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REPORT
Bleaching susceptibility of aquarium corals collected
across northern Australia
Morgan S. Pratchett
1
•Ciemon F. Caballes
1
•Stephen J. Newman
2
•
Shaun K. Wilson
3,4
•Vanessa Messmer
1
•Deborah J. Pratchett
1
Received: 1 December 2019 / Accepted: 15 April 2020 / Published online: 30 April 2020
ÓThe Author(s) 2020
Abstract There are a wide range of Scleractinian corals
that are collected for the global reef aquarium market, often
from non-reefal environments. The sustainability of coral
harvesting is potentially threatened by increasing anthro-
pogenic disturbances and climate change, though it is
unknown to what extent many commonly harvested corals
are susceptible to environmental change, or actually bleach
during marine heatwaves. In this study, we experimentally
tested the temperature sensitivity and bleaching suscepti-
bility of six coral species (Homophyllia australis,Micro-
mussa lordhowensis,Catalaphyllia jardinei,Trachyphyllia
geoffroyi,Duncanopsammia axifuga, and Euphyllia glab-
rescens), which are important components of the aquarium
coral fisheries across northern Australia, in Western Aus-
tralia, the Northern Territory, and/or Queensland. Inter-
specific differences were evident in the temperature
sensitivity and bleaching susceptibility among the study
species. Homophyllia australis, and M. lordhowensis were
found to be particularly susceptible to elevated
temperatures, whereby all corals subjected to elevated
temperatures died within the course of the experimental
treatment (75 d). Catalaphyllia jardinei and E. glabrescens
also exhibited significant increases in mortality when
exposed to elevated temperatures, though some of the
corals did survive, and C. jardinei mostly died only after
exposure to elevated temperatures. The other species (T.
geoffroyi and D. axifuga) exhibited marked bleaching when
exposed to elevated temperatures, but mortality of these
corals was similar to that of conspecifics held at ambient
temperatures. This study highlights the potential for envi-
ronmental change to impact the sustainability and viability
of Australian coral harvest fisheries. More importantly, this
study highlights the need for specific and targeted in situ
monitoring for important stocks of coral fishery target
species, to assess their vulnerability to fishery and fishery-
independent effects.
Keywords Controlled experiment Scleractinia
Temperature Light intensity Survivorship
Introduction
Mass coral bleaching is an increasingly familiar and
recurring phenomenon, whereby many different species of
zooxanthellate corals lose their endosymbionts and asso-
ciated photosynthetic pigments (Glynn 1984), mainly in
response to environmental stress, including freshwater
inundation, aerial exposure, sedimentation and anomalous
temperatures (Wiedenmann et al. 2013). The severity,
extent and frequency of mass coral bleaching has increased
since the 1980s (Hughes et al. 2018a) in line with ocean
warming and increasing incidence of marine heatwaves
(Heron et al. 2016; Hobday et al. 2018; Skirving et al.
Topic Editor Andrew Hoey
&Morgan S. Pratchett
morgan.pratchett@jcu.edu.au
1
ARC Centre of Excellence for Coral Reef Studies, James
Cook University, Townsville, QLD 4811, Australia
2
Western Australian Fisheries and Marine Research
Laboratories, Department of Primary Industries and Regional
Development, Government of Western Australia, Hillarys,
WA 6025, Australia
3
Marine Science Program, Department of Biodiversity,
Conservation and Attractions, Western Australian
Government, Kensington, WA 6151, Australia
4
Oceans Institute, University of Western Australia, Crawley,
WA 6009, Australia
123
Coral Reefs (2020) 39:663–673
https://doi.org/10.1007/s00338-020-01939-1
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
2019). Marine heatwaves are now the foremost cause of
mass coral bleaching and elevated coral mortality (Hughes
et al. 2018a,b), threatening the population viability of
vulnerable coral species and undermining the ecological
integrity and function of reef ecosystems. Climate-induced
coral bleaching, as well as other causes of coral mortality,
may also directly undermine the sustainability and viability
of harvest fisheries that collect corals from the wild, mainly
for home and public aquaria (Harriott 2003; Rhyne et al.
