• Energy Research

Early naturalists suggested that predation intensity increases toward the tropics, affecting fundamental ecological and evolutionary processes by latitude, but empirical support is still limited. Several studies have measured consumption rates across latitude at large scales, with variable results. Moreover, how predation affects prey community composition at such geographic scales remains unknown. Using standardized experiments that spanned 115° of latitude, at 36 nearshore sites along both coasts of the Americas, we found that marine predators have both higher consumption rates and consistently stronger impacts on biomass and species composition of marine invertebrate communities in warmer tropical waters, likely owing to fish predators. Our results provide robust support for a temperature-dependent gradient in interaction strength and have potential implications for how marine ecosystems will respond to ocean warming.

AbstractAmbient UV radiation has substantially increased during the last decades, but its impact on marine benthic communities is hardly known. The aim of this study was to globally compare and quantify how shallow hard‐bottom communities are affected by UV during early succession. Identical field experiments in 10 different coastal regions of both hemispheres produced a consistent but unexpected pattern: (i) UV radiation affected species diversity and community biomass in a very similar manner, (ii) diversity and biomass were reduced to a larger extent by UVA than UVB radiation, (iii) ambient UV levels did not affect the composition of the communities, and (iv) any UV effects disappeared during species succession after 2–3 months. Thus, current levels of UV radiation seem to have small, predictable, and transient effects on shallow marine hard‐bottom communities.

Damage by small herbivores can have disproportionately large effects on the fitness of individual plants if damage is concentrated on valuable tissues or on select individuals within a population. In marine systems, the impact of tissue loss on the growth rates of habitat-forming algae is poorly understood. We quantified the grazing damage by an isopod Amphoroidea typa on two species of large kelps, Lessonia spicata and Macrocystis pyrifera, in temperate Chile to test whether non-lethal grazing damage could reduce kelp growth rates and photosynthetic efficiency. For L. spicata, grazing damage was widespread in the field, unevenly distributed on several spatial scales (among individuals and among tissue types) and negatively correlated with blade growth rates. In field experiments, feeding by A. typa reduced the concentration of photosynthetic pigments and led to large reductions (~80%) in blade growth rates despite limited loss of kelp biomass (0.5% per day). For M. pyrifera, rates of damage in the field were lower and high densities of grazers were unable to reduce growth rates in field experiments. These results demonstrate that even low per capita grazing rates can result in large reductions in the growth of a kelp, due the spatial clustering of herbivores in the field and the selective removal of photosynthetically active tissues. The impacts of small herbivores on plant performance are thus not easily predicted from consumption rates or abundance in the field, and vary with plant species due to variation in their ability to compensate for damage.

Large herbivores such as sea urchins and fish consume a high proportion of benthic primary production and frequently control the biomass of marine macrophytes. By contrast, small mesograzers, including gastropods and peracarid crustaceans, are abundant on seaweeds but have low per capita feeding rates and their impacts on marine macrophytes are difficult to predict. To quantify how mesograzers can affect macrophytes, we examined feeding damage by the herbivorous amphipodsSunamphitoe lessoniophilaandBircennasp., which construct burrows in the stipes of subtidal individuals of the kelpLessonia berteroanain northern-central Chile, southeast Pacific. Infested stipes showed a characteristic sequence of progressive tissue degeneration. The composition of the amphipod assemblages inside the burrows varied between the different stages of infestation of the burrows. Aggregations of grazers within burrows and microhabitat preference of the amphipods result in localized feeding, leading to stipe breakage and loss of substantial algal biomass. The estimated loss of biomass of single stipes varied between 1 and 77%. For the local kelp population, the amphipods caused an estimated loss of biomass of 24–44%. Consequently, small herbivores can cause considerable damage to large kelp species if their feeding activity is concentrated on structurally valuable algal tissue.

Abstract Marine plastic debris floating on the ocean surface is a major environmental problem. However, its distribution in the ocean is poorly mapped, and most of the plastic waste estimated to have entered the ocean from land is unaccounted for. Better understanding of how plastic debris is transported from coastal and marine sources is crucial to quantify and close the global inventory of marine plastics, which in turn represents critical information for mitigation or policy strategies. At the same time, plastic is a unique tracer that provides an opportunity to learn more about the physics and dynamics of our ocean across multiple scales, from the Ekman convergence in basin-scale gyres to individual waves in the surfzone. In this review, we comprehensively discuss what is known about the different processes that govern the transport of floating marine plastic debris in both the open ocean and the coastal zones, based on the published literature and referring to insights from neighbouring fields such as oil spill dispersion, marine safety recovery, plankton connectivity, and others. We discuss how measurements of marine plastics (both in situ and in the laboratory), remote sensing, and numerical simulations can elucidate these processes and their interactions across spatio-temporal scales.

Current knowledge about the performance of floating seaweeds as dispersal vectors comes mostly from mid latitudes (30°-40°), but phylogeographic studies suggest that long-distance dispersal (LDD) is more common at high latitudes (50°-60°). To test this hypothesis, long-term field experiments with floating southern bull kelp Durvillaea antarctica were conducted along a latitudinal gradient (30°S, 37°S and 54°S) in austral winter and summer. Floating time exceeded 200d in winter at the high latitudes but in summer it dropped to 90d, being still higher than at low latitudes (<45d). Biomass variations were due to loss of buoyant fronds. Reproductive activity diminished during long floating times. Physiological changes included mainly a reduction in photosynthetic (Fv/Fm and pigments) rather than in defence variables (phlorotannins and antioxidant activity). The observed long floating persistence and long-term acclimation responses at 54°S support the hypothesis of LDD by kelp rafts at high latitudes.

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.

The persistence of floating seaweeds, which depends on abiotic conditions but also herbivory, had previously been mostly tested in outdoor mesocosm experiments. In order to investigate if the obtained mesocosm results of high seaweed persistence under natural environmental conditions and under grazing pressure can be extrapolated to field situations, we conducted in situ experiments. During two summers (2007 and 2008), Macrocystis pyrifera was tethered (for 14 d) to lines in the presence and absence of the amphipod Peramphithoe femorata at three sites (Iquique, Coquimbo, Calfuco). We hypothesized that grazing damage and seaweed persistence vary among sites due to different abiotic factors. By incubating the sporophytes in mesh bags, we were either able to isolate (grazing) or exclude (control) amphipods. To test for a mesh bag artifact, a set of sporophytes was incubated without mesh bags (natural). Mesh bags used to exclude herbivores influenced sporophyte growth and physiological performance. The chlorophyll a (Chl a) content depended largely on grazers and grazed sporophytes grew less than natural and control sporophytes within the two summers. A decrease in Chl a content was found for the sites with the highest prevailing irradiances and temperatures, suggesting an efficient acclimation to these sea surface conditions. Our field‐based results of sporophyte acclimation ability even under grazing pressure widely align with previous mesocosm results. We conclude that M. pyrifera and other temperate floating seaweeds can function as long‐distance dispersal vectors even with hitchhiking mesoherbivores.