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Evaluating the effects of large marine predators on mobile prey behavior across subtropical reef ecosystems

Wiley
Ecology and Evolution
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The indirect effect of predators on prey behavior, recruitment, and spatial relationships continues to attract considerable attention. However, top predators like sharks or large, mobile teleosts, which can have substantial top–down effects in ecosystems, are often difficult to study due to their large size and mobility. This has created a knowledge gap in understanding how they affect their prey through nonconsumptive effects. Here, we investigated how different functional groups of predators affected potential prey fish populations across various habitats within Biscayne Bay, FL. Using baited remote underwater videos (BRUVs), we quantified predator abundance and activity as a rough proxy for predation risk and analyzed key prey behaviors across coral reef, sea fan, seagrass, and sandy habitats. Both predator abundance and prey arrival times to the bait were strongly influenced by habitat type, with open homogenous habitats receiving faster arrival times by prey. Other prey behaviors, such as residency and risk‐associated behaviors, were potentially driven by predator interaction. Our data suggest that small predators across functional groups do not have large controlling effects on prey behavior or stress responses over short temporal scales; however, habitats where predators are more unpredictable in their occurrence (i.e., open areas) may trigger risk‐associated behaviors such as avoidance and vigilance. Our data shed new light on the importance of habitat and context for understanding how marine predators may influence prey behaviors in marine ecosystems. Assessing behavioral risk effects of marine predators on mobile prey species across varying habitats in Biscayne Bay, FL. Providing new insights into the role marine predators play in influencing prey behavior in a variety of contexts.
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Ecology and Evolution. 2019;9:13740–13751.
www.ecolevol.org
1 | INTRODUCTION
Top predators are characterized by some of the largest, most enig‐
matic, and threatened species today on Earth (Hammerschlag &
Gallagher, 2017). Often occupying upper trophic tiers, predators
can influence prey directly through consumption and also indirectly
via the perceived risk of predation. These nonconsumptive effects
can drive food‐risk trade‐of fs that alter behavior, physiology, and
foraging strategies in potential prey (Beauchamp, Wahl, & Johnson,
2007; Heithaus, Frid, Wirsing, & Worm, 2008; Rasher, Hoey, & Hay,
2017). In doing so, predators drive important ecosystem processes
that may induce cascading effects throughout entire ecosystems
(Estes et al., 2011). Despite the impor tant roles they play in eco‐
system dynamics, many populations of large predators are declin‐
ing rapidly as a result of overexploitation, and habitat loss, among a
myriad of other threat s (Lennox, Gallagher, Ritchie, & Cooke, 2018).
Received: 22 October 2018 
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Revised: 25 Februar y 2019 
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Accepted: 25 S eptember 2019
DOI: 10.100 2/ece3.5784
ORIGINAL RESEARCH
Evaluating the effects of large marine predators on mobile prey
behavior across subtropical reef ecosystems
Lindsay M. Phenix1,2 | Dana Tricarico1| Enrique Quintero1| Mark E. Bond3|
Simon J. Brandl4| Austin J. Gallagher1
This is an op en access article under t he terms of the Creat ive Commons Attributio n License, which permits use, dist ribution and reproduc tion in any medium,
provide d the orig inal work is proper ly cited .
© 2019 The Authors. Ecology and Evol ution pub lished by J ohn Wiley & Sons Ltd.
1Beneath the Waves, Herndon, VA, USA
2Three Seas Progr am, Nor theas tern
University, Nahant, MA, USA
3Florida International Universit y, North
Miami, FL , USA
4Depar tment of Biologic al Sciences, Simon
Fraser Universit y, Burnaby, BC , Canada
Correspondence
Lindsay M. Phenix, Beneath the Waves , PO
Box 126, Herndon, VA 20172, USA.
Email: phenix.l@husky.neu.edu
Funding information
Herbert W. Hoover Foundation; C. and
M.Jones
Abstract
The indirect effect of predators on prey behavior, recruitment, and spatial relation‐
ships continues to attract considerable attention. However, top predators like sharks
or large, mobile teleosts, which can have substantial top–down effects in ecosystems,
are often difficult to study due to their large size and mobility. This has created a
knowledge gap in understanding how they affect their prey through nonconsumptive
effects. Here, we investigated how different functional groups of predators affected
potential prey fish populations across various habitats within Biscayne Bay, FL. Using
baited remote underwater videos (BRUVs), we quantified predator abundance and
activity as a rough proxy for predation risk and analyzed key prey behaviors across
coral reef, sea fan, seagrass, and sandy habitats. Both predator abundance and prey
arrival times to the bait were strongly influenced by habitat type, with open homog‐
enous habitats receiving faster arrival times by prey. Other prey behaviors, such as
residency and risk‐associated behaviors, were potentially driven by predator interac
tion. Our data suggest that small predators across functional groups do not have large
controlling effects on prey behavior or stress responses over short temporal scales;
however, habitats where predators are more unpredictable in their occurrence (i.e.,
open areas) may trigger risk‐associated behaviors such as avoidance and vigilance.
Our data shed new light on the importance of habitat and context for understanding
how marine predators may influence prey behaviors in marine ecosystems.
KEYWORDS
baited remote under water video stations, predation risk, predator, risk effects, sharks
    
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PHENIX Et a l.