2012).
International ornamental and aquarium coral fisheries
involve the annual trade of hundreds of thousands of small
coral pieces and are worth millions of dollars (Wood et al.
2012). An increasing portion of the coral sold comes from
aquaculture; however the majority is still collected from
the wild, from countries like Indonesia and the Philippines
(Rhyne et al. 2012). In Australia, coral harvesting is a
relatively minor cause of coral loss, and the annual biomass
of coral removed is negligible compared to reef-wide levels
of coral biomass and productivity (Harriott 2003). For the
Queensland Coral Fishery (QCF) the annual Total Allow-
able Commercial Catch (TACC) is 200 tonnes, with fishing
activity spread across a large area, and prohibited within
no-take marine reserves (QDEEDI 2009). Reported catches
have also been \50% of the TACC throughout the last
decade (DAF 2018). Coral fisheries in other jurisdictions
(Western Australia, Northern Territory, and the Coral Sea)
have much smaller quotas. Despite the limited overall
harvesting, it is possible that specific species may be over-
exploited where harvesting is concentrated on rare species.
Aquarium corals are mostly selected based on appearance,
especially colour, as well as their amenability to harvest-
ing, transport and maintenance within aquaria. Few juris-
dictions have species-specific quotas, and there is
insufficient knowledge of wild stocks to even propose
relevant harvest limits for most species (Roelofs and Sil-
cock 2008). Aside from fisheries effects, widespread and
accelerating degradation of coral reef ecosystems is placing
increasing pressure on coral fisheries globally, leading to
greater public and political scrutiny regarding the sustain-
ability of coral harvesting (Albert et al. 2015). The prin-
cipal concern relates to the potential risk of localized
depletion for vulnerable and slow-growing coral species
(Harriott 2003; Garrabou et al. 2017). This concern is
further magnified where harvested corals are simultane-
ously being impacted by fisheries-independent threats,
including rapid and accelerating environmental change
(Montero-Serra et al. 2019). Importantly, marine heat-
waves have caused severe and widespread coral bleaching
across Australia in recent years (Hughes et al. 2017), but it
is largely unknown how these events impacted many of the
corals (other than Acropora spp.) harvested by aquarium
coral fisheries.
All zooxanthellate organisms are susceptible to tem-
perature-induced bleaching at some level (Buddemeier and
Fautin 1993), and very severe marine heatwaves can cause
comprehensive bleaching and mortality across a wide
range of different coral species (e.g., Vargas-Angel et al.
2019). There are however, apparent taxonomic differences
in the susceptibility and responses of corals to increasing
temperature (Loya et al. 2001; Grottoli et al. 2014; Hoey
et al. 2016; Claar and Baum 2019). Among common,
widespread and well-studied coral taxa, the rank order of
bleaching susceptibility (based on the proportion of colo-
nies that bleach or die) appears to be fairly conserved
among geographic locations (e.g., McClanahan et al.
2004), whereby Acropora spp. are often the first to bleach
and experience the highest mortality rates (Baird and
Marshall 2002; Pratchett et al. 2013; Burt et al. 2019; but
see Guest et al. 2012; Chou et al. 2016). Conversely, other
corals, such as Turbinaria spp. are rarely observed to
bleach (e.g., Marshall and Baird 2000) and appear partic-
ularly capable of withstanding thermal stress. There are
many coral taxa for which we know very little about
temperature sensitivity and bleaching susceptibility, mostly
because they do not occur on shallow carbonate reefs,
where in situ studies of coral bleaching are predominantly
conducted (e.g., Hughes et al. 2017; Gilmour et al. 2019;
Raymundo et al. 2019; but see Camp et al. 2018). This
includes many of the coral taxa that are collected for the
aquarium fishery from turbid intertidal habitats.
The purpose of this study was to assess the temperature
sensitivity and bleaching susceptibility of six commonly
harvested aquarium corals (Homophyllia australis,Micro-
mussa lordhowensis,Catalaphyllia jardinei,Trachyphyllia
geoffroyi,Duncanopsammia axifuga, and Euphyllia glab-
rescens), by exposing each of these coral species to ele-
vated temperatures in aquaria. While such experimental
studies are highly constrained in their capacity to assess
how corals respond to elevated temperatures in the wild
(Camp et al. 2018), there is a paucity of data regarding the
bleaching susceptibility of these study species and experi-
mental studies provide the most tractable way to assess
relative bleaching susceptibility of poorly studied species.
Methods
Experimental set-up
This study was conducted in the Marine Aquarium
Research Facility (MARFU) at James Cook University, in
Townsville, Australia. Licensed coral collectors in
Queensland (both CQ and NQ), WA and NT provided a
total of 257 distinct corals (mostly whole colonies or
individual polyps, but sometimes fragments) across 6
664 Coral Reefs (2020) 39:663–673
123
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different study species (H. australis,M. lordhowensis,C.
jardinei,T. geoffroyi,D. axifuga, and E. glabrescens) that
were transported to Townsville within 1–2 weeks of col-
lection. Where possible, samples of each coral species were
obtained from Western Australia (WA), Northern Territory
(NT), north Queensland (NQ) and central Queensland (CQ)
(Table 1). All corals were mounted on ceramic discs,
which were coded to distinguish individual corals and their
provenance. Corals (1–2 individuals per species per loca-
tion) were randomly assigned to each one of 12 different
tanks across four different treatments (Fig. 1).
To test the bleaching responses and temperature sensi-
tivity of the different corals, corals within the ‘‘heated
treatments’’ were subject to gradual warming (1.0 °C
change per week) until the temperature reached a maxi-
mum of 32 °C. The reason for using prolonged heating to
relatively high maximum temperatures was intended to
explicitly assess interspecific and regional variation in
bleaching susceptibility, based on the time until individual
corals exhibited bleaching. Temperatures in control tanks
started at 25.6 °C, and varied between 25.1 and 27.5 °C
through the course of the experiment. Given most of the
study species come from turbid inshore or deeper inter-
reefal habitats, it was possible that bleaching susceptibility
would be moderated by the light environment. To test this,
we further divided corals into high and low light treat-
ments, whereby the maximum light intensity (measured
using a Li-Cor portable light meter during peak irradiance)
was 208.0 (±10.6 SE) and 48.7 (±2.8 SE) lmol m
-2
-
s
-1
, respectively. These different light intensities are
equivalent to those used to assess the role of light
([180 lmol m
-2
s
-1
) in previous experimental bleaching
studies (e.g., Wiedenmann et al. 2013), and are approxi-
mately equivalent to light regimes recorded in open reef
environments versus shaded environments (e.g., within
caves) at a depth of 5 m (Anthony and Hoegh-Guldberg
2003).
All colonies were acclimated to experimental conditions
(ambient temperature and low light) for a minimum of
1-week before being subject to high light and/or experi-
mental warming. The day that warming was initiated (April
9th 2018) was set as Day 1, and corals were subject to
experimental conditions until Day 75, at which time
experimental tanks with high temperatures were reduced to
ambient temperatures over 72 h. We then continued to
monitor all surviving colonies until Day 150. Corals were
inspected every 1–2 d to record survival, and scored for
colour, following Siebeck et al. (2006) every 1–2 weeks.
Survival of individual coral colonies was recorded as the
sum of the proportion of time a coral survived during the
heating experiment plus the proportion of time the coral
survived post treatment; i.e. corals that survived to day 75
(end of heating experiment) were assigned a survivorship
of 1.0, and corals that survived to day 150 (end of study
period) were assigned survivorship of 2.0. Changes in
colour were based on changes in colour saturation (mea-
sured on a 6-point scale), between initial records taken on
Day 1 versus Day 75 (or the last record of colour hue taken
prior to mortality). Bleaching was defined as a change in
colour saturation of 2 units or more, following Siebeck
et al. (2006).
