DOI: 10.5061/dryad.ht76hdrrd
title: Abiotic factors that prompt major ecological transitions: are fish on land to escape an intolerable aquatic environment?

description: Colonisation of novel habitats are important event in evolution, but the
 factors that initially prompt such ecological transitions are often
 unknown. The invasion of land by fish is an extreme habitat transition
 that offers an opportunity to empirically investigate the causes of major
 ecological transitions. The intertidal ecotone—and rockpools in
 particular—have been an important staging ground for transitions onto
 land. Classic hypotheses focus on the adverse abiotic conditions of
 rockpools at low tide as the instigator of fish voluntarily stranding
 themselves out of water, which can then lead to the evolution of an
 amphibious lifestyle. To test these hypotheses, we studied the abiotic
 conditions of 54 rockpools on the island of Guam where there are various
 species of aquatic, amphibious, and terrestrial blenny fishes. We found
 little support for the expected deterioration of abiotic conditions in
 standing pools at low tide (salinity, pH, and oxygen), and fish were not
 seen to be excluded from those pools that were found to exhibit poor
 abiotic conditions (temperature, salinity, and pH). Hypoxia was the only
 factor that might account for the absence of blennies from certain
 rockpools. Next, we experimentally measured oxygen depletion by an
 aquatic, mildly amphibious, and highly amphibious species of blenny in a
 simulated rockpool to infer the proportion of rockpools at low tide
 outside the tolerable range of blennies. Rockpools were found to have
 oxygen levels within the requirements of most blennies and other marine
 fishes. We conclude that the abiotic environment of rockpools alone was
 unlikely to have instigated the evolution of amphibious behaviour in
 blennies. Instead, the broad range of abiotic conditions experienced in
 rockpools suggests these conditions could have primed blennies to better
 endure the novel conditions on land. Any ecotone typified by fluctuations
 or gradients in abiotic conditions is likely a key transitional
 environment for the invasion of novel habitats and, as such, is an
 important location for adaptive evolution and species diversification.
description: # Abiotic factors that prompt major ecological transitions: are fish on
 land to escape an intolerable aquatic environment?
 [https://doi.org/10.5061/dryad.ht76hdrrd](https://doi.org/10.5061/dryad.ht76hdrrd) ## Description of the data and file structure All data were collected or compiled by Terry Ord ([t.ord@unsw.edu.au](mailto:t.ord@unsw.edu.au)). Related manuscript (MS) information * MS Reference Number: FE-2024-01331 * MS Title: Abiotic factors that prompt major ecological transitions: are fish on land to escape an intolerable aquatic environment? * MS Authors: Ord, Terry J; Surovic, Elizabeth; Vaz, Diego; Irisarri, Iker * MS Journal: Functional Ecology ## OrdTJ\_FE-2024-01331\_rockpool\_volumes.csv Data used to validate the method for estimating rockpool volume #### FILE STRUCTURE AND UNITS OF MEASUREMENTS The file is a .csv file that can be opened using any text, spreadsheet, or statistical program. There are no missing values. * rockpool = The unique ID label for each rockpool surveyed. * TrueVol_L = The actual volume of rockpool in litres recorded by manual emptying. *  EstiVol_L = The estimated volume of rockpool in litres based on an ellipsoid formula based on the length, width, and depth of the rockpool ## OrdTJ\_FE-2024-01331\_rockpool\_conditions.csv Data used to test changes in abiotic conditions and abundance of blenny fishes and primary producers in rock pools at low tide versus high tide.  #### FILE STRUCTURE AND UNITS OF MEASUREMENTS The file is a .csv file that can be opened using any text, spreadsheet or statistical program. Missing values are indicated by NA. * rockpool = The unique ID label for each rockpool surveyed. * date_LOW = date (day-month-year) that rockpool was surveyed at low tide. * max_tempC_LOW = maximum water temperature in degrees Celsius recorded by miniDOT logger at low tide. * min_Oxy_mgL_LOW = minimum dissolved oxygen in micrograms per litre recorded by miniDOT logger at low tide. * min_OxyPercentSATURATION_LOW = minimum percentage oxygen saturation recorded by miniDOT logger at low tide. * inclusive_of_exact_lowtide = whether miniDOT loggers were in rock pools over the exact time of low tide, coded as “yes” or “no” * water_tempC_LOW = point estimate of water temperature in degrees Celsius taken using a handheld digital meter at low tide. * pH_LOW = point estimate of pH taken using a handheld digital meter at low tide. * salinity_ppt_LOW = point estimate of water salinity in parts per thousand (ppt) taken using a handheld digital meter at low tide. * air_tempC_LOW = point estimate of air temperature in degrees Celsius taken using a handheld thermo-windmeter at low tide. * esti_vol_ml_LOW = estimated volume of rockpool water based on a formula for an ellipsoid using the width, length and depth measurements of the rockpool at low tide. * blenny_abundance = the qualitative abundance of blennies in a rockpool at low tide using the scale of absent (0), low (1), moderate (2), and high (3). * primaryproducer_abundance = the qualitative abundance of primary producers in a rockpool at low tide using the scale of absent (0), some (1), and abundant (2). * flushing_LOW = instances where a rockpool was observed to have seawater flushing at low tide recorded as none, some, and frequent.  * date_HIGH = date (day-month-year) that rockpool was surveyed at high tide. * max \_tempC_HIGH = maximum water temperature in degrees Celsius recorded by miniDOT logger at high tide. * min_Oxy_mgL_HIGH = minimum dissolved oxygen in micrograms per litre recorded by miniDOT logger at high tide. * min_OxyPercentSATURATION_HIGH = minimum percentage oxygen saturation recorded by miniDOT logger at high tide. * inclusive_of_exact_hightide = whether miniDOT loggers were in rock pools over the exact time of high tide, coded as “yes” or “no” * water_tempC_HIGH = point estimate of water temperature in degrees Celsius taken using a handheld digital meter at high tide. * pH_HIGH = point estimate of pH taken using a handheld digital meter at high tide. * salinity_ppt_HIGH = point estimate of water salinity in parts per thousand (ppt) taken using a handheld digital meter at high tide. * air_tempC_HIGH = point estimate of air temperature in degrees Celsius taken using a handheld thermo-windmeter at high tide. * max_tempC_DELTA = maximum water temperature in degrees Celsius recorded by miniDOT logger computed as the difference between low and high tide. * min_Oxy_mgL_DELTA = minimum dissolved oxygen in micrograms per litre recorded by miniDOT logger computed as the difference between low and high tide. * min_OxyPercentSATURATION_DELTA = minimum percentage oxygen saturation recorded by miniDOT logger computed as the difference between low and high tide. * water_tempC_DELTA = point estimate of water temperature in degrees Celsius taken using a handheld digital meter computed as the difference between low and high tide. * pH_DELTA = point estimate of pH taken using a handheld digital meter computed as the difference between low and high tide. * salt_ppt_DELTA = point estimate of water salinity in parts per thousand (ppt) taken using a handheld digital meter computed as the difference between low and high tide. * air_tempC_DELTA = point estimate of air temperature in degrees Celsius taken using a handheld thermo-windmeter computed as the difference between low and high tide. ## OrdTJ\_FE-2024-01331\_oxygendepletion\_experiment.csv Data from the oxygen depletion experiment was used to infer the oxygen consumption of blennies as a function of species and body size. #### FILE STRUCTURE AND UNITS OF MEASUREMENTS The file is a .csv file that can be opened using any text, spreadsheet, or statistical program There are no missing values. species = species of blenny used in the experiment * ID = unique ID label for individual fish * sex = sex of blenny used given as either male, female, or unknown. * date = date (day/month/year) that individual fish was tested. * pre_tempC = point estimate of water temperature in degrees Celsius taken using a handheld digital meter prior to fish being placed in the aquarium. * pre_pH = point estimate of pH taken using a handheld digital meter prior to fish being placed in the aquarium. * pre_saltppt = point estimate of water salinity in parts per thousand (ppt) taken using a handheld digital meter prior to fish being placed in the aquarium. * post_tempC = point estimate of water temperature in degrees Celsius taken using a handheld digital meter at the end of the experiment when fish had been removed from the aquarium. * post_pH = point estimate of pH taken using a handheld digital meter at the end of the experiment when fish had been removed from the aquarium. * post_saltppt = point estimate of water salinity in parts per thousand (ppt) taken using a handheld digital meter at the end of the experiment when fish had been removed from the aquarium. * SL_cm = the standard length of fish in centimetres. * time_min = elapsed time in minutes from the start of the experiment * Oxy_PercentSat = percentage oxygen saturation recorded by miniDOT logger placed inside the aquarium. ## OrdTJ\_FE-2024-01331\_Pcrit\_literature.csv Data obtained from the meta-analysis conducted by Rogers et al. (2006) was used to infer a partial pressure critical threshold cut-off as a function of water temperature. #### FILE STRUCTURE AND UNITS OF MEASUREMENTS The file is a .csv file that can be opened using any text, spreadsheet, or statistical program There are no missing values. * taxa = the species of fish  * tempC = water temperature in degrees Celsius that critical partial pressure was estimated. * Pcrit = critical partial pressure in kPa estimated for species. * source = source of data was from Rogers, N. J., M. A. Urbina, E. E. Reardon, D. J. McKenzie, and R. W. Wilson. 2016. A new analysis of hypoxia tolerance in fishes using a database of critical oxygen level (*P*crit). *Conservation Physiology* 4: 1-19.