Matrix composition and patch edges influence plant-herbivore interactions in marine landscapes

38 páginas, 4 figuras, 3 tablas.1. The functioning of ecosystems can be strongly driven by landscape attributes. Despite its importance, however, our understanding of how landscape influences ecosystem function derives mostly from species richness and abundance patterns, with few studies assessing how these relate to actual functional rates. 2. We examined the influence of landscape attributes on the rates of herbivory in seagrass meadows, where herbivory has been identified as a key process structuring these relatively simple systems. The study was conducted in three representative Posidonia oceanica meadows. The principal herbivores in these meadows are the fish Sarpa salpa and the sea urchin Paracentrotus lividus, and we hypothesised that differences in their interaction with landscape attributes would significantly influence herbivory rates. 3. We measured herbivore abundance, herbivory rates, primary production and plant quality (C:N) in seagrass patches embedded either in rock or in sand (matrix attribute), in patches either near or far from a rocky reef (distance attribute) and at the edges and interior of meadows. 4. Our results show that matrix and meadow edges significantly affected the actual levels of herbivory. Herbivory rates were higher in seagrass patches embedded in a rocky matrix compared to those on sand, and herbivory at the centre of seagrass meadows was higher than at the edges. In contrast, patch distance to rocky reefs did not affect herbivory. Neither herbivore abundance nor food quality explained the patterns across different landscape attributes. This suggests that variation in herbivory across the landscape may be related much more to behavioural differences between species in their evaluation of risk, movement, and food preference in relation to the landscape structure. 5. Our results indicate that richness and abundance patterns may mask critical interactions between landscape attributes and species responses, which result in considerable heterogeneity in the way key functional processes like herbivory are distributed across the ecosystem mosaic.The Spanish Ministry of Science and Innovation funded this research (projects CTM2010-22273-C02-01 and 02). The Spanish Ministry of Education supported JP (scholarship AP2008-01601) and the Spanish National Research Council supported AG (scholarship JAEPre_08_00466).Peer reviewe

Matrix composition and patch edges influence plant-herbivore interactions in marine landscapes

38 páginas, 4 figuras, 3 tablas.1. The functioning of ecosystems can be strongly driven by landscape attributes. Despite its importance, however, our understanding of how landscape influences ecosystem function derives mostly from species richness and abundance patterns, with few studies assessing how these relate to actual functional rates. 2. We examined the influence of landscape attributes on the rates of herbivory in seagrass meadows, where herbivory has been identified as a key process structuring these relatively simple systems. The study was conducted in three representative Posidonia oceanica meadows. The principal herbivores in these meadows are the fish Sarpa salpa and the sea urchin Paracentrotus lividus, and we hypothesised that differences in their interaction with landscape attributes would significantly influence herbivory rates. 3. We measured herbivore abundance, herbivory rates, primary production and plant quality (C:N) in seagrass patches embedded either in rock or in sand (matrix attribute), in patches either near or far from a rocky reef (distance attribute) and at the edges and interior of meadows. 4. Our results show that matrix and meadow edges significantly affected the actual levels of herbivory. Herbivory rates were higher in seagrass patches embedded in a rocky matrix compared to those on sand, and herbivory at the centre of seagrass meadows was higher than at the edges. In contrast, patch distance to rocky reefs did not affect herbivory. Neither herbivore abundance nor food quality explained the patterns across different landscape attributes. This suggests that variation in herbivory across the landscape may be related much more to behavioural differences between species in their evaluation of risk, movement, and food preference in relation to the landscape structure. 5. Our results indicate that richness and abundance patterns may mask critical interactions between landscape attributes and species responses, which result in considerable heterogeneity in the way key functional processes like herbivory are distributed across the ecosystem mosaic.The Spanish Ministry of Science and Innovation funded this research (projects CTM2010-22273-C02-01 and 02). The Spanish Ministry of Education supported JP (scholarship AP2008-01601) and the Spanish National Research Council supported AG (scholarship JAEPre_08_00466).Peer reviewe