Data analyses
We modelled colour change and survival in corals as a
function of ‘Temperature’ and ‘Light’ using linear mixed-
effects models (Bates et al. 2015). ‘Species’, ‘Tempera-
ture’, and ‘Light’ were included as fixed effects. We also
included the individual ‘Tank’ where the corals were
placed as a random effect to account for the non-inde-
pendence of replicates tested within the same aquarium.
‘Region’ was not included as a factor since some species
were only sourced from one locality (see Table 1). Alter-
native models were compared using Akaike’s information
criterion corrected for small sample sizes (AICc) following
Burnham and Anderson (2002). Models were fitted using
the ‘lmer’ function (library lme4) in R 3.0.1 (R Core Team
2019). Post hoc comparisons were conducted for survival
data using the Tukey method in the R package emmeans
(Lenth et al. 2018).
To better resolve differences in survival among corals,
we obtained nonparametric estimates of the shape of the
survivorship curves for each coral species under the two
temperature treatments using Kaplan–Meier product-limit
Table 1 Identity and provenance of corals used in the controlled
bleaching experiment to test for interspecific differences in suscep-
tibility to elevated temperature and light
Species NT NQ CQ WA Total
Family Lobophyllidae
Homophyllia australis 17 17
Micromussa lordhowensis 18 18
Family Merulinidae
Catalaphyllia jardinei 18 20 38
Trachyphyllia geoffroyi 18 23 15 56
Family Dendrophylliidae
Duncanopsammia axifuga 20 18 19 21 78
Family Euphyllidae
Euphyllia glabrescens 18 16 16 50
Total 20 72 113 52 257
Source region: NT Northern Territory (Darwin), NQ North Queens-
land (Cairns), CQ Central Queensland (Mackay), WA Western Aus-
tralia (Karratha). Corals were equally distributed among the four
treatments
Coral Reefs (2020) 39:663–673 665
123
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Ambient temp.
Low light
Ambient temp.
High light
Warming
Low light
Warming
High light
H. australisM. lordhowensisC. jardineiT. geoffroyiD. axfugaE. glabrescens j
666 Coral Reefs (2020) 39:663–673
123
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analysis. The Kaplan–Meier model is based on estimating
conditional probabilities at each time point when an event
occurs, and taking the product limit of those probabilities
to estimate the survival rate at each point in time (Kaplan
and Meier 1958). Survival probabilities were calculated
using the ‘survfit’ function in the R package survival
(Therneau 2015) and visualised by plotting survival curves
using the ‘ggsurvplot’ function in the R package survminer
(Kassambara et al. 2017). To test whether survival trends
were significantly different for each treatment, survival
probabilities were compared using the Log-rank test, which
takes into account both individuals that died during the
course of the experiment and individuals that were still
alive at the end of the study, i.e. right-censored data
(Walker and Shostak 2010). All plots and analyses were
implemented in R 3.0.1 (R Core Team 2019).
To assess interspecific and regional variation in the
tolerance of corals to temperature and light treatments,
standardised mean differences (SMDs), using Hedges’
G(Hedges 1981) as an effect size metric, were calculated
using the ‘metacont’ function in the R package meta
(Schwarzer 2007). Calculated effect sizes and 95% confi-
dence intervals were used to generate forest plots in R 3.0.1
(R Core Team 2019).
