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Implications of changing ocean temperature and pH for the predatory whelk Trochia cingulata
Thesis (PhD)--Stellenbosch University,2022.
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Stellenbosch : Stellenbosch University
2022
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| author | Martin, Nicole |
| author2 | Robinson-Smythe, Tammy
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| author_browse | Martin, Nicole Robinson-Smythe, Tammy |
| author_facet | Robinson-Smythe, Tammy
Martin, Nicole |
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| description | Thesis (PhD)--Stellenbosch University,2022. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/125014 |
| institution | Stellenbosch University (South Africa) |
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| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
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| spelling | oai:scholar.sun.ac.za:10019.1/125014 Implications of changing ocean temperature and pH for the predatory whelk Trochia cingulata Martin, Nicole Robinson-Smythe, Tammy Clusella-Trullas, Susana Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology. Trochia cingulata -- Ecology -- South Africa Ocean acidification -- Environmental aspects Seawater -- Carbon dioxide content -- Environmental aspects Climatic changes Ocean-atmosphere interaction Marine ecology -- Effect of temperature on Ocean -- Effect of human beings on UCTD Thesis (PhD)--Stellenbosch University,2022. ENGLISH ABSTRACT: The continual emission of carbon dioxide into the atmosphere by humans is substantially altering ocean temperature and pH. Globally ocean surface waters are predicted to warm by 0.3 – 4.8°C and acidify by 0.3 to 0.5 pH units by 2100. Regional consequences of climate change can, however, differ from these global predictions. For example, climate-driven intensified upwelling on the west coast of South Africa has resulted in cooling as opposed to warming. Current knowledge on how these predicted changes will impact marine biota remains limited, particularly in relation to South Africa. This thesis addresses this knowledge gap with a focus on a gastropod that is endemic to the west coast of southern Africa, the Girdled Dogwhelk, Trochia cingulata. The overarching aims of this thesis were to assess the effects of warming, cooling and concurrent acidification on T. cingulata and how changes in these environmental variables impact the predator-prey interaction between this whelk and its native and alien mussel prey. To assess the effects of altered temperature and acidification on shell traits and survival of T. cingulata, whelks were exposed to three temperatures (cooling scenario: 9°C, current average temperature: 13°C, and warming scenario: 17°C) and three pH levels (current conditions: 8.0, intermediate decrease: 7.7 and extreme decrease: 7.5) in a full factorial experiment for 12 weeks. Acidification did not influence whelk survival, while mortality increased with increasing temperature. As most whelks died after being exposed to warming for two weeks, only the implications of cooling and acidification on shell taits could be considered. Shells were thinner and more elongated after six weeks of exposure to cooling, while acidification reduced shell strength. After 12 weeks, shell thickness was the same in all treatments. However, cooling changed shells to become more rounded and accentuated the effects of pH with the weakest shells being found in the cold, extreme acidic treatment. These findings demonstrate that T. cingulata is more sensitive to changes in temperature than pH, with warming increasing mortality and cooling compromising shell strength and morphology. Colder waters lower the saturation state of calcium carbonate and cooling reduces metabolic capacity. The weaker, thinner, and rounded shells that result from cooling thus likely reflect undermined shell building and maintenance capabilities of T. cingulata when exposed to colder conditions. To gain a better understanding of this whelk’s vulnerability to predicted future temperatures, the thermal tolerance and acclimation capacity of T. cingulata were determined. To account for the predicted future decrease in pH, the influence of