This article was downloaded by: [Yrkeshögskolan Novia]On: 28 July 2014, At: 01:39Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registeredoffice: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK

Marine and Freshwater Behaviour andPhysiologyPublication details, including instructions for authors andsubscription information:http://www.tandfonline.com/loi/gmfw20

The effects of short-term pH decreaseon the reproductive output of thecopepod Acartia bifilosa – a laboratorystudyJonna Engström-Östab, Towe Holmbornc, Andreas Brutemarkab,Hedvig Hogforsc, Anu Vehmaab & Elena Gorokhovad

a ARONIA Coastal Zone Research Team, Novia University of AppliedSciences & Åbo Akademi University, Ekenäs, Finlandb Tvärminne Zoological Station, University of Helsinki, Hangö,Finlandc Calluna AB, Stockholm, Swedend Department of Applied Environmental Science, StockholmUniversity, Stockholm, SwedenPublished online: 27 May 2014.

To cite this article: Jonna Engström-Öst, Towe Holmborn, Andreas Brutemark, Hedvig Hogfors,Anu Vehmaa & Elena Gorokhova (2014) The effects of short-term pH decrease on the reproductiveoutput of the copepod Acartia bifilosa – a laboratory study, Marine and Freshwater Behaviour andPhysiology, 47:3, 173-183, DOI: 10.1080/10236244.2014.919096

To link to this article: http://dx.doi.org/10.1080/10236244.2014.919096

PLEASE SCROLL DOWN FOR ARTICLE

Taylor & Francis makes every effort to ensure the accuracy of all the information (the“Content”) contained in the publications on our platform. However, Taylor & Francis,our agents, and our licensors make no representations or warranties whatsoever as tothe accuracy, completeness, or suitability for any purpose of the Content. Any opinionsand views expressed in this publication are the opinions and views of the authors,and are not the views of or endorsed by Taylor & Francis. The accuracy of the Contentshould not be relied upon and should be independently verified with primary sourcesof information. Taylor and Francis shall not be liable for any losses, actions, claims,proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or

howsoever caused arising directly or indirectly in connection with, in relation to or arisingout of the use of the Content.

This article may be used for research, teaching, and private study purposes. Anysubstantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions

Dow

nloa

ded

by [

Yrk

eshö

gsko

lan

Nov

ia]

at 0

1:39

28

July

201

4

The effects of short-term pH decrease on the reproductive output ofthe copepod Acartia bifilosa – a laboratory study

Jonna Engström-Östa,b*, Towe Holmbornc, Andreas Brutemarka,b, Hedvig Hogforsc,Anu Vehmaab and Elena Gorokhovad

aARONIA Coastal Zone Research Team, Novia University of Applied Sciences & Åbo AkademiUniversity, Ekenäs, Finland; bTvärminne Zoological Station, University of Helsinki, Hangö,Finland; cCalluna AB, Stockholm, Sweden; dDepartment of Applied Environmental Science,Stockholm University, Stockholm, Sweden

(Received 25 November 2013; accepted 27 April 2014)

This laboratory study reports some reproductive responses of the copepodAcartia bifilosa to rapid variations in pH. The imposed changes mimic thosethat copepods could experience due to coastal upwelling, changed mixingconditions or vertical migration. We measured effects of low pH on eggproduction, hatching and early nauplii development (H0: no effects on responsevariables between low and ambient pH). On treatment with low pH, we foundpositive effects on egg production rate and nauplii development time. Thepositive response to low pH could be an initial stress response or show thatA. bifilosa is tolerant to the experimental pH values. The result suggests thatA. bifilosa is adapted to pH changes as it performs daily migrations between thedepths with differing pH. It could also be advantageous for populationdevelopment if eggs hatch at high speed and so reduce the possibility that theywill sink into anoxic and low pH waters.

Keywords: copepod; Acartia bifilosa; ambient pH; reproduction; eggproduction; egg hatching; nauplii development

Introduction

Upwelling events changed mixing conditions or vertical migration can exposezooplankton to rapidly changing low pH of the sea water (Feely et al. 2008; Barry,Widdicombe, & Hall-Spencer 2011). During summer, the most important growth seasonin northern latitudes, there can be pronounced pH differences between surface and bot-tom water, especially where there is eutrophication. This is notable where the bloomsrise and change the surface pH as they photosynthesise (Hansen 2002). Animals, suchas copepods that migrate between the depths can encounter large pH differences duringtheir lifetime due to e.g. upwelling events (Feely et al. 2010). Estuaries and coastalareas will be important in the future as natural laboratories for the study of ecosystemchange due to increased upwelling (Feely et al. 2010; Wootton & Pfister 2012). Arecent, rapid pH decline has been detected over an eight-year period off WashingtonState. The phenomenon was caused by enhanced upwelling of waters resulting fromchanges in regional ocean circulation (Wootton, Pfister, & Forester 2008). Using a large

