Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Biogeosciences Discuss., 8, 8423–8450, 2011 www.biogeosciences-discuss.net/8/8423/2011/ Biogeosciences doi:10.5194/bgd-8-8423-2011 Discussions BGD © Author(s) 2011. CC Attribution 3.0 License. 8, 8423–8450, 2011 This discussion paper is/has been under review for the journal Biogeosciences (BG). Effect of salinity Please refer to the corresponding final paper in BG if available. induced pH changes on benthic foraminifera R. Saraswat et al. Effect of salinity induced pH changes on benthic foraminifera: a laboratory culture Title Page experiment Abstract Introduction Conclusions References R. Saraswat, M. Kouthanker, S. Kurtarkar, R. Nigam, and V. N. Linshy Tables Figures Micropaleontology Laboratory, National Institute of Oceanography, Goa, 403004, India J I Received: 4 August 2011 – Accepted: 15 August 2011 – Published: 23 August 2011 Correspondence to: R. Saraswat ([email protected]) J I Published by Copernicus Publications on behalf of the European Geosciences Union. Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion 8423 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Abstract BGD The coastal water pH varies with salinity. Therefore, to study the effect of salinity in- duced pH variations on benthic foraminifera, live specimens of Rosalina globularis were 8, 8423–8450, 2011 subjected to different salinities (10, 15, 20, 25, 30, 35 and 40 ‰) with pH varying from 5 7.2 to 8.2. A total of 210 specimens were used and the experiment was conducted in Effect of salinity replicates. It was observed that the salinity induced pH changes affect the calcification induced pH changes of foraminifera. However the response is not linear. The maximum growth is reported in on benthic the specimens kept at 35 ‰ salinity (pH 8.0) while the rest of the specimens maintained foraminifera at salinity higher or lower than 35 ‰, showed comparatively lesser growth. A significant 10 drop in pH severely hampers the calcification capability of benthic foraminifera. Spec- R. Saraswat et al. imens kept at 10 and 15 ‰ (pH 7.2 and 7.5, respectively) became opaque within two days of lowering the salinity and later on their tests dissolved within 24 and 43 days, respectively. Besides calcification capability, pH also affects reproduction. No speci- Title Page men reproduced at 10 and 15 ‰ salinity while only a few specimens (3 %) reproduced Abstract Introduction 15 at 20 ‰. As compared to 10–20 ‰ salinity, ∼ 60 % reproduction was observed in spec- imens subjected to 25–40 ‰ salinity. The drop in pH also decreased the calcification Conclusions References rate as specimens at 20 ‰ salinity took twice the time to reach maturity than normal Tables Figures range (25–40 ‰). We conclude that salinity induced drop in pH adversely affects the calcification capability and reproduction in benthic foraminifera. It is inferred that the J I 20 time required to reach reproductive maturity increases at the extreme salinity tolerance limits. However, beyond a certain limit, a further increase in pH does not affect benthic J I foraminifera; rather they respond to salinity as per their salinity tolerance range. Back Close 1 Introduction Full Screen / Esc While the increasing open ocean acidification (OA) is the result of enormous input Printer-friendly Version 25 of CO2 in the atmosphere by various anthropogenic activities (Caldeira and Wickett, 2003), local factors like fresh water runoff, coastal erosion, fertilizer input have also Interactive Discussion 8424 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | lead to the development of regions of increased ocean acidification (Doney et al., 2007, 2009; Cheung et al., 2009; Cooley and Doney, 2009; Kelly et al., 2011). Such shallow BGD water OA zones are responsible for the declining fish catch, changing marine diver- 8, 8423–8450, 2011 sity and ocean ecosystem (Cheung et al., 2009; Doney et al., 2009). However, the 5 capability of marine organisms to adapt to the increasing OA is not well known. Lab- oratory culture studies have shown that marine calcifiers will be adversely affected Effect of salinity under increasing ocean acidification as decline in seawater pH hampers the capability induced pH changes of marine calcareous organisms to secrete calcite (Gattuso et al., 1998; Bijma, 1999; on benthic Marubini and Atkinson, 1999; Leclercq et al., 2000; Riebesell et al., 2000; Langdon foraminifera 10 et al., 2000). The response, however is not uniform as increased calcification under projected OA has been reported in case of a few taxa (Iglesias-Rodrıguez et al., 2008; R. Saraswat et al. Ries et al., 2009). The growth of a few non calcifying organisms also increases under high CO2 conditions (Palacios and Zimmerman, 2007). Therefore the effect of OA on Title Page marine organisms has to be studied in detail. The benthic foraminifers, unicellular pref- 15 erentially marine microorganisms are amongst the dominant group of organisms with Abstract Introduction calcareous exoskeleton (test), living in the