acidification on this whelk’s thermal tolerance and acclimation capacity were also considered. After exposure to average environmental conditions, whelks had a critical thermal minimum, CTmin and maximum, CTmax of -1.3°C and 36.7°C respectively, and an optimal temperature, Topt, of 13.7°C. After warm acclimation, CTmin, CTmax and Topt increased while only Topt shifted down in response to cold acclimation. CTmax increased after acclimation to acidic conditions indicating that acidification did not narrow the thermal tolerance of T. cingulata or limit its acclimation ability. This suggests that T. cingulata possesses adaptations that minimise stress caused by acidification. Such adaptations were likely derived in response to the periodic low pH levels that can be associated with upwelling. This whelk’s resilience to acidification, ability to withstand very low temperatures and plasticity in Topt demonstrate that T. cingulata can cope well with predicted cooling. As T. cingulata experiences predominantly cool conditions, its high CTmax and warm-acclimation ability were unexpected but demonstrate that this whelk may not be as vulnerable to warming as suggested by the first chapter. While gathering information on the vulnerability of species to altered environmental conditions is valuable, studying how these changes could interfere with processes that shape marine communities are also needed. In answer to this need, the implications of concurrent alterations in temperature and pH for the predatory interaction between T. cingulata and its mussel prey were assessed using the same experimental approach described above. Regardless of temperature or pH, whelks retained their established preference for the alien mussel Semimytilus algosus. These findings suggest that the predator-prey relationship between this whelk and its mussel prey is unlikely to be disrupted under future conditions. Semimytilus algosus contributes approximately 95% to mussel bed assemblages at the study site, Elands Bay. Preference for this dominant alien mussel thus likely reflects the selection of the most profitable prey. Despite prey selection being unaffected by altered conditions, warming significantly increased consumption rate, likely in compensation for the increased energetic demands associated with operating under these conditions. These findings demonstrate how the consequences of changing environmental conditions for a single species are not necessarily carried through to their, direct biotic interactions. Understanding how species may respond to projected changes in temperature and pH, together with how these changes may affect biotic interactions, is needed to accurately anticipate the consequences of changing marine environments. The results from this thesis add to the limited knowledge held on the vulnerabilities of African marine species to predicted future environments. Novel insights into the vulnerability of T. cingulata to future conditions were enabled by considering the sensitivity of a diversity of traits to future environmental conditions. Thermal tolerance and acclimation capacity of T. cingulata highlighted that thermal stress may be buffered by plasticity, while this shelled gastropod was largely unaffected by changes in pH predicted to occur by the end of the century. This resilience may be imparted by exposure to episodic low pH events often associated with upwelling. If this finding is broadly applicable to other taxa endemic to the region, it suggests that this and other upwelling systems may hold innate resilience to ocean acidification. AFRIKAANSE OPSOMMING: Koolstofdioksied wat voortdurend deur mens in die atmosfeer vrygestel word, is besig om die oseaan temperatuur en pH wensenlik te verander. Daar word voorspel dat teen 2100, die globale oseaan oppervlak temperatuur met 0.3 - 4.8°C kan styg en die suurinhoud van die water met 0.3 – 0.5 pH eenhede kan verhoog. Dit is belangrik om in ag te neem dat die gevolge van klimaatsverandering wel kan verskil van streek tot streek ten spyte van die globale voorspellings. Verhoogde opwellings wat klimaatsgedrewe was, het byvoorbeeld aan die Weskus van Suid Afrika koeler toestande, in teenstelling met warmer toestande veroorsaak. Huidige kennis ten opsigte van die invloed van hierdie voorspellings