Effects of seawater pCO2 and temperature on calcification and productivity in the coral genus Porites spp. : an exploration of potential interaction mechanisms

This work was supported by the UK Natural Environment Research Council (Award NE/I022973/1) to AAF and NA.Understanding how rising seawater pCO2 and temperatures impact coral aragonite accretion is essential for predicting the future of reef ecosystems. Here we report 2 long term (10-11 month) studies assessing the effects of temperature (25 and 28°C) and both high and low seawater pCO2 (180-750 μatm) on the calcification, photosynthesis and respiration of individual massive Porites spp. genotypes. Calcification rates were highly variable between genotypes but high seawater pCO2 reduced calcification significantly in 4 of 7 genotypes cultured at 25°C but in only 1 of 4 genotypes cultured at 28°C. Increasing seawater temperature enhanced calcification in almost all corals but the magnitude of this effect was seawater pCO2 dependent. The 3°C temperature increase enhanced calcification rate on average by 3% at 180 μatm, by 35% at 260 μatm and by >300% at 750 μatm. The rate increase at high seawater pCO2 exceeds that observed in inorganic aragonites. Responses of gross/net photosynthesis and respiration to temperature and seawater pCO2 varied between genotypes but rates of all these processes were reduced at the higher seawater temperature. Increases in seawater temperature, below the thermal stress threshold, may mitigate against ocean acidification in this coral genus but this moderation is not mediated by an increase in net photosynthesis. The response of coral calcification to temperature cannot be explained by symbiont productivity or by thermodynamic and kinetic influences on aragonite formation.Publisher PDFPeer reviewe

Actualizing the rights of the learner:The role of pedagogical listening

This response to Crystal Kalinec-Craig’s article on the Rights of the Learner (RotL) aims to take up and build on the author’s ideas about how the RotL framework can promote equitable mathematics teaching and learning. Specifically, this response examines how listening is implied in the work of teachers who support young mathematicians as they exercise their rights to be confused, claim mistakes, and say and write what makes sense. In doing so, we seek to highlight some of the opportunities and challenges that can emerge for teachers attempting to support all learners to actualize these rights

Resolving the interactions of ocean acidification and temperature on coral calcification media pH

This work was supported by the UK Natural Environment Research Council (award NE/I022973/1) to AAF and NA.Ocean acidification typically reduces the calcification rates of massive Porites spp. corals but increasing seawater temperatures (below the stress and bleaching threshold) can offset this effect. Here we use δ11B to reconstruct the pH of the calcification media (pHECM) used to precipitate the skeleton in poritid corals cultured over a range of seawater pCO2 and at 25°C and 28°C. Increasing temperature had no significant effect on pHECM at high pCO2 although corals increased their calcification rates. pHECM was reduced at 28°C compared to 25°C at low seawater pCO2, although calcification rates remained constant. Increasing calcification rates could reflect the positive influence of temperature on aragonite precipitation rate, an increase in calcification media saturation state or a change in the concentration/behaviour of the skeletal organic matrix. The 2 temperatures utilized in this study were within the seasonal range at the coral collection site and do not represent a heat stress scenario. Increasing seawater temperatures may promote calcification in some corals in the future but are unlikely to benefit the majority of corals, which are already living close to their maximum thermal tolerance limits.Publisher PDFPeer reviewe

Understanding cold bias : variable response of skeletal Sr/Ca to seawater pCO2 in acclimated massive Porites corals

This work was supported by the UK Natural Environment Research Council (award NE/I022973/1).Coral skeletal Sr/Ca is a palaeothermometer commonly used to produce high resolution seasonal sea surface temperature (SST) records and to investigate the amplitude and frequency of ENSO and interdecadal climate events. The proxy relationship is typically calibrated by matching seasonal SST and skeletal Sr/Ca maxima and minima in modern corals. Applying these calibrations to fossil corals assumes that the temperature sensitivity of skeletal Sr/Ca is conserved, despite substantial changes in seawater carbonate chemistry between the modern and glacial ocean. We present Sr/Ca analyses of 3 genotypes of massive Porites spp. corals (the genus most commonly used for palaeoclimate reconstruction), cultured under seawater pCO2 reflecting modern, future (year 2100) and last glacial maximum (LGM) conditions. Skeletal Sr/Ca is indistinguishable between duplicate colonies of the same genotype cultured under the same conditions, but varies significantly in response to seawater pCO2 in two genotypes of Porites lutea, whilst Porites murrayensis is unaffected. Within P. lutea, the response is not systematic: skeletal Sr/Ca increases significantly (by 2-4%) at high seawater pCO2 relative to modern in both genotypes, and also increases significantly (by 4%) at low seawater pCO2 in one genotype. This magnitude of variation equates to errors in reconstructed SST of up to -5°C.Publisher PDFPeer reviewe

