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Variation in Righting Times of Holothuria atra, Stichopus chloronotus, and Holothuria edulis in Response to Increased Seawater Temperatures on Heron Reef in the Southern GBR

Variation in Righting Times of Holothuria atra, Stichopus chloronotus, and Holothuria edulis in... Hindawi Journal of Marine Biology Volume 2019, Article ID 6179705, 6 pages https://doi.org/10.1155/2019/6179705 Research Article Variation in Righting Times of Holothuria atra, Stichopus chloronotus, and Holothuria edulis in Response to Increased Seawater Temperatures on Heron Reef in the Southern GBR 1 1,2 1,3 4 Elizabeth Buccheri , Matthias W. Foellmer, Beth A. Christensen , Paul Langis, 1 5 1,2 Stefani Ritter, Esther Wolf, and Aaren S. Freeman Environmental Studies Program, Adelphi University, New York, USA Department of Biology, Adelphi University, New York, USA Department of Environmental Science, Rowan University, New Jersey, USA Department of Exercise Science, Health Studies, Physical Education and Sport Management, Adelphi University, New York, USA Department of Art and Art History, Adelphi University, New York, USA Correspondence should be addressed to Aaren S. Freeman; afreeman@adelphi.edu Received 13 August 2018; Accepted 6 March 2019; Published 2 April 2019 Academic Editor: Robert A. Patzner Copyright © 2019 Elizabeth Buccheri et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Sea cucumbers can mitigate some impacts of climate change through digestion of benthic sands and production of calcium carbonate. eTh projected ecological benefits of sea cucumbers in warmer, more acidic oceans are contingent on the capacities of individuals to acclimate and populations to adapt to climatic changes. The goal of this experiment was to evaluate the degree to which warming waters would impact three abundant species of sea cucumbers on the Heron Reef in Queensland, Australia. We conducted a behavioral assay using three species of sea cucumbers, Holothuria atra, Stichopus chloronotus,and Holothuria edulis.Individuals from each species were subjected to three conditions mimicking current summer temperatures, current winter temperatures, and an elevated temperature consistent with future ocean warming by the year 2100. Sea cucumber reactions were evaluated using righting time as a proxy for their stress levels and overall tolerance of warming events. eTh three sea cucumber species reacted differently to water temperature changes: H. atra’s righting times declined with temperature, S. chloronotus had greater righting times at high and low temperature extremes, and H. edulis’s righting times remained relatively constant throughout. Our results suggest that each of these species might respond differently to ocean warming and while some may be able to continue to combat climate change in benthic communities, others may decline in ecological function. 1. Introduction benthic communities, like coral reef ecosystems, are some of the most vulnerable to ocean warming and acidification. Warming oceans play a dominant role in the gradual yet dras- Sea cucumbers are crucial members of these benthic tic destruction of coral reef systems on the Great Barrier Reef communities. They play an important ecological role in many [1], and on a global scale [2]. Excess anthropogenic carbon coral reef ecosystems and may mitigate local climate change dioxide in the atmosphere also leads to ocean acidification impacts. On the Heron reef flat, on the Great Barrier Reef in and inhibits the ability of corals to produce calcium carbonate Queensland, Australia, they act as bioeroders and are con- skeletons [3]. us, Th higher water temperatures and decreased sidered to be a keystone species [5]. Through their digestion levels of calcium carbonate in the ecosystem have already of benthic sands and particulate matter, sea cucumbers can reduced coral reef resiliency and are predicted to continue to decrease seawater acidity locally and aid in the production of do so in the future [4]. There is evidence that ocean acidifica- sediment calcium carbonate. They also secrete ammonia as a tion will impact the shallow marine systems more drastically than the deeper ocean environments [5]. Therefore, shallow byproduct of their digestive processes, which enhances coral 2 Journal of Marine Biology reef productivity by increasing the nutrient levels in the water second most abundant, accounting for just over 11% of the [6]. area, and Holothuria edulis represent 7% of the sea cucumber However, the long-term ability for sea cucumbers to mit- species in this area [5]. We chose these three species because igate ocean acidification may depend on individual species’ they were not only three of the most abundant on the reef, thermal reaction norms; certain species function optimally but also the most feasible to collect due to their tendencies under different thermal conditions [7]. With increased tem- to situate themselves amongst coral beds and out in the open perature and acidity of the oceans, benthic invertebrates’ in the sands of the reef flat during the