Coral reef resilience differs among islands within the Gulf of Mannar, southeast India, following successive coral bleaching events

We used a 12-yr data set of benthic cover (2005�2017), spanning two bleaching events, to assess changes in benthic cover and coral community composition along 21 islands within Gulf of Mannar (GoM), southeast India. Overall, between 2005 and 2017 reefs had a simultaneous decrease in relative coral cover (avg. = ? 36%) and increase in algal cover (avg. = + 45%). Changes in benthic cover were not consistent among islands, ranging from ? 34 to + 5% for coral cover and from ? 0.3 to + 50% for algae. There was a spatial gradient in coral mortality, which increased among islands from west to east. However, there was a disconnect between coral loss and subsequent increases in algae. Algal cover increased more on islands in west GoM where coral loss was minimal. Environmental co-factors (coral cover, percent bleaching, degree heating weeks, fish densities, Chl-a, pollution) explained > 50% of the benthic cover responses to successive bleaching. Coral survival was favored on islands with higher fish densities and chlorophyll-a levels, and increases in algal cover were associated with higher measures of pollution from terrestrial runoff. Coral morphotypes differed in their response following successive bleaching resulting in changes in the relative abundance of different coral morphotypes. Existing climate projections (RCP8.5) indicate a 22-yr gap in the onset of annual severe bleaching (ASB) for reefs in the east versus west GoM, and ASB was ameliorated for all reefs under the RCP4.5 projections. There is limited knowledge of the resilience of GoM reefs, and this study identifies coral morphotypes and reefs that are most likely to recover or decline from successive bleaching, in the context of forecasts of the frequency of future bleaching events in GoM. � 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.Climate projections for GoM were done under the Third NATCOM (National Communication) to the United Nations Framework Convention on Climate Change (UNFCCC) project of Ministry of Environment, Forest and Climate Change (MoEF & CC), Government of India�(GOI). The authors are thankful to the MoEF & CC,�GOI; Tamil Nadu Forest Department (TNFD), Government of Tamil Nadu (GOTN); Department of Environment, GOTN; Gulf of Mannar Biosphere Reserve Trust, GOTN; Coral Reef Degradation in Indian Ocean, Sweden; and V.O.Chidambaranar Port Trust (VOCPT), GOI for funding support. Thanks are also due to Chief Wildlife Warden, TNFD; Wildlife Warden, Gulf of Mannar Marine National Park (GOMMNP), GOTN; and Chairman, VOCPT, GOI, for research permissions to carry out coral reef surveys and monitoring within the Marine National Park and harbour area and to Suganthi Devadason Marine Research Institute for logistical support.�Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.Scopu

Decoupling photo- and thermoperiod by projected climate change perturbs bud development, dormancy establishment and vernalization in the model tree Populus

Abstract Background The performance and survival of deciduous trees depends on their innate ability to anticipate seasonal change. A key event is the timely production of short photoperiod-induced terminal and axillary buds that are dormant and freezing-tolerant. Some observations suggest that low temperature contributes to terminal bud initiation and dormancy. This is puzzling because low temperatures in the chilling range universally release dormancy. It also raises the broader question if the projected climate instabilities, as well as the northward migration of trees, will affect winter preparations and survival of trees. Results To gauge the response capacity of trees, we exposed juvenile hybrid aspens to a 10-h short photoperiod in combination with different day/night temperature regimes: high (24/24 °C), moderate (18/18 °C), moderate-low (18/12 °C) and low (12/12 °C), and analysed bud development, dormancy establishment, and marker gene expression. We found that low temperature during the bud formation period (pre-dormancy) upregulated dormancy-release genes of the gibberellin (GA) pathway, including the key GA biosynthesis genes GA20oxidase and GA3oxidase, the GA-receptor gene GID1, as well as GA-inducible enzymes of the 1,3-β-glucanase family that degrade callose at plasmodesmal Dormancy Sphincter Complexes. Simultaneously, this pre-dormancy low temperature perturbed the expression of flowering pathway genes, including CO, FT, CENL1, AGL14, LFY and AP1. In brief, pre-dormancy low temperature compromised bud development, dormancy establishment, and potentially vernalization. On the other hand, a high pre-dormancy temperature prevented dormancy establishment and resulted in flushing. Conclusions The results show that pre-dormancy low temperature represents a form of chilling that antagonizes dormancy establishment. Combined with available field data, this indicates that natural Populus ecotypes have evolved to avoid the adverse effects of high and low temperatures by initiating and completing dormant buds within an approximate temperature-window of 24-12 °C. Global warming and erratic temperature patterns outside this range can therefore endanger the successful propagation of deciduous perennials