Predator prey interactions between predatory gastropod Reishia clavigera, barnacle Amphibalanus amphitrite amphitrite and mussel Brachidontes variabilis under ocean acidification

Marine Pollution Bulletin 152 (2020) 110895

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Predator prey interactions between predatory gastropod Reishia clavigera, barnacle Amphibalanus amphitrite amphitrite and mussel Brachidontes variabilis under ocean acidification F. Lia, F.-H. Mua, X.-S. Liua, X.-Y. Xub, S.G. Cheungb,c,

T

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a

College of Marine Life, Ocean University of China, Qingdao, China Department of Chemistry, City University of Hong Kong, Hong Kong c State Key Laboratory of Marine Pollution, City University of Hong Kong, Hong Kong b

A R T I C LE I N FO

A B S T R A C T

Keywords: Ocean acidification Predator prey interactions Gastropod Mussel Barnacle

Since the response to ocean acidification is species specific, differences in responses between predator and prey will alter their interactions, hence affect the population dynamics of both species. Changes in predator prey interactions between a predatory muricid gastropod Reishia clavigera and its prey, the barnacle Amphibalanus amphitrite amphitrite and mussel Brachidontes variabilis under three pCO2 levels (380, 950, and 1250 μatm) were investigated. The searching time for barnacles increased and the ability to locate them decreased at higher pCO2 levels. The movement speed and the prey consumption rate, however, were independent of pCO2. There was no preference towards either B. variabilis or A. amphitrite amphitrite regardless of pCO2. Exposure experiments involving multiple generations are suggested to assess transgenerational effects of ocean acidification and the potential compensation responses before any realistic predictions on the long term changes of population dynamics of the interacting species can be made.

1. Introduction An increase in the atmospheric carbon dioxide concentration drives changes in seawater carbonate chemistry and reduces pH (Gattuso and Buddemeier, 2000), resulting in the current pH of surface oceans being 0.1 unit lower, or 30% more acidic, than pre-industrial time (Caldeira and Wickett, 2003). Several reports have projected that pCO2 levels could exceed 900 μatm by the end of this century (Meinshausen et al., 2011) with a further decline in the ocean pH of 0.3–0.4 units (Caldeira and Wickett, 2003). It is well-known that ocean acidification affects the process of calcification in a number of shelled organisms (Martin and Gattuso, 2009; Melzner et al., 2011; Sanford et al., 2014), but there is growing evidence that elevated CO2 levels can have wide ranging effects on survival, growth, behaviour and metabolism (Kroeker et al., 2010; Li et al., 2018; Watson et al., 2017; Widdicombe and Spicer, 2009). Since responses to ocean acidification are species specific, differential responses among species will modulate biological interactions such as predation and competition (Cripps et al., 2011; Ferrari et al., 2011; Gaylord et al., 2015), and eventually lead to long term changes in population and community structures. However, it is impossible to predict the final

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outcome solely based on individuals' responses to ocean acidification as biological interactions and community responses change in an unpredictable way (Lord et al., 2017, 2019; Northfield and Ives, 2013). Predation is pivotal in maintaining ecosystem health and structuring marine communities (Bailey et al., 2010; Hixon, 1991; Paine, 1966). In the marine environment, a large number of animal species rely on chemical, auditory, and/or visual cues for prey/predator detection. Numerous studies have demonstrated that the perception of these cues is altered by elevated CO2 (see review of Ashur et al., 2017). For example, at reduced pH visual risk assessment in marine fishes is reduced (Ferrari et al., 2012) and anti-predator responses in fish and gastropods are impaired (Dixson et al., 2010; Watson et al., 2014). Hermit crabs, crabs and gastropods reduce their ability in locating food source (de la Haye et al., 2011, 2012; Dodd et al., 2015; Xu et al., 2017). Sensory impairment under ocean acidification is thought to be related to acidbase regulation. Under elevated pCO2, the acid-base regulation results in an increase of HCO3– and pCO2 but a decrease in Cl−, in contrast to an influx of both HCO3– and Cl− under normal conditions (Heuer and Grosell, 2014). This ionic shift changes the ion gradients which eventually lead to an excitation of GABAA receptors. These receptors are inhibitory neurotransmitter receptors playing a role in chemosensation.