*Corresponding author. Email: jonna.engstrom-ost@novia.fi

© 2014 Taylor & Francis

Marine and Freshwater Behaviour and Physiology, 2014Vol. 47, No. 3, 173–183, http://dx.doi.org/10.1080/10236244.2014.919096

Dow

nloa

ded

by [

Yrk

eshö

gsko

lan

Nov

ia]

at 0

1:39

28

July

201

4

data-set, the authors showed considerable variation in coastal pH. Apart from the over-all declining trend, the coastal pH could vary ~0.25 pH units in a 24-h period and 1.5units seasonally over a 10-years period.

Both short- and long-term impacts of low pH on marine organisms warrant morestudy. It is unclear, for example, whether the net calcification rate of crustacean chitin-ous exoskeletons will be adversely affected by low pH (Whiteley 2011). Crustaceangrowth and reproductive success can also be affected directly by low pH (Kurihara2008; Whiteley 2011). In copepods, as in most marine invertebrates, their early devel-opmental and reproductive stages are thought to be particularly vulnerable to low pH(Kurihara 2008). Studies on copepods have measured decreased egg production,egg-hatching success and nauplius survival with decreasing pH in Acartia erythraea,A. steueri and Calanus finmarchicus (Mayor et al. 2007; Kurihara 2008).

Although copepods play a major role in coastal ecosystems, feeding on microalgaeand ciliates, and serving as prey for fish and mysids (Beaugrand & Kirby 2010), infor-mation about the effects of pH on their biology is scarce. Copepods perform diel verti-cal migration (DVM) and therefore experience a range of different pH. In the summer,pH commonly varies >1 pH unit between surface and deeper waters (Fabry et al. 2008;Olafsson et al. 2009) due to benthic respiration, limited photosynthesis and low CO2

exchange with the atmosphere (Sunda & Cai 2012). In the Baltic Sea, Acartia spp. arethe dominant copepods inhabiting the coastal zone (Ackefors 1981). As Acartia bifilosaperforms DVM below the thermocline (Holliland et al. 2012), it is a suitable species forstudying biological responses to pH fluctuations.

The aim of this study was to measure the instantaneous response in reproductiveoutput in the laboratory. We measured egg production rate, egg-hatching success andthe development of early nauplii stages NI-NII of A. bifilosa during abrupt changes inpH to mimic those that are commonly encountered during coastal upwelling, changedmixing conditions or DVM. Based on earlier studies (Kurihara, Shimode, & Shirayama2004; Mayor et al. 2007), we hypothesised that lowered pH would negatively affectegg production, hatching and development.

Materials and methods

Sampling

Copepod incubation was carried out in the laboratory in early August 2010 atTvärminne Zoological Station (University of Helsinki, Finland) in the western Gulf ofFinland. Sampling was performed at the Storfjärden monitoring station, an open pelagicarea (59° 50′ N, 23° 15′ E). Copepods were collected by vertical net hauls from 25 mdepth, using a net (mesh-size 200 μm, ø 50 cm) equipped with a 1 l cod-end. Copepodswere rinsed and placed into large containers with ~15 l of water collected at 10 m depth,and brought to the lab, where they were transferred to a 17 °C climate chamber untilsorting commenced. Copepods were sorted under dissection microscopes (magnifica-tions <50×) using wide-mouth pipettes. Mature A. bifilosa (26 ± 6 females and 3 ± 1males, mean ± SD) were transferred into each of the 24 beakers filled with 200 mlexperimental medium (see below) with ambient pH. The numbers of females and malesare based on microscopy counting following the experiment. The number of livefemales was used for EPR calculation estimates. Mortality during the incubation was2.8 ± 0.3 females in each treatment.

Water was sampled twice (31 July and 1 August) from 10 m depth at Storfjärden andbrought to the laboratory in large containers for acclimation and experimental medium

174 J. Engström-Öst et al.

Dow

nloa

ded

by [

Yrk

eshö

gsko

lan

Nov

ia]

at 0

1:39

28

July

201

4

preparation. The water from the first collection was used for acclimation and that fromthe second for egg production and hatching/development incubations. The salinity was5.4 psu and mean temperature 18.75 °C (N = 2) during sampling. At the sampling site,pH ranged from 7.5 (bottom) to 8.5 (surface) and the average pH for the collectednon-processed water used for incubations was 8.3 (N = 2) (Figure 1, Table 1).