day. Sea cucumbers ecological processes may be altered. Mating periods, larval exhibit a temperature-dependent diel burying schedule. They dispersal, and community structures will be aec ff ted and are generally inactive and buried for at least eight hours a these impacts will be species dependent [8]. Previous studies day and are most ideally surveyed during midday hours [21]. have shown that thermal stress experienced by two unrelated Therefore, we surveyed the collection site and gathered our test subjects during midday hours. All sea cucumbers used in sea cucumber species (Holothuria scabra and Apostichopus japonicus) led to immune and antioxidant responses to our assays were larger individuals collected from the shallow attempt to avoid damage and maintain homeostasis [9, 10] subtidal zone and therefore likely sexually reproducing mor- but, overall, high temperature stress will impact immune photypes [22]. function [11]. Four laboratory trials were conducted using two individ- Righting time assays are a proxy for physiological func- uals from each of the three species at a time. Sample sizes were tion and organismal stress in crabs [12], sea urchins [13, 14], limited due to National Park sampling permit restrictions. and sea stars [15, 16]; yet, this method has not been widely The sea cucumbers were collected from the inner and mid used among sea cucumbers. In our experiments righting reef at a depth of about 1-2 meters MLW on the southwest time was used to determine the influence of temperature on side of the island. The temperature of the seawater was taken the sea cucumber’s reaction time and stress. Although not at the time and location of collection. The average seawater temperature was 23 commonly used on holothuroids, the use of this type of assay C. Therefore, in our experiments, the is particularly relevant for sea cucumber species because they 23 C tanks acted as our control and represented the general rely on their podia to secure themselves to substrates and temperature that the sea cucumbers experience during the keep them safe from predation [17, 18]. During a righting time Australian winter. Before each trial, each individual’s body assay, animals are flipped to expose their more vulnerable, length was measured and they were weighed (Table 1) using ventral side and timed to determine their return to a more a calibrated spring scale (accuracy of approximately +/- 1%) natural, ventral-down position. The amount of time taken with a pan attachment. to reach this recovered state can relate to and ultimately Seven tanks were arranged in flowing seawater systems determine the animals’ physiological capacity and stress level with air stones: vfi e tanks simulated the ocean temperatures as a function of the environmental changes occurring around experienced by the sea cucumbers during local winters (23 C, them. comparable to our season of study), one tank contained To compare how holothuroids in the GBR may acclimate submersible heaters to raise the water temperature to sim- to climate change conditions on a more physical level, we ulate local summer (29 C), and one tank had submersible conducted a behavioral assay evaluating righting timing of heaters to raise the water to the predicted local temper- three of the most abundant sea cucumbers on the back reef aturefor theyear 2100 (33 C) (based on [19]). We were of Heron Reef. We used the holothurids Holothuria atra, limited by the amount of submersible heaters available at Stichopus chloronotus,and Holothuria edulis and evaluated our disposal consequently; we were only able to heat one righting times under conditions mimicking current summer tank to each of the desired warmer temperatures (29 C temperatures, current winter temperatures, and the elevated and 33 C). The remaining five tanks were maintained at temperature of the oceans predicted to result from climate 23 C. This setup allowed us to randomly distribute all six change by the year 2100 [19]. sea cucumbers to a given temperature and allow them time to acclimate on their own to each environment while also having an extra holding tank available for use when 2. Methods necessary. At the start of each round of experimentation, each sea The studywas carried outatthe researchstation ofthe University of Queensland on Heron Island in June 2017. To cucumber was randomly assigned to and placed in a tank determine which three species of cucumbers to include, we and allowed to acclimate for thirty minutes. The animals were then flipped onto their dorsal side at the center of the base of reviewed the Heron Reef flat report of 2014 and conducted simple field surveys at the scientific collection site southwest the tank and timed to determine how long it took to flip back ∘ ∘ of Heron Island, at a site centered on 23.44313 S, 151.91351 E. onto their ventral side. The time was measured for each sea Of the 127 species of sea cucumbers on the Great Barrier cucumber to return all of its podia to the base of the tank Reef, vfi e have been reported to be the most abundant on [15]. Each righting time assay was repeated three times [15] and ten-minute rest time was given to each animal between Heron Reef (Holothuria atra, Holothuria leucospilota, Sticho- pus chloronotus, Holothuria edulis, and Stichopus variegatus) each trial. All sea cucumbers were returned to the collection [5]. Of these vfi e species, Holothuria atra is the most abundant site at the end of each trial. By the end of the experiment, we completed four rounds of testing with six sea cucumbers in allotting for 70% of the sea cucumbers in the study area surrounding Heron Island [5]. Stichopus chloronotus is the each round. Journal of Marine Biology 3 Table 1: Summary statistics for body length, body mass, and the righting times at the three experimental temperatures for the three species. Given are the means± standard deviations. Species H. atra H. edulis S. chloronotus Body length (cm) 16.81± 3.830 18.50± 5.507 16.88± 2.986 Body mass (kg) 1.38± 0.612 1.13± 0.612 1.63± 0.495 Righting time (s) at 23C97.10± 42.915 76.42± 40.377 78.65± 39.237 Righting time (s) at 29C53.83± 20.332 83.66± 51.088 51.51± 26.186 Righting time (s) at 33C59.97± 22.442 99.29± 64.953 72.19± 27.489 2.1. Statistical Analyses. We used linear mixed modeling to Table 2: Results of the linear mixed model with log-transformed righting time as the response using the function lmer of the R analyze the data. We analyzed righting time as a function of package lmerTest (fit by REML). eTh random eeff cts are shown as species, temperature, the species x temperature interaction, given by the simple summary of the model. eTh fixed eeff cts are body length, and the residuals of the regression of body mass shown as summarized by the function mixed of the package afex on length (see Results). Individuals and trials were included (type 3 tests, Kenward-Roger approximation for degrees of freedom) as random factors. We first attempted to keep the response [20]. Number of observations = 216; number of trials = 36; number variable on its original scale by specifying generalized models of individuals = 24. with Poisson and negative binomial error structure. However, none of these models converged to a solution. Hence, we (a) Random eeff cts log -transformed righting time and ran general linear mixed Groups Variance Standard Deviation models (LMM), assuming normally distributed errors. We Trial 0.001009 0.03176 verified model assumptions by plotting the residual distri- Individual 0.070234 0.26502 bution, as well as residuals versus tfi ted values and each Residual 0.122942 0.35063 predictor in the model [23]. All analyses were carried out in Rv3.4.0 (RCore Team 2017).Weused the package lmerTest (b) Fixed effects v2.0-33 [24] to run our models and to conduct the stepwise Effect df F p-value model selection (function step in lmerTest, direction set Temperature 2, 31.53 14.56 < 0.0001 to “both”). We estimated the repeatability of righting time Species 2, 20.94 1.09 0.36 and tested for individual differences based on the simplified Temp.: Species 4, 157.33 7.55 < 0.0001 model using the packages rptR [25]. 3. Results Accordingly, the random eeff ct accounting for between- individual variation explained a significant amount of vari- The three species did not differ signicfi antly in body length ation in our mixed model estimating temperature effects (Table 1; one-way ANOVA; F = 114.89; p = 0.6938) but did 2,21 (Table 2). On the other hand, the random eeff ct trial and differ in body mass, independent of length, indicating dif- hence the order of the experimental trials accounted for ferences in body shape (ANCOVA with type II test; Species: almost zero variation. F = 6.08; p< 0.01; Length: F = 32.27; p< 0.001; Species 2,18 1,18 X Length interaction: F = 0.33; p = 0.7233). Therefore, 2,18 we included body length and the residuals of the regression 4. Discussion of body mass on length as covariates in our linear mixed models. We selected the best model through stepwise removal We found that the three sea cucumber species respond of nonsignificant predictors using the Akaike Information differently to temperature uc fl tuations. Holothuria atra had Criterion. the slowest righting time at 23 C but faster righting times at ∘ ∘ warmer temperatures (29 Cand 33 C). Stichopus chloronotus The effect of temperature on righting time depended on had optimal righting times at 29 C and slower and more species (Table 1). Body length and length-independent body varied righting times at cooler and warmer temperatures mass were not significant and were removed from the final ∘ ∘ (23 Cand 33 C), while Holothuria edulis had righting times model (Table 2, Figure 1). As indicated by the 95% confidence that were seemingly unaffected by the temperature changes. intervals for the effects estimated by the linear mixed model (Figure 1), for Holothuria atra,at 29 and 33 Cthe righting Of the three species’ global geographic distributions times were lower than at 23 C. For Stichopus chloronotus, Holothuria atra is a tropical species that is known to inhabit the righting time was lowest at 29 Cwhereas the times did the warmer equatorial, and, occasionally, subtropical regions not differ at 23 and 33 C, and, surprisingly, for H. edulis the [26–28]. H. atra’s tropical distribution could explain some righting time did not change with temperature. of the tendencies for this species to perform optimally in The repeatability for righting time was significant (R = the higher temperature environments. In contrast, Stichopus 0.362; Std. Error = 0.093; 95% CI = 0.181 - 0.532), indicating chloronotus is geographically limited to the tropics [26–28] that it is a behavioral trait with consistent between-individual suggesting that this species would fare better in their expected variation, independent of other internal or external factors. temperature range; yet our results imply that the species’ 4 Journal of Marine Biology H. atra H. edulis S. chloronotus 4.6 4.4 4.2 4.0 3.8 3.6 24 26 28 30 32 24 26 28 30 32 24 26 28 30 32 Temperature ( C) Figure 1: Eec ff ts of temperature on log -transformed righting time within 95% confidence limits on the three sea cucumber species as estimated by the linear mixed model (see Table 2 for model specifics). Current evidence also suggests that terrestrial ectotherms ability to adapt to above average warming could be limited. Lastly, while Holothuria edulis is most commonly present in exhibit some degree of plasticity with regard to upper thermal tropical regions, it is also found in more subtropical regions limits and the ability to respond to selection for increased than that of the two other species discussed [26–28]. H. temperature tolerances, albeit to a limited extent in the light edulis quite possibly experience the widest range of ocean of projected temperature changes [31]. For echinoderms, temperatures as a species in comparison with H. atra and S. despite exhibiting some adaptive capabilities, the rate and chloronotus which could explain their tendencies to perform success of these responses are also somewhat dependent on similarly in all of the temperatures tested in this study. the rate of the water temperature change [14]. Therefore, The variations in righting times could also suggest that the potential for holothuroids to adapt to rising ocean the reaction norms for key physiological functions, as approx- temperatures may be dependent on not only species, but also imated by our experimental assay, differ among the three geographic location. Previous research on juvenile sea cucumbers, Aposti- species. u Th s, at the future temperature ranges predicted by climate change models [19], these sea cucumbers may be chopus japonicas, has suggested that increased exposure of aec ff ted differently. In a similar study using righting time to parental generations to heat variations will increase the upper evaluate the stress level of sea urchins, each species tested thermal limit of their offspring [32]. Similarly, transgener- responded to warming waters differently as well, exhibiting ational mechanisms could improve the tolerance of several varied thermal tolerances [14]. holothuroid species during future warming events. In the past, ocean warming has occurred as a gradual Our results, while illustrative, are not comprehensive. shift that allowed individuals to acclimate and populations to It is important to note that there were some limitations to evolve. However, the rapid pace of modern climate change the experimental design. The time the sea cucumbers had is potentially catastrophic for many species, particularly to acclimate to the experimental water temperatures was those with slower rates of evolution [29]. The ability of limited. Clearly climate change, while fast, is occurring at a slower pace than our experiments [33], perhaps allowing certain species to adapt to climate change impacts can be determined by evaluating their upper thermal tolerance sea cucumbers to acclimate to higher water temperatures. limits, which biological systems set these limits, and the Nevertheless, regional changes in ocean currents, for exam- species acclimatization capabilities to ultimately alter their ple, can lead to relatively rapid shifts in local sea tempera- own thermal tolerances [30]. Some species of algae have tures, and this is potentially exacerbated by global average been shown to respond through adaptation to changes in temperature increases. Certainly, the recently documented temperatureover short periods of time(Lohbecketal. 2012), detrimental effects of climate change-driven coral bleaching aiding in their ability to overcome rapid temperature shifts. events are due to short duration and quick, intense changes loA (Righting time) ? Journal of Marine Biology 5 in temperature [1], conditions that are somewhat mimicked [9] E. Kamyab, H. Kuhnho ¨ ld, S. C. Novais et al., “Eeff cts of thermal stress on the immune and oxidative stress responses of juvenile in our experiments. sea cucumber Holothuria scabra,” Journal of Comparative Phys- As stated previously, sea cucumbers will play a role in iology B,vol.187,no. 1, pp.51–61, 2017. combatting climate change in benthic marine communities. Therefore, the variety of responses to warming waters by each [10] D. Yunwei, J. Tingting, and D. 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Variation in Righting Times of Holothuria atra, Stichopus chloronotus, and Holothuria edulis in Response to Increased Seawater Temperatures on Heron Reef in the Southern GBR

