DOI: 10.5061/dryad.8sf7m0cq7
title: Coupled changes in pH, temperature and dissolved oxygen impact the physiology and ecology of herbivorous kelp forest grazers

description: Understanding species’ responses to upwelling may be especially important
 in light of ongoing environmental change. Upwelling frequency and
 intensity are expected to increase in the future, while ocean
 acidification and deoxygenation are expected to decrease the pH and
 dissolved oxygen of upwelled waters. However, the acute effects of a
 single upwelling event and the integrated effects of multiple upwelling
 events on marine organisms are poorly understood. Here, we use in situ
 measurements of pH, temperature, and dissolved oxygen to characterize the
 covariance of environmental conditions within upwelling-dominated kelp
 forest ecosystems. We then test the effects of acute (0-3 days) and
 chronic (1-3 month) upwelling on the performance of two species of kelp
 forest grazers, the echinoderm, Mesocentrotus franciscanus, and the
 gastropod, Promartynia pulligo. We exposed organisms to static conditions
 in a regression design to determine the shape of the relationship between
 upwelling and performance and provide insights into the potential effects
 in a variable environment. We found that respiration, grazing, growth, and
 net calcification decline linearly with increasing upwelling intensity for
 M. francicanus over both acute and chronic timescales. Promartynia pulligo
 exhibited decreased respiration, grazing, and net calcification with
 increased upwelling intensity after chronic exposure, but we did not
 detect an effect over acute timescales or on growth after chronic
 exposure. Given the highly correlated nature of pH, temperature, and
 dissolved oxygen in the California Current, our results suggest the
 relationship between upwelling intensity and growth in the 3-month trial
 could potentially be used to estimate growth integrated over long-term
 dynamic oceanographic conditions for M. franciscanus. Together, these
 results indicate current exposure to upwelling may reduce species
 performance and predicted future increases in upwelling frequency and
 intensity could affect ecosystem function by modifying the ecological
 roles of key species.
description: Biological data were collected during Spring 2019 (Experiment 1)
 and Summer 2020 (Experiment 2). During each experiment, red sea urchins,
 Mesocentrotus franciscanus, and brown turban snails, Tegula pulligo, were
 reared across a gradient of upwelling conditions in a laboratory mesocosm
 system. Within each replicate treatment aquarium, we placed sea urchins
 and gastropods (N = 4-8 and N = 9-10 respectively) in individual 0.5 L
 cages where they were fed ad libitum for the duration of the experiment
 (except during respirometry and grazing trials). For experiment 1, at the
 beginning and after one month, two months and three months in treatment
 conditions, we measured wet and buoyant weight. After one, two and three
 months we measured respiration rate and per capita grazing rate of all
 individuals. For experiment 2, we measured respiration rate and per capita
 grazing rate of all individuals immediately after being placed in
 experimental conditions and after 48 hours. Chemistry
 data were collected during two mesocosm experiments testing the effects of
 (1: chronic, 2: acute) upwelling on kelp forest grazers. These data were
 used to characterize the carbonate chemistry system in experimental
 treatments. Discrete samples for carbonate chemistry analyses were
 collected approximately every two weeks for the duration of both
 experiments using best practices for ocean CO2 measurements. Associated
 salinity, temperature and dissolved oxygen measurements were made within
 an hour of discrete sample collection.