While effects of apex predators are relatively well studied in
terrestrial ecosystems (e.g., Suraci, Clinchy, Dill, Roberts, & Zanette,
2016), their roles in marine systems are generally less understood
(e.g., Casey et al., 2017; Sandin et al., 2008). Sharks, for instance,
are traditionally considered the de facto top predator in marine
ecosystems, and their vulnerabilities to fishing (Gallagher, Kyne, &
Hammerschlag, 2012) and general patterns of population decline
(e.g., Ferretti, Worm, Britten, Heithaus, & Lotze, 2010) have rein‐
forced the import ance of understanding the implications of their re‐
movals on ma rine ecosystem s. Often unifor mly characte rized as apex
predators due to their size and trophic position in marine food webs
(Heupel, Knip, Simpfendorfer, & Dulvy, 2014; Hussey et al., 2014),
sharks may exert strong controlling influences on prey through be‐
haviorally‐mediated, nonconsumptive processes (i.e., predation risk)
(Heithaus et al., 2008; Heithaus, Wirsing, Burkholder, Thomson, &
Dill, 2009). However, the degree to which sharks actually influence
the behavior and physiology of prey species remains understudied
and controversial (Casey et al., 2017; Roff et al., 2016; Rupper t,
Travers, Smith, Fortin, & Meekan, 2013). Studies have suggested
that on coral reefs, herbivorous fish reduce their feeding rates when
exposed to a larger, stationary shark decoy (C atano, Barton, Boswell,
& Burkepile, 2017; Madin, Gaines, & Warner, 2010; Rizzari, Frisch,
Hoey, & McCormick, 2014), but it is unknown whether this acute
suppression actually triggers a long‐term reduction in feeding or if it
simply redistributes the prey fish to a different area. Similarly, it re
mains unknown how other sympatric marine teleost predators, such
as barracudas (family Sphyraenidae) or morays (family Muraenidae),
compare to sharks with regard to their nonconsumptive effects on
prey. Nonconsumptive effects would be expected to be particularly
prevalent in shallow, open ecosystems where a larger prey item's
opportunity for escape from roving, apex predators are limited
(Heithaus et al., 2009), thus suggesting a potential ef fect of habitat
complexity.
The lack of a generalizable predator effect (consistency in direc‐
tion and strength) may be expected in diverse, three‐dimensional
ecosystems such as coral reefs where water is clear and opportu‐
nities to shelter temporarily are extensive. These habitats provide
increased visibility for and detectability of mobile, roving predators.
Studies have suggested that in coral reef food webs, reef‐associated
sharks and large teleosts occupy similar trophic niches (Bond et al.,
2018; Frisch et al., 2016; Roff et al., 2016), which may allow for the
detection of generalizable effects of predators on prey or may divert
or dilute the nonconsumptive effects of species traditionally consid‐
ered apex predators on larger prey species. Our knowledge of non
consumptive effects of marine predators on prey may benefit from
examining predator–prey interactions under varying environmental
conditions.
An increasingly popular technique for noninvasively assessing
the relative abundance and behavior of mobile fish populations,
while removing diver bias, is baited remote underwater video (BRUV)
surveys (Whitmarsh, Fairweather, & Huveneers, 2017). BRUVs con
sist of an underwater camera focused on a standardized bait source
positioned in the field of view (FOV), with the unit orient ated down
current from the camera. Individuals attracted to the bait that swim
into the FOV are “captured” on camera (Armstrong, Bagley, & Priede,
1992), providing a permanent record of observations that can be re‐
viewed multiple times. This record improves the accuracy of the data
and allows for detailed analyses such as those required for examin
ing animal behavior. They have also been used in studies assessing
predator–prey relationships (e.g., Klages, Broad, Kelaher, & Davis,
2014) and could be readily used to investigate the potential effects
of marine predators on a suite of prey species, across a variety of
habitats and conditions.
Here, we used BRUVs to examine the nonconsumptive effects
of multiple marine predators on various mobile prey species, across
the varying habitats of Biscayne Bay, Florida. We evaluated these
predator–prey interactions in three ways: (a) inferring ambient risk
in each habitat by quantif ying relative predator abundance and for
aging activity; (b) assessing habitat‐specific responses of potential
prey species by measuring prey arrival (as a prox y for apprehensive‐
ness); and (c) gauging risk‐associated behaviors of prey as well as
prey residency at the bait stations (Bond et al., 2019). We hypothe
sized that (a) predator activity would be greater in complex habitat s
(Bruno, Stachowicz, & Bertness, 2003; Hutchinson, 1957); (b) prey
would take longer to arrive in less complex, more open habitats due
to limited shelter opportunities; (c) prey residencies would increase
and the number of risk‐associated behaviors would decrease in more
complex habitats (Bruno et al., 2003).
2 | METHODS
2.1 | Study site
This study was conducted from January 21 to August 31, 2017 in the
waters of Biscayne Bay, Florida, USA, including within the boundaries
of Biscayne National Park (BNP; 25°45′42.05″N, 80°11′30.44″W;
Figure 1). This area extends from Key Biscayne to Key L argo and
connects to the Florida Reef Tract, the third largest coral reef system
worldwide. The area is defined by a mixture of coral reefs, seagrass
beds, sof t corals, and sand flats. Biscayne Bay is a shallow water la‐
goon in which a variety of habitat s provide important functional, on‐
togenetic , and trophic value for mangrove and reef‐associated fish,
including sharks and rays, as well as sea tur tles and marine mammals
(Serafy, Valle, Faunce, & Luo, 2007).
2.2 | Baited Remove Underwater Video
(BRUV) surveys
Predator–prey interactions among and between mobile elas
mobranch and teleost communities were assessed throughout
Biscayne Bay and Biscayne National Park using baited remote un
derwater video (BRUV) sur veys. Each BRUV consisted of a 48‐cm
tall metal pyramid frame with the sides converging at a flat, square
platform (Figure 2). Additional weights (two, 0.5 kg dive weights)
were added to each BRUV frame to increase stability. Each BRUV
was equipped with a 100‐cm PVC bait pole, with a mesh bait bag
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(150 mm × 200 mm) attached at the end (via zip ties) containing
~450 g of freshly minced Spanish sardines (Sardinella spp.). High‐
definition action cameras (GoPro Hero and Hero+) were secured to
the square platform and positioned to face outward, with the bait
bag within the estimated 160° FOV, all lights and flashing sensors
on the cameras were deactivated. All footage was shot at 1,080p
high‐definition at 30 frames per second.
All BRUVs were deployed from a boat and lowered to the
sea floor via 30‐m ropes att ached to a visible sur face buoy.