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Hindawi Journal of Marine Biology Volume 2019, Article ID 6179705, 6 pages https://doi.org/10.1155/2019/6179705 Research Article Variation in Righting Times of Holothuria atra, Stichopus chloronotus, and Holothuria edulis in Response to Increased Seawater Temperatures on Heron Reef in the Southern GBR 1 1,2 1,3 4 Elizabeth Buccheri , Matthias W. Foellmer, Beth A. Christensen , Paul Langis, 1 5 1,2 Stefani Ritter, Esther Wolf, and Aaren S. Freeman Environmental Studies Program, Adelphi University, New York, USA Department of Biology, Adelphi University, New York, USA Department of Environmental Science, Rowan University, New Jersey, USA Department of Exercise Science, Health Studies, Physical Education and Sport Management, Adelphi University, New York, USA Department of Art and Art History, Adelphi University, New York, USA Correspondence should be addressed to Aaren S. Freeman; afreeman@adelphi.edu Received 13 August 2018; Accepted 6 March 2019; Published 2 April 2019 Academic Editor: Robert A. Patzner Copyright © 2019 Elizabeth Buccheri et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Sea cucumbers can mitigate some impacts of climate change through digestion of benthic sands and production of calcium carbonate. eTh projected ecological benefits of sea cucumbers in warmer, more acidic oceans are contingent on the capacities of individuals to acclimate and populations to adapt to climatic changes. The goal of this experiment was to evaluate the degree to which warming waters would impact three abundant species of sea cucumbers on the Heron Reef in Queensland, Australia. We conducted a behavioral assay using three species of sea cucumbers, Holothuria atra, Stichopus chloronotus,and Holothuria edulis.Individuals from each species were subjected to three conditions mimicking current summer temperatures, current winter temperatures, and an elevated temperature consistent with future ocean warming by the year 2100. Sea cucumber reactions were evaluated using righting time as a proxy for their stress levels and overall tolerance of warming events. eTh three sea cucumber species reacted differently to water temperature changes: H. atra’s righting times declined with temperature, S. chloronotus had greater righting times at high and low temperature extremes, and H. edulis’s righting times remained relatively constant throughout. Our results suggest that each of these species might respond differently to ocean warming and while some may be able to continue to combat climate change in benthic communities, others may decline in ecological function. 1. Introduction benthic communities, like coral reef ecosystems, are some of the most vulnerable to ocean warming and acidification. Warming oceans play a dominant role in the gradual yet dras- Sea cucumbers are crucial members of these benthic tic destruction of coral reef systems on the Great Barrier Reef communities. They play an important ecological role in many [1], and on a global scale [2]. Excess anthropogenic carbon coral reef ecosystems and may mitigate local climate change dioxide in the atmosphere also leads to ocean acidification impacts. On the Heron reef flat, on the Great Barrier Reef in and inhibits the ability of corals to produce calcium carbonate Queensland, Australia, they act as bioeroders and are con- skeletons [3]. us, Th higher water temperatures and decreased sidered to be a keystone species [5]. Through their digestion levels of calcium carbonate in the ecosystem have already of benthic sands and particulate matter, sea cucumbers can reduced coral reef resiliency and are predicted to continue to decrease seawater acidity locally and aid in the production of do so in the future [4]. There is evidence that ocean acidifica- sediment calcium carbonate. They also secrete ammonia as a tion will impact the shallow marine systems more drastically than the deeper ocean environments [5]. Therefore, shallow byproduct of their digestive processes, which enhances coral 2 Journal of Marine Biology reef productivity by increasing the nutrient levels in the water second most abundant, accounting for just over 11% of the [6]. area, and Holothuria edulis represent 7% of the sea cucumber However, the long-term ability for sea cucumbers to mit- species in this area [5]. We chose these three species because igate ocean acidification may depend on individual species’ they were not only three of the most abundant on the reef, thermal reaction norms; certain species function optimally but also the most feasible to collect due to their tendencies under different thermal conditions [7]. With increased tem- to situate themselves amongst coral beds and out in the open perature and acidity of the oceans, benthic invertebrates’ in the sands of the reef flat during the day. Sea cucumbers ecological processes may be