Corresponding author at: Department of Chemistry, City University of Hong Kong, Hong Kong. E-mail address: [email protected] (S.G. Cheung).

https://doi.org/10.1016/j.marpolbul.2020.110895 Received 19 July 2019; Received in revised form 5 January 2020; Accepted 8 January 2020 Available online 17 January 2020 0025-326X/ © 2020 Elsevier Ltd. All rights reserved.

Marine Pollution Bulletin 152 (2020) 110895

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A change from inhibition to excitation of these receptors results in sensory impairment (Nilsson et al., 2012). Muricid gastropods can recognize the presence of prey at a distance through chemical cues released from the prey (Carriker, 1981). They attack mussels and barnacles through either drilling the shell with the aid of strong acid (Crothers, 1985) or prying open them directly (Tong, 1986). Reishia clavigera is a muricid gastropod commonly found on rocky shores in Hong Kong with the barnacle Amphibalanus amphitrite amphitrite and mussel Brachidontes variabilis being its preferred prey (Lee, 1999; Tong, 1986). Both barnacles and mussels are dominant species on intertidal habitats in tropical regions including Hong Kong. They play important roles as bioengineers and provide microhabitats for various species (Gutiérrez et al., 2003; Cole and McQuaid, 2010; Pappalardo et al., 2017). The predator-prey interaction between R. clavigera and the mussel B. variabilis under elevated pCO2 levels has shown that the prey searching time increased with pCO2 but the prey consumption rate remained unchanged. The prey size preference of R. clavigera also changed with pCO2 with larger mussels being preferred at the intermediate level of pCO2 (950 μatm) (Xu et al., 2017). Since both A. amphitrite amphitrite and B. variabilis are the most preferred prey of R. clavigera, changes in their predator-prey interactions under ocean acidification would affect the long term populations of these species. The present study investigated predation of R. clavigera on A. amphitrite amphitrite as well as the preference of R. clavigera between the two prey species under elevated pCO2. We hypothesized that ocean acidification increased prey searching time and reduced prey locating ability in R. clavigera but prey consumption rate remained unchanged. Since responses to ocean acidification is species specific, differential responses of barnacles and mussels to ocean acidification would alter their relative attractiveness to R. clavigera, hence affect the long term populations of both prey species.

Table 1 Environmental parameters of the treatments with different pCO2 levels.

Temperature (°C) Salinity (psu) pCO2 (μatm) pH At (mg l−1) ΩCa ΩAr

380 μatm

950 μatm

1250 μatm

29 ± 0.2 29 ± 0.4 393 ± 14 8.11 ± 0.05 227 ± 11 5.9 3.9

29 ± 0.2 29 ± 0.3 965 ± 54 7.80 ± 0.07 233 ± 8 3.19 2.11

29 ± 0.1 29 ± 0.4 1257 ± 67 7.37 ± 0.04 220 ± 4 2.11 1.10

gas was dried by pumping it into a conical flask containing silica gel before it was fed to individual experimental chambers. The CO2 concentration of the mixed gas was checked by a CO2 analyzer (LT-260, LiCor Company, Switzerland). Each experimental chamber was sealed with a plastic lid with a small hole to allow the access of an air tube which bubbled a continuous stream of either air (380 μatm CO2) or CO2-enriched air (950 or 1250 μatm) into the water. Temperature, salinity, pCO2, and pH were recorded before and after the experiment on each snail. Salinity was measured using a hand held refractometer and pH using electronic pH probe (HANNA, HI84431, Germany). Software CO2SYS (Lewis and Wallace, 1998) was used to calculate the saturation of calcite (ΩCa) and aragonite (ΩAr), and total alkalinity (At). The environmental parameters measured during the experiments are shown in Table 1. 2.3. Effect of OA on prey searching time Prey searching time and prey type selection were investigated using a Y-maze design as described in Xu et al. (2017). Water at a desired pCO2 level was pumped from a reservoir tank into the two arms of a Ymaze. The water leaving the maze passed through a filter containing filter sponge and activated charcoal before returning to the reservoir tank (Xu et al., 2017). There were four sets of experiment for every pCO2 level. In Set 1 and Set 2, the same amount of live A. amphitrite amphitrite (30 individuals each, diameter: 1.2–1.3 cm) was placed near to the entrance of one arm, while the other arm was left empty. In Set 1 A. amphitrite amphitrite were placed in the left arm but in the right arm in Set 2. Set 3 and Set 4 were similar to Set 1 and Set 2, except that instead of leaving the arm empty, empty shells of A. amphitrite amphitrite were used. R. clavigera was placed at the end of the long arm of the Y-maze. All the experiments were repeated 10 times as replicates and all the individuals of R. clavigera were used only once. The time required for R. clavigera to reach A. amphitrite amphitrite or empty shells was measured. Since the movement was intermittent, time spent in locomotion and that spent remaining stationary were recorded. Movement speed was calculated as the total distance moved per unit time spent in locomotion. R. clavigera and A. amphitrite amphitrite were acclimated to experimental pCO2 levels for 1 month prior to experimentation.