Deployment depths ranged from 1.3 m to 12.8 m with an aver
age depth of 6.7 m. In‐water free‐divers were occasionally used to
navigate the BRUVs away from living corals and to ensure proper
orientation on the benthic substrate. BRUVs were deployed in
contiguous areas in groups of three to five, spaced ~300–500 m
apart, and were allowed to soak for 60 min. Deployments were
focused in the following habitat types: coral reef (defined by the
presence of coral colonies and structures), sea fan (defined by
the presence of patchy sea fans), seagrass (defined by contiguous
areas dominated by seagrass), and sand (defined by low‐rugose
habitat s with open sandy areas). Deployments occurred during
daylight hours, bet ween 08 00 and 1330 hr. During each round
of BRUV deployments, we measured depth and water tempera
ture (°C) using a HANNA handheld probe (Hanna Instruments, HI
98193). Temperature was recorded as a control to account for any
possible anomalies; average water temperature was 24.4°C across
seasons. We characterized the habitat type as coral reef, sand, sea
fan, or seagrass (based on 50% coverage or higher) and whether
the site was inside or outside the boundaries of Biscayne National
FIGURE 1 Map of BRUV sur vey
deployments in Biscayne Bay, FL, USA.
Red dots = dr y season, green dots = wet
season. White line represents boundary of
Biscayne National Park
    
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PHENIX Et a l.
Park (a national park with varying fishing regulations, though it is
not a no‐take zone nor a marine reserve).
2.3 | Video analysis and variables considered
Each 60 ‐min vi d e o wa s re v i e w e d an d an a l y zed in re a l ti m e . An al y s i s
be ga n onc e the BRUV was fi rmly planted in t he be nt hos (~15–30 s)
after deployment. Predators were categorized into three trophic
tiers. Upper trophic predators included barracudas (Sphyraena bar-
racuda), as well as large bodied (>2 m) mid‐water feeding sharks.
Large bodied mid‐trophic predators included large benthic feeding
sharks and green moray eels (Gymnothorax funebris), while small
bodied mid‐trophic predators encompassed small bodied sharks
(<2 m) and spotted moray eels (Gymnothorax moringa). Groupings
were determined based on relative size and the presumed corre
lating trophic pressures they placed on the ecosystem (Bond et
al., 2018; LaymanWinemiller, Arring ton, & Jepsen, 2005). Seven
common prey families were identified and used to measure habitat
risk and ri sk ef fec ts: filefi sh (famil y Mon ac ant hi dae), gru nt s (family
Haemulidae), jacks (family Carangidae), porgies (family Sparidae),
rays (family Dasyatidae & Urotrygonidae), snappers (family
Lutjanidae), and triggerfish (family Balistidae). These prey families
were chosen due to their observed abundance in the surveyed
habitat s, and since they reflect a range of consumed prey items
for members of the trophic levels listed above. For example, bar
racuda are known to be import ant predators of the selected fami
lies in our study region (Hansen, 2015). Large shark species found
in Biscayne Bay and Florida Bay, such as blacktip (Carcharhinus
limbatus), bull (Carcharhinus leucas), great hammerhead (Sphyrna
mokarran), and lemon sharks (Negaprion brevirostris), retain higher
trophic positions than many of the prey families and are known
fish predators (Gallagher, Shiffman, Byrnes, Hammerschlag‐Peyer,
& Hammerschlag, 2017; Hammerschlag, Luo, Irschick, & Ault,
2012; Matich, Heithaus, & Layman, 2011; Roemer, Gallagher, &
Hammerschlag, 2016). Bonnetheads (Sphyrna turbo) and Atlantic
sharpnose (Rhizoprionodon terraenovae) sharks may have varying
feeding patterns, but are primarily inshore feeders with diets con
si s tin g of tel e ost s, cru sta cea ns, an d ceph a lop ods (Plu mle e & Well s,
2016). Similarly, grunts, jacks, and snapper have been found inside
the stomachs of nurse sharks in Florida (Castro, 20 00). While there
is limited data on moray eel diet in our study area, work from other
Caribbean areas suggest s that they are piscivorous and readily
consume snappers or grunts (Randall, 1967; Young & Winn, 20 03).
The relative risk of each habitat where a BRUV was deployed
was estimated using t wo predator‐focused variables: (a) predator
abundance (maxNb and maxN) and (b) predator foraging activity.
Predator abundance was quantified for each trophic grouping
(maxNb) by tallying the number of distinctly different individuals,
determined by family, sex, size, and markings, observed throughout
the entire video duration (Bond et al., 2012). Additionally, a com
bined predator abundance was taken from each BRUV in the form
of maxN, which represents the maximum number of predators,
regardless of grouping, present together at one time (Bond et al.,
2012). We quantified predator foraging activity rates on the bait
bags by recording the number of bites from predators and whether
severe damage occurred to the bag (0 = no damage, 1 = severe
FIGURE 2 (a) The BRUV assembly; base 74 cm × 74 cm, slant height 72 cm, total height 48cm. (b) Still image captured from BRUV
deployment with a bonnethead shark (Sphyrna tiburo) in frame. (c) Still image captured from BRUV deployment with schooling yellow
snappers (Ocyurus chrysurus) and a southern stingray (Hypanus americanus) in frame
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damage). Bait bags were categorized as “severe damage” if the bag
had major lacerations or rips, or if the bag was totally removed from
the pole. Nonpredatory fish also have the potential to inflict dam
age to the bags (i.e., triggerfish), so any instances of damage to the
bags from nonpredatory fishes (ascer tained via video validation)
that could have confounded the detectability of our bait were not
included in these analyses.
Potential responses of prey species to ambient predation risk
were estimated using arrival times for each prey family (as a proxy
for apprehensiveness), as well as evaluating three prey‐focused be‐
haviors (burst swimming, schooling, and bait residency). Arrival time
(s) was measured by recording the total elapsed time until the first
individual from each prey family arrived on camera. Burst swimming
events (defined as a short, rapid swimming behavior away from the
frame; Gallagher, Brandl, & Stier, 2016; Gallagher, Lawrence, Jain‐
Schlaepfer, Wilson, & Cooke, 2016) and schooling events (defined as
instances where groups of five or more conspecific individuals were
present; Viscido, Parrish, & Grünbaum, 2005) were recorded for the
previously defined prey groups. Bait residency (sec) was evaluated
for each replicate as follows: the first fish, regardless of species, to
make contact with the bait was monitored until it had moved an esti‐
mated three or more body lengths distance from the bait bag (Bond
et al., 2019).
