DOI: 10.5061/dryad.j9kd51cp2
title: Food limitation erodes the thermal tolerance of larvae in an ecologically influential marine herbivore

description: Biologists often use organismal thermal tolerance to help explain or
 forecast responses of populations to climate change.  Yet many
 studies quantify thermal tolerance under isolated laboratory conditions
 despite extreme events, such as heatwaves, often coinciding with other
 stressors such as nutrient or food limitation. These oversights may be
 consequential as recent theory suggests thermal tolerance itself can be
 fundamentally altered by food limitation. Here, we experimentally test how
 food limitation affects long-term survival, development, and growth across
 a present-day range of temperatures in the most sensitive life stages of a
 key marine herbivore, purple sea urchins (Strongylocentrotus
 purpuratus).  We show food limitation substantially erodes
 thermal tolerance in terms of survival, but when provided ample food,
 larvae exhibited robust survival across temperatures currently experienced
 by larvae in nature. Reductions in food however lowered optimal survival
 temperatures and shifted thresholds of collapse to those conditions
 observed during recent marine heatwaves. These results are consistent with
 the “metabolic meltdown” hypothesis - shifting optima and upper limits to
 cooler temperatures- and illustrate how present day warming with lower
 productivity may lead to substantial, unexpected declines in larval
 recruitment. In contrast to survival, developmental rates and time to
 metamorphic competency were driven largely by temperature with little
 impact of food concentration. Our findings relate to historical
 observations of collapses in larval supply at the southern edge of the
 species range. Overall, these results have broad-reaching implications
 beyond these sea urchins known to control productivity of kelp forests. We
 provide a core example of how laboratory derived thermal reaction norms
 can under-estimate effects of climate change and may explain unexpected
 vital rate declines of sensitive life-stages in nature.
description: # Food limitation erodes the thermal tolerance of larvae in an
 ecologically influential marine herbivore Dataset DOI:
 [10.5061/dryad.j9kd51cp2](10.5061/dryad.j9kd51cp2) ## Description of the
 data and file structure We experimentally test how food limitation
 (500-10,000 cells mL-1) affects long-term survival, development, and
 growth across a present-day range of temperatures (10-20ºC) in the larval
 stages of a key marine herbivore, purple sea urchins (*Strongylocentrotus
 purpuratus*).  ### Files and variables #### File: dpf_stage_temp_food.csv
 **Description:** Number of days to reach each stage of larval development
 and metamorphic competency across food and temperature treatments #####
 Variables * temp: temperature treatment in ºC * food: microalgal food
 treatment in cells mL-1 * days_settled: number of days to reach
 metamorphic competency * days_prism: number of days to reach prism stage *
 days_fourarm: number of days to reach four arm stage * days_sixarm: number
 of days to reach six arm stage * days_eightarm: number of days to reach
 eight arm stage * n/a: no data available * dead: larval culture died
 before reaching settlement #### File: larvae_measurements_scaled.csv
 **Description:** Measurements for body length, stomach area, and postoral
 arm length across temperature treatments, food treatments, bottle
 replicates, and 4-, 9- and 15-day timepoints ##### Variables * dpf: days
 post fertilization * temp: experimental temperature treatment in ºC *
 food: experimental microalgal food treatment in cells mL-1 * rep: bottle
 replicate * individual: within each bottle replicate, 20 individuals were
 measured. 'individual' refers to the 1-20 individuals measured *
 POA1: measurement of the first postoral arm in µm * POA2: measurement of
 the second postoral arm in µm * BL: measurement of body length in µm *
 SW: measurement of stomach width in µm * SH: measurement of stomach height
 in µm * POA: averaged length of the first and second postoral arm
 measurements in µm * SA: calculated stomach area using area of a circle
 with stomach width and length measurements #### File:
 roller_density_counts.csv **Description:** Raw counts from the subsets of
 larval samples taken every other day throughout the experiment. #####
 Variables * date: calendar day the sample was taken * temp: experimental
 temperature treatment in ºC * food: experimental microalgal food treatment
 in cells mL-1 * rep: bottle replicate * count: indicate which count within
 each replicate 1 through 5 * count_value: number of larval individuals
 counted in each of the 5 1mL subsamples * avg_count: average count across
 the five subsamples * volume: total volume in which the 5 subsamples were
 taken from * avg_bottle: average number of algae scaled from the 5 1mL
 subsample counts and total volume * date1: indicator of each day the
 larvae were sampled * dpf: days post fertilization #### File:
 TableS1*survmort***perbottle_**modeloutput.csv **Description:** Estimated
 survival from model outputs across temperature treatments, food
 treatments, bottle replicates, and density count days. ##### Variables *
 bottle_id: bottle replicate * treatment: unique number provided for each
 distinct treatment combination * date1: indicator of each day the larvae
 were sampled * temp: experimental temperature treatment in ºC * food:
 experimental microalgal food treatment in cells mL-1 * dpf: days post
 fertilization * obs: binary value to indicate if an observation was made
 (1) or not made (0) * est: means for instantaneous mortality * est_surv:
 estimates for cumulative survival #### File:
 TableS2_survival15daypairwise.csv **Description:** Pariwise comarpisons
 between all treatment combinations at the 15 day timepoint. Values below
 0.05 are considered significantly different survival values between the
 two paired treatments. ##### Variables * variable format: first
 number_second number * first number: experimental temperature treatment in
 ºC * second number: experimental microalgal food treatment in cells mL-1
 #### File: TableS3_morphometricpairwise.xlsx **Description:** Pairwise
 comparisons of each larval morphometric body measurements (body length,
 stomach area, and postoral arm length) at each of the timepoints,
 represented in each tab of the data file. ##### Variables * variable
 format: first number_second number * first number: experimental
 temperature treatment in ºC * second number: experimental microalgal food
 treatment in cells mL-1 * BL: measurement of body length in µm * POA:
 averaged length of the first and second postoral arm measurements in µm *
 SA: calculated stomach area using area of a circle with stomach width and
 length measurements ## Code/software R version 4.4.0 (2024-04-24) ##
 Access information Other publicly accessible location of the data: DOI:
 10.26008/1912/bco-dmo.963415.1