shallow water regions of the world oceans. Conclusions References The foraminifers sequester huge amount of CO2 and help in its removal from the atmo- sphere, thus helping in mitigating the effect of anthropogenic CO2. It is expected that Tables Figures calcareous benthic foraminifers will also be adversely affected due to the increasing 20 ocean acidification. However benthic foraminifera are capable of increasing the pH of J I vacuolized seawater at the site of calcification by one unit above seawater pH to secret calcite (Nooijer et al., 2009). The capability of benthic foraminifers to modulate the J I pH of vacuolized seawater under different seawater pH conditions is not known. Even Back Close the lowest pH that calcareous benthic foraminifera can tolerate is not clear (ter Kuile 25 et al., 1989; Le Cadre et al., 2003; Kuroyanagi et al., 2009; Kurtarkar et al., 2011). It Full Screen / Esc is expected that the pH tolerance range will vary from species to species as different benthic foraminiferal species are adapted to different habitats. Under such a scenario it Printer-friendly Version is difficult to predict the response of benthic foraminifers to increasing ocean acidifica- tion. Controlled laboratory culture studies can help understand the response of benthic Interactive Discussion 8425 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | foraminifera to OA. Since riverine influx is one of the major factors for the development of localized zones of increased ocean acidification (Padmavati and Goswami, 1996; BGD Kurtarkar et al., 2011), here we have studied the response of benthic foraminifera to 8, 8423–8450, 2011 salinity induced seawater pH changes, under controlled conditions in laboratory. 5 2 Materials and method Effect of salinity induced pH changes To understand the relationship between seawater salinity and pH, water samples were on benthic collected from the Mandovi and Zuari estuaries which bring freshwater to the shallow foraminifera water coastal regions off Goa during the southwest monsoon season. The water was collected from the mouth of the estuaries till the inner reaches (to cover a wide range of R. Saraswat et al. 10 salinity) by using Niskin water sampler. The water was transferred into narrow mouth 1 l bottles and kept in dark and its salinity and pH was measured on the same day by using autocell and pH meter. Title Page To get live benthic foraminifera specimens, material including the top 1 cm of the Abstract Introduction sediments as well as sea grass attached to the perennially submerged rocky cliffs was 15 collected from the waters off Dias beach, Goa coast. The sea water was also collected Conclusions References for further use in laboratory as media. The sea grass was transferred to a plastic tub containing sea water and shaked vigorously to detach foraminifera attached to it. Tables Figures The entire material was sieved through 1000 and 63 µm sieves to remove extraneous material. After thoroughly cleaning the sample, 63–1000 µm fraction was transferred to J I 20 glass beakers with sea water. J I In the laboratory, the material was scanned under stereo-zoom microscope (Olym- pus SZX16) to separate live benthic foraminifera. Probable live specimens were Back Close picked using a micropipette or a very fine tipped brush and transferred to multi-well Full Screen / Esc (6-wells) culture petri-dishes (Axygen). The live specimens separated under binocular 25 microscope were subsequently scanned under inverted microscope (Nikon ECLIPSE Printer-friendly Version TE2000-U) for pseudopodial activity, movement, food collection, etc., to confirm their live status. Once confirmed to be live, the specimens were divided into several Interactive Discussion batches and kept at different ecological conditions (salinity varying from 20 to 40 ‰ and 8426 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | temperature varying from 15 to 30 ◦C) to facilitate reproduction. The offsprings of the reproduced specimens, that is the juveniles with two-three chambers, were subjected BGD to different salinities. All the juveniles were taken from specimens kept at 35 ‰ salinity 8, 8423–8450, 2011 as maximum reproduction was observed at this salinity. The advantage of conducting 5 experiments on juveniles is that there is ample time for the specimens to respond to physico-chemical conditions, before they mature and reproduce. Effect of salinity The experimental specimens were subjected to seven different salinities (10, 15, induced pH changes 20, 25, 30, 35, 40 ‰) with pH varying from 7.2 to 8.2. This salinity range was se- on benthic lected based on continuous monitoring of physico-chemical parameters in the field foraminifera 10 from where live specimens were collected (Rodrigues, 1984; Nigam et al., 2008), and ◦ R. Saraswat et al. expected possible change in salinity in future. Temperature (27 C) was kept constant throughout the experiment. Five juvenile specimens were kept in each well of the 6-well culture petri-dish and thus each dish contained 30 specimens.