Decreased light availability can amplify negative impacts of ocean acidification on calcifying coral reef organisms

Abstract

Coral reef organisms are increasingly and simultaneously affected by global and local stressors such as ocean acidification (OA) and reduced light availability. However, knowledge of the interplay between OA and light availability is scarce. We exposed 2 calcifying coral reef species (the scleractinian coral Acropora millepora and the green alga Halimeda opuntia) to combinations of ambient and increased pCO 2 (427 and 1073 µatm, respectively), and 2 light intensities (35 and 150 µmol photons m −2 s −1 ) for 16 d. We evaluated the individual and combined effects of these 2 stressors on weight increase, calcification rates, O 2 fluxes and chlorophyll a content for the species investigated. Weight increase of A. millepora was significantly reduced by OA (48%) and low light intensity (96%) compared to controls. While OA did not affect coral calcification in the light, it decreased calcification in the dark by 155%, leading to dissolution of the skeleton. H. opuntia weight increase was not affected by OA, but decreased (40%) at low light. OA did not affect algae calcification in the light, but decreased calcification in the dark by 164%, leading to dissolution. Low light significantly reduced gross photosynthesis (56 and 57%), net photosynthesis (62 and 60%) and respiration (43 and 48%) of A. millepora and H. opuntia, respectively. In contrast to A. millepora, H. opuntia significantly increased chlorophyll content by 15% over the course of the experiment. No interactive effects of OA and low light intensity were found on any response variable for either organism. However, A. millepora exhibited additive effects of OA and low light, while H. opuntia was only affected by low light. Thus, this study suggests that negative effects of low light and OA are additive on corals, which may have implications for management of river discharge into coastal coral reefs.

Coral responses to temperature, irradiance and acidification stress: linking physiology to satellite remote sensing

“…"Chlorophyll" is abbreviated as "Chl.". Data sources were: (Reynaud et al 2003;Anthony et al 2008;Marubini et al 2008;Hii et al 2009;Crawley et al 2010;Krief et al 2010;Godinot et al 2011;Houlbrèque et al 2012;Iguchi et al 2012;Kaniewska et al 2012;Ogawa et al 2013;Schoepf et al 2013;Tremblay et al 2013;Enochs et al 2014;Horwitz and Fine 2014;Wall et al 2014;Biscéré et al 2015;Towle et al 2015;Vogel et al 2015;Hoadley et al 2016;Noonan and Fabricius 2016;Baghdasarian et al 2017 (b) The cycle of seawater pCO 2 over a 24 hour period in each experimental combination of light and pCO 2 , colour-coded as Blue: low light, control pCO 2 ; Purple: high light, control pCO 2 ; Orange: low light, elevated pCO 2 ; Red: high light, elevated pCO 2 . Measurements were taken during the time intervals of 2200-2300 hr, 0400-0500 hr, 1000-1100 hr, and 1600-1700 hr.…”

“…Changes in light level received by reefs as a result of changes in cloud cover and turbidity could impact on the coral-dinoflagellate symbiotic relationship (Mumby et al 2001b). Importantly, changes in sea temperature, light levels, and ocean pH are expected to interact, synergistically enhancing the negative effects on corals of the individual stressors (Vogel et al 2015;Prada et al 2017). …”

“…The interactive effect of ocean acidification and light on coral calcification has been debated for some time and demonstrated in some circumstances (Dufault et al 2013;Vogel et al 2015).…”

Efeitos de estressores múltiplos no impacto da acidificação oceânica na biota marinha

“…Embora escassas, investigações sobre os potenciais efeitos da AO associada a estes tipos de estressores antrópicos locais são essenciais para compreender as respostas da biota frente à interação entre mudanças ambientais globais e os impactos antropogênicos locais em ecossistemas costeiros. Os poucos estudos relacionados a esta abordagem demonstram aumento da sensibilidade de organismos marinhos à AO pela ocorrência de estressores tipicamente costeiros (Lewis et al, 2013;Vogel et al, 2015). Lewis et al (2013), por exemplo, indicam maior vulnerabilidade de larvas do poliqueto Pomatoceros lamarckii ao pH reduzido quando expostos a poluição crônica de metais (e.g.…”

“…Adicionalmente, a descarga excessiva de nutrientes nestas regiões, advinda da agricultura e/ou centros urbanos, provoca o aumento da turbidez da água e redução na disponibilidade de luz (Fabricius et al, 2013), além de criar zonas de hipóxia (i.e., baixa concentração de oxigênio) (Rabalais et al, 2002). Espécies de corais tem demonstrado vulnerabilidade à redução de disponibilidade de luz, quando combinada à AO, o que causa efeitos aditivos na redução do crescimento e calcificação (Vogel et al, 2015). Similarmente, Suggett et al (2013) demonstra que os efeitos deletérios da AO sobre a fotossíntese e calcificação dos corais são intensificados em condições de redução de disponibilidade de luz.…”