2.4 | Statistical analyses
Because data violated assumptions of normality and homogeneity
of variance (confirmed using Shapiro–Wilk's and Levene's tests),
we performed a zero‐inflated generalized linear model (GLM)
with a negative binomial error distribution and a log‐link func
tion to assess the ambient risk of each habitat , with habitat type
and its interaction with predator functional groups specified as
the independent variables and predator maxNb as the response
variable. Similarly, we per formed a GLM with a negative binomial
error distribution on prey arrival times, with the response vari
able being the arrival time of prey species and the independent
var iables bein g habitat type, preda tor maxN, and their interactio n.
Instances where an individual from a prey family did not appear
on the BRUV footage (i.e., not arriving) were excluded from the
model. Because this resulted in low replicates for some prey fish
species (e.g., rays), we did not specify prey species as an independ
ent variable and assumed that effects of predators are general
ized across all prey species. For both GLMs, we used the obtained
parameters for predictions and then plotted the predicted values
against the raw data to visualize both the obtained patterns and
the model fit.
Predator foraging activity and prey behaviors were then visual
ized using a nonmetric multidimensional scaling ordination (nMDS)
based on a Man hat tan distance. Further more, a PERM ANOVA was
run on the same distance matrix in order to determine if habitat
type, predator maximum abundance, or their interaction affected
prey behavior. Finally, we analyzed correlations bet ween predator
foraging and prey risk‐associated behaviors for each habitat using
a set of Spearman rank correlation analyses . All st atistical analyses
were performed using R Studio (R Core Team).
3 | RESULTS
A total of 194 deployments were made, within a total survey area
of ~15 km2. Of these, 37 deployments were discarded due to the
BRUV tipping over in heavy current or poor visibility, leaving a
total of 157 videos (n = 157) that were used in analyses ( Table 1).
A total of 184 predators were recorded by the BRUVs through
out the sampling period (Table 2). Of those predators, 80 indi
vidual elasmobranchs from eight species (7 shark species, 1 ray
species) were recorded, in addition to 88 barracuda and 16 moray
eels. There were limited seasonal differences in maximum preda
tor abundances (maxN) and prey arrival times across habitats, ex
cept for seagrass beds, where maximum predator abundance was
substantially higher in the wet season (0.690 ± 0.0.123 individuals,
mean ± SE) than in the dr y season (0.091 ± 0.063). In fact, no barra
cudas or large bodied mid‐trophic predators were observed in sea
grass habitats during the dry seasons. However, prey arrival times
in seagrass beds did not differ between the two seasons.
Predator abundances (maxNb) were significantly different
among habitat types, with coral reefs having the highest average
maximum number of predators per deployment (2.21 ± 2.04), fol
lowed by sea fan habitats, sand, and seagrass habitats (Table 3,
Table 4). Predictions from the GLM further suggest an interaction
effect between trophic level grouping and habitat. Coral reefs had
the greatest mean abundance of upper trophic and large bodied
mid‐trophic predators, whereas sea fan habitats had the greatest
mean abundances of small bodied mid‐trophic predators (Figure 3).
Prey arrival times were significantly influenced by the interactive
effects of habitat and the cumulative maximum number of preda
tors (maxN) (Table 5). Grunts, porgies, and snappers arrived com
paratively early at the BRUV deployments, while stingrays arrived
substantially later. The GLM revealed that the effect of maximum
predator numbers in sand, sea fan, and seagrass habitats are neg
ative and significantly different from effects of predators on coral
reefs, where cumulative predator maximum number and prey ar
rival time were positively correlated. This is further supported by
the predictions from the model, which show a steep negative re
lationship in sand and seagrass habitat s, a nearly flat but slightly
TABLE 1 BRUV deployments by season and habitat type
Habitat
Season
Dry (January–April)
Wet
(May–December)
Coral reef 4 15
Sea fan 934
Seagrass 22 30
Sand 16 27
    
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PHENIX Et a l.
negative relationship in sea fan habitats and a positive relationship
for coral reefs (Figure 4).
The nMDS ordination of bo t h pr e d a t o r for a ging ac t i v i t y (i.e., num
ber of bites) and prey behavior in response to habitat type showed
little variation among habitats (Figure 5). Generalized predator for‐
aging activity was not significantly influenced by any habit at type,
although BRUVs deployed on coral reefs experienced the highest
average number of predatory bites (2.211 ± 3.441 bites, mean ± SE)
and instances of severe damage to the bait bag (0.263 ± 0.452 in‐
stances, mean ± SE). Prey burst swimming (4.579 ± 7.932 events)
and schooling events (6.053 ± 4.801 events) also had the highest
average occurrences on coral reefs when compared to sand, sea
fans, and seagrass habitats (Table 6). Average prey residency at the
bait was the greatest in sea fan habitats (32.211 ± 32.527 s). The
PERMANOVA to test the explanator y power of habitat, predator
maximum number, and their interac tion on different behaviors, al‐
beit revealing a significant habitat effect (p = .001), only explained
~10% of the variation in the data and no effect of predator maximum
number or its interaction with habitat was observed. The Spearman
rank correlation test showed significant correlations between pred
ator and prey behaviors in sand, seagrass, and sea fan habitats, but
not on coral reefs (Figure 6). Schooling behavior was the only one to
show a positive relationship with predator maximum numbers across
sand, seagrass, and sea fan habitats.