op die marine biota is nog beperk, veral met betrekking tot Suid Afrika. Die tesis spreek hierdie kennisgaping aan met die fokus op ‘n gastropod, ‘n tipe seeslak, bekend as die Girdled Dogwhelk, Trochia cingulata wat endemies aan die Weskus van suidelike Afrika voorkom. Die oorkoepelende doel van hierdie tesis was om vas te stel wat die effek van verwarming, afkoeling en gelyktydige versuring op T. cingulata het asook die impak op die veranderlikes van die omgewing ten opsigte van roofdier-prooi interaksie tussen T. cingulata en sy inheemse en uitheemse mosselprooi is. Om die gevolge van die veranderde temperatuur en versuring op die skulp morfologie en oorlewing van T. cingulata vas te stel was T. cingulata blootgestel aan drie temperature (afkoelings scenario: 9° C, huidige gemiddelde temperatuur: 13°C en verwarmings scenario: 17°C) plus drie pH vlakke (huidige voorwaardes: 8.0 : intermediêre afname: 7.7 en uiterste afname: 7.5) in ‘n volle faktorieële eksperiment vir ‘n tydperk van 12 weke. Versuring het nie die oolewing van T. cingulata beïnvloed nie alhoewel die sterftesyfer toegeneem het soos tempertature gestyg het. Na blootstelling aan verwarming vir twee weke waarin meeste T. cingulata nie kon oorleef nie, was dit moontlik om die implikasie van verkoeling en versuring op skulp morfologie te oorweeg. Skulpe was dunner en meer langwerpig na ses weke van blootstelling aan verkoeling, terwyl versuring die skulp omhulsel as sulks verswak het. Na 12 weke,was die dikte van die skulpe in al die verskillende omstandighede dieselfde. Alhoewel afkoeling die skulpe as sulks verander het om meer gerond voor te kom het dit ook die effek van pH met die swakste skulpe wat blootgestel was aan die koue, uiterste versuring beklemtoom. Die waarnemings demonstreer dat T. cingulata meer sensitief is vir veranderings in temperatuur in vergelyking met pH, verwarming het die die sterftesyfer verhoog en afkoeling het die skulp morfologie gekrompomiseer. Koeler water lei tot laer versadigingstoestande van kalsiumkarbonaat en verkoeling verminder metaboliese kapasiteit. Die swakker, dunner en geronde skulpe wat waargeneem was as gevolg van verkoeling, dui waarskynlik op die ondermyning van dop bou-en onderhoud vermoëns van T. cingulata met blootstelling aan kouer toestande. Om ‘n beter begrip te verkry van die kwesbare vermoëns T. cingulata om toekomstige temperature te voorspel was die termiese toleransie sowel as die akklimatiserings kapasiteit van die T. cingulata ook vasgestel. Om die voospelde toekomstige afname in pH in berekening te bring, was die invloed van versuring op T. cingulata se termiese uithouvermoëns en akklimatiseringskapasiteit ook in oorweging gebring. Na blootstelling aan gemiddelde omgewings toestande was ‘n kritieke termiese minimum, CTmin en maksimum, CTmax van -1.3°C en 36.7°C onderskeidelik waargeneem en ‘n optimale temperatuur van Topt 13.7°C. Na warm akklimatisering het , CTmin, CTmax en Topt gestyg terwyl slegs Topt gedaal het in reaksie op koue akklimatisering. CTmax het toegeneem na akklimatisering van versuringstoestande wat daarop dui dat versuring nie die termiesie toleransie of die akklimatiese vermoë van T. cingulata beperk het nie. Dit dui daarop dat T. cingulata die aanpassingsvermoë besit om die stress wat deur versuring veroorsaak word te minimaliseer. Sulke aanpassings het waarskynlik ontwikkel as gevolg van ‘n reaksie op periodieke lae pH vlakke wat met opwelling geassosieer kan word. T. cingulata se veerkragtigheid ten opsigte vanversuring, die vermoë om baie lae temperature te weerstaan asook die elastisiteit van Topt bewys dat T. cingulata afkoeling soos voorpel, goed kan hanteer. Namate T. cingulata oorwegende koel omstandighede ervaar het, was hulle hoë CTmax en warm akklimatiseringsvermoë ‘n onverwagte waarneming, dit demonstreer dat T. cingulata moontlik minder kwesbaar is ten opsigte van verwarming soos voorheen beweer in die eerste hoofstuk. Terwyl die versameling van inligting met betrekking tot die kwesbaarheid van spesies in veranderende omgewingtoestande waardevol is, is dit belangrik om vas te stel wat die uitwerking van hierdie veranderinge teweeg sal bring ten opsigte van die prosesse wat die marine gemeenskappe vorm. Om aan hierdie behoefte te voldoen moes die implikasies van die gelyktydige