/).
Environmental Tide Pool Data: ..., , # Factorial field manipulation reveals multi-stressor effects on a critical habitat-forming shellfish

This file contains the information about the datasets used in Rangel et al. 2025 where we conducted a 6-month long field manipulation of pH and temperature in 20 tide pools in Sitka, Alaska and measured effects on the mussel *Mytilus trossulus* shell traits and function. We measured mussel shell thickness, strength, and corrosion.

**File names:** DayCarbChem_Mussel.csv

* Sample ID: Number of sample in collection sequence
* Date: Date sample was collected
* Month: Month sample was collected
* Year: Year sample was collected
* DayNight: Whether the sample was collected during daytime or nighttime
* OnOff: On means climate manipulations were on and off means when climate manipulations were turned off
* Timepoint: Time point during each tide when sample was taken (1-3) with 3 being the time point after the longest time of separation from the ocean
* Pool: Tide pool number where sample wa...,