Robust Stability of Multi-Hop Networks

We propose formal models for analyzing robustness of multi-hop control networks, where data from sensors to controllers and from controllers to actuators is sent through a multi-hop communication network subject to disruptions. When communication disruptions are long, compared to the speed of the control system, we propose to model them as permanent link failures. We show that the complexity of analyzing such failures is NP-hard, and discuss a way to overcome this limitation for practical cases using compositional analysis. For typical packet transmission errors (errors with short time span), we propose a transient error model where links fail for one time slot independently of the past and of other links. We provide sufficient conditions for almost sure stability (stability with probability one) in presence of transient link failures, and give efficient decision procedures. The last part of the paper deals with errors that have random time span. We show that, under some conditions, the permanent failure model can be used as a reliable abstraction

The richness of small pockets:Decapod species peak in small seagrass patches where fish predators are absent

Este artículo contiene 6 páginas, 3 figuras, 3 tablas.Patchy landscapes behave differently from continuous ones. Patch size can influence species behaviour, movement, feeding and predation rates, with flow-on consequences for the diversity of species that inhabit these patches. To understand the importance of patchiness on regional species pools, we measured decapod richness and abundance in several seagrass patches with contrasting sizes. Additionally, we evaluated potential drivers of patch-specific species distribution including resource abundance, predator habitat use and the structural complexity of patches. Our results showed a non-random distribution of decapod species: small patches were clear hotspots of diversity and abundance, particularly of larger-bodied epifaunal decapods. Interestingly, these hotspots were characterized by lower nutrient resources, lower canopy height, but also lower predator use. Small fish invertivores such as Coris julis and several species of Symphodus were mostly restricted to large patches. These resident predators may be critical in clumping predation in large patches with consequences for how biodiversity of their prey is distributed across the seascape. Our results highlight the idea that a habitat mosaic with both large and small seagrass patches would potentially bolster biodiversity because preys and predators may seek refuge in patches of different sizes.This research was funded by the Spanish Ministry of Science and Innovation (CTM2017-86695-C3-3-R) and supported J. B. (scholarship BES-2011-043630).Peer reviewe

The effect of a centenary storm on the long-lived seagrass Posidonia oceanica

We used the disturbance resulting from a once in a 100‐yr storm on the northwest Mediterranean coast to examine the extent of the disturbance, the tolerance thresholds to burial, and the medium‐term response of the long‐lived Posidonia oceanica seagrass. Sediment burial at 12 surveyed areas was particularly strong in shallow meadows, with 23% of their surfaces buried, on average, under more than 10 cm of sediment. In contrast, less than 5% of the meadow was affected at deeper locations. At three sites, we tracked short‐term mortality along a gradient of sediment burial. Survival response to burial was clearly nonlinear, with a significant threshold at 4-5 cm, beyond which shoot mortality was 100%. To track medium‐term potential recovery, we established permanent plots subject to three sediment burial levels (0-5, 5-10, and > 10 cm burial) in four meadows. Where the initial shoot mortality was 100%, we recorded no shoot recovery over the 4‐yr period. In the remaining plots, where some shoots remained alive, we detected either further mortality or shoot recovery of 7% per year on average. Extreme storm events can result in sudden catastrophic losses of seagrass cover in shallow P. oceanica meadows. In the long term and due to the long return time of such storms, the species may still be able to recover despite its low recovery potential. However, added anthropogenic stressors, including climate change, may seriously test the ability of long‐lived shallow seagrass ecosystems to resist high‐intensity natural disturbances and may be critical for its persistence

Detecting the impacts of harbour construction on a seagrass habitat and its subsequent recovery

Managing coastal development requires a set of tools to adequately detect ecosystem and water column degradation, but it also demands tools to detect any post-disturbance improvement. Structural seagrass indicators (such as shoot density or cover) are often used to detect or assess disturbances, but while they may be very sensitive to the impact itself, it is unclear if those indicators on their own can effectively reflect recovery at time scales relevant to managers. We used the construction of a harbour affecting a nearby Posidonia oceanica seagrass community to test the ability of a set of indicators (structural and others) to detect alterations and to evaluate their sensitivity to recovery of environmental quality after harbour construction was complete and the disturbance ceased. We used a Beyond Before After Control Impact (BBACI) design to evaluate effects on one impacted and three control meadows where we used structural, morphological, community and physiological indicators (26 in total) to asses disturbance impacts. Additionally, we measured some of the potential environmental factors that could be altered during and after the construction of the harbour and are critical to the survival of the seagrass meadow (light, sediment organic matter, sediment accrual). Harbour construction caused a clear increase in sediment organic matter and in sediment deposition rates, especially fine sand. Light availability was also reduced due to suspended sediments. Sediment and light conditions returned to normal levels 5 and 15 months after the construction began. As expected, seagrass structural indicators responded unequivocally to these environmental changes, with clear reductions in shoot density. Additionally, reduced light conditions quickly resulted in a decline in carbohydrate content in affected meadows. Unexpectedly, we also recorded a significant increase in metal content in plant tissues. No response was detected in the physiological indicators related to eutrophication (e.g. N and P content in tissues) and in morphological (shoot biomass) and community (epiphyte biomass) indicators. More than three years after the completion of the harbour, structural indicators did not show any sign of recovery. In contrast, physiological indicators, mainly heavy metal and carbohydrates content, were much better in detecting the improvement of the environmental conditions over the fairly short period of this study. These results indicate that while structural indicators are critical to evaluate the immediate effect of disturbances and the recovery on impacted systems, specific physiological indicators may be much better suited to determining the timing of environmental quality recovery. The design of impact and monitoring protocols in the wake of coastal developmental projects need to consider the differential effectiveness and time-response of measured indicators carefully

Landscape fragmentation and resilience in seagrass meadows / Fragmentación del paisaje y resiliencia en praderas de fanerógamas marinas

[spa] En general, la tesis pretende acercarse a los ecosistemas de fanerógamas marinas desde el punto de vista del paisaje, con el objetivo final de incrementar el conocimiento acerca de los procesos que generan los patrones a gran escala espacial, y entender como estos patrones interactúan con otros procesos funcionales de las fanerógamas marinas. Específicamente, a lo largo de la tesis nos hemos centrado en: (i) entender las dinámicas de la fragmentación del hábitat (capítulo 1), (ii) como esta fragmentación interactúa con otras perturbaciones, como el hidrodinamismo, la sedimentación y el herbivorismo (capítulos 2 y 3), y (iii) cual pueden ser las consecuencias de dicha fragmentación en la biodiversidad y los procesos del ecosistema (capítulo 4). Además de estos cuatro capítulos, se incluye un capítulo final (capítulo 5) que relaciona el estado de las praderas de fanerógamas marinas con las características fotosintéticas. Todos los capítulos se han redactado partiendo desde observaciones de campo (cap. 1, 2, 4 y 5) o experimentos manipulativos (cap. 3), y plantean tanto preguntas individuales como hipótesis generales en el marco de las dinámicas de fragmentación del hábitat a escala de manchas y de paisaje.[eng] Overall, this thesis is an attempt at approaching seagrass ecosystems from a landscape perspective, with the aim of increasing knowledge about the processes generating patterns at large spatial scales, and understanding how these patterns interact with other drivers of seagrass function. Specifically, we focus on (i) understanding the dynamics of habitat fragmentation (Chapter 1), (ii) how this fragmentation interact with other seagrass disturbances, such as hydrodynamism, sedimentation and herbivory (Chapter 2 and 3) and which are the consequences of such fragmentation to biodiversity and ecosystem processes (Chapter 4). The thesis is structured in five chapters, the first four focus on the different objectives outlined above. Additionally we have included another chapter (Chapter 5) that relates seagrass quality with photosynthetic performances. All chapters originated from field observations (Chapter 1, 2, 4 and 5) or experimental manipulative experiments (Chapter 3) that posed individual questions and general hypothesis within the frame of the dynamics of habitat fragmentation at patch-size and landscape scale. For the two first chapters, we take advantage of extreme storm events and in one of them we exploit long-term data series (15-20 years). Thus, we will first aim to integrate the different results related to the effects of habitat fragmentation and the interactions with external and internal disturbances. In this thesis we have observed how storms can be an important agent of fragmentation in shallow Posidonia oceanica meadows. One of the main causes is the limited capacity of this slowgrowing seagrass species to resist and recover from extreme storm events. This has been observed either by the response of the plant to a specific storm event (Chapter 1) than by the observed responses to storms in a long-term series (Chapter 2). Once the process of fragmentation was identified, we attempted to evaluate the resilience of the meadows to external and internal disturbances. In the case of the external disturbances we compared the storms effects on continuous and fragmented meadows in two congeneric species of Posidonia. The effect was much stronger in the fragmented meadows pointing out that fragmentation makes seagrass meadows less resilient and that the Mediterranean P. oceanica is particularly vulnerable due to its limited recovery potential. Evident limitation in this study was the low level of replication. This was not due to a design error, but to the rarity of the occurrence of extreme storm events and the limited availability of long data series. In spite of this, our results are consistent in stressing that fragmentation can be a critical factor for shallow seagrass maintenance. When we add to this disturbance the natural processes that ecosystems are facing, such as herbivory, fragmentation becomes even more critical as both factors are interacting in a combined way (Chapter 3). Consequently as both factors (fragmentation and herbivory) affect additively the same processes small fragmented patches tend to have lowest canopy height (i.e. less structure), less nutrient retention and lowest primary production. Interestingly, the influence of fragmentation on biodiversity and abundance of low mobility species, which was tested in chapter 4, showed opposite effects than expected. Specifically small fragments presented a much higher biodiversity of decapods, used as a model group, although it is not fully generalizable as the observed effect was site-specific. The apparently contradictory result could be in part explained by the low habitat use by predators observed in these small fragments. This final result points out the importance that small seagrass patches might have, as potential hotspots, for the maintenance of biodiversity. Finally we discuss the potential scenario that P. oceanica fragmented meadows might face under climate change. One of the clearest effects of climate change in several regions is that atmospheric and ocean regional conditions are expected to be modified, increasing the frequency of high-intensity cyclonic formations that can even strengthen the role of disturbances on these systems