Experimental set-up

As filtration can shift the carbonate chemistry of the sea water, CO2 bubbling shouldtake place after filtration (Riebesell et al. 2010). At first, the water was filtered througha plankton net (<10 μm) and subsequently with a Sartobran 300 filter capsule(<0.2 μm). The pH of the filtered sea water (ambient treatment) was measured with aTUNZE pH-controller (7070/2), which was calibrated daily. The pH of the low pHtreatment was adjusted by bubbling the experimental media with industrial CO2 gasusing a TUNZE pH/CO2-controller-set (7074/2) until the pH of the water was ~0.4pH-units lower than that of the ambient water. The pH adjustments (low pH) were donetwice, before the egg production experiment and before the egg hatching/nauplii devel-opment incubation (Table 1). The low pH level used corresponds approximately to theexpected pH change prediction for upwelling water (Feely et al. 2008) and higher thanwhat copepods experience in the deep water (Fabry et al. 2008). The pH (TUNZE pH-controller 7070/2) was measured in triplicate from random samples of each treatmentbefore and after the acclimation. For the other incubations, pH was measured in tripli-cate from large containers with experimental medium prior to the incubations, and fromeach bottle immediately after it was opened, following the egg production and eggdevelopment incubation periods. Dissolved inorganic carbon (DIC) was measuredaccording to Salonen (1981). The DIC values correspond well to pH values (Table 1)and are therefore not revisited in further discussions (cf. Dickson, Sabine, & Christian2007). Oxygen levels (Pro ODO YSI Inc.) were measured in the initial collected waterand were monitored in few replicates (maximum 3) before and after egg developmentincubation synchronously with pH and DIC.

Figure 1. Vertical gradient of water pH between the surface and bottom at 5 m intervals at thesampling station Storfjärden before and after the study, 13 July and 11 August 2010, respectively.Data are based on monitoring measurements performed regularly at the Tvärminne ZoologicalStation.

Marine and Freshwater Behaviour and Physiology 175

Dow

nloa

ded

by [

Yrk

eshö

gsko

lan

Nov

ia]

at 0

1:39

28

July

201

4

Brachiomonas submarina (TV15, Tvärminne Zoological Station) was grown as anaerated batch culture at a final volume of 2 l in 3 l Erlenmeyer bottles. The culture wasgrown at 18 °C under 16 : 8 h light : dark cycle and 13.7 μmol photons m−2 s−1 in f/2medium without silica (Guillard 1975). To create a food suspension for the copepods,B. submarina cells were harvested by centrifuging 50 ml tubes, containing B. submarinaculture, at 1200 g for 25 min at 4 °C. The supernatant was discarded and 100 μlsub-aliquots of the concentrated algae were pipetted into Eppendorf tubes and stored nolonger than one month in −80 °C.

We acclimated animals to food and temperature by adding 20 μl of the concentratedB. submarina (final concentration: 561 ± 12 μg C l−1) to each 200 ml beaker containingcopepods and filtered sea water with ambient pH. The beakers were then incubated for24–26 h at 17 °C under 16 : 8 h light : dark regime.

Egg production incubation was initiated by gently sieving females and males afterthe acclimation using 200 μm mesh, and transferring the to 1.2 l bottles containingfiltered sea water with pre-determined pH (ambient or low pH, 12 replicates of each).Concentrated B. submarina (100 μl) was added to each bottle so that the final concen-tration was the same as during acclimation. Bottles were mounted on a rotating plank-ton wheel (1 rpm) and incubated for 38–42 h at the same temperature and light as thatused during acclimation.

Egg development incubation was initiated at the end of the egg production incuba-tion by picking eggs from each replicate under a dissection microscope (<50×) using awide mouth pipette, and transferring them to a 20 ml scintillation vial filled with filteredsea water with the respective pH treatment. No food was provided. The eggs (mean 38eggs vial−1) were incubated for 30 or 66 h on a rotating plankton wheel in the sametemperature and light as indicated above (6 replicates/treatment). The egg-hatchingsuccess and developmental index (DI) were estimated separately for each time period.The remaining part of the bottle contents was inspected, after removal of eggs for eggdevelopment incubation (live/dead females, general appearance), and preserved with

Table 1. Average pH at the beginning and end of different A. bifilosa incubations.