Results
Bleaching susceptibility
A total of 257 small (\60 mm diameter) corals were used
in the experiment (Table 1). Of these, 128 (49.8%) corals
exhibited declines in colour saturation through the course
of the experiment, with bleaching (where declines in colour
saturation were [2) recorded for 74 corals (28.8%). All
six species exhibited bleaching (Fig. 2). The incidence of
bleaching was consistently higher for corals subject to
experimental warming (35.6%), though 16.67% of the
colonies maintained at ambient temperatures also bleached
(Fig. 2). The overall incidence of bleaching (across all
treatments) was greatest for M. lordhowensis (38.9%,
n= 18) and E. glabrescens (38.0%, n= 50). Lower inci-
dence of bleaching was recorded for C. jardinei (26.3%,
n= 38) and T. geoffroyi (23.2%, n= 56), and particularly
for H. australis (17.6%, n= 17) and D. axifuga (11.5%,
n= 78). For D. axifuga, bleaching incidence ranged from
10 to 17% with no obvious regional differences. For E.
glabrescens, however, it was notable that only colonies
collected from the GBR (NQ and CQ) exhibited bleaching
(even when exposed to high light at ambient temperatures),
whereas none of the colonies from WA exhibited major
colour loss even when exposed to elevated temperature.
The best models to explain variation in the extent of
colour loss recorded during this study included ‘Species’,
‘Temperature’, ‘Light’, and the interaction between
‘Temperature’ and ‘Light’ (Table 2). For M. lordhowensis,
C. jardinei,T. geoffroyi and D. axifuga, bleaching (declines
in colour saturation [2) was more prevalent and more
pronounced for corals subject to warming, but the extent of
colour loss was also exacerbated by exposure to high light
(Fig. 2). Based on standardised mean differences, elevated
temperature resulted in significant colour change for C.
jardinei,T. geoffroyi, and D. axifuga, while high light
intensity accounted for significant colour loss in M. lord-
howensis and D. axifuga (Fig. 3). For E. glabrescens, the
median level of colour loss was greatest in the high tem-
perature and high light treatment, but bleaching was
recorded across all treatments (Fig. 2). For H. australis, the
incidence of bleaching was low across all treatments
(Fig. 2).
Survivorship
Eighty-five (out of 257; 33.1%) corals survived to the end
of the experiment (150 d). Survivorship was lower (21.3%)
among corals subject to warming, than for corals main-
tained at ambient temperatures (57.8%). However, there
was also marked interspecific variation in the survival of
corals between the two temperature treatments. The best
model (based on wAICc) for explaining variation in sur-
vivorship included the interaction between ‘Species’ and
‘Temperature’, but did not include light levels (Table 2).
Post hoc pairwise comparisons showed that there were
significant differences in survival between corals subject to
warming versus ambient temperatures for H. australis
(p\0.001), M. lordhowensis (p\0.001), C. jardinei
(p= 0.028), and E. glabrescens (p\0.001); but not for T.
geoffroyi (p= 0.791) and D. axifuga (p= 0.270).
Survivorship of the different coral species varied both in
extent and timing. For H. australis and M. lordhowensis,
survival declined sharply from day 1 to day 75, during the
treatment period for corals subject to warming (Fig. 4).
Importantly, many colonies of H. australis died without
exhibiting prior bleaching. For C. jardinei and E. glab-
rescens, there were also significant differences in survival
with respect to temperature treatments, though this differ-
ence was most pronounced after the recovery period, on
Day 150. For C. jardinei, differences in survival between
temperature treatments were limited (92% vs. 81%) during
bFig. 1 Select images of experimental colonies to indicate interspeci-
fic differences in responses of the six coral species (H. australis,M.
lordhowensis,C. jardinei,T. geoffroyi,D. axifuga, and E.
