Persistence of Corals in Marginal Habitats: the Role of the Environment, and Symbiont Diversity and Ecophysiology

<p>Many corals live in marginal habitats, close to their survival thresholds of water temperature, light penetration and aragonite saturation. Living under these highly variable and extreme conditions is likely facilitated by specific physiological adaptations and/or the presence of unique species of coral and their symbionts but data on these factors are limited. The specific objectives of the study were to: (1) examine the diversity and distribution patterns of corals in marginal environments, (2) investigate the diversity, distribution patterns and host specificity of symbionts in corals in marginal environments, (3) assess the influence of environmental variables on host and symbiont distribution in marginal environments, in comparison to 'optimal' environments, and (4) examine the physiological responses to changing environmental conditions and stress of corals and their symbionts in marginal environments. Surveys of coral community patterns were conducted at the Kermadec Islands (KI), New Zealand, and Palmyra Atoll, USA, with local scale environmental parameters (i.e. wave exposure and sedimentation) found to control the diversity and distribution of the coral communities. Symbiodinium types were identified to subcladal level in a range of coral species at each of the survey sites, using ITS2-DGGE. A high diversity of C type symbionts (19 types in 13 host genera), and reduced host specificity was observed at the high latitude site of Lord Howe Island (LHI), Australia, with similarly high diversity at the KI (10 types in 9 genera). Thirteen novel clade C types were identified in corals at LHI, with two of these types also present in hosts at the KI. The reduced host specificity of symbionts at LHI, compared to tropical sites, implies that the evolution of novel holobionts may be an important mechanism whereby corals can cope with variable and stressful conditions. Further, physiological assessment of the novel LHI symbionts led to the suggestion that Symbiodinium at LHI may be specialised for cooler and more variable temperatures, so contributing to the success of corals at this marginal location. In contrast, a low diversity of generalist symbionts (C and D types) were uncovered at the equatorial site of Palmyra Atoll (10 types in 13 genera), attributed to the stressful environmental regime resulting in a reduced population of stresstolerant symbionts. The variation in environmental parameters, particularly sedimentation, around Palmyra Atoll has led to diversification of coral communities, however this environmental variation has not affected the symbiont communities. While it has been suggested that marginal coral communities might be better adapted for survival in an environment modified by global climate change, the local scale environmental factors are also important drivers of both coral and symbiont distributions, and should be considered when making predictions for the future. Further, assessment of the physiological tolerance ranges of both the multiple, novel symbionts at high latitudes, and the few, potentially stress-tolerant symbionts at Palmyra should be conducted, to help determine whether they have the ability to adjust to new environmental conditions.</p>

Persistence of Corals in Marginal Habitats: the Role of the Environment, and Symbiont Diversity and Ecophysiology

<p>Many corals live in marginal habitats, close to their survival thresholds of water temperature, light penetration and aragonite saturation. Living under these highly variable and extreme conditions is likely facilitated by specific physiological adaptations and/or the presence of unique species of coral and their symbionts but data on these factors are limited. The specific objectives of the study were to: (1) examine the diversity and distribution patterns of corals in marginal environments, (2) investigate the diversity, distribution patterns and host specificity of symbionts in corals in marginal environments, (3) assess the influence of environmental variables on host and symbiont distribution in marginal environments, in comparison to 'optimal' environments, and (4) examine the physiological responses to changing environmental conditions and stress of corals and their symbionts in marginal environments. Surveys of coral community patterns were conducted at the Kermadec Islands (KI), New Zealand, and Palmyra Atoll, USA, with local scale environmental parameters (i.e. wave exposure and sedimentation) found to control the diversity and distribution of the coral communities. Symbiodinium types were identified to subcladal level in a range of coral species at each of the survey sites, using ITS2-DGGE. A high diversity of C type symbionts (19 types in 13 host genera), and reduced host specificity was observed at the high latitude site of Lord Howe Island (LHI), Australia, with similarly high diversity at the KI (10 types in 9 genera). Thirteen novel clade C types were identified in corals at LHI, with two of these types also present in hosts at the KI. The reduced host specificity of symbionts at LHI, compared to tropical sites, implies that the evolution of novel holobionts may be an important mechanism whereby corals can cope with variable and stressful conditions. Further, physiological assessment of the novel LHI symbionts led to the suggestion that Symbiodinium at LHI may be specialised for cooler and more variable temperatures, so contributing to the success of corals at this marginal location. In contrast, a low diversity of generalist symbionts (C and D types) were uncovered at the equatorial site of Palmyra Atoll (10 types in 13 genera), attributed to the stressful environmental regime resulting in a reduced population of stresstolerant symbionts. The variation in environmental parameters, particularly sedimentation, around Palmyra Atoll has led to diversification of coral communities, however this environmental variation has not affected the symbiont communities. While it has been suggested that marginal coral communities might be better adapted for survival in an environment modified by global climate change, the local scale environmental factors are also important drivers of both coral and symbiont distributions, and should be considered when making predictions for the future. Further, assessment of the physiological tolerance ranges of both the multiple, novel symbionts at high latitudes, and the few, potentially stress-tolerant symbionts at Palmyra should be conducted, to help determine whether they have the ability to adjust to new environmental conditions.</p>

