DOI: 10.5061/dryad.g79cnp648
title: Data and code from: Chemical cues facilitate foraging across the water-land interface in a resident predatory fish

description: Transitional ecosystems, such as the land-sea interface, propagate
 nutrient flow and species interactions. Organisms spanning these
 boundaries act as important models for understanding of the evolution of
 sensory modalities that promote movement between physically distinct
 media, and the ecological consequences of ecosystem connectivity. Behavior
 is fundamentally guided by sensory processing, yet how sensory information
 is transmitted and collected is heavily dependent on the physical
 environmental medium. The flow of stimuli across the land-sea interface
 and the behavioral responses to stimuli are understudied. Vertebrates that
 span the land-sea boundary offer the opportunity to document how stimuli
 can be used to complete complex behaviors across transitional ecosystems.
 We determined that California moray eels (Gymnothorax mordax) can use
 chemical stimuli (odor and taste) to locate prey across intertidal
 boundaries on Santa Catalina Island. We tested moray responses to chemical
 stimuli from four prey types during high and low tidal conditions, the
 latter requiring emergence from the water to navigate the land-sea
 interface. Gymnothorax mordax can navigate to a prey source using only
 chemical stimuli, both when fully submerged underwater and when emerged in
 the intertidal. Morays showed greater discernment between prey types when
 exposed in the intertidal. In the intertidal eels rubbed their faces on
 the substrate, suggesting multimodality in using odor for detection and
 taste to further assist in prey location. This research broadens our
 understanding of ecosystem connectivity, illustrating how stimuli can
 cross the land-sea boundary and be used to facilitate predation through a
 combination of multi-sensory modalities.
description: <strong>Study location & sampling
 sites</strong><br> University of Southern California’s Wrigley
 Marine Science Center in Big Fisherman Cove on Santa Catalina Island,
 California (33.4452, - 118.4847). 
 <strong>Chemical stimuli</strong><br>
 <strong>Prey Stimuli:</strong> kelp bass (<em>Paralabrax
 clathratus</em>), two-spot octopus (<em>Octopus
 bimaculoides</em>), anchovy (<em>Engraulis</em>
 <em>sp.</em>), and California market squid
 (<em>Doryteuthis opalescens</em>) <br>
 <strong>Control:</strong> 50 μm filtered seawater<br>
 <br> <strong>Trial format & experimental
 apparatus</strong><br> Our experimental apparatus was designed
 to administer controlled pulses of chemical stimuli into a target area
 within our sample site. The experimental apparatus was fixed with an
 underwater camera (GoPro Hero 8), recording the entire duration of the
 trial. Treatments were injected to the site via vinyl tubing (4 mm
 diameter) into a 30 cm long, 10 cm diameter white PVC tube. The PVC tube
 acted as a “foraging crevice” (mimicking rocky crevices in the habitat)
 and is henceforth referred to as the “target”. The target required morays
 to navigate to a specific area from where the cue was emanating. We
 limited our observations to a 1500 cm<sup>2</sup> framed area
 (50 x 30 cm) around the target tube. Trials lasted 15 minutes, with 100 ml
 of the treatment injected in the first minute, and 30 ml injected every
 two minutes with the last injection occurring at minute 13, at which point
 the vinyl injection hosing was flushed with seawater.
 Each of the 4 prey treatments and the control were administered
 at high (submerged condition) and low (exposed condition) tide, with
 treatment order being randomized. A site would only be administered one of
 the four prey treatments on a given day, either at high or low tide, and
 was not revisited for at least 48 hours. We strived to test each site (n =
 8) at both tidal levels (high/submerged and low/exposed) for each of the 5
 treatments. Thus, each site was visited a total of 10 times throughout an
 8-week field season. We repeated these procedures over 2 consecutive field
 seasons (2022 and 2023), using the same 8 sites. As such, for each
 treatment and tidal condition combination (e.g., control:submerged or
 anchovy:exposed) we have 8 trials per summer, and up to 16 total trials
 across two summers. <strong>Summary of key
 terms</strong><br> We refer to the PVC tube itself as the
 “target” because this is the release site of the chemical information. The
 immediate 1500 cm<sup>2</sup> vicinity around the target is
 referred to as the “frame”. Treatments refer to any of the injected
 liquids, with “control” referring to seawater and “stimuli” referring to
 any of the four prey treatments. “Submerged” refers to trials occurring
 fully underwater, while “exposed” refers to trials occurring at the
 land-sea interface, requiring morays to at least partially emerge from the
 water.  <strong>Video
 analysis</strong><br> We tallied (yes/no) if an eel entered
 the frame or target. An individual was considered to have “entered” the
 frame or target the moment their eye passed the frame edge or target
 entrance, as apparent chemosensory organs are anterior to the eye in
 morays. We documented the total duration at least one moray was present
 within the target (“Target Duration”), and the maximum number of
 individuals within the target observed at one time. For duration data, an
 individual was considered to have “exited” the target after the complete
 removal of the face, from the eye to the end of the rostrum. .