glabrescens) with exposure to increasing temperature and high levels
of light intensity
Coral Reefs (2020) 39:663–673 667
123
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the treatment period, from day 1 to day 75, but overall
survivorship (at day 150) was much lower for corals
subjected to warming (19%) compared to colonies main-
tained at ambient temperatures (75%) (Fig. 4c). There was
Low High
(a) Homophyllia australis
Low High
(b) Micromussa lordhowensis
Low High
Colour Change
(c) Catalaphyllia jardinei
Low High
(d) Trachyphyllia geoffroyi
Low High
Light Intensity
(e) Duncanopsammia axifuga
Low High
(f) Euphyllia glabrescens
Temperature: Ambient Hot
−6
−4
−2
0
2
−6
−4
−2
0
2
−6
−4
−2
0
2
−6
−4
−2
0
2
−6
−4
−2
0
2
−6
−4
−2
0
2
Fig. 2 Boxplots showing species-specific colour change response to
temperature and light intensity treatments. Plots show median (bold
line), 25th and 75th percentile range (box), 5th and 95th percentile
range (error bars), and jitter points (large coloured circles) pooled
across temperature treatments for each light treatment
668 Coral Reefs (2020) 39:663–673
123
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no difference in survival of T. geoffroyi or D. axifuga with
respect to temperature treatments (Fig. 4). For D. axifuga,
\50% of corals survived 50 d, and there was ongoing
mortality throughout the subsequent treatment and recov-
ery period (Fig. 4e). Survival of T. geoffroyi was much
higher than for D. axifuga, but there were sustained levels
of mortality throughout the experiment both for corals
exposed to elevated temperatures and those maintained at
ambient temperatures (Fig. 4).
Based on standardised mean differences, elevated tem-
perature had a substantial negative effect on the survival of
H. australis (as well as for M. lordhowensis, which was
excluded from analyses due to zero variance in the ‘Am-
bient’ treatment, i.e. 100% survival) and E. glabrescens
(Fig. 3). Warming also had a moderate effect on the sur-
vival of C. jardinei, but we did not observe any adverse
effect on T. geoffroyi and D. axifuga. For those species that
did exhibit significant differences in survival between
temperature treatments, interspecific differences in tem-
perature sensitivity are also reflected in the time to median
(50%) survival, which was lowest for H. australis (51 d),
but also \75 d for M. lordhowensis (58 d) and E. glab-
rescens (60 d), and longest for C. jardinei (118 d).
Discussion
This study explored the temperature sensitivity and
bleaching susceptibility of six different coral species (H.
australis,M. lordhowensis,C. jardinei,T. geoffroyi,D.
axifuga, and E. glabrescens), which are important target
species for aquarium fisheries in QLD, WA and/or NT
(DEEDI 2012; DPIR 2019; Newman et al. 2019). All six
corals species exhibited bleaching to a greater or lesser
Light Intensity Effect Size
on Colour Change
Temperature Effect Size
on Colour Change
Temperature Effect Size
on Survival
−3 −2 −1 0 1 −3 −2 −1 0 1 −25 −20 −15 −10 −5 0
H. australis
M. lordhowensis
C. jardinei
T. geoffroyi
D. axifuga
E. glabrescens
Fig. 3 Inter-specific differences in the effect of light intensity and
temperature on colour change and the effect of high temperature on
survival, based on Hedge’s G(i.e. effect size). Red dashed line
indicates zero effect, while points to the left of this line suggest a
negative treatment effect on colour change or survival
Table 2 Linear mixed-effects
model (LMM) results for
(a) survival and (b) colour
change predicted as a function
of ‘Species’, ‘Temperature’,
‘Lighting’, and their interaction
effects
Model df LL AICc wAICc Adj R
2
(a) Colour change
Species ?temperature ?light ?(1 | Tank) 10 -421.3 863.5 0.347 0.229
Species ?temperature 9light ?(1 | Tank) 11 -420.7 864.5 0.207 0.229
(1|| Tank) 3 -432.5 871.1 0.008 0.131
Species 9temperature 9light ?(1 | Tank) 26 -410.0 878.2 0.000 0.253
(b) Survival
Species 9temperature ?(1 | Tank) 14 -177.3 384.3 0.922 0.535