altered. Mating periods, larval exhibit a temperature-dependent diel burying schedule. They dispersal, and community structures will be aec ff ted and are generally inactive and buried for at least eight hours a these impacts will be species dependent [8]. Previous studies day and are most ideally surveyed during midday hours [21]. have shown that thermal stress experienced by two unrelated Therefore, we surveyed the collection site and gathered our test subjects during midday hours. All sea cucumbers used in sea cucumber species (Holothuria scabra and Apostichopus japonicus) led to immune and antioxidant responses to our assays were larger individuals collected from the shallow attempt to avoid damage and maintain homeostasis [9, 10] subtidal zone and therefore likely sexually reproducing mor- but, overall, high temperature stress will impact immune photypes [22]. function [11]. Four laboratory trials were conducted using two individ- Righting time assays are a proxy for physiological func- uals from each of the three species at a time. Sample sizes were tion and organismal stress in crabs [12], sea urchins [13, 14], limited due to National Park sampling permit restrictions. and sea stars [15, 16]; yet, this method has not been widely The sea cucumbers were collected from the inner and mid used among sea cucumbers. In our experiments righting reef at a depth of about 1-2 meters MLW on the southwest time was used to determine the influence of temperature on side of the island. The temperature of the seawater was taken the sea cucumber’s reaction time and stress. Although not at the time and location of collection. The average seawater temperature was 23 commonly used on holothuroids, the use of this type of assay C. Therefore, in our experiments, the is particularly relevant for sea cucumber species because they 23 C tanks acted as our control and represented the general rely on their podia to secure themselves to substrates and temperature that the sea cucumbers experience during the keep them safe from predation [17, 18]. During a righting time Australian winter. Before each trial, each individual’s body assay, animals are flipped to expose their more vulnerable, length was measured and they were weighed (Table 1) using ventral side and timed to determine their return to a more a calibrated spring scale (accuracy of approximately +/- 1%) natural, ventral-down position. The amount of time taken with a pan attachment. to reach this recovered state can relate to and ultimately Seven tanks were arranged in flowing seawater systems determine the animals’ physiological capacity and stress level with air stones: vfi e tanks simulated the ocean temperatures as a function of the environmental changes occurring around experienced by the sea cucumbers during local winters (23 C, them. comparable to our season of study), one tank contained To compare how holothuroids in the GBR may acclimate submersible heaters to raise the water temperature to sim- to climate change conditions on a more physical level, we ulate local summer (29 C), and one tank had submersible conducted a behavioral assay evaluating righting timing of heaters to raise the water to the predicted local temper- three of the most abundant sea cucumbers on the back reef aturefor theyear 2100 (33 C) (based on [19]). We were of Heron Reef. We used the holothurids Holothuria atra, limited by the amount of submersible heaters available at Stichopus chloronotus,and Holothuria edulis and evaluated our disposal consequently; we were only able to heat one righting times under conditions mimicking current summer tank to each of the desired warmer temperatures (29 C temperatures, current winter temperatures, and the elevated and 33 C). The remaining five tanks were maintained at temperature of the oceans predicted to result from climate 23 C. This setup allowed us to randomly distribute all six change by the year 2100 [19]. sea cucumbers to a given temperature and allow them time to acclimate on their own to each environment while also having an extra holding tank available for use when 2. Methods necessary. At the start of each round of experimentation, each sea The studywas carried outatthe researchstation ofthe University of Queensland on Heron Island in June 2017. To cucumber was randomly assigned to and placed in a tank determine which three species of cucumbers to include, we and allowed to acclimate for thirty minutes. The animals were then flipped onto their dorsal side at the center of the base of reviewed the Heron Reef flat report of 2014 and conducted simple field surveys at the scientific collection site southwest the tank and timed to determine how long it took to flip back ∘ ∘ of Heron Island, at a site centered on 23.44313 S, 151.91351 E. onto their ventral side. The time was measured for each sea Of the 127 species of sea cucumbers on the Great Barrier cucumber to return all of its podia to the base of the tank Reef, vfi e have been reported to be the most abundant on [15]. Each righting time assay was repeated three times [15] and ten-minute rest time was given to each animal