Hearing Silence: Understanding the Complexities of Silence in Democratic Classrooms and Our Responsibility as Teachers and Teacher Educators. A Response to Creating a Democratic Mathematics Classroom: The Interplay of the Rights and Responsibilities of the Learner.

This response to Priya Prasad’s and Crystal Kalinec-Craig’s article on the interplay of the Rights and Responsibilities of the Learner aims to engage with and add on to the authors’ exploration of learners overexercising or opting out of their rights. While grappling with these challenges alongside the authors, our curiosity deepened about a significant and understudied facet of democratic classrooms: silence. Through this response, we consider the multifaceted dimension of silence and how a focus on silence may help us more fully understand the tension between learners’ rights and responsibilities to self, each other, and the collective. Specifically, we engage in dialogue around three questions: If students have the right to speak, listen, and be heard, do they also have a right to be silent, or is that right surpassed by a responsibility to contribute verbally, because classmates will not be able to learn from unexpressed thinking? If a student is silent, how do we distinguish if they are choosing to be silent or are being silenced? What might it look like to think about rights and responsibilities as collective rather than individual

The KD Sr/Ca in cultured massive Porites spp. corals are reduced at low seawater pCO2

This work was supported by the UK Natural Environment Research Council (award NE/I022973/1) to AAF and NA.Coral skeletal Sr/Ca has valuable potential as a proxy of sea surface temperatures (SSTs). However seawater pCO2 can influence skeletal Sr incorporation and Sr/Ca-SST calibrations derived from present day corals may not be applicable to ancient specimens or older sections of modern corals deposited under lower seawater pCO2 than the present day. In this study we analysed skeletal Sr/Ca in multiple genotypes of massive Porites spp. cultured over a range of seawater pCO2 (from 180 to 750 μatm) and temperature (25°C and 28°C). Multiple linear regression analysis indicates that the Sr/Ca aragonite partition coefficient, KD Sr/Ca is inversely related to seawater temperature and positively related to seawater pCO2 (equivalent to changes in skeletal Sr/Ca of 0.046 mmol mol-1 °C-1 and 0.0002 mmol mol–1 µatm-1 respectively). Applying present day Sr/Ca-SST equations to older coral skeletons growing at lower pCO2 could underestimate seawater temperatures. However KD Sr/Ca vary significantly between some coral genotypes cultured at the same seawater pCO2 indicating that other unidentified processes also influence skeletal Sr/Ca and it is unknown how these processes varied when ancient corals were deposited. We do not observe a significant relationship between KD Sr/Ca and coral calcification rate after combining all coral genotypes to allow identification of the correct KD Sr/Ca to apply to coral records.PostprintPeer reviewe

Hearing Silence:Understanding the complexities of silence in democratic classrooms and our responsibilities as teachers and teacher educators. A response to "Creating a Democratic Mathematics Classroom: The Interplay of the Rights and Responsibilities of the Learner."

This response to Priya Prasad’s and Crystal Kalinec-Craig’s article on the interplay of the Rights and Responsibilities of the Learner aims to engage with and add on to the authors’ exploration of learners overexercising or opting out of their rights. While grappling with these challenges alongside the authors, our curiosity deepened about a significant and understudied facet of democratic classrooms: silence. Through this response, we consider the multifaceted dimension of silence and how a focus on silence may help us more fully understand the tension between learners’ rights and responsibilities to self, each other, and the collective. Specifically, we engage in dialogue around three questions: If students have the right to speak, listen, and be heard, do they also have a right to be silent, or is that right surpassed by a responsibility to contribute verbally, because classmates will not be able to learn from unexpressed thinking? If a student is silent, how do we distinguish if they are choosing to be silent or are being silenced? What might it look like to think about rights and responsibilities as collective rather than individual