Species 9temperature 9light ?(1 | Tank) 26 -179.3 416.8 0.000 0.555
(1 | Tank) 3 -232.4 471.0 0.000 0.080
All models include the tank as the random effect. Shown above are the degrees of freedom (df), maximum
log-likelihood (LL), Akaike’s information criterion corrected for small sample sizes (AICc), AICc weight
(wAICc), and the adjusted R
2
(adj R
2
). Only models with DAICc\2 are shown, in addition to the saturated
and null models, and are ordered by increasing AICc
Coral Reefs (2020) 39:663–673 669
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p < 0.001
0.00
0.25
0.50
0.75
1.00
0 25 50 75 100 125 150
p < 0.001
0.00
0.25
0.50
0.75
1.00
0 25 50 75 100 125 150
p < 0.001
0.00
0.25
0.50
0.75
1.00
0 25 50 75 100 125 150
p = 0.003
0.00
0.25
0.50
0.75
1.00
0 25 50 75 100 125 150
Survival Probability
p = 0.560
0.00
0.25
0.50
0.75
1.00
0 25 50 75 100 125 150
p = 0.360
0.00
0.25
0.50
0.75
1.00
0 25 50 75 100 125 150
Time (da
y
s)
Temperature: Ambient Hot
(a) Homophyllia australis (b) Micromussa lordhowensis
(c) Catalaphyllia jardinei (d) Trachyphyllia geoffroyi
(e) Duncanopsammia axifuga (f) Euphyllia glabrescens
670 Coral Reefs (2020) 39:663–673
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extent. Most notably, M. lordhowensis, C. jardinei, D.
axifuga and T. geoffroyi exhibited significant colour loss
(or bleaching) when exposed to elevated temperatures, and
bleaching was exacerbated by high light intensity for M.
lordhowensis and. D. axifuga. Even more concerning
however, were the high levels of coral mortality ([80%)
recorded for H. australis,M. lordhowensis,E. glabrescens
and C. jardinei when these corals were subjected to ele-
vated temperatures. Maximum temperatures to which cor-
als were exposed in this experiment (32 °C) were high,
though corals living in the shallow subtidal and intertidal
zones in northern Australia may be exposed to tempera-
tures C32 °C during severe heatwaves (Moore et al. 2012)
or in areas where water pools for extended periods at low
tide (Dandan et al. 2015).
While bleaching is commonly recorded among sclerac-
tinian corals exposed to elevated temperatures and/or high
light intensity, there are marked interspecific differences in
the responses of corals (Loya et al. 2001; Hueerkamp et al.
2001; Dandan et al. 2015; Hughes et al. 2018b). In this
study, H. australis was extremely sensitive to elevated
temperature, whereby all colonies subjected to elevated
temperatures had died within 60 d, even though this spe-
cies rarely exhibited bleaching. Rather than losing colour,
tissues of H. australis would retract in response to warming
(Fig. 1) prior to complete mortality of the corals. Con-
versely, T. geoffroyi exhibited a high incidence of bleach-
ing when exposed to elevated temperatures, but low levels
of mortality (\50%). We observed yet another response
for C. jardinei, for which, tissues would often detach from
the underlying skeleton when subject to elevated temper-
ature (Fig. 1). In many instances, the free-living tissue
persisted ex situ and retained its colour intensity for the
duration of the experiment. However, this is likely to be an
experimental artefact, as free-living tissues of C. jardinei
would likely be vulnerable to smothering or predation once
dislodged in the wild. The only corals that exhibited more
pronounced bleaching with increased light intensity were
M. lordhowensis and D. axifuga, but this did not translate
to differences in survivorship. Temperature and light act
synergistically to influence bleaching susceptibility (Jokiel
and Coles 1990), such that high turbidity in some nearshore
environments may actually moderate bleaching-induced
mortality during marine heatwaves (e.g., Fisher et al. 2019;
Teixeira et al. 2019). However, this study shows that ele-
vated temperatures are the predominant cause of bleaching
and mortality, and the overriding concern for the corals
considered in this study.
Interspecific differences in the environmental sensitivity
and bleaching susceptibility among the six study species
(H. australis,M. lordhowensis,C. jardinei,T. geoffroyi,D.
axifuga, and E. glabrescens) may partially account for
apparent differences in their abundance in different regions
and habitats, or at least reflect the limited area over which
corals were collected. Notably, the two coral species that
were most susceptible to experimental warming (H. aus-
tralis and M. lordhowensis) were provided exclusively
from CQ, having been collected from the southern GBR in
areas where these corals are relatively abundant. Both these
corals are distributed further north on the GBR in much
warmer waters (Veron et al. 2019), and it is possible that
colonies from lower latitudes might exhibit greater resi-
lience to elevated temperatures (sensu Hoegh-Guldberg
1999). Accordingly, E. glabrescens collected from WA
exhibited much greater resilience to changing temperatures
and light regimes, than conspecifics from the GBR. How-
ever, there was limited evidence of geographical variation
in temperature sensitivity and bleaching susceptibility for
D. axifuga (which was sampled from all four locations),
nor for T. geoffroyi (sampled from WA, NQ and CQ).
Although, this experiment did not specifically account for
local temperature regimes from where individual corals
were collected (and then test bleaching susceptibility
against regionally specific bleaching thresholds), we would
have expected that corals provided from lower latitudes
and warmer water in WA and NT would be more resistant
to elevated temperatures than corals from CQ (sensu
Hoegh-Guldberg 1999). Ultimately, it would be best to
explicitly account for the specific environmental conditions
in habitats from where each individual coral was collected,
but this was not possible given that corals were provided by
licenced coral collectors and their individual provenance
was only broadly known.
This study shows that at least some Australian aquarium
coral fishery target species (specifically, H. australis,M.
lordhowensis,E. glabrescens and C. jardinei) are suscep-
tible to elevated temperatures, thereby highlighting the
potential for sustained and ongoing environmental change
to undermine the sustainability and viability of these fish-
eries. More importantly, there is an increasing shift in
aquarium coral collections and exports towards small polyp
coral species (mainly, Acropora spp., Dee et al. 2014;
Barton et al. 2017) which are, in general, even more sus-
ceptible to environmental change (Baird and Marshall
2002; Pratchett et al. 2013; Hughes et al. 2018b; Burt et al.
2019), though vulnerability assessments will need to be
undertaken for the specific species that are targeted and
habitats from which they are taken. Similarly, results for
this preliminary experimental study should not be used to
bFig. 4 Species-specific Kaplan–Meier-estimated survival probabili-
ties under two temperature treatments. pvalues for the log-rank test
comparing survival curves between ‘Ambient’ and ‘Hot’ treatments
are shown. Dashed line indicates termination of experimental
treatments and start of recovery period at 75 d
Coral Reefs (2020) 39:663–673 671
123
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infer relative or absolute vulnerability of the coral fishery
target species to ocean warming, marine heatwaves, or
changing environmental conditions. Rather, this study
highlights the need for specific and targeted in situ moni-
toring for important stocks of coral fishery target species, to
assess their vulnerability to fishery and fishery-independent
effects.
Acknowledgements This study was funded in part by the Fisheries
Research and Development Corporation (FRDC; Project 2014-029),
with additional support from the WA Government Department of
Biodiversity, Conservation and Attractions and also Pro-Vision Reef.
In-kind support, through the provision of samples, was provided by
many licensed coral collectors in WA, NT and QLD. Experimental
studies were conducted at the JCU Marine Aquarium Research
Facility (MARFU), and we are grateful to all MARFU staff for sig-
nificant logistic support.
Open Access This article is distributed under the terms of the
Creative Commons Attribution 4.0 International License (http://crea
tivecommons.org/licenses/by/4.0/), which permits unrestricted use,
distribution, and reproduction in any medium, provided you give
appropriate credit to the original author(s) and the source, provide a
link to the Creative Commons license, and indicate if changes were
made.
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