Combined effects of fragmentation and herbivory on Posidonia oceanica seagrass ecosystems

9 páginas,3 figuras, 1 tabla.1. Fragmentation is a major agent for seagrass meadow decline, yet little is known about how it interacts with processes like herbivory, an important functional driver of seagrass meadows. The interaction with external stressors like fragmentation could exacerbate the effects of internal ecosystem drivers like herbivory, with distinct implications for ecosystem management. 2. We used manipulative field experiments to assess these interactive effects in two Posidonia oceanica seagrass meadows. We monitored replicated plots in small and large patches in two meadows suffering fragmentation with and without herbivores (using exclusion cages) to test whether fragment size and herbivory could act together to alter ecosystem functioning. We measured changes in defoliation rates, primary production, canopy height and nutrient content in all plots after 4 months of herbivore exclusion. 3. Our results show that herbivores increased defoliation rates resulting in reduced primary production, nutrient content and canopy structure (canopy height). Patch size (fragment) on its own also reduced primary production, nutrient content and canopy structure. We also observed significant additive interactions between herbivores and fragmentation on canopy structure and production responses. In addition, small patches showed nutrient limitation but were able to accumulate more carbohydrate reserves, probably due to a higher light availability. This may explain why small patches can persist under significant herbivore pressure. 4. Synthesis. While fragmentation has already been identified as an important external agent of seagrass decline, the combination of fragmentation and herbivory can seriously exacerbate structural losses and affect primary production, profoundly compromising the role of seagrasses as habitatforming ecosystems. These interactions between external stressors and internal drivers may result in large unexpected consequences that may flow on to the rest of the ecosystem.This research has been funded by the Spanish Ministry of Science and Innovation (projects CTM2010-22273- C02-01 and 02). The Consejo Superior de Investigaciones Científicas (CSIC) supported A.G. (scholarship JAEPre_08_00466) and the Spanish Ministry of Education supported J.P. (scholarship AP2008-01601).Peer reviewe