between Heron Reef (Holothuria atra, Holothuria leucospilota, Sticho- pus chloronotus, Holothuria edulis, and Stichopus variegatus) each trial. All sea cucumbers were returned to the collection [5]. Of these vfi e species, Holothuria atra is the most abundant site at the end of each trial. By the end of the experiment, we completed four rounds of testing with six sea cucumbers in allotting for 70% of the sea cucumbers in the study area surrounding Heron Island [5]. Stichopus chloronotus is the each round. Journal of Marine Biology 3 Table 1: Summary statistics for body length, body mass, and the righting times at the three experimental temperatures for the three species. Given are the means± standard deviations. Species H. atra H. edulis S. chloronotus Body length (cm) 16.81± 3.830 18.50± 5.507 16.88± 2.986 Body mass (kg) 1.38± 0.612 1.13± 0.612 1.63± 0.495 Righting time (s) at 23C97.10± 42.915 76.42± 40.377 78.65± 39.237 Righting time (s) at 29C53.83± 20.332 83.66± 51.088 51.51± 26.186 Righting time (s) at 33C59.97± 22.442 99.29± 64.953 72.19± 27.489 2.1. Statistical Analyses. We used linear mixed modeling to Table 2: Results of the linear mixed model with log-transformed righting time as the response using the function lmer of the R analyze the data. We analyzed righting time as a function of package lmerTest (fit by REML). eTh random eeff cts are shown as species, temperature, the species x temperature interaction, given by the simple summary of the model. eTh fixed eeff cts are body length, and the residuals of the regression of body mass shown as summarized by the function mixed of the package afex on length (see Results). Individuals and trials were included (type 3 tests, Kenward-Roger approximation for degrees of freedom) as random factors. We first attempted to keep the response [20]. Number of observations = 216; number of trials = 36; number variable on its original scale by specifying generalized models of individuals = 24. with Poisson and negative binomial error structure. However, none of these models converged to a solution. Hence, we (a) Random eeff cts log -transformed righting time and ran general linear mixed Groups Variance Standard Deviation models (LMM), assuming normally distributed errors. We Trial 0.001009 0.03176 verified model assumptions by plotting the residual distri- Individual 0.070234 0.26502 bution, as well as residuals versus tfi ted values and each Residual 0.122942 0.35063 predictor in the model [23]. All analyses were carried out in Rv3.4.0 (RCore Team 2017).Weused the package lmerTest (b) Fixed effects v2.0-33 [24] to run our models and to conduct the stepwise Effect df F p-value model selection (function step in lmerTest, direction set Temperature 2, 31.53 14.56 < 0.0001 to “both”). We estimated the repeatability of righting time Species 2, 20.94 1.09 0.36 and tested for individual differences based on the simplified Temp.: Species 4, 157.33 7.55 < 0.0001 model using the packages rptR [25]. 3. Results Accordingly, the random eeff ct accounting for between- individual variation explained a significant amount of vari- The three species did not differ signicfi antly in body length ation in our mixed model estimating temperature effects (Table 1; one-way ANOVA; F = 114.89; p = 0.6938) but did 2,21 (Table 2). On the other hand, the random eeff ct trial and differ in body mass, independent of length, indicating dif- hence the order of the experimental trials accounted for ferences in body shape (ANCOVA with type II test; Species: almost zero variation. F = 6.08; p< 0.01; Length: F = 32.27; p< 0.001; Species 2,18 1,18 X Length interaction: F = 0.33; p = 0.7233). Therefore, 2,18 we included body length and the residuals of the regression 4. Discussion of body mass on length as covariates in our linear mixed models. We selected the best model through stepwise removal We found that the three sea cucumber species respond of nonsignificant predictors using the Akaike Information differently to temperature uc fl tuations. Holothuria atra had Criterion. the slowest righting time at 23 C but faster righting times at ∘ ∘ warmer temperatures (29 Cand 33 C). Stichopus chloronotus The effect of temperature on righting time depended on had optimal righting times at 29 C and slower and more species (Table 1). Body length and length-independent body varied righting times at cooler and warmer temperatures mass were not significant and were removed from the final ∘ ∘ (23 Cand 33 C), while Holothuria edulis had righting times model (Table 2, Figure 1). As indicated by the 95% confidence that were seemingly unaffected by the temperature changes. intervals for the effects estimated by the linear mixed model (Figure 1), for Holothuria atra,at 29 and 33 Cthe righting Of the three species’ global geographic distributions times were lower than at 23 C. For Stichopus chloronotus, Holothuria atra is a tropical species that is known to inhabit the righting time was lowest at 29 Cwhereas the times did the warmer equatorial, and, occasionally, subtropical regions not differ at 23 and 33 C, and, surprisingly, for H. edulis