Ocean acidification impact swimming and settlement ...

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copper pollution (e.g., Marshall,. 2008). Precent larvae settled. 2h. 4h. Literature Cited: • Marshall, D.J., Pechenik, J.A., Keough, M.J., 2003. Larval activity levels ...
Ocean acidification impact swimming and settlement of Bugula neritina Antoine Pecquet1,2, Narimane Dorey2, Kit Yu Karen Chan2 University of La Rochelle, France 2. Division of Life Science, Hong Kong University of Science and Technology, Hong Kong. Corresponding email: [email protected] 1.

Quantiative Plankton Ecology

•Ocean acidification (OA) caused by anthropogenic CO2 emission is predicted to reduce surface ocean pH by 0.4 unit and signifcantly alter carbonate chemistry by 2100. Previous studies often focus on calficying species. • We focus on a comosopolitican species, Bugula nertina, a fouling organism that thrives in area with high human influence and high natural variablility in environmental condictions, inlcuding Hong Kong coastal waters. Hypothesis: B. nertina’s life history strategy, esp. their non-feeding larvae, help confer resilience to OA. Key findings: • Settlement is delayed by elevated pCO2 under acute exposure, but successful metamorphsis still occured at pH as low as 6.5. • Larval swimming speed increased with acidification (pH 7.6 compared to pH 8.0), settled juveniles grew faster in the low pH treatment. • Therefore, this nusiance species is likely to continue to flourish under future ocean conditions.

Experiment One: Acute Exposure

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Time after spawning 2 hr 4 hr

1 hr

Adults from Trois Beach were exposed to light to induce spawning.

6 hr

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Percent larvae settled

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Larvae were genlted pipetted into a tube with filtered seawater (FSW) at differerent pHs (6.5 - 8.0)

T=17°C

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pH T

T=17°C

• Larvae reach 100% settlement at higher pH faster. • Settlement still occured at low pH, but only after 4 hours, compared to 1 hr at pH 7.8. • Estimated time to 100% settlement was shorter at pH 8.0 (292 min) compared to 539 min at pH 6.5. >>> Delaying settlement could increase predation risk and loss through advection (Marshall et al., 2003).

Experiment Two: Chronic Exposure 1 Control pH 7.89 2 aquaria

3

1, 2, 4, 6 hours After spawning

Starting pHT

6.46 6.95 7.21 7.4 7.6

7.67 7.95 8.05

Mean final pHT 6.72 7.10 7.29 7.43 7.53 7.58 7.74 7.97 3 replicates per pH, experiment repeated 3 times

Number of settled larvae were counted and percent settled were computed

Adults were removed and fixed. Average wet weight 4.68 ± 0.43

30 min light exposure Spawning induction

2

30 min

N.B. on the design • Adults were collected from Trios Beach. • Experiment s was repeated 3

48 h acclimation

3 Larvae were sampled (3 x30ml or 2 x 50ml samples) and counted

Low pH pH 7.61

•pH did NOT affect the number of larvae spawned (F = 0.10, p = 0.75).

2 aquaria pHs shown are average of 3 replicate trials

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Larvae were transfered into darkened tissue culture flasks with FSW at the experimental pHs. 19

y axis (mm)

17 15 13 11 9

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x axis (mm)

Groos swiming speed (mm s-1)

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Example trajectories of larval B. neritina swimming for 2 minutes (top).

PVC plate or petri dishes were used as substrate for settlement and later photographed for coutning and sizing.

• Larger juveneiles (~ 30 µm, approx 5% of total length) at low pH at 48 hours post settlement (F=7.65, df = 1, p =0.006). >>> Despite increase swimming activity, B. nertina larvae settled at low pH grew faster, suggesting the species would thrive under OA conditions.

n : number of video clip analysed

Swimming speeds were computed from video of larvae inside these flasks

• Swimming speed significantly incrased with acification (F=114.3, df=2, p =0.0001). >>>Increased swimming activity could reduce energy avaliable for metamorphsis and later development (Wendt, 1996 and 1998)

• Addition of copper (Cu at 72 µgL ) increased settlement success (•) regardless of the pH level. • pH had no significant effect on settlement when copper was present. >>> This species performed well in copper pollution (e.g., Marshall, 2008) 2+

-1

2h

100 Precent larvae settled

Teaser Information: Copper counteract the negative effect of OA

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4h

• This work is part of AP master thesis internship with funding support from the PGSO, HKUST. ND is partially supported by VPRG, HKUST. Funding for the project comes from the Research Grant Counil (Project Number: 26102515) to KC. KC is additionally supported by the Croucher Foundation, Hong Kong. • We thank Ms. Jenny Ngo, Mr. Elizaldy Mabaloc, and Dr. Tam Yi Ki for their kind assistance with the project. We are grateful to Prof. P.Y. Qian and Dr. Y.H. Wong for their input on local byrozoans.

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Acknowlegements:

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Literature Cited: = = =

0 pH T

• Marshall, D.J., Pechenik, J.A., Keough, M.J., 2003. Larval activity levels and delayed metamorphosis affect post-larval performance in the colonial ascidian Diplosoma listerianum. Marine Ecology Progress Series 246, 153-162. • Marshall, D.J., 2008. Transgenerational plasticity in the sea: context-dependent maternal effects across the life history. Ecology 89, 418-427. • Morton, B., 1987. Recent marine introductions into Hong Kong. Bulletin of Marine Science 41, 503-513. • Wendt, D.E., 1996. Effect of larval swimming duration on success of metamorphosis and size of the ancestrular lophophore in Bugula neritina (Bryozoa). The Biological Bulletin 191, 224-233. • Wendt, D.E., 1998. Effect of larval swimming duration on growth and reproduction of Bugula neritina (Bryozoa) under field conditions. The Biological Bulletin 195, 126-135.