Ambient pH (DIC, mmol l−1) Low pH (DIC, mmol l−1)

EPR* start 7.87 7.60(1.76–1.79) (1.82–1.84)

EPR end 7.47 7.15(1.75–1.78) (1.79–1.81)

HS and DI, 30 h* end 7.58 7.17(1.78–1.81) (1.84–1.86)

HS and DI, 66 h* end 7.61 7.21(1.93) (1.94–1.96)

Notes: EPR (egg production rates). HS30/HS60: a 30 or 66 h incubation for assessment ofegg-hatching success (HS). DI: development index. DIC (dissolved inorganic carbon) valuesare reported as ranges with minimum and maximum within respective treatments (ambient andlow pH).*Indicates significant (p < 0.05) pH differences between ambient and low pH. Salinity was 5.4and mean temperature 18.75 °C during the study. The reason for the pH decrease in thetreatments is respiration by copepods and eggs (and bacteria). The difference in pH betweenambient and low never exceeded 0.41 units (cf. Feely et al. 2008).

176 J. Engström-Öst et al.

Dow

nloa

ded

by [

Yrk

eshö

gsko

lan

Nov

ia]

at 0

1:39

28

July

201

4

acid Lugol’s solution. The contents of the scintillation vials were also preserved withLugol’s solution after the egg development incubation, and all Lugol samples were ana-lysed to assess egg production rate, egg-hatching success and nauplii DI, using 50 mlsedimentation chambers and an inverted microscope (Leitz Labovert 125×).

No signs of egg cannibalism were observed during the experiment, because brokeneggs or egg parts were not found (Kang & Poulet 2001). Egg production rate (EPR,eggs female−1 d−1), egg-hatching success (HS, %) and DI were calculated based on themicroscopic analyses.

EPR and HS were calculated according to Runge and Roff (2000), and DI thatintegrates egg viability and early nauplial development were calculated according toKnuckey et al. (2005). In this index, each developmental stage is assigned a score (inour case; eggs (E) = 0, nauplius stage I (N1) = 1, nauplius stage II (N2) = 2). # denotesthe total number of eggs or nauplii. DI is then calculated as:

DI ¼ ð#E � 0þ#N1 � 1þ#N2 � 2Þð#E þ#N1 þ#N2Þ

Data analysis

An unpaired T-test was used to identify the effects of lowered pH on the egg productionrate and development index. All data were normally distributed as inferred fromWilk-Shapiro’s test and visual data inspection. Homogeneity of variance was assessedusing Bartlett’s test of Equal Variances and Levene’s test. For development index, trans-formation did not homogenise the variance and the T-test assuming non-equal variances(Welch extension) are reported. The pH differences between the treatments were evaluatedwith a Mann–Whitney U-test. The analyses were performed in SPSS 21.0. Egg-hatchingsuccess data were analysed between low and ambient pH, separately for 30 and 66 h bylogistic regression using S-Plus 6.1. All data are presented untransformed.

Results

Integrated pH during acclimation to food and temperature averaged 7.99 ± 0.02 (N = 6),with a minimum/maximum of 7.97 and 8.01, respectively. pH decreased during theexperiment in both the treatments. However, the 0.4 pH difference between the treat-ments remained similar throughout the experiment (Table 1).

Oxygen content in the current study ranged from 8.9 mg O2 l−1 (saturation 97%) in

the initial collected water to 8.8 mg O2 l−1 (saturation 97%) and 8.9 mg O2 l

−1 (satura-tion 97%) in the low and ambient pH treatments at the start of the egg developmentincubation. At the end of the same incubation, oxygen measured 8.3 mg O2 l

−1 (satura-tion 95%) and 8.3 mg O2 l

−1 (saturation 94%) in the low and ambient pH treatments,respectively, after the short (30 h) incubation, and 8.4 mg O2 l

−1 (saturation 94%; N = 2)and 7.7 mg O2 l

−1 (saturation 84%) in the low and ambient treatment, respectively, afterlong (66 h) incubation.

The egg production rate was generally low and averaged 1.9 and 1.0 eggs female−1 d−1

in the low and ambient treatments, respectively (Figure 2). There was, however, a signifi-cant positive effect of lowered pH on egg production rate (t-test, t22 = 3.572, p = 0.002;Figure 2). Hatching success was on average 71 ± 11% in low pH and 57 ± 22% in ambientpH, except the 30 h incubation in the ambient pH treatment (HS = 50%). Low pH did not

Marine and Freshwater Behaviour and Physiology 177

Dow

nloa

ded

by [

Yrk

eshö

gsko

lan

Nov

ia]

at 0

1:39

28

July

201

4

have a significant effect on the hatching success in either the 30 h incubation (Logisticregression, F10 = 4.4, p = 0.061) or the 66 h incubation (F10 = 0.86, p > 0.05; Figure 3(A)).

Similarly for the development index, a positive response to low pH during the first30 h (t-test, t7.64 = 2.33, p = 0.05) and no significant difference after 66 h were observed(t8.725 = −0.123, p = 0.905; Figure 3(B)). The development index was, on average, 1.25± 0.23 in low pH and 1.03 ± 0.47 in ambient pH, except in the 30 h ambient pH treat-ment (development index = 0.8). For both development index and hatching success, thevariation among replicates was slightly higher, but not statistically significant, in eitherambient pH compared with low pH for both 30 and 66 h incubation times (Bartlett’stest of Equal Variances, p > 0.05 in all cases).

Discussion

Our experimental results showed that Acartia’s reproductive output, in terms of egg pro-duction, and development index, increased as a response to short-term incubations in lowpH. So, our hypothesis was rejected. A similar response in egg production was found byMayor and colleagues (2007) after a two-day long incubation of C. finmarchicus at pH6.95. Vehmaa, Brutemark and Engström-Öst (2012) also found a similar response to a 0.4decrease in pH in Acartia sp. in which the average egg production increased; in particular:day 1–2: egg production (EP) higher in low than in ambient pH; day 3: same EP in ambi-ent as in low pH; day 4–5: lower EP in low than in ambient pH in response to lowered pHat 17 °C. In the current study, egg production increased in lower pH, and the developmentindex (DI) increased after 33 h, whereas egg-hatching success and DI remained high incomparison to the control after 66 h. The shrimp Palaemon pacificus can respond simi-larly but on a long-term basis; moulting frequency was higher in low pH compared withthe control values (Kurihara et al. 2008). Fitzer et al. (2012) showed that copepod naupliiproduction increased in low pH (in pH 7.95 and 7.67, compared with the control pH8.10). This occurred simultaneously with a decrease in prosome length which suggeststhat copepods allocated energy from somatic growth to reproductive output in low pH.

Figure 2. Egg production rates (EPR; eggs female-1 d-1) for the copepod A. bifilosa in twotreatments ambient and low pH (N = 12). Central horizontal line of the boxes indicates the medianand the ends of the boxes represent the upper and lower quartiles of the data, whiskers markmaximum and minimum values. The asterix indicates significance at level 0.05.

178 J. Engström-Öst et al.

Dow

nloa

ded

by [

Yrk

eshö

gsko

lan

Nov

ia]

at 0

1:39

28

July

201

4

The authors attributed the results to an initial stress response or to a positive responsewhen exposed to low levels of stressor (Fitzer et al. 2012). It is interesting to note thatstimulatory effects on reproduction have been reported for other organism groups too;Miller et al. (2013) found that the cinnamon anemone fish increased reproductive outputwhen exposed to elevated CO2 concentrations. Individuals can either reduce their invest-ment in current reproduction and save energy for future reproduction when exposed tostressors (Clutton-Brock 1984; Hamel, Cote, & Festa-Bianchet 2011). Alternatively, indi-viduals can invest more energy into current reproduction, in an attempt to counterbalanceany negative effects of environmental stress on reproductive output and to potentiallyincrease offspring survival (Paul, Kuester, & Podzuweit 1993).

The egg production in our experiment was low, but in the same range as forcon-specifics in the area (Hogfors et al. 2011). The low egg production could occur forvarious reasons such as temperature, food or female condition (Koski et al. 2010). Inthe experiment, we used 1 °C lower than that of the in situ surface temperature duringthe incubations, and no major changes occurred in the temperature environment of thecopepods, except briefly during sorting procedure. The green alga provided was

Figure 3. Egg-hatching success (%) (A) and development index (B) of A. bifilosa for each of thetwo treatments (ambient pH; clear boxes, and low pH; grey boxes; N = 6) after 30 and 66 h,respectively. Central horizontal line of the boxes indicates the median and the ends of the boxesrepresent the upper and lower quartiles of the data. Whiskers mark maximum and minimumvalues. The asterix indicates significance according to Table 1.

Marine and Freshwater Behaviour and Physiology 179

Dow

nloa

ded

by [

Yrk

eshö

gsko

lan

Nov

ia]

at 0

1:39

28

July

201

4

saturated and its quality was moderately high (Koski et al. 1999). The water quality atthe sampling station may, however, have been suboptimal, due to the cyanobacteriablooms that commonly occur in late summer (Suikkanen et al. 2013).

Experimental studies have shown that single effects by pH on copepod reproductiveoutput are either not significant (Kurihara & Ishimatsu 2008), or that there are pHeffects, but they appear in experiments studying major CO2 leakages (Kurihara,Shimode, & Shirayama 2004; Mayor et al. 2007), in conjunction with other factors suchas temperature or food quality (Rossoll et al. 2012; Vehmaa, Brutemark, & Engström-Öst 2012; Vehmaa et al. 2013). Why did A. bifilosa females increase their reproductiveoutput as a response to lowered pH? The pH level in which we incubated the femaleswas not harmful to the copepods on a short-term basis. A. bifilosa is a species thatinhabits the coastal areas (Ackefors 1981) and appears to be a species that tolerates sud-den decreases in pH within the range used in this study. Lewis et al. (2013) demon-strated that adult Calanus did not respond to pH manipulations as the result correlatedwith their migration behaviour and their natural exposure to low pH in deep waters.The authors further showed that copepod nauplii ( juveniles) that spent more time thanthe adults in upper waters were more sensitive to low pH. Fabry et al. (2008) suggestedthat vertically migrating zooplankton are well adapted to changing conditions, becausethey are exposed to large gradients in CO2, O2 and pH. In regions with pronouncedoxygen minimum layers (i.e. both oceans and the Baltic Sea), wide variations in pHoccur (Fabry et al. 2008) because many factors affect the local biochemistry(Andersson, Mackenzie, & Lerman 2005; Waldbusser & Salisbury 2014). In addition,hypoxia may amplify the effects of pH (Melzner et al. 2013).

Copepods inhabiting deeper areas are more tolerant to low pH than shallow-livingcopepods (Watanabe et al. 2006). The explanation for why A. bifilosa copepodsincreased the reproductive output in the present study could be that the copepods arefairly well adapted to the pH regime we used in the treatment because they performDVM between the deep and the mid-waters (Holliland et al. 2012). The pH, forexample, was 7.3 at the bottom (30 m depth) in Storfjärden on 11 August 2010).Further, the eggs broadcast by the females sink so that it may be beneficial to speed uphatching to avoid them sinking into unfavourable waters characterised by anoxia andlow pH. The reported disappearance of spawned copepod eggs termed ‘apparent mortal-ity’ (Tang, Dam, & Feinberg 1998; Dam & Tang 2001) could perhaps be explained byegg sinking.

In conclusion, our results showed a stimulating effect of lowered pH on the copepodrecruitment. The results indicate that A. bifilosa copepods are tolerant to a significantpH gradient, similar to that experienced during DVM, upwelling episodes and changedmixing conditions in the Baltic Sea. Further, they respond to low pH with changedreproductive output. Our results suggest that A. bifilosa may have considerable capacityto adapt to future pH decline, such as may occur with ocean acidification, because it isalready adapted to pH gradients and shifting pH environments. The data also suggestthat their migratory and reproductive behaviour may change concomitantly giving riseto altered population recruitment, energy transfer between trophic levels and food webdynamics.

AcknowledgementsThe work was supported by funding from the Academy of Finland (projects 125251, 255566),Maj and Tor Nessling Foundation, Walter and Andrée de Nottbeck Foundation, R & D InstituteAronia, The Swedish Research Council for Environment, Agricultural Sciences and Spatial

180 J. Engström-Öst et al.

Dow

nloa

ded

by [

Yrk

eshö

gsko

lan

Nov

ia]

at 0

1:39

28

July

201

4

Planning (FORMAS) and Stockholm University’s strategic marine environmental researchprogram “Baltic Ecosystem Adaptive Management”. We thank the staff at Tvärminne ZoologicalStation. The authors have no conflicts of interest to declare.

References

Ackefors H. 1981. Zooplankton. In: Voipio A, editor. The Baltic Sea. Elsevier OceanographySeries, No 30. Oxford: Elsevier Scientific Publishing Company; p. 238–254.

Andersson AJ, Mackenzie FT, Lerman A. 2005. Coastal ocean and carbonate systems in the highCO2 world of the anthropocene. Am J Sci. 305:875–918.

Barry JP, Widdicombe S, Hall-Spencer JM. 2011. Effects of ocean acidification on marine biodi-versity and ecosystem function. In: Gattuso J-P, Hansson L, editors. Ocean acidification.Oxford: Oxford University Press; p. 192–209.

Beaugrand G, Kirby RR. 2010. Climate, plankton and cod. Glob Change Biol. 16:1268–1280.Clutton-Brock TH. 1984. Reproductive effort and terminal investment in iteroparous animals. Am

Nat. 123:212–229.Dam HG, Tang KW. 2001. Affordable egg mortality: constraining copepod egg mortality with life

history traits. J Plankton Res. 23:633–640.Dickson AG, Sabine CL, Christian JR. 2007. Guide to best practices for ocean CO2 measure-

ments. Sidney (BC): North Pacific Marine Science Organization: PICES Publication 3.Fabry VJ, Seibel BA, Feely RA, Orr JC. 2008. Impacts of ocean acidification on marine fauna

and ecosystem processes. ICES J Mar Sci. 65:414–432.Feely RA, Alin SR, Newton J, Sabine CL, Warner M, Devol A, Krembs C, Maloy C. 2010. The

combined effects of ocean acidification, mixing, and respiration on pH and carbonate satura-tion in an urbanized estuary. Estuar Coast Shelf Sci. 88:442–449.

Feely RA, Sabine CL, Hernandez-Ayon JM, Ianson D, Hales B. 2008. Evidence for upwelling ofcorrosive “acidified” water on to the continental shelf. Science. 320:1490–1492.

Fitzer SC, Caldwell GS, Close AJ, Clare AS, Upstill-Goddard RC, Bentley MG. 2012. Oceanacidification induces multi-generational decline in copepod naupliar production with possibleconflict for reproductive resource allocation. J Exp Mar Biol Ecol. 418–419:30–36.

Guillard RRL. 1975. Culture of phytoplankton for feeding marine invertebrates. In: Smith WL,Chanley MH, editors. Culture of marine invertebrate animals. New York, NY: Plenum Press;p. 29–60.

Hamel S, Cote SD, Festa-Bianchet M. 2011. Tradeoff between offspring mass and subsequentreproduction in a highly iteroparous mammal. Oikos. 120:690–695.

Hansen PJ. 2002. Effect of high pH on the growth and survival of marine phytoplankton: implica-tions for species succession. Aquat Microb Ecol. 28:279–288.

Hogfors H, Holmborn T, Hajdu S, Gorokhova E. 2011. Does female RNA content reflect viableegg production in copepods? A test with the Baltic copepod Acartia tonsa. J Plankton Res.33:1460–1463.

Holliland PB, Ahlbeck I, Westlund E, Hansson S. 2012. Ontogenetic and seasonal changes in dielvertical migration amplitude of the calanoid copepods Eurytemora affinis and Acartia spp. ina coastal area of the northern Baltic proper. J Plankton Res. 34:298–307.

Kang H-K, Poulet SA. 2001. Reproductive success in Calanus helgolandicus as a function of dietand egg cannibalism. Mar Ecol Prog Ser. 201:241–250.

Knuckey RM, Semmens GL, Mayer RJ, Rimmer MA. 2005. Development of an optimal microal-gal diet for the culture of the calanoid copepod Acartia sinjiensis: effect of algal species andfeed concentration on copepod development. Aquaculture. 249:339–351.

Koski M, Dutz J, Klein Breteler WK, Rampen S, Noordeloos A. 2010. Seasonal changes in foodquantity and quality of the common North Sea copepods Temora longicornis and Pseudocal-anus elongatus: a bioassay approach. Mar Ecol Prog Ser. 399:141–155.

Marine and Freshwater Behaviour and Physiology 181

Dow

nloa

ded

by [

Yrk

eshö

gsko

lan

Nov

ia]

at 0

1:39

28

July

201

4

Koski M, Rosenberg M, Viitasalo M, Tanskanen S, Sjölund U. 1999. Is Prymnesium patelliferum-toxic for copepods? – Grazing, egg production, and egestion of the calanoid copepodEurytemora affinisin mixtures of “good” and “bad” food. ICES J Mar Sci. 56:131–139.

Kurihara H. 2008. Effects of CO2-driven ocean acidification on the early developmental stages ofinvertebrates. Mar Ecol Prog Ser. 373:275–284.

Kurihara H, Ishimatsu A. 2008. Effects of high CO2 seawater on the copepod (Acartia tsuensis)through all life stages and subsequent generations. Mar Poll Bull. 56:1086–1090.

Kurihara H, Matsui M, Furukawa H, Hayashi M, Ishimatsu A. 2008. Long-term effects ofpredicted future seawater CO2 conditions on the survival and growth of the marine shrimpPalaemon pacificus. J Exp Mar Biol Ecol. 367:41–46.

Kurihara H, Shimode S, Shirayama Y. 2004. Effects of raised CO2 concentration on the eggproduction rate and early development of two marine copepods (Acartia steueri and Acartiaerythraea). Mar Poll Bull. 49:721–727.

Lewis CN, Brown KA, Edwards LA, Cooper G, Findlay HS. 2013. Sensitivity to ocean acidificat-ion parallels natural pCO2 gradients experienced by arctic copepods under winter sea ice.Proc Nat Acad Sci USA. 110:E4960–E4967.

