Nutrient conditions determine the strength of herbivore-mediated stabilizing feedbacks in barrens.

Abiotic environmental conditions can significantly influence the way species interact. In particular, plant-herbivore interactions can be substantially dependent on temperature and nutrients. The overall product of these relationships is critical for the fate and stability of vegetated ecosystems like marine forests. The last few decades have seen a rapid spread of barrens on temperate rocky reefs mainly as a result of overgrazing. The ecological feedbacks that characterize the barren state involve a different set of interactions than those occurring in vegetated habitats. Reversing these trends requires a proper understanding of the novel feedbacks and the conditions under which they operate. Here, we explored the role of a secondary herbivore in reinforcing the stability of barrens formed by sea urchin overgrazing under different nutrient conditions. Combining comparative and experimental studies in two Mediterranean regions characterized by contrasting nutrient conditions, we assessed: (i) if the creation of barren areas enhances limpet abundance, (ii) the size-specific grazing impact by limpets, and (iii) the ability of limpets alone to maintain barrens. Our results show that urchin overgrazing enhanced limpet abundance. The effects of limpet grazing varied with nutrient conditions, being up to five times more intense under oligotrophic conditions. Limpets were able to maintain barrens in the absence of sea urchins only under low-nutrient conditions, enhancing the stability of the depauperate state. Overall, our study suggests a greater vulnerability of subtidal forests in oligotrophic regions of the Mediterranean and demonstrates the importance of environment conditions in regulating feedbacks mediated by plant-herbivore interactions.

Understanding the depth limit of the seagrass Cymodocea nodosa as a critical transition: Field and modeling evidence.

Changes in light and sediment conditions can sometimes trigger abrupt regime shifts in seagrass meadows resulting in dramatic and unexpected die-offs of seagrass. Light attenuates rapidly with depth, and in seagrass systems with non-linear behaviours, can serve as a sharp boundary beyond which the meadow transitions to bare sand. Determining system behaviour is therefore essential to ensuring resilience is maintained and to prevent stubborn critical ecosystem transitions caused by declines in water quality. Here we combined field and modelling studies to explore the transition from meadow to bare sand in the seagrass Cymodocea nodosa at the limit of its depth distribution in a shallow, light-limited bay. We first describe the relationship between light availability and seagrass density along a depth gradient in an extensive unfragmented meadow (Alfacs bay, NE Spain). We then develop a simple mechanistic model to characterise system behaviour. In the field, we identified sharp decline in shoot density beyond a threshold of ∼1.9 m depth, shifting from a vegetated state to bare sand. The dynamic population model we developed assumes light-dependent growth and an inverse density-dependent mortality due to facilitation between shoots (mortality rate decreases as shoot density increases). The model closely tracked our empirical observations, and both the model and the field data showed signs of bistability. This strongly suggests that the depth limit of C. nodosa is a critical transition driven by photosynthetic light requirements. While the mechanisms still need to be confirmed with experimental evidence, recognizing the non-linear behaviour of C. nodosa meadows is vital not only in improving our understanding of light effects on seagrass dynamics, but also in managing shallow-water meadows. Given the shallow threshold (<2m), light-limited systems may experience significant and recalcitrant meadow retractions with even small changes in sediment and light conditions. Understanding the processes underlying meadow resilience can inform the maintenance and restoration of meadows worldwide.

Exploring coexistence mechanisms in a three-species assemblage.

Interactions among species are essential in shaping ecological communities, although it is not always clear under what conditions they can persist when the number of species involved is higher than two. Here we describe a three-species assemblage involving the seagrass Cymodocea nodosa, the pen shell Pinna nobilis and the herbivore sea urchin Paracentrotus lividus, and we explore the mechanisms allowing its persistence through field observations and manipulative experiments. The abundance of pen shells was higher in seagrass beds than in bare sand, suggesting a recruitment facilitation. The presence of sea urchins, almost exclusively attached or around pen shells, indicated habitat facilitation for sea urchins, which overgrazed the meadow around the pen shells forming seagrass-free halos. Our results suggest that this system persists thanks to: (i) the behavioral reluctance of sea urchins to move far from pen shells, making their impact on seagrass strictly local, (ii) the sparse distribution of pen shells and (iii) the plant's resistance mechanisms to herbivory. Unpacking these mechanisms allows a better understanding of how ecological communities are assembled.

Recovery of a fast-growing seagrass from small-scale mechanical disturbances: Effects of intensity, size and seasonal timing.

