The onshore deposition of macroalgal and macrophyte wrack provides a potentially significant marine subsidy to intertidal and supratidal herbivore and decomposer communities. Based on the study of daily input loads to beaches, we estimated summer wrack deposition of up to 140 Mg (dry mass)/km shoreline in Barkley Sound, British Columbia. However, input rates were highly variable depending on beach type, nearshore hydrodynamics, and buoyancy characteristics of the wrack. Cobble beaches retained ∼10 times and 30 times more wrack than did gravel and sand beaches, respectively. Cobble and gravel beaches also differed in species composition of new (fresh) wrack input, with Macrocystis integrifolia being characteristic for the former and Nereocystis luetkeana for the latter, which we attribute to buoyancy characteristics of the floating debris. On sand beaches, Phyllospadix spp. and Enteromorpha spp. were the dominant wrack species. Species composition of freshly deposited wrack also depended on wave exposure, but predictability based on the species pool within a beach's catchment was restricted. Drift lines of aging wrack differed from freshly deposited wrack in species composition, probably due to wrack decomposition that results in fluxes of nutrients and energy between the adjacent marine and terrestrial habitats. We hold that the characteristics of a given beach, e.g., substratum and wave exposure, and their effects on wrack input, will have important ecological and biogeochemical implications for the marine–terrestrial ecotone.

The fate of subtidally drifting macrophytal detritus after its deposition ashore was studied based on short-term mass loss effects and species composition of beach-cast detritus. Different species of macroalgae and seagrass varied in both physical and microbial decay, as well as faunal decomposition rates. Their preferred status as food for detritivorous amphipods also varied. Thus, beach-cast detritus changed in species composition during detritus aging. Estimated turnover rates, based on daily input rates and mass loss rates, ranged from <1 d for Nereocystis luetkeana, Macrocystis integrifolia and Ulva spp. to roughly 30 d for Fucus spp. and Phyllospadix spp. Thus, the dynamics of nutrient fluxes within the marine-terrestrial ecotone depends not only on the spatial distribution and amount of beach-cast detritus, but also on its species composition.KEY WORDS: Marine-terrestrial ecotone · Beach-cast wrack · Decomposition · Macroalgae · Seagrass · Talitrid amphipods Resale or republication not permitted without written consent of the publisher

Ecological interactions often vary geographically. Work in salt marshes on the Atlantic Coast of the United States has documented community-wide latitudinal gradients in plant palatability and plant traits that may be driven in part by greater herbivore pressure at low latitudes. To determine if similar patterns exist elsewhere, we studied six taxa of saltmarsh plants (Atriplex , Juncus , Limonium , Salicornia , Spartina and Suaeda ) at European sites at high (Germany and the Netherlands) and low (Portugal and Spain) latitudes. We conducted feeding assays using both native and non-native consumers, and documented patterns of herbivore damage in the field. As in the United States, high-latitude plants tended to be more palatable than low-latitude plants when offered to consumers in paired feeding assays in the laboratory, although assays with grasshopper consumers were less consistent than those with crab consumers, and plants in the field at low-latitude sites tended to experience greater levels of herbivore pressure than plants at high-latitude sites. Similarly, high-latitude leaf litter was more palatable than litter from low-latitude plants when offered to consumers in paired feeding assays in the laboratory. Latitudinal gradients in plant palatability and herbivore pressure may be a general phenomenon, and may contribute to latitudinal gradients in decomposition processes.

Ecological interactions often vary geographically. Work in salt marshes on the Atlantic Coast of the UnitedStates has documented community-wide latitudinal gradients in plant palatability and plant traits that may be driven in part by greater herbivore pressure at low latitudes. To determine if similar patterns exist elsewhere, we studied six taxa of saltmarsh plants (Atriplex , Juncus , Limonium , Salicornia , Spartina and Suaeda ) at European sites at high (Germany and the Netherlands) and low (Portugal and Spain) latitudes. We conducted feeding assays using both native and non-native consumers, and documented patterns of herbivore damage in the field. As in the United States, high-latitