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The desiccation tolerance of the intertidal seagrass Zostera japonica has been demonstrated in a number of studies; however, the factors limiting expansion of intertidal seagrass species into subtidal zones remain controversial. We transplanted Z. japonica shoots from the intermediate intertidal zone into the plots with and without Z. marina shoots in both the lower intertidal and shallow subtidal zones to investigate the factors controlling Z. japonica growth in these zones. Daily photon flux density at the Z. japonica canopy level was attenuated by both water depth and coexisting Z. marina shoots but more strongly by Z. marina shoots than water depth in the transplant plots. The shoot density and biomass of Z. japonica transplants were significantly lower in transplant plots in the subtidal zone than in the lower intertidal zone. Although the photon flux density was significantly lower in transplant plots containing Z. marina shoots, the growth of Z. japonica transplants did not differ significantly between plots with and those without Z. marina shoots. Z. japonica transplants exhibited photoacclimatory responses such as increased shoot height and chlorophyll content under the lower-light conditions, offsetting the reduced light availability so that no significant differences in transplant growth occurred between plots with and those without Z. marina shoots. As the growth of Z. japonica transplants decreased significantly in the subtidal zone, the interactive effects of environmental stresses associated with tidal inundation and reduced light availability may restrict penetration of the intertidal seagrass Z. japonica into the subtidal zone. The persistence of high photosynthetic performance after air exposure and a regular arrangement of the densely overlapped leaves atop wet sediments may be desiccation tolerance mechanisms for Z. japonica in the intertidal zone.

Caulerpa, a (sub) tropical seaweed, is a notorious taxonomic group and an invasive seaweed worldwide. Similar to several species that have been introduced to benthic habitats through aquariums, Caulerpa sertularioides has also been introduced into Korean aquariums, although it is not native to the region. Thus, it is necessary to evaluate the potential of this species for invading domestic macroalgal habitats. Therefore, an indoor mesocosm experiment was conducted to examine the ecophysiological invasion risk of non-native seaweed C. sertularioides under various climate conditions and exposure to three future climate scenarios: acidification (doubled CO2), warming (5 °C increase from ambient temperature), and greenhouse (GR: combination of acidification and warming); additionally, we compared the invasion risk between future and present climates (control: 20 °C and 470 µatm CO2). High CO2 concentrations and increased temperatures positively affected the photosynthesis and growth of C. sertularioides. Photosynthesis and growth were more synergistically increased under GR conditions than under acidification and warming. Consequently, the performance of this potentially invasive species in the native macroalgal Korean habitat will be higher in the future in coastal environments. Therefore, proper management is required to prevent the geographic expansion of C. sertularioides in the Korean coastal ocean.

Seagrass meadows have a disproportionally high organic carbon (Corg) storage potential within their sediments and thus can play a role in climate change mitigation via their conservation and restoration. However, high spatial heterogeneity is observed in Corg, with wide differences seen globally, regionally, and even locally (within a seagrass meadow). Consequently, it is difficult to determine their contributions to the national remaining carbon dioxide (CO2) budget without introducing a large degree of uncertainty. To address this spatial heterogeneity, we sampled 20 locations across the German Baltic Sea to quantify Corgstocks and sources inZostera marinaseagrass-vegetated and adjacent unvegetated sediments. To predict and integrate the Corginventory in space, we measured the physical (seawater depth, sediment grain size, current velocity at the seafloor, anthropogenic inputs) and biological (seagrass complexity) environment to determine regional and local drivers of Corgvariation. Here we show that seagrass meadows in Germany constitute a significant Corgstock, storing on average 1,920 g C/m2, three times greater than meadows from other parts of the Baltic Sea, and three-fold richer than adjacent unvegetated sediments. Stocks were highly heterogenous; they differed widely between (by 22-fold) and even within (by 1.5 to 31-fold) sites. Regionally, Corgwas controlled by seagrass complexity, fine sediment fraction, and seawater depth. Autochthonous material contributed to 12% of the total Corgin seagrass-vegetated sediments and the remaining 88% originated from allochthonous sources (phytoplankton and macroalgae). However, relics of terrestrial peatland material, deposited approximately 6,000 years BP during the last deglaciation, was an unexpected and significant source of Corg. Collectively, German seagrasses in the Baltic Sea are preventing 2.01 Mt of future CO2emissions. Because Corgis dependent on high seagrass complexity, the richness of this pool may be contingent on seagrass habitat health. Disturbance of this Corgstock could act as a source of CO2emissions. However, the high spatial heterogeneity warrant site-specific investigations to obtain accurate estimates of blue carbon, and a need to consider millennial timescale deposits of Corgbeneath seagrass meadows in Germany and potentially other parts of the southwestern Baltic Sea.