We studied the recovery of the fast-growing seagrass Cymodocea nodosa from disturbances of different intensities (shoots removal or the entire plant), plot sizes (from 0.04 to 1 m2) and in different seasons (spring and autumn) in a shallow coastal bay. We monitored recovery over 27 months and measured plant traits at the end. Shoot density and canopy height recovered faster (1 month) when only shoots were removed compared to when the entire plant was removed (10-25 months). Small areas took longer to recover than large ones, probably due to limited light availability or the accumulation of detritus. Plants disturbed in autumn took 9 months longer to recover than those disturbed in spring. After the 27-month, all plant traits were similar to those of control plots, except rhizome biomass, which was lower. Our results suggest that mechanical disturbances might exert a negative effect on the long-term resilience of seagrasses.

Interactive effects of global warming and eutrophication on a fast-growing Mediterranean seagrass.

Coastal ecosystems, such as seagrasses, are subjected to local (e.g. eutrophication) and global (e.g. warming) stressors. While the separate effects of warming and eutrophication on seagrasses are relatively well known, their joint effects remain largely unstudied. In order to fill this gap, and using Cymodocea nodosa as a model species, we assessed the joint effects of warming (three temperatures, 20 °C, 30 °C and 35 °C) with two potential outcomes of eutrophication: (i) increase in nutrients concentration in the water column (30 and 300 µM), and (ii) organic enrichment in the sediment). Our results confirm that temperature in isolation clearly affects plant performance; while plants exposed to 30 °C performed better than control plants, plants exposed to 35 °C showed clear symptoms of deterioration (e.g. decline of photosynthetic capacity, increase of incidence of necrotic tissue). Plants were unaffected by high ammonium concentrations; however, organic enrichment of sediment had deleterious effects on plant function (photosynthesis, growth, demographic balance). Interestingly, these negative effects were exacerbated by increased temperature. Our findings indicate that in addition to the possibility of the persistence of C. nodosa being directly jeopardized by temperature increase, the joint effects of warming and eutrophication may further curtail its survival. This should be taken into consideration in both predictions of climate change consequences and in local planning.

Multilevel assessments reveal spatially scaled landscape patterns driving coastal fish assemblages.

Ecological research, particularly in marine environments, tends to focus on single habitats and often single spatial scales, and thus not account for ecological processes operating at multiple spatial scales. Here we aim to explore how coastal fish assemblages are influenced by landscape patterns integrating multiple spatial scales, to assess the strength of these associations and to identify the most relevant spatial scales at which these associations occur. We use a multiscale approach through multilevel modelling to evaluate the association of landscape metrics with fish assemblages, at three nested spatial scales, in temperate coastal seascapes composed of seagrass meadows, sandy bottoms and rocky reefs. Landscape composition metrics, expressed as cover of vegetated habitats, significantly influenced fish assemblages at small (metres) and intermediate (hundred of metres) scales, while landscape configuration metrics did it at all three scales assessed (from metres to kilometres). Species richness was only influenced by small scale landscape patterns (cover of rocky reefs, positive association), whereas total abundance was associated with landscape patterns measured at small and intermediate scales, encompassing metrics associated with landscape composition (rocky reef cover, positive association), and those indicating landscape heterogeneity (negative association). Similarly, the abundances of different functional groups were influenced by metrics consistent with their mobility and their ecological and behavioural traits at all the spatial scales assessed. These results show how landscape patterns influence coastal fish assemblages, and particularly show that spatially scaled landscape patterns, measured in complex ecological systems as a whole, act simultaneously but not always equally on species assemblages.

Seagrass-bivalve facilitative interactions: Trait-mediated effects along an environmental gradient.

Facilitative interactions are important forces in shaping community structure and function, and understanding how they respond to environmental changes has become an increasing concern in ecology. Lucinid bivalves play a significant role in seagrass meadows, through a mutualism in which the seagrass provides habitat and oxygen via the roots, while the bivalves and their associated bacteria eliminate sulfides from pore water, improving thus plant performance. In this study, we evaluated how this mutualism is modified along a gradient of organic matter content in the sediment, in a coastal bay dominated by Cymodocea nodosa meadows. We used a correlative approach, seeking statistical association between sediment organic matter content, lucinid abundance, and plant traits. Lucinid abundance was higher in vegetated that in bare areas. In vegetated areas, lucinid abundance decreased as organic matter content in the sediment increased, decrease seemingly associated to modification in plant traits, i.e. root abundance and morphology. In organic-rich sediments, roots are less abundant and less branched, reducing the potential habitat for lucinids and suggesting a weakening of the interaction. This finding contributes to our understanding of how facilitative interactions can be modified along human disturbance gradients, and how disturbances can reduce resilience of seagrasses through this modification.