2. Materials and methods 2.1. Study organisms R. clavigera (shell length: 30–35 mm) and its prey, barnacle A. amphitrite amphitrite and mussel B. variabilis were collected from a rocky shore near the Wu Kai Sha Pier, Hong Kong (22.25°N, 114.14°E). Immediately after collection, they were placed in separate aquaria in the laboratory where they were allowed to acclimate to laboratory conditions in seawater at 29 °C and 30 psu under three experimental pCO2 levels (380, 950 or 1250 μatm) of which the corresponding pH values represent the natural fluctuations at the present day as well as projected ranges predicted to occur for the year 2100 at the collection site. The pH value of 7.8 (950 μatm CO2) represents the minimum value experienced in the present day in the summer (HKEPD, 2018) as well as the mean pH value expected to occur by 2100 at the collection site whereas the pH value of 7.4 (1250 μatm CO2) is the extreme low-pH value expected by 2100 (IPCC, 2014; Campanati et al., 2018). During acclimation, A. amphitrite amphitrite and B. variabilis were fed twice a week with the green alga Dunaliella tertiolecta, whereas R. clavigera were fed with A. amphitrite amphitrite and B. variabilis in alternate days. Seawater was changed once a week to avoid the accumulation of metabolic wastes.

2.4. Effect of OA on prey species preference Prey type selection was investigated using the Y-maze design as mentioned above. Before the experiment, R. clavigera were fed on alternate days with A. amphitrite amphitrite and B. variabilis for one week to avoid feeding bias. There were two sets of experiment for every pCO2 level. In Set 1, 30 individuals of A. amphitrite amphitrite (diameter: 1.2–1.3 cm) were placed in the left arm of the maze and the same number of B. variabilis (shell length: 1.2–1.3 cm) were placed in the right arm and vice versa in Set 2. R. clavigera was placed at the end of the long arm of the Y-maze. The two experiments were repeated 10 times and each time a new individual of R. clavigera was used. The prey type chosen by individual R. clavigera was recorded. Since B. variabilis were sparsely populated and occurred at lower abundance, they were

2.2. Experimental set up Groups of 10 individuals of R. clavigera were used as replicates and maintained separately in small glass chambers which were filled with CO2 at one of the following concentrations: 380, 950 or 1250 μatm. pCO2 of 380 μatm was obtained by bubbling air into the containers which served as the control. For CO2 enriched treatments, air was mixed with pure CO2 in a conical flask and the flow rate of CO2 was controlled by a digital flow meter (GCR-B9SA-BA15, Vogtlin, Sweden) and that of air was controlled by a mechanical flow meter. The mixed 2

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collected in several occasions and therefore exposed to experimental pCO2 levels for 1 week only before experimentation. To reduce bias, barnacles used in this experiment were also exposed to 1 week only, in contrast to those in the experiment on prey searching time in which they were exposed to experimental pCO2 for 1 month.

b

Prey searching time (min)

20

2.5. Effect of OA on prey consumption rate For each pCO2 level, 10 individuals of R. clavigera were placed in separate experimental tanks and starved for three days before A. amphitrite amphitrite were offered. R. clavigera was allowed to feed for 72 h and the number of A. amphitrite amphitrite consumed was recorded. Each individual R. clavigera was offered 30 individuals of A. amphitrite amphitrite (diameter: 1.2–1.3 cm) which were replaced by new ones every 24 h. For each pCO2 level, an additional small glass bottle containing A. amphitrite amphitrite only was used to estimate the non-predation mortality (Xu et al., 2017) which was found to be 10%. The experiment lasted for 3 days. Both R. clavigera and A. amphitrite amphitrite were acclimated to experimental pCO2 levels for 1 month prior to experimentation.

b

390 µatm 950 µatm 1250 µatm

15

a

a

10

a

a

Set 1 + Set 2

Set 3 + Set 4

5

0

Fig. 1. Prey searching time (n = 20, mean + SD) in the Y-maze experiment under different pCO2 levels. (In Set 1 and Set 2, one arm of the maze contained live A. amphitrite amphitrite while the other arm was left empty. In Set 3 and Set 4, one arm contained live A. amphitrite amphitrite while empty shells of A. amphitrite amphitrite in the other. Shared letters denote a lack of significant difference between bars.