The effect of a centenary storm on the long-lived seagrass Posidonia oceanica

9 páginas, 3 tablas, 4 figuras.We used the disturbance resulting from a once in a 100-yr storm on the northwest Mediterranean coast to examine the extent of the disturbance, the tolerance thresholds to burial, and the medium-term response of the long-lived Posidonia oceanica seagrass. Sediment burial at 12 surveyed areas was particularly strong in shallow meadows, with 23% of their surfaces buried, on average, under more than 10 cm of sediment. In contrast, less than 5% of the meadow was affected at deeper locations. At three sites, we tracked short-term mortality along a gradient of sediment burial. Survival response to burial was clearly nonlinear, with a significant threshold at 4–5 cm, beyond which shoot mortality was 100%. To track medium-term potential recovery, we established permanent plots subject to three sediment burial levels (0–5, 5–10, and . 10 cm burial) in four meadows. Where the initial shoot mortality was 100%, we recorded no shoot recovery over the 4-yr period. In the remaining plots, where some shoots remained alive, we detected either further mortality or shoot recovery of 7% per year on average. Extreme storm events can result in sudden catastrophic losses of seagrass cover in shallow P. oceanica meadows. In the long term and due to the long return time of such storms, the species may still be able to recover despite its low recovery potential. However, added anthropogenic stressors, including climate change, may seriously test the ability of long-lived shallow seagrass ecosystems to resist high-intensity natural disturbances and may be critical for its persistence.This research was funded by the Spanish Ministry of Science and Innovation (projects CTM2010-22273-C02-01 and 02) and from an Intramural Project from Consejo Superior de Investigaciones Cientı´ficas (CSIC, 201330E062). The CSIC supported AG (scholarship JAEPre_08_00466), the Spanish Ministry of Education supported J.P. (scholarship AP2008-01601), and the Catalan Government supported G.R. (scholarship GR 080126).Peer reviewe

Detecting the impacts of harbour construction on a seagrass habitat and its subsequent recovery

9 páginas, 6 figuras, 2 tablas.Managing coastal development requires a set of tools to adequately detect ecosystem and water columndegradation, but it also demands tools to detect any post-disturbance improvement. Structural seagrassindicators (such as shoot density or cover) are often used to detect or assess disturbances, but while theymay be very sensitive to the impact itself, it is unclear if those indicators on their own can effectivelyreflect recovery at time scales relevant to managers. We used the construction of a harbour affecting anearby Posidonia oceanica seagrass community to test the ability of a set of indicators (structural andothers) to detect alterations and to evaluate their sensitivity to recovery of environmental quality afterharbour construction was complete and the disturbance ceased. We used a Beyond Before After ControlImpact (BBACI) design to evaluate effects on one impacted and three control meadows where we usedstructural, morphological, community and physiological indicators (26 in total) to asses disturbanceimpacts. Additionally, we measured some of the potential environmental factors that could be alteredduring and after the construction of the harbour and are critical to the survival of the seagrass meadow(light, sediment organic matter, sediment accrual).Harbour construction caused a clear increase in sediment organic matter and in sediment depositionrates, especially fine sand. Light availability was also reduced due to suspended sediments. Sediment andlight conditions returned to normal levels 5 and 15 months after the construction began. As expected,seagrass structural indicators responded unequivocally to these environmental changes, with clear reduc-tions in shoot density. Additionally, reduced light conditions quickly resulted in a decline in carbohydratecontent in affected meadows. Unexpectedly, we also recorded a significant increase in metal content inplant tissues. No response was detected in the physiological indicators related to eutrophication (e.g.N and P content in tissues) and in morphological (shoot biomass) and community (epiphyte biomass)indicators. More than three years after the completion of the harbour, structural indicators did not showany sign of recovery. In contrast, physiological indicators, mainly heavy metal and carbohydrates content,were much better in detecting the improvement of the environmental conditions over the fairly shortperiod of this study. These results indicate that while structural indicators are critical to evaluate theimmediate effect of disturbances and the recovery on impacted systems, specific physiological indicatorsmay be much better suited to determining the timing of environmental quality recovery. The design ofimpact and monitoring protocols in the wake of coastal developmental projects need to consider thedifferential effectiveness and time–response of measured indicators carefully.This study was performed with the financial support of theAgència Catalana de l’Aigua CV04000002 (Departament de MediAmbient i Habitatge, Generalitat de Catalunya), which stronglyencouraged our work and of WISER (Water bodies in Europe: Inte-grative Systems to assess Ecological status and Recovery) fundedunder the 7th EU Framework Programme, Theme 6 (Environmentincluding Climate Change), Contract No.: 226273). This research hasbeen partly funded by the Spanish Ministry of Science and Innova-tion (projects CTM2010-22273-C02-01 and -02). Agència de Gestiód’Ajuts Universitaris i de Recerca of Generalitat de Catalunya sup-ported G.R. (Scholarship FI-DGR 2012). Initial data of the descriptivevariables of the Harbor meadow were collected in collaborationwith Xatrac and S’Agulla SCUBA divers funded through the project2009 ACOM 00049 of the “Generalitat de Catalunya”.Peer reviewe