Contrasting effects of ocean warming on different components of plant-herbivore interactions.

There is increasing uncertainty of how marine ecosystems will respond to rising temperatures. While studies have focused on the impacts of warming on individual species, knowledge of how species interactions are likely to respond is scant. The strength of even simple two-species interactions is influenced by several interacting mechanisms, each potentially changing with temperature. We used controlled experiments to assess how plant-herbivore interactions respond to temperature for three structural dominant macrophytes in the Mediterranean and their principal sea urchin herbivore. Increasing temperature differentially influenced plant-specific growth, sea urchin growth and metabolism, consumption rates and herbivore preferences, but not movement behaviour. Evaluating these empirical observations against conceptual models of plant-herbivore performance, it appears likely that while the strength of herbivory may increase for the tested macroalga, for the two dominant seagrasses, the interaction strength may remain relatively unchanged or even weaken as temperatures rise. These results show a clear set of winners and losers in the warming Mediterranean as the complex factors driving species interactions change.

Effects of Copper Exposure on Photosynthesis and Growth of the Seagrass Cymodocea nodosa: An Experimental Assessment.

Seagrasses form some of the most important coastal habitats. They may be negatively affected by trace metal contamination in certain coastal areas. In this study we experimentally assessed selected morphological and physiological traits of the seagrass Cymodocea nodosa, with increasing concentrations of copper (Cu) under controlled laboratory conditions. Short term (21 days) sub-lethal effects such as decreased maximum quantum yield, increased leaf necrosis and decreased shoot growth and shoot recruitment were clearly observed at the highest Cu exposure (5 mg L(-1)), while the effects were weaker at the intermediate concentration (2.5 mg L(-1)) and almost absent at the lowest concentration (1 mg L(-1)), indicating that this species is highly tolerant to copper exposure, at least in the short term. This fact could help to explain its distribution in relatively polluted coastal waters.

Ethological study of manual laterality in naturalistic housed chimpanzees (Pan troglodytes) from the Mona Foundation Sanctuary (Girona, Spain).

During recent years, handedness of nonhuman primates has been the subject of several studies, especially focused on our closest relatives: the chimpanzees. These studies have dealt with both wild and captive chimpanzees, and they seem to point to divergent conclusions, which have been interpreted as a by-product of the human influence in the captive samples. Here we present the results of a study of 10 chimpanzees (Pan troglodytes). In the past, they were trained in circus and marketing tasks (humanised behaviours), until they were confiscated and accepted into the Mona Foundation (in northeast Spain) in 2000, where they live in a semi-naturalistic environment. This study has been performed through observational bouts without systematic human influence, recording the actions carried out by chimpanzees when performing spontaneous activities. Our results indicate that chimpanzees that were under strong human influence in the past show the same trend in handedness as those living in freedom: few significant lateralities were observed among either individuals or tasks. So, laterality may not be influenced by humanisation. However, this conclusion must be taken as preliminary because very few individuals were studied.

Características del discurso escrito de los estudiantes en las clases de ciencias / Characteristics of students’ written discourse in Science classes

La importancia que en la actualidad tienen los estudios acerca del lenguaje para la Educación en Ciencias reside, entre otros aspectos, en sus funciones como vía comunicativa privilegiada en la enseñanza y en el aprendizaje y como mediador y regulador del desarrollo del pensamiento de los estudiantes. Se presentan primero algunos aspectos de la función comunicativa del lenguaje y algunos elementos relacionados con su función semiótica y su función de regulación de procesos centrales en la Educación en Ciencias. Se presentan en seguida resultados parciales del análisis de textos escritos elaborados en el campo conceptual de la respiración por estudiantes del grado llamado “primero de bachillerato” en el sistema educativo español (16-17 años), siendo los objetivos centrales del análisis caracterizar el lenguaje usado por dichos estudiantes, analizar la coherencia discursiva y el tipo de representación lingüística de los textos escritos por ellos e identificar posibles obstáculos lingüísticos para el aprendizaje. Dentro de los principales resultados se encuentran la elaboración de textos con coherencia local únicamente. Asimismo, son frecuentes las secuencias de oraciones relacionadas mediante conectores causales en las que no es clara la función de cada oración dentro del texto completo. Se encontró baja estructuración global de los textos de los estudiantes y una mezcla de diferentes modelos explicativos de la respiración.Palabras clave: Educación en ciencias, ciencias naturales, discurso, lenguaje, enseñanza, aprendizaje.