2.6. Statistical analysis Normality and homogeneity of the data were checked by the KeW test and Levene's test, respectively. Data were subjected to transformation if the above tests failed. The effect of OA on the prey searching time was analyzed by one-way ANOVA followed by pairwise multiple comparison procedure. The effect of OA on the prey consumption rate was analyzed by two-way ANOVA followed by pairwise multiple comparison procedure. Chi-square test was used to compare the prey type preference at three pCO2 levels.

Movement speed (i.e., distance travelled divided by the time used), however, was not significantly affected by pCO2 for both groups of setup (Set 1 + Set 2: KeW test, n = 20, H = 4.21, df = 2, p = 0.122; Set 3 + Set 4: KeW test, n = 20, H = 3.52, df = 2, p = 0.172) although the higher the pCO2, the lower the movement speed (Fig. 2). At 1250 μatm CO2, 30% of R. clavigera from Set 3 + Set 4 moved to the arm containing empty shells of A. amphitrite amphitrite before moving to the one with live prey.

3. Results 3.2. Effect of OA on prey species preference and prey consumption rate 3.1. Effect of OA on prey searching time For the prey species preference experiment, the results between Set 1 and Set 2 were statistically indistinguishable so the results were pooled, i.e., Set 1 + Set 2. The higher the pCO2, the higher was the percentage of barnacles consumed, although the differences were statistically indistinguishable (Table 3). In the 3-day barnacle consumption experiment, the number of A. amphitrite amphitrite consumed by R. clavigera varied significantly with time (df = 2, F = 3.96, p < 0.05), but did not vary with pCO2 (df = 2, F = 1.35, p = 0.266) and the pCO2-time interaction (df = 4, F = 0.98, p = 0.422) (Fig. 3).

All the individuals of R. clavigera were successful in locating A. amphitrite amphitrite. As the results on prey searching time and movement speed between Set 1 and Set 2 as well as between Set 3 and Set 4 were statistically indistinguishable (p > 0.05), the results of Set 1 and Set 2 were pooled (i.e., Set 1+ Set 2) and the same was done for Set 3 and Set 4, i.e., Set 3 + Set 4. An increase in pCO2 reduced the responsiveness of R. clavigera. The mean number of individuals started moving immediately after being placed in the Y-maze decreased significantly with pCO2 (n = 4, df = 2, F = 37.5, p < 0.001) with the mean number at the three pCO2 levels being significantly different from each other as tested by one-way ANOVA followed by Holm-Sidak multiple comparison procedure (Table 2). The time remaining stationary before initiation of prey searching also increased from a mean duration of 3 mins at 380 μatm to 15 mins at 1250 μatm (Table 2). CO2 enriched water increased prey searching time, with that at 1250 μatm being significantly longer than that at 380 μatm and 950 μatm, irrespective of the presence or absence of empty shell in one of the arms (Fig. 1) (Set 1 + Set 2: KeW test, H = 11.95, df = 2, p < 0.005; Set 3 + Set 4: KeW test, H = 12.06, df = 2, p < 0.005).

4. Discussion Our findings show that the effect of elevated pCO2 on the prey searching time in R. clavigera followed a dose–response relationship, resulting in the higher the pCO2 level, the longer was the searching time. The effect is probably due to the weakening of either the chemosensory function of R. clavigera in response to prey cues or the ability of the prey species to produce cues or both. This is supported by three independent responses. Firstly, in the presence of prey cues from the barnacle A. amphitrite amphitrite, R. clavigera respond by moving

Table 2 Effect of elevated pCO2 on percentage of individuals of R. clavigera moved immediately after being placed in the Y-maze and the mean time remaining stationary before initiation of prey searching. 380 μatm Set 1 % individuals moved immediately Mean time remaining stationary before initiation of prey searching (mins ± SD)