The social life of mangroves: Neoliberal development and mangrove conservation in the changing landscape of Kutch

This article explores the convergence of neoliberal development and mangrove conservation in marginal environments, which are becoming the new resource frontiers. We focus on Kutch, a border district in western India and highlight how the contested trajectories of accelerated and aggressive industrialisation and its convergence with state and corporate-led conservation programmes are shaping the social life of mangroves on the Kutchi coast. We focus on the discourses, practices and politics of value-making and un-making that constitute the multiple modalities of repair as mangroves are depleted and securitised simultaneously. Although these trends are augmenting capitalist accumulation on the coast, they are also giving rise to new kinds of alliances that seek to challenge the logic and practice of repair by highlighting the synergistic relationship of coastal communities with their mangrove habitats.

Tornadoes in Hurricane Harvey

Tropical cyclone tornadoes pose a unique challenge to warning forecasters given their often marginal environments and radar attributes. In late August 2017 Hurricane Harvey made landfall on the Texas coast and produced 52 tornadoes over a record-breaking seven consecutive days. To improve warning efforts, this case study of Harvey’s tornadoes includes an event overview as well as a comparison of near-cell environments and radar attributes between tornadic and nontornadic warned cells. Our results suggest that significant differences existed in both the near-cell environments and radar attributes, particularly rotational velocity, between tornadic cells and false alarms. For many environmental variables and radar attributes, differences were enhanced when only tornadoes associated with a tornado debris signature were considered. Our results highlight the potential of improving warning skill further and reducing false alarms by increasing rotational velocity warning thresholds, refining the use of near-storm environment information, and focusing warning efforts on cells likely to produce the most impactful tornadoes.

Extreme reefs: Analyses of modern bryostromatolite ("bryolith") reefs from marginal environments in the Netherlands with comparisons to ancient analogues

&lt;p&gt;Marginal environments sometimes serve as natural time machines, replicating conditions of ancient environments and thus inducing similar adaptations and symbioses. Few environments are more marginal than the brackish, arsenic and titanium rich, and periodically euxinic ponds found in the Zeeland (Netherlands). These ponds contain layered, stationary bioherms of alternating bryozoans and microbialites (bryostromatolites); similar structures are known from the Late Miocene of the Paratethys and the isotopic excursions in the Silurian as well as recent hypersaline lagoons in Australia. Critical study of the modern bryostromatolites will help paleontologists understand the conditions under which bryostromatolites formed in the past.&lt;/p&gt;&lt;p&gt;This study applied modern methods to analyze the microstructures and minerology of bryostromatolites from the Netherlands. These bryostromatolites contained alternations of &lt;em&gt;Einhornia crustulenta&lt;/em&gt; bryozoans and gypsum-cemented microbes. Bryostromatolites formed in distinct stages, alternating between a phase of bryozoan layers and a phase where microbes and cements grew in tandem over the dead bryozoans; this microbial phase likely coincides with temporary anoxia/euxinia. The microbes, tentatively identified as cyanobacteria, showed a thrombolitic texture cemented with gypsum. This gypsum was deposited while the microbes were alive, suggesting they were alive during the euxinic phases and participating in sulfide-based photosynthesis. The bryoliths were otherwise poor in fauna, containing only a few species of mollusks, arthropods, polychaetes, and diatoms. All of these factors highlight the extreme environment under which modern and possibly ancient bryoliths formed.&lt;/p&gt;