the [26–28]. H. atra’s tropical distribution could explain some righting time did not change with temperature. of the tendencies for this species to perform optimally in The repeatability for righting time was significant (R = the higher temperature environments. In contrast, Stichopus 0.362; Std. Error = 0.093; 95% CI = 0.181 - 0.532), indicating chloronotus is geographically limited to the tropics [26–28] that it is a behavioral trait with consistent between-individual suggesting that this species would fare better in their expected variation, independent of other internal or external factors. temperature range; yet our results imply that the species’ 4 Journal of Marine Biology H. atra H. edulis S. chloronotus 4.6 4.4 4.2 4.0 3.8 3.6 24 26 28 30 32 24 26 28 30 32 24 26 28 30 32 Temperature ( C) Figure 1: Eec ff ts of temperature on log -transformed righting time within 95% confidence limits on the three sea cucumber species as estimated by the linear mixed model (see Table 2 for model specifics). Current evidence also suggests that terrestrial ectotherms ability to adapt to above average warming could be limited. Lastly, while Holothuria edulis is most commonly present in exhibit some degree of plasticity with regard to upper thermal tropical regions, it is also found in more subtropical regions limits and the ability to respond to selection for increased than that of the two other species discussed [26–28]. H. temperature tolerances, albeit to a limited extent in the light edulis quite possibly experience the widest range of ocean of projected temperature changes [31]. For echinoderms, temperatures as a species in comparison with H. atra and S. despite exhibiting some adaptive capabilities, the rate and chloronotus which could explain their tendencies to perform success of these responses are also somewhat dependent on similarly in all of the temperatures tested in this study. the rate of the water temperature change [14]. Therefore, The variations in righting times could also suggest that the potential for holothuroids to adapt to rising ocean the reaction norms for key physiological functions, as approx- temperatures may be dependent on not only species, but also imated by our experimental assay, differ among the three geographic location. Previous research on juvenile sea cucumbers, Aposti- species. u Th s, at the future temperature ranges predicted by climate change models [19], these sea cucumbers may be chopus japonicas, has suggested that increased exposure of aec ff ted differently. In a similar study using righting time to parental generations to heat variations will increase the upper evaluate the stress level of sea urchins, each species tested thermal limit of their offspring [32]. Similarly, transgener- responded to warming waters differently as well, exhibiting ational mechanisms could improve the tolerance of several varied thermal tolerances [14]. holothuroid species during future warming events. In the past, ocean warming has occurred as a gradual Our results, while illustrative, are not comprehensive. shift that allowed individuals to acclimate and populations to It is important to note that there were some limitations to evolve. However, the rapid pace of modern climate change the experimental design. The time the sea cucumbers had is potentially catastrophic for many species, particularly to acclimate to the experimental water temperatures was those with slower rates of evolution [29]. The ability of limited. Clearly climate change, while fast, is occurring at a slower pace than our experiments [33], perhaps allowing certain species to adapt to climate change impacts can be determined by evaluating their upper thermal tolerance sea cucumbers to acclimate to higher water temperatures. limits, which biological systems set these limits, and the Nevertheless, regional changes in ocean currents, for exam- species acclimatization capabilities to ultimately alter their ple, can lead to relatively rapid shifts in local sea tempera- own thermal tolerances [30]. Some species of algae have tures, and this is potentially exacerbated by global average been shown to respond through adaptation to changes in temperature increases. Certainly, the recently documented temperatureover short periods of time(Lohbecketal. 2012), detrimental effects of climate change-driven coral bleaching aiding in their ability to overcome rapid temperature shifts. events are due to short duration and quick, intense changes loA (Righting time) ? Journal of Marine Biology 5 in temperature [1], conditions that are somewhat mimicked [9] E. Kamyab, H. Kuhnho ¨ ld, S. C. Novais et al., “Eeff cts of thermal stress on the immune and oxidative stress responses of juvenile in our experiments. sea cucumber Holothuria scabra,” Journal of Comparative Phys- As stated previously, sea cucumbers will play a role in iology B,vol.187,no. 1, pp.51–61, 2017. combatting climate change in benthic marine communities. Therefore, the variety of responses to warming waters by each [10] D. Yunwei, J. Tingting, and D. 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