Mayor DJ, Matthews C, Cook K, Zuur AF, Hay S. 2007. CO2-induced acidification affects hatch-ing success in Calanus finmarchicus. Mar Ecol Prog Ser. 350:91–97.

Melzner F, Thomsen J, Koeve W, Oschlies A, Gutowska MA, Bange HW, Hansen HP,Körtzinger A. 2013. Future ocean acidification will be amplified by hypoxia in coastalhabitats. Mar Biol. 160:1875–1888.

Miller GM, Watson S-A, McCormick MI, Munday PI. 2013. Increased CO2 stimulates reproduc-tion in a coral reef fish. Glob Change Biol. 19:3037–3045.

Olafsson J, Olafsdottir SR, Benoit-Cattin A, Danielsen M, Arnarson TS, Takahashi T. 2009. Rateof Iceland Sea acidification from time series measurements. Biogeosciences. 6:2661–2668.

Paul A, Kuester J, Podzuweit D. 1993. Reproductive senescence and terminal investment infemale Barbary macaques (Macaca sylvanus) at Salem. Int J Primatol. 14:105–124.

Riebesell U, Fabry VJ, Hansson L, Gattuso J-P. 2010. Guide to best practises for ocean acidificat-ion research and data reporting. Brussels: European Commission Publications Office of theEuropean Union.

Rossoll D, Bermúdez R, Hauss H, Schulz KG, Riebesell U, Sommer U, Winder M. 2012. Oceanacidification-induced food quality deterioration constrains food transfer. PLOS ONE. 7:e34737.

Runge JA, Roff JC. 2000. The measurement of growth and reproductive rates. In: Harris R,Wiebe P, Lenz J, Skjoldal HR, Huntley M, editors. ICES zooplankton methodology manual.London: Academic Press; p. 401–454.

Salonen K. 1981. Rapid and precise determination of total inorganic carbon and some gases inaqueous solutions. Water Res. 15:403–406.

Suikkanen S, Pulina S, Engström-Öst J, Lehtiniemi M, Lehtinen S, Brutemark A. 2013. Climatechange and eutrophication induced shifts in northern summer plankton communities. PLOSONE. 8:e66475.

Sunda WG, Cai W-J. 2012. Eutrophication induced CO2-acidification of subsurface coastal waters:interactive effects of temperature, salinity and atmospheric pCO2. Environ Sci Technol.46:10651–10659.

Tang KW, Dam HG, Feinberg LR. 1998. The relative importance of egg production rate, hatchingsuccess, hatching duration and egg sinking in population recruitment of two species of marinecopepods. J Plankton Res. 20:1971–1987.

Vehmaa A, Brutemark A, Engström-Öst J. 2012. Maternal effects as adaptation mechanism forcopepods facing temperature and pH changes. PLOS ONE. 7:e48538.

Vehmaa A, Hogfors H, Gorokhova E, Brutemark A, Holmborn T, Engström-Öst J. 2013. Pro-jected marine climate change: effects on copepod oxidative status and reproduction. EcolEvol. 3:4548–4557.

182 J. Engström-Öst et al.

Dow

nloa

ded

by [

Yrk

eshö

gsko

lan

Nov

ia]

at 0

1:39

28

July

201

4

Waldbusser GG, Salisbury JE. 2014. Ocean acidification in the coastal zone from an organism’sperspective: multiple system parameters, frequency domains, and habitats. Annu Rev MarSci. 6:221–247.

Watanabe Y, Yamaguchi A, Ishida H, Harimoto T, Suzuki S, Sekido Y, Ikeda T, Shirayama Y,Mac Takahashi M, Ohsumi T, Ishizaka J. 2006. Lethality of increasing CO2 levels ondeep-sea copepods in the western North Pacific. J Oceanogr. 62:185–196.

Whiteley NM. 2011. Physiological and ecological responses of crustaceans to ocean acidification.Mar Ecol Prog Ser. 430:257–271.

Wootton JT, Pfister CA. 2012. Carbon system measurements and potential climatic drivers at asite of rapidly declining ocean pH. PLOS ONE. 7:e53396.

Wootton JT, Pfister CA, Forester JD. 2008. Dynamic patterns and ecological impacts of decliningocean pH in a high-resolution multi-year dataset. Proc Nat Acad Sci USA. 105:18848–18853.

Marine and Freshwater Behaviour and Physiology 183

Dow

nloa

ded

by [

Yrk

eshö

gsko

lan

Nov

ia]

at 0

1:39

28

July

201

4