4 | DISCUSSION
Predator–prey interactions can structure marine habitats by ac
tively changing habitat use, foraging behaviors, and food‐web
dynamics (Morosinotto, Thomson, & Korpimäki, 2010). We pre
dicted that prey fishes would be more apprehensive and thus
arrive later in the field of view of the BRUV in habitats with in
creased predator abundance and vice versa in those with fewer
TABLE 2 Summary of predatory species observed on BRUVs in the present study
Upper trophic Large mid‐trophic Small mid‐trophic
Barracuda (Sphyraena sp.) 88 Green Moray (Gymnothorax
funebris)
4Atlantic Sharpnose (Rhizoprionodon
terraenovae)
14
Blacktip (Carcharhinus limbatus) 3 Nurse (Ginglymostoma cirratum)22 Blacknose (Carcharhinus acronotus) 3
Bull (Carcharhinus leucas) 2 Sawfish (Pristis pectinata) 1 Bonnethead (Sphyrna turbo)34
Great Hammerhead (Sphyrna
mokarran)
1 Spotted Moray (Gymnothorax moringa)12
Tot al 94 27 63
Upper trophic Large mid‐trophic Small mid‐trophic Max Nb
Coral reef 1.16 (±0.384) 0.474 (±0.140) 0.579 (±0.318) 2.21 (±2.04)
Sand 0.674 (±0.169) 0.093 (±0.045) 0.140 (±0.053) 0.907 (±1.231)
Sea fan 0.581 (±0.245) 0.256 (±0.067) 0.721 (±0.206) 1.56 (±1.94)
Seagrass 0.346 (±0.095) 0.058 (±0.033) 0.288 (±0.092) 0.692 (±1.15)
TABLE 3 Mean predator abundance
per BRUV deployment across the four
habitat t ypes (coral reef, sand, sea fan, and
seagrass), decomposed into the different
trophic levels and their combined
abundance (MaxNb)
Coefficients Estimate SE Z value Pr (>|z|)
Intercept (coral reef:large
mid‐trophic)
−9. 041 0.43 −21. 03 ***
Sand −1. 5 98 0.685 −2.3 3 *
Sea fan −0. 659 0.555 −1. 19 ns
Seagrass −2. 137 0.739 −2.8 9 **
CR Upper trophic 0.886 0. 551 1 .61 ns
Small mid‐trophic 0.2 52 0.591 0.43 ns
SD Upper trophic 1.993 0 .594 3.35 ***
Small mid‐trophic 0.435 0. 697 0.62 ns
SF Upper trophic 0.82 0.443 1.85 .
Small mid‐trophic 1.016 0.434 2.34 *
SG Upper trophic 1.766 0.667 2.65 **
Small mid‐trophic 1.594 0 .675 2.36 *
Note: Significant codes: ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1.
TABLE 4 Summary results from a zero‐
inflated negative binomial generalized
linear model used to test the effects
of habitat t ype on predator abundance
(maxNb) by trophic level
13746 
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predators. Our results suggest that this pattern held true only for
coral reefs, where predator numbers appeared to have a negative
effect on prey arrival, while in all other habitat s, the two vari
ables were positively correlated. While coral reefs offer increased
structural complexit y and refuge for prey, they also increase po
tential predation risk by obscuring prey fish's field of view (Bond
et al., 2019). These components of the habitat may provide preda
tors with a functional advantage when hunting, thereby creating
a more dangerous environment and increasing prey vigilance in
these areas. Thus, the interaction between habitat features and
the probability of predator detection and successful escape can
result in altered prey risk‐associated behaviors and vigilance
(Heithaus et al., 2009). It has been recently argued that predators
may exact greater influences on prey behavior where predation
risk is predictable (Creel, 2018). While we did not measure pre
dictability of predation risk in our study, abundance of predators
in certain habitats, a potential prox y for exposure, may have re
sulted in a pro‐active response of apprehensiveness toward the
bait, although this remains speculative.
Pre dators are know n to ma tch p rey dis tr i b u t ions on small sc ales
when prey is abundant (Heithaus & Dill, 2006), and, as observed
in the present study, coral reefs generally contain high numbers of
piscivores (Hixon & Beets, 1993), which can inversely affect prey
abundance on reefs (Beukers‐Stewart, Beukers‐Stewart, & Jones,
2011). On average, grunts and snappers arrived on coral reefs and
in sea fans long before any predators. Whether predation risk is
“predictable” or chronic on coral reefs remains unknown, but our
findings offer an interesting potential link to the predicted food‐
risk effects as described in the “control of risk” hypothesis (Creel,
2018).
Animals often express their antipredator‐behaviors in high
risk situations that are brief and infrequent (Lima & Bednekoff,
1999). These acute “reactive” responses are linked to areas of
FIGURE 3 Mean predicted predator abundance (±95% confidence inter vals) from a zero‐inflated negative binomial GLM across four
habitat t ypes: coral reef (CR), sand (SD), sea fan (SF), and seagrass (SG). Predicted predator abundance values, as well as mean predicted
abundance by habitat (dashed lines) are overlaid on top of raw observational data
Upper TrophicLarge Mid-TrophicSmall Mid-Trophic
TABLE 5 Summary results of a negative binomial generalized
linear model of the effects of habitat type on maximum combined
predator abundance (maxN)
Coefficients Estimate SE Z value Pr (>|z|)
Intercept (coral
reef)
5.865 0.156 37.6 ***
Sand 1.331 0 .172 7. 73 ***
Sea fan 0.463 0.174 2.66 **
Seagrass 1.035 0.168 6.18 ***
maxN 0.167 0.10 0 1. 67 ns
Sand: maxN −0.601 0.141 −4.26 ***
Sea fan: maxN 0.247 0 .114 −2 .17 *
Seagrass: maxN −0.366 0.130 −2. 8 2 **
    
|
 13747
PHENIX Et a l.
FIGURE 4 Predicted mean prey arrival time (y‐axis) as a function of maximum combined predator abundance (x‐axis) across four habitat
types based on a negative binomial GLM. Predicted fits (±95% confidence intervals) are overlaid on top of raw observational data of seven
prey families across four habitat types. CR, coral reef; SD, sand; SF, sea fan; SG, seagrass
0
1,000
2,000
3,000
4,000
02468
Predicted arrival time of prey (in seconds elapsed 95% CI)
Filefish Jack SnapperGrunt Tr iggerfish
Porgy Ray
Coral reef
Sand
Seafan
Seagrass
FIGURE 5 Multidimensional ordination
of predator foraging activit y (predator
bites and bait damage) and prey risk‐
associated behaviors (burst swimming,
schooling, and prey residency) across four
habitat t ypes. Colors match the previously
used habitat‐specific colors
−1.5 −1.0 −0.5 0.00.5 1.