 <strong>Data analysis</strong><br> RStudio
 (Version 2024.12.0+467) was used for statistical analysis. We analyzed all
 data using Generalized Linear Mixed Effects Models (GLMM), with the glmer
 function from the lme4 package (Bates et al. 2015). This allowed us
 include “site” (i.e., the experimental location) and “summer” (2022 and
 2023) as random effects when the addition of these parameters lowered the
 AIC value.  To report differences between the control
 and prey treatments for trials and target visitation, we modeled the data
 using a GLMM with a binomial distribution. To compare the duration spent
 within the target we used a GLMM with a gamma distribution and log link
 function. If no eels were present within the trial (i.e., no eels observed
 within the framed area), the duration inside the target was logged as
 “NA”. If eels were present within the frame but failed to find the target,
 the duration was logged as 0 seconds in the target. We differentiated
 between these scenarios because we were interested in tracking the
 duration in the target when eels were fully known to be within the area.
 In cases where zero values were present in the data, a small constant
 value of 0.1 was added to avoid violating the assumptions of gamma
 distributions. For the control treatment we observed 2 morays in the
 submerged context and 1 moray in the exposed context throughout the two
 summers. As such, duration data for the control was deficient (e.g.,
 composed of NA’s for trials without eels) and incompatible in our
 analysis. We excluded the control from this comparison to instead focus on
 the differences between the four prey treatments.
 <strong>Ethical note</strong><br> This research
 was conducted on Santa Catalina Island following California Department of
 Fish and Wildlife guidelines (Permit 190830002-19986-001). Morays were not
 handled or harmed during this experiment. 
description: # **Title:** ***Chemical cues facilitate foraging across the water-land
 interface in a resident predatory fish*** # Authors: **Maya M. McElfish**
 - University of California Santa Cruz \ Contact Information -
 [mmcelfis@ucsc.edu](mailto:mmcelfis@ucsc.edu) or
 [maya.mcelfish@gmail.com](mailto:maya.mcelfish@gmail.com) Nicholas A. Hess
 - Eckerd College\ Helena B. Lewis - Eckerd College\ Sacha E. O'Connor
 - University of California Santa Cruz\ Rita S. Mehta - University of
 California Santa Cruz # Research Goals: 1. Document if *Gymnothorax
 mordax* can use chemical stimuli alone to detect prey and to navigate to a
 specific prey location 2. Assess if behavioral responses vary between
 chemical cues from different prey species 3. Test if these cues can be
 used in both fully submerged and partial exposed (intertidal) contexts. #
 **General Experimental Details:** We conducted two summers (2022, 2023) of
 field-based behavioral experiments in Big Fisherman Cove on Santa Catalina
 Island, California, operating out of the Wrigley Institute. We tested
 chemical stimuli from four prey types (anchovy, squid, kelp bass, and
 octopus) and a control (sea water), administering cues during both high
 and low tidal conditions. Low tide trials required morays to emerge from
 the water. **Ethical note**\ This research was conducted on Santa Catalina
 Island following California Department of Fish and Wildlife guidelines
 (Permit 190830002-19986-001). Morays were not handled or harmed during
 this experiment.  **Recommended Citation**\ McElfish, M., Hess, N., Lewis,
 H., O'Connor, S., and R. S. Mehta. *In Review.* Chemical cues
 facilitate foraging across the water-land interface in a resident
 predatory fish. Behavioral Ecology. # R Software & Required Packages
 RStudio Version 2024.12.0+467 (2024.12.0+467)\ \ **Packages:** \
 tidyverse\ ggplot2\ gamlss\ ggpubr\ rstatix\ png\ lme4\ ggsignif\ glmmTMB\
 emmeans\ dplyr\ MASS\ DHARMa\ patchwork\ ggridges # Data & Code
 Information: **IntertidalMoray.Rmd** is the R script for data analysis and
 figure building.  It uses the datafile **MultiSummer.csv** -- below are
 listed the column names and a description of the contents for each column
 **Summer:** Sampling year - 2022 or 2023 **Site:** Sample Sites 1-8
 (experimental location, repeatedly tested for each treatment, tidal
 condition, and year) **Depth:** Submerged or Exposed (Submerged = &gt; 1m,
 Exposed &lt; 5cm) **Treatment:** Anchovy, Kelpbass, Squid, Octopus,
 Control (types of chemical cue) **Trial Length:** Time in Seconds - should
 be ~900, but some trials ran shorter due to disturbances.
 **Trial_Length_Frame_Adjusted:** Trial length, but starting when the eel
 enters the frame for the first time -- so 1st frame enter = start of the
 trial [NOT USED IN THESE ANALYSES] **VisitedTrial:** Yes/No (Did an eel
 visit this trial??) **Arrival_Frame:** Time stamp in seconds for the first
 eel arriving into the frame **VisitedTube:** Yes/No (Did an eel visit the
 target tube during this trial)? **Arrival_Tube:** Time stamp in seconds
 for Arrival of first eel to enter target tube **Tube_Location_Time:** Time
 in seconds (How long it took the eel to find the target tube after
 entering the frame) **DurationTube:** Time in seconds (time span at least
 1 eel was present in the target tube); NA if no eels were present in the
 frame during the entire trial **MaxTube:** Integer (maximum eels in target
 tube at a time) **TubeEnter:** Integer Tally (number of times any eel
 during a trial entered the target tube) **FrameEnter23:** Integer Tally
 (for the 2023 trials only; the number of times any eel entered the frame)
 - Data not used here **Notes:** Any notes related to the trial