Opposing indirect effects of domestic herbivores on saltmarsh erosion

Herbivores can sometimes influence the geomorphology of landscapes, particularly in systems dominated by hydrology. Salt marshes deliver globally valuable benefits, including coastal protection, yet they sometimes rapidly erode. Triggers for erosion are often unknown, but livestock grazing is a suspected cause in many regions of the world where agricultural use of saltmarshes is pervasive. To understand the influence of grazing on saltmarsh erosion, we sampled the plant community, soil chemistry and soil mechanical properties along 2–5 creeks in grazed and ungrazed marshes. Erosion was quantified as: (1) the rates of erosion of extracted soil–plant cores in a hydrological flume and (2) the number of erosional break-offs (‘slump blocks’) per creek. We found that domestic herbivores influenced saltmarsh geomorphology via two indirect and opposing pathways: one involving soil mechanical properties and the other mediated by plant traits and bare soil cover, all within a soil physico-chemical environment. The net effect of grazing results in a reduction in saltmarsh lateral erodibility and thus an increase in marsh resilience. Our results highlight the role of herbivores not only as controllers of the flow of energy and materials through the trophic web, but also as modifiers of the abiotic environment. Managers and scientists must remain vigilant to both the obvious direct and the more nuanced indirect pathways, which can influence grazed ecosystems. This study calls for a closer look to the biological side of the equation when assessing biogeomorphic feedbacks and plant–soil–animal interactions

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

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

Este artículo contiene 11 páginas, 6 figuras, 1 tabla.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 plantherbivore 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.The Spanish Ministry of Science and Innovation funded this research (projects CMT2010-22273- C02-01-02 and CMT2013-48027-C03-R) and supported JB (scholarship BES-2011-043630). The Spanish National Research Council supported RA's visitorship (CSIC-201330E062). TS was supported by an Australian Government Endeavour Fellowship. JFP acknowledges financial support from the Welsh Government and Higher Education Funding Council for Wales through the Sȇr Cymru National Research Network for Low Carbon, Energy and Environment. Support to FT was provided by the Ramón y Cajal Programme (RYC-2011-08572).Peer reviewe

Herbivory on freshwater and marine macrophytes: A review and perspective

Until the 1990s, herbivory on aquatic vascular plants was considered to be of minor importance, and the predominant view was that freshwater and marine macrophytes did not take part in the food web: their primary fate was the detritivorous pathway. In the last 25 years, a substantial body of evidence has developed that shows that herbivory is an important factor in the ecology of vascular macrophytes across freshwater and marine habitats. Herbivores remove on average 40-48% of plant biomass in freshwater and marine ecosystems, which is typically 5-10 times greater than reported for terrestrial ecosystems. This may be explained by the lower C:N stoichiometry found in submerged plants. Herbivores affect plant abundance and species composition by grazing and bioturbation and therewith alter the functioning of aquatic ecosystems, including biogeochemical cycling, carbon stocks and primary production, transport of nutrients and propagules across ecosystem boundaries, habitat for other organisms and the level of shoreline protection by macrophyte beds. With ongoing global environmental change, herbivore impacts are predicted to increase. There are pressing needs to improve our management of undesirable herbivore impacts on macrophytes (e.g. leading to an ecosystem collapse), and the conflicts between people associated with the impacts of charismatic mega-herbivores. While simultaneously, the long-term future of maintaining both viable herbivore populations and plant beds should be addressed, as both belong in complete ecosystems and have co-evolved in these long before the increasing influence of man. Better integration of the freshwater, marine, and terrestrial herbivory literatures would greatly benefit future research efforts

Data set: Opposing indirect effects of domestic herbivores on saltmarsh erosion

This file contains all the data used in the manuscript 'Opposing indirect effects of domestic herbivores on saltmarsh erosion', which has been accepted for publication in Ecosystem