01
.5
−1.0 −0.5 0.00.5
NMDS1
NMDS2
pred.bites
prey.res
schooling
burst.swm
13748 
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   PHENIX Et al.
unpredictable predation risk (Creel, 2018). We hypothesized that
potential behavioral risk effects might be highest in open areas.
Interestingly, we obser ved faster prey arrival times in more open,
homogenous habitats such as sea fans, sandy areas, and seagrass.
The lack of resources in these open, plain habitats may have ren
dered our BRUVs a more attractive source of food, resulting in
both prey and predators arriving sooner; in our study, we found
that grunts and snappers were much quicker to arrive to a habi
tat where predators were more abundant (Nagelkerken & Velde,
2004). It is also possible that these open and homogenous habitats
provide increased escape routes to prey if needed, thus making
the m worth the “risk.” Addition ally, since predators are often tran
sient in these habitats (Hammerschlag, Morgan, & Serafy, 2010),
attacks may be less predictable. Therefore, our obser ved patterns
for behavioral effects in these habitats may stem from a combi
nation of resource provisioning and unpredictability of predation
risk.
In general, juvenile and small bodied sharks (i.e., small mid‐tro
phic predators) can be found in shallow waters to minimize their own
preda tion risk (Gu tt ri dge et al., 2012; He up el et al., 2014). Mor e th an
half of the sharks captured on the BRUVs were species that reach
maximum sizes of <2 m. While it stands to reason that smaller pred‐
ators induce a weaker response in prey than larger conspecifics or
species (due to gape limitations), smaller mesopredators (hawkfish,
Parrachirrhites arcatus) have been found to have equal nonconsump
tive effects compared to larger conspecifics (Gallagher, Brandl, et al.,
2016; Gallagher, Lawrence, et al., 2016). Most predators (regardless
of trophic grouping) in our videos did not stay for prolonged periods
of time and, as such, they represent an acute, but relatively inconsis‐
tent, pulsed source of predation risk. Finally, some small species (e.g.,
bonnetheads) may also have limited ef fects on prey because both ju‐
veniles and adults primarily feed on crabs, lobsters, and cephalopods
(Bethea et al., 2007).
The extrapolation of our results beyond our study design is hin‐
dered by several caveat s. Firstly, we do not know whether arrival
times are truly a consequence of perceived predation risk or if they
are a function of var ying densities of individuals which could not
be controlled. We also did not measure water currents at each of
TABLE 6 Mean predator foraging activity (bites and severe damage) and prey response behavior (burst swimming, schooling, and
residency) across four habitat types
Predator bites Severe damage Burst swimming Schooling Prey residency
Coral reef 2.211 (±3.441) 0.263 (±0.452) 4.579 (±7.324) 6.052 (±4.8 01) 24.316 (±18.973)
Sand 0.791 (±1.684) 0.070 (±0.259) 0.698 (±3.377) 1.395 (±2.555) 8.814 (±17.14)
Sea fan 1.558 (±4.078) 0.136 (±0.351) 1.605 (±3.13) 4. 628 (±4.232) 32.211 (±32.527)
Seagrass 0.865 (±2 .360) 0.096 (±0.298) 0.745 (±1.741) 2 .980 (±3.906) 20.192 (±27.652)
FIGURE 6 Correlation plot of prey risk
behaviors (burst swimming, schooling,
and prey residency) compared to predator
foraging activity (bites and damage) across
four habit at types
(c) Sea fan (n = 43)
(a)
Coral reef (n = 19)(b) Sand (n = 43)
(d) Seagrass (n = 52)
    
|
 13749
PHENIX Et a l.
our BRUV stations, which could have affected the bait dispersal at
different rates, thus changing detection potential by prey species.
Furthermore, our statistical power was weakened by poor visibility
(resulting in the exclusion of 37 replicates) and a category 5 hur‐
ricane, which ended data collection a bit early and thus prevented
extended sampling. In future studies, dusk or night time deploy
ments should be added to observe predator–prey interactions after
dark, which may be especially important for sharks on coral reefs
(Hammerschlag et al., 2017).
The role of “apex”‐predators on reefs has been brought into
question in recent years (see Roff et al., 2016). While we caution
overextending the results of this study to other regions, our dat a
suggest that predators regardless of their trophic position do
not significantly control mobile prey behavior on short temporal
scales, across habitats. Instead, a habitat‐specific response to a
consistent signal of mobile predators on reefs may result in pro
active prey vigilance and subtle food‐risk trade‐offs. Specifically,
less complex habitats where predators are known to patrol yet re
main temporally unpredictable in their occurrence due to limited
numbers and potentially wider activity areas may induce different
reactive behavioral effects such as schooling and burst swimming,
which, when extended over larger time scales, could have meta
bolic and fitness‐level impacts on prey. Taken together, these re
sults suggest that context is important when trying to disentangle
the effects of top predators on prey in costal marine habitats, and
future studies should examine the interactions between mobile
predators and habit at in order to link predation risk theory to
observations.
ACKNOWLEDGMENTS
This work was supported by funding to Beneath the Waves from the
Herber t W. Hoover Foundation, as well as from C. and M. Jones. We
are grateful to M. Riera, E. Pritchard, C. Perry, R. Tricarico, Shake‐A‐
Leg, and the International Seakeepers Society for their assistance
with this project. This work was conducted under a Biscayne
National Park permit BISC‐0 0076 to AJG.
CONFLICT OF INTEREST
The authors declare no competing interests.
AUTHOR CONTRIBUTIONS
A. J. G., M. E. B., and S. J. B. conceived and designed the study. L. M.
P., D. T., E. Q., and A. J. G. conduced the field work. L. M. P. and S.
J. B. performed the analyses. All authors contributed to writing the
manuscript and gave approval.
ORCID
Lindsay M. Phenix https://orcid.org/0000‐00017462‐878X
Simon J. Brandl https://orcid.org/0000‐0002‐66492496
Austin J. Gallagher https://orcid.org/0000‐0003‐1515‐3440
DATA AVAIL ABI LIT Y S TATEM ENT
All data are deposited and available in Dryad at the following address
https ://doi.org/10.5061/dryad.wm37p vmh5.
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How to cite this article: Phenix LM, Tricarico D, Quintero E,
Bond ME, Brandl SJ, Gallagher AJ. Evaluating the effects of
large marine predators on mobile prey behavior across
subtropical reef ecosystems. Ecol Evol. 2019;9:13740–13751.
https ://doi.org/10.1002/ece3.5784
... Recently, behavioural metrics such as time to arrival (time taken for first individual of a species to appear in the field of view of stereo-BRUVs) and number of interactions with a bait bag have been used to examine interactions between predatory species and their prey [25][26][27][28][29] . These studies hypothesized that prey would take longer to arrive in the field of view of stereo-BRUVs in less structurally complex habitats that offer little refuge from predators 27 or are in areas with exposure to sharks 28 . ...
... Recently, behavioural metrics such as time to arrival (time taken for first individual of a species to appear in the field of view of stereo-BRUVs) and number of interactions with a bait bag have been used to examine interactions between predatory species and their prey [25][26][27][28][29] . These studies hypothesized that prey would take longer to arrive in the field of view of stereo-BRUVs in less structurally complex habitats that offer little refuge from predators 27 or are in areas with exposure to sharks 28 . Additionally, rays are less likely to forage from the bait bag in areas with higher predator exposure [25][26][27][28][29] . ...
... These studies hypothesized that prey would take longer to arrive in the field of view of stereo-BRUVs in less structurally complex habitats that offer little refuge from predators 27 or are in areas with exposure to sharks 28 . Additionally, rays are less likely to forage from the bait bag in areas with higher predator exposure [25][26][27][28][29] . This framework can be expanded to investigate the effect of proximity to human activities on the behaviour of sharks on coral reefs. ...
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Keywords: dynamic Brownian bridge movement model earth mover's distance elasmobranch endangered movement ecology wildlife provisioning By changing the spatiotemporal availability of resources, tourism-related feeding can have potentially detrimental impacts on the movement ecology of animals, thus possibly undermining its own conservation benefits. A lack of baseline data on natural behaviour and the noninclusion of observation data that adequately incorporates the previous experience of animals with tourism-related feeding have generated contradictory results, causing the true impacts of feeding to remain obscure. Further, the relationship between the energy consumption of fed animals and their space use remains unexplored. Here, we coupled passive acoustic telemetry with previously published observation data at a tourism-related feeding site to investigate how direct feeding affects space use and residency patterns of great hammerhead sharks, Sphyrna mokarran, in Bimini, The Bahamas, at various timescales (ranging from days to 8 years). We first constructed movement models for 28 known fed and naïve sharks (i.e. those that were present at the study site but never attended feeding events) to quantify differences in space use and spatial overlap between those groups. We then compared bait uptake of fed sharks with their space use. Fed sharks showed a marked reduction in space use in response to feeding events and an amplification of these impacts over 5 consecutive years. In contrast, naïve shark space use remained unchanged over the same period. The seasonal residency of fed and naïve great hammerheads remained stable across 8 years, with the sharks leaving the study site during the summer of each year. Our study underscores how the intensification of tourism-related direct feeding progressively alters the space use of apex predators across short and long timescales, with enduring effects on fed animals. Our study further highlights the utility of a naïve animal group for assessing feeding impacts in the absence of baseline data.
... The BRUV units were distributed in the following four park zones: marine tourism, marine protection, traditional fisheries and core zones. Six BRUV units were used with a modified structure following the design used by Phenix et al. (2019), namely, a pyramid steel frame with dimensions of 50 × 50 cm (base) × 25 × 25 cm (top) × 60 cm (slant height) and 30 × 30 cm plus shaped camera platform in the middle of the frame (Fig. 2). Each BRUV unit was equipped with a 100 cm long, 1″ (~2.5 cm) diameter PVC bait pole and a 30 cm long, 3″ (~7.6 cm) diameter PVC bait canister attached at the end. ...
... The BRUV units were distributed in the following four park zones: marine tourism, marine protection, traditional fisheries and core zones. Six BRUV units were used with a modified structure following the design used by Phenix et al. (2019), namely, a pyramid steel frame with dimensions of 50 × 50 cm (base) × 25 × 25 cm (top) × 60 cm (slant height) and 30 × 30 cm plus shaped camera platform in the middle of the frame (Fig. 2). Each BRUV unit was equipped with a 100 cm long, 1″ (~2.5 cm) diameter PVC bait pole and a 30 cm long, 3″ (~7.6 cm) diameter PVC bait canister attached at the end. ...
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Context Giant guitarfish (Family: Glaucostegidae) and wedgefish (Family: Rhinidae) (Critically Endangered, IUCN Red List and CITES Appendix II) are highly exploited throughout their distribution because of their highly valued fins in the international market. Both are commonly caught as bycatch or secondary valuable catch in the Java Sea, including in Karimunjawa National Park, Central Java, Indonesia. Aims Assess the presence and relative abundance of giant guitarfish and wedgefish species in Karimunjawa National Park and adjacent waters. Methods Data were collected using baited remote underwater video (BRUV) surveys across 40 sites, covering multiple zonation areas and depth ranges. All species were identified to the species level and their relative abundance was tested with one-way PERMANOVA based on sites, zonation areas and depths. Key results Two target species, Glaucostegus typus and Rhynchobatus australiae, were present in the study area with a maximum number of 3 and 6 and relative abundance of 0.0048 and 0.0096 respectively, over 477 BRUVs and 623.9 h of videos. Their presence during the study was not affected by sites, zonations or depth. Implications The presence and relative abundance of both G. typus and R. australiae were low, which may be a result of decades of overfishing, and have provided the first information to the urgency of managing the species in the areas.
... The ability of prey to detect an approaching threat can influence the level of wariness and willingness to take risks 67,68 . Visual acuity is expected to increase in larger fish 69 , allowing them to detect the approaching threat before smaller fishes. ...
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... Further records will help to determine the range of species involved in these interactions and therefore the extent of animals affected if these behavioural connections are lost. The use of remote video systems has been expanded from standard metrics to include a range of new outputs from the footage collected [63,[70][71][72]. BRUVS are a useful tool for behavioural observations as they allow large amounts of footage to be collected, increasing the chances of recording rare events and allow these events to be replayed and analysed in detail through post-processing. ...
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... It is likely that a range of factors not evaluated here, such as spatial and temporal variations in temperature, salinity, depth, habitat type, nutrients, and dissolved oxygen concentrations, directly or indirectly influence shark residency patterns. Such factors have previously been shown to affect relative abundance rates of great hammerheads as well as bull and nurse sharks in Biscayne Bay (Phenix et al. 2019, Tinari & Hammerschlag 2021, Rider et al. 2021a). Therefore, we recommend that future research seek to incorporate such environmental and water quality factors into assessments of shark space use and residency patterns in Biscayne Bay and how these parameters interact with proximity to the North Bay Urban zone. ...
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Predators shape ecosystem structure and function through their direct and indirect effects on prey, which permeate through ecological communities. Predators are often perceived as competitors or threats to human values or well-being. This conflict has persisted for centuries, often resulting in predator removal (i.e. killing) via targeted culling, trapping, poisoning, and/or public hunts. Predator removal persists as a management strategy but requires scientific evaluation to assess the impacts of these actions, and to develop a way forward in a world where human-predator conflict may intensify due to predator reintroduction and rewilding, alongside an expanding human population. We reviewed literature investigating predator removal and focused on identifying instances of successes and failures. We found that predator removal was generally intended to protect domestic animals from depredation, to preserve prey species, or to mitigate risks of direct human conflict, corresponding to being conducted in farmland, wild land, or urban areas. Because of the different motivations for predator removal, there was no consistent definition of what success entailed so we developed one with which to assess studies we reviewed. Research tended to be retrospective and correlative and there were few controlled experimental approaches that evaluated whether predator removal met our definition of success, making formal meta-analysis impossible. Predator removal appeared to only be effective for the short-term, failing in the absence of sustained predator suppression. This means predator removal was typically an ineffective and costly approach to conflicts between humans and predators. Management must consider the role of the predator within the ecosystem and the potential consequences of removal on competitors and prey. Simulations or models can be generated to predict responses prior to removing predators. We also suggest that alternatives to predator removal be further developed and researched. Ultimately, humans must coexist with predators and learning how best to do so may resolve many conflicts.
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Non-consumptive effects (NCEs) of predators occur as prey alters their habitat use and foraging decisions to avoid predation. Although NCEs are recognized as being important across disparate ecosystems, the factors influencing their strength and importance remain poorly understood. Ecological context, such as time of day, predator identity, and prey condition, may modify how prey species perceive and respond to risk, thereby altering NCEs. To investigate how predator identity affects foraging of herbivorous coral reef fishes, we simulated predation risk using fiberglass models of two predator species (grouper Mycteroperca bonaci and barracuda Sphyraena barracuda) with different hunting modes. We quantified how predation risk alters herbivory rates across space (distance from predator) and time (dawn, mid-day, and dusk) to examine how prey reconciles the conflicting demands of avoiding predation vs. foraging. When we averaged the effect of both predators across space and time, they suppressed herbivory similarly. Yet, they altered feeding differently depending on time of day and distance from the model. Although feeding increased strongly with increasing distance from the predators particularly during dawn, we found that the barracuda model suppressed herbivory more strongly than the grouper model during mid-day. We suggest that prey hunger level and differences in predator hunting modes could influence these patterns. Understanding how context mediates NCEs provides insight into the emergent effects of predator–prey interactions on food webs. These insights have broad implications for understanding how anthropogenic alterations to predator abundances can affect the spatial and temporal dynamics of important ecosystem processes.
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The nonconsumptive consequences of predators on prey behavior, survival, and demography have recently garnered significant attention by ecologists. However, the impacts of top predators on free-ranging prey are challenging to evaluate because the most common fright response for prey is to leave the area of risk. Additionally, the top-down impacts of avian predators on aquatic environments are surprisingly overlooked. Here we investigated the nonconsumptive effects of avian predators on parental care in pumpkinseed (Lepomis gibbosus (L., 1758)) through use of a realistic model of a predatory bird, the Osprey (Pandion haliaetus (L., 1758)). Our predator model exacted dramatic metabolic fright responses and inducible defenses in experimental fish resulting in significant behavioral changes with respect to their parental care. Key parental behaviors including in-nest rotations and egg and nest maintenance were noticeably altered by predator treatments demonstrating as much as an order of magnitude difference in parental performance, suggesting that even transient predation risk might decrease reproductive fitness. Our data provide important new insights on how the landscape of fear operates along the air–water interface and suggests that avian predators may have greater controlling effects on fish populations than previously thought.
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Flagship species are commonly used as conservation tools, but to be effective, local public support is crucial. A country's national animal symbol is often selected for holding cultural and historical significance. Therefore, national animal symbols may serve as ideal flagships within their associated countries. Here, we evaluate the extinction risk and primary threats facing the world's national animal symbols and assess their levels of protection. Analysis of International Union for Conservation of Nature data revealed that 35% of symbols are threatened and 45% are exhibiting population declines. Two symbols are extinct, and four have been extirpated from their associated country. If population trends persist, over half of these symbols may face future extinction. The primary threats facing national animal symbols are exploitation, human–wildlife conflict and habitat loss. Only 16% of these symbols are nationally protected, whereas 50% receive international trade restrictions. Given their significance to national identity, it may be relatively easy to garner support for national animal symbols as flagship species.