La richesse en espèces est la mesure de la biodiversité la plus couramment utilisée mais controversée dans les études sur les aspects de la stabilité des communautés tels que la composition structurelle ou la productivité. L'ambiguïté apparente des résultats théoriques et expérimentaux peut en partie être due à des lacunes expérimentales et/ou à l'hétérogénéité des échelles et des méthodes dans des études antérieures. Cela a conduit à un appel urgent à des expériences améliorées et plus réalistes. Dans une série d'expériences reproduites à l'échelle mondiale, nous avons déplacé plusieurs centaines de communautés marines de fond dur vers de nouveaux environnements simulant un changement environnemental rapide mais modéré. Par la suite, nous avons mesuré leur taux de changement de composition (restructuration) qui, dans la grande majorité des cas, représentait une convergence compositionnelle vers les communautés locales. La restructuration est motivée par la mortalité des composantes communautaires (espèces originales) et l'établissement de nouvelles espèces dans le contexte environnemental modifié. Le taux de cette restructuration a ensuite été lié à diverses propriétés du système. Nous montrons que la disponibilité du substrat libre est liée négativement tandis que la richesse en taxons est liée positivement à la persistance structurelle (c.-à-d., aucune restructuration ou restructuration lente). Ainsi, face aux changements environnementaux, les communautés riches en taxons conservent leur composition originale plus longtemps que les communautés pauvres en taxons. L'effet de la richesse taxonomique, cependant, interagit avec un autre aspect de la diversité, la richesse fonctionnelle. En effet, la richesse des taxons est positivement liée à la persistance dans les communautés fonctionnellement dépaupérées, mais pas dans les communautés fonctionnellement diverses. L'interaction entre la diversité taxonomique et fonctionnelle en ce qui concerne le comportement des communautés exposées au stress environnemental peut aider à comprendre certaines des conclusions apparemment contrastées de recherches antérieures. La riqueza de especies es la métrica de biodiversidad más utilizada pero controvertida en estudios sobre aspectos de la estabilidad de la comunidad, como la composición estructural o la productividad. La aparente ambigüedad de los hallazgos teóricos y experimentales puede deberse en parte a deficiencias experimentales y/o heterogeneidad de escalas y métodos en estudios anteriores. Esto ha llevado a un llamado urgente para experimentos mejorados y más realistas. En una serie de experimentos replicados a escala global, trasladamos varios cientos de comunidades marinas de fondo duro a nuevos entornos que simulan un cambio ambiental rápido pero moderado. Posteriormente, medimos su tasa de cambio compositivo (reestructuración) que en la gran mayoría de los casos representaba una convergencia compositiva hacia las comunidades locales. La reestructuración está impulsada por la mortalidad de los componentes de la comunidad (especies originales) y el establecimiento de nuevas especies en el contexto ambiental cambiado. La tasa de esta reestructuración se relacionó con varias propiedades del sistema. Mostramos que la disponibilidad de sustrato libre se relaciona negativamente, mientras que la riqueza de taxones se relaciona positivamente con la persistencia estructural (es decir, ninguna o lenta reestructuración). Por lo tanto, cuando se enfrentan al cambio ambiental, las comunidades ricas en taxones conservan su composición original durante más tiempo que las comunidades pobres en taxones. El efecto de la riqueza de taxones, sin embargo, interactúa con otro aspecto de la diversidad, la riqueza funcional. De hecho, la riqueza de taxones se relaciona positivamente con la persistencia en comunidades funcionalmente depauperadas, pero no en comunidades funcionalmente diversas. La interacción entre la diversidad taxonómica y funcional con respecto al comportamiento de las comunidades expuestas al estrés ambiental puede ayudar a comprender algunos de los hallazgos aparentemente contrastantes de investigaciones pasadas. Species richness is the most commonly used but controversial biodiversity metric in studies on aspects of community stability such as structural composition or productivity. The apparent ambiguity of theoretical and experimental findings may in part be due to experimental shortcomings and/or heterogeneity of scales and methods in earlier studies. This has led to an urgent call for improved and more realistic experiments. In a series of experiments replicated at a global scale we translocated several hundred marine hard bottom communities to new environments simulating a rapid but moderate environmental change. Subsequently, we measured their rate of compositional change (re-structuring) which in the great majority of cases represented a compositional convergence towards local communities. Re-structuring is driven by mortality of community components (original species) and establishment of new species in the changed environmental context. The rate of this re-structuring was then related to various system properties. We show that availability of free substratum relates negatively while taxon richness relates positively to structural persistence (i.e., no or slow re-structuring). Thus, when faced with environmental change, taxon-rich communities retain their original composition longer than taxon-poor communities. The effect of taxon richness, however, interacts with another aspect of diversity, functional richness. Indeed, taxon richness relates positively to persistence in functionally depauperate communities, but not in functionally diverse communities. The interaction between taxonomic and functional diversity with regard to the behaviour of communities exposed to environmental stress may help understand some of the seemingly contrasting findings of past research. ثراء الأنواع هو مقياس التنوع البيولوجي الأكثر استخدامًا ولكنه مثير للجدل في الدراسات المتعلقة بجوانب الاستقرار المجتمعي مثل التكوين الهيكلي أو الإنتاجية. قد يرجع الغموض الواضح في النتائج النظرية والتجريبية جزئيًا إلى أوجه القصور التجريبية و/أو عدم تجانس المقاييس والأساليب في الدراسات السابقة. وقد أدى ذلك إلى دعوة عاجلة لإجراء تجارب محسنة وأكثر واقعية. في سلسلة من التجارب المكررة على نطاق عالمي، نقلنا عدة مئات من مجتمعات القاع الصلب البحرية إلى بيئات جديدة تحاكي تغيرًا بيئيًا سريعًا ولكن معتدلًا. بعد ذلك، قمنا بقياس معدل التغيير التركيبي (إعادة الهيكلة) الذي يمثل في الغالبية العظمى من الحالات تقاربًا تركيبيًا تجاه المجتمعات المحلية. تكون إعادة الهيكلة مدفوعة بموت مكونات المجتمع (الأنواع الأصلية) وإنشاء أنواع جديدة في السياق البيئي المتغير. ثم تم ربط معدل إعادة الهيكلة هذه بخصائص النظام المختلفة. نظهر أن توافر الطبقة التحتية الحرة يرتبط سلبًا بينما يرتبط ثراء الأصناف بشكل إيجابي بالثبات الهيكلي (أي عدم وجود إعادة هيكلة أو بطئها). وبالتالي، عندما تواجه المجتمعات الغنية بالضرائب تغيرًا بيئيًا، فإنها تحتفظ بتكوينها الأصلي لفترة أطول من المجتمعات الفقيرة بالضرائب. ومع ذلك، يتفاعل تأثير ثراء الأصناف مع جانب آخر من جوانب التنوع، وهو الثراء الوظيفي. في الواقع، يرتبط ثراء الأصناف بشكل إيجابي بالاستمرار في المجتمعات المحرومة وظيفيًا، ولكن ليس في المجتمعات المتنوعة وظيفيًا. قد يساعد التفاعل بين التنوع التصنيفي والوظيفي فيما يتعلق بسلوك المجتمعات المعرضة للإجهاد البيئي في فهم بعض النتائج المتناقضة على ما يبدو للبحوث السابقة.

Ocean acidification is considered as a crucial stressor for marine communities. In this study, we tested the effects of the IPCC RPC6.0 end-of-century acidification scenario on a natural plankton community in the Gullmar Fjord, Sweden, during a long-term mesocosm experiment from a spring bloom to a mid-summer situation. The focus of this study was on microzooplankton and its interactions with phytoplankton and mesozooplankton. The microzooplankton community was dominated by ciliates, especially small Strombidium sp., with the exception of the last days when heterotrophic dinoflagellates increased in abundance. We did not observe any effects of high CO2 on the community composition and diversity of microzooplankton. While ciliate abundance, biomass and growth rate were not affected by elevated CO2, we observed a positive effect of elevated CO2 on dinoflagellate abundances. Additionally, growth rates of dinoflagellates were significantly higher in the high CO2 treatments. Given the higher Chlorophyll a content measured under high CO2, our results point at mainly indirect effects of CO2 on microzooplankton caused by changes in phytoplankton standing stocks, in this case most likely an increase in small-sized phytoplankton of <8 μm. Overall, the results from the present study covering the most important part of the growing season indicate that coastal microzooplankton communities are rather robust towards realistic acidification scenarios.