Set 2

90 90 3 ± 0.2

3

950 μatm Set 3

Set 4

Set 1

Set 2

90

90

70 70 8 ± 0.4

1250 μatm Set 3

Set 4

Set 1

Set 2

70

60

50 40 15 ± 1.0

Set 3

Set 4

30

30

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Brachindontes variabilis was offered at 950 μatm pCO2 (Xu et al., 2017). A disruption of the ability in locating prey was also reported on the hermit crab Pagurus bernhardus at pH 6.8 with an overall decline in locomotory activity (de la Haye et al., 2012). A disturbance in chemosensory function but not locomotory activity was observed in a jumping conch snail Gibberulus (previously Strombus) gibberulus gibbosus at 961 μatm pCO2, resulting in an impairment of escape behaviour (Watson et al., 2014). A number of fish species failed to process information from waterborne cues when confronted with the scent of predators (Dixson et al., 2010). Such an impaired chemosensory function under OA appeared to originate from altered neurotransmitter and ion channel functions (Nilsson et al., 2012; Hamilton et al., 2013) which could be restored completely by treatment with gabazine, a GABA antagonist (Heaulme et al., 1986), and GABAA - like antagonist in some invertebrate nervous systems (Pierobon et al., 2004; Tsang et al., 2007). This indicates potential interference of neurotransmitter receptor functions by elevated pCO2, as previously observed in marine fishes and gastropods (Nilsson et al., 2012; Watson et al., 2014). Under normal conditions, opening of the GABA-A receptors of fish associated with an inflow of Cl− leads to hyperpolarization and inhibition of the neurons. Under high CO2 circumstances, marine organisms rely on the uptake of HCO3−, associated with an efflux of Cl−, to compensate for hypercapnic acidosis, which renders some GABA-A receptors excitatory, thereby impairs sensory functions (Nilsson et al., 2012). The total number of A. amphitrite amphitrite consumed by R. clavigera was independent of the pCO2 level in the present study. McDonald et al. (2009) demonstrated that adult Amphibalanus amphitrite raised at pH 7.4 had the central shell wall plates weakened rapidly due to dissolution that would increase the vulnerability of the organisms to predation. R. clavigera, however, did not enjoy an increase in prey consumption rate in the present study, probably because there was no weakening of central wall plates of the barnacles as demonstrated by McDonald et al. (2009) although the same barnacle species was used in both studies. Another possible reason was the magnitude of the effect of increased CO2 levels on both the predator and prey was similar. Both hypotheses, however, could not explain the independence of consumption rate from pH satisfactorily because the same phenomenon was also observed in our study on the same predator (R. clavigera) feeding on the mussel Brachidontes variabilis (Xu et al., 2017). The predation rate of the Atlantic oyster drill Urosalpinx cinereal on Olympia oysters (Ostrea lurida) was found independent of pCO2. Sanford et al. (2014) attributed this to the chitinous radula teeth, the drilling apparatus, which may not be influenced by decreased pH (Amaral et al., 2012). This reason, however, could not explain what we observed for R. clavigera which inserted the proboscis directly between the operculum plates of barnacles without using radula. If the increase in prey searching time was due to the weakened ability of the prey species A. amphitrite amphitrite in producing chemical cues, then the prey consumption rate should be independent of the pCO2 level. Another explanation could be a lower pH which affected chemosensory functions in particular but not the neural control in general, hence other physiological processes such as digestion and locomotion were not affected by pH. Since intertidal animals are relatively tolerant to fluctuating environmental conditions such as temperature, pH and salinity (Tomanek and Helmuth, 2002), a limited extent of the effect of pH on the physiology of R. clavigera may be a result of partial or complete physiological compensation as an adaptation for surviving in a highly stressful environment. No drill hole was observed on both barnacles and mussels in the present study. Muricid gastropods attack shelled prey by either drilling a hole on the shell or prying open it and inserting the proboscis between the operculum plates of barnacles or valve gaps of bivalves (Clelland and Webster, 2017). Since drilling is costly in terms of both time and energy, gastropods forego drilling whenever possible (Wood, 1968; Barnett, 1979; Rovero et al., 1999). As attacking barnacles and mussels

8

Movement speed (cm/min)

390 µatm 950 µatm 1250 µatm 6

4

2

0

Set 1 + Set 2

Set 3 + Set 4

−1

Fig. 2. Movement speed (cm min ) of R. clavigera (n = 20, mean + SD) in the Y-maze experiment under different pCO2 levels. (In Set 1 and Set 2, one arm of the maze contained live A. amphitrite amphitrite while the other arm was left empty. In Set 3 and Set 4, one arm contained live A. amphitrite amphitrite while empty shells of A. amphitrite amphitrite in the other.