veranderinge in temperatuur en pH, vir die roofdier interaksie, tussen T. cingulata en sy mossel prooi vasgestel word. Trochia cingulata het, ongeag die temperatuur of die pH, hulle gevestigde voorkeur vir die uitheemse mossel, Semimytilus algosus behou. Na aanleiding van hierdie bevindings is die gevolgtrekking dat dit onwaarskynlik is dat die roofdier-prooi verhouding tussen T. cingulata en sy mosselprooi in die toekoms onder ander omstandighede ontwrig sal word. Semimytilus algosus dra ongeveer 95% by tot die samestelling van die mossel-bed in die studie area, Elandsbaai. Die versameling van hierdie mees winsgewende prooi reflekteer waarskynlik die voorkeur vir hierdie dominante uitheemse mossel. Ten spyte daarvan dat die keuse van prooi nie beiinvloed word deur veranderde omstandighede nie, het verwarming ‘n aansienlik toename in verbuikingstempo gehad, waarskynlik om te kompenseer vir verhoogde energie behoeftees wat met die bedryf van sulke omstandighede geassosieer word. Hierdie bevindings demonstreer hoe die gevolge van veanderde omgewingstoestande vir ‘n enkele spesie nie noodwendig deurgevoer word na hulle direkte biotiese interaksies nie. Om te kan verstaan hoe spesies mag reageer op die geprojekteerde veranderinge in temperatuur en pH, asook die invloed wat hierdie veranderinge op biotiese interaksieses mag hê, moet die verwagte gevolge van veranderende marine omgewings akkuraat bereken word. Die resultaat van hierdie tesis dra by tot die beperkte kennis, waaroor ons tans beskik, met betrekking tot die kwesbaarheid van die Afika marine spesies ten opsigte van die voorspelde veranderende toekomstige omgewings. Nuwe insigte ten opsigte van die kwesbaarheid van T. cingulata, in die lig van toekomstige omstandighede, was bekom deur die sensitiwiteit van ‘n diversiteit van eienskappe op toekomstige omgewingsvoorwaardes te oorweeg. Termiese tolleransie en akklimatiseringskapasiteit van T. cingulata beklemtoon dat termiese spanning verskans mag word deur elastisiteit, terwyl die pH van die skulp buikpotiges byna geen verskil getoon het ten opsigte van verandereinge wat voorspel word teen die einde van die eeu nie. Hierdie veerkragtigheid mag benadeel word deur blootstelling aan episodiese lae pH verskynsels wat dikwels geassosieer word met opwellings. Indien hierdie bevinding grootliks van toepassing is op ander taksa wat endemies tot die omgewing is, kan die gevolgtrekking gemaak word dat hierdie, asook ander opwellings-sisteme, aangebore veerkragtigheid besit ten opsigte van oseaanversuring. Doctorate 2022-01-31T07:11:18Z 2022-04-29T12:50:25Z 2022-01-31T07:11:18Z 2022-03 Thesis http://hdl.handle.net/10019.1/125014 en_ZA Stellenbosch University viii, 96 pages : illustrations, maps application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Trochia cingulata -- Ecology -- South Africa Ocean acidification -- Environmental aspects Seawater -- Carbon dioxide content -- Environmental aspects Climatic changes Ocean-atmosphere interaction Marine ecology -- Effect of temperature on Ocean -- Effect of human beings on UCTD Martin, Nicole Implications of changing ocean temperature and pH for the predatory whelk Trochia cingulata |
| title | Implications of changing ocean temperature and pH for the predatory whelk Trochia cingulata |
| title_full | Implications of changing ocean temperature and pH for the predatory whelk Trochia cingulata |
| title_fullStr | Implications of changing ocean temperature and pH for the predatory whelk Trochia cingulata |
| title_full_unstemmed | Implications of changing ocean temperature and pH for the predatory whelk Trochia cingulata |
| title_short | Implications of changing ocean temperature and pH for the predatory whelk Trochia cingulata |
| title_sort | implications of changing ocean temperature and ph for the predatory whelk trochia cingulata |
| topic | Trochia cingulata -- Ecology -- South Africa Ocean acidification -- Environmental aspects Seawater -- Carbon dioxide content -- Environmental aspects Climatic changes Ocean-atmosphere interaction Marine ecology -- Effect of temperature on Ocean -- Effect of human beings on UCTD |
| url | http://hdl.handle.net/10019.1/125014 |
| work_keys_str_mv | AT martinnicole implicationsofchangingoceantemperatureandphforthepredatorywhelktrochiacingulata |