Table 3 Number of individuals of each prey type selected by R. clavigera in the Y-maze experiment (n = 20 for each pCO2 level). Prey items

380 μatm

950 μatm

1250 μatm

Barnacle Mussel Chi-square value p Value

11 9 0.2 > 0.05

12 8 0.8 > 0.05

14 6 3.2 > 0.05

20 390 µatm 950 µatm 1250 µatm

Number of barnacles consumed

18 16 14 12 10 8 6 4 2 0 Day 1

Day 2

Day 3

Fig. 3. Total number of A. amphitrite amphitrite consumed on three consecutive days at three pCO2 levels (n = 10, mean + SD).

immediately towards the prey once the snail was put in the experimental maze. At higher pCO2 levels, however, the response to the prey cues was delayed. The higher the pCO2 level, the longer was the delay. Secondly, the longer prey searching time was not due to disturbance to physiological functions such as muscular movement because the speed of locomotion did not change with pCO2 level, rather R. clavigera stopped moving more frequently during prey searching to locate the origin of prey cues. Thirdly, the power in distinguishing cues between empty shells and live individuals of A. amphitrite amphitrite was weakened at 1250 μatm pCO2, resulting in moving into the arm of the experimental set-up with empty shells. A similar increase in the prey searching time of R. clavigera was observed when the mussel 4

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by inserting the proboscis through the shell gap is possible in R. clavigera, the more energy demanding drilling was abandoned. Both A. amphitrite amphitrite and B. variabilis were the most preferred prey of R. clavigera on intertidal shores in Hong Kong (Tong, 1986). No prey preference was observed at the normal pCO2 level but there was a tendency to consume more barnacles when pCO2 level increased, although the difference was statistically insignificant. Since there was no preference towards either barnacles or mussels under normal pCO2, an apparent shift in the preference towards barnacles at higher pCO2 is more likely due to differential responses of the two prey species to ocean acidification with barnacles becoming more vulnerable to predatory attack. A longer exposure experiment comparing the vulnerability to predation between barnacles and mussels is required to test this hypothesis as both prey species in this experiment only exposed to elevated pCO2 for 1 week. In fact, under long term (40–60 days) exposure to pH 7.4, dissolution rapidly weakened the wall shells of the barnacle Amphibalanus amphitrite, resulting in significantly less force to penetrate than those of individuals raised at pH 8.2 (McDonald et al., 2009). The blue mussel Mytilus edulis grown under ocean acidification produced more amorphous calcium carbonate, resulting in harder and less elastic shells, making them being more prone to fracture, hence more vulnerable against predation (Fitzer et al., 2016). The natural fluctuation of pH at the collection site was between 8.1 and 7.8 (HKEPD, 2018). This is the range within which R. clavigera is most likely to exhibit adaptations hence no noticeable change in prey searching efficiency was observed. However, when pH was reduced to 7.4, the extreme low-pH value expected by 2100 at the collection site (IPCC, 2014; Campanati et al., 2018), the prey searching time was prolonged. A longer prey searching time implies a lower feeding efficiency hence a reduction in energy intake, as well as a higher risk of being exposed to predation. The situation can be even worse as some gastropods, e.g., Nucella, decrease their behavioural avoidance to predator due to disturbance to chemosensory function under ocean acidification (Manriquez et al., 2014; Watson et al., 2014). As both the predator and prey in the present study were exposed to reduced pH for one month only, prolonged experiments involving multiple generations are suggested to assess transgenerational effects of ocean acidification and the potential compensation responses (Pedersen et al., 2014; Borges et al., 2018) before any realistic predictions on the long term changes of population dynamics of the interacting species can be made.

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CRediT authorship contribution statement F. Li:Investigation.F.-H. Mu:Conceptualization, Funding acquisition.X.-S. Liu:Conceptualization, Funding acquisition.X.-Y. Xu:Investigation.S.G. Cheung:Conceptualization, Funding acquisition, Supervision, Writing - original draft, Writing - review & editing. Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgments Our work was fully supported by a Shenzhen Key Laboratory for the Sustainable Use of Marine Biodiversity (SUMP) Internal Grant. References Amaral, V., Cabral, H.N., Bishop, M.J., 2012. Effects of estuarine acidification on predator–prey interactions. Mar. Ecol. Prog. Ser. 445, 117–127. Ashur, M.M., Johnston, N.K., Dixson, D.L., 2017. Impacts of ocean acidification on sensory function in marine organisms. Integr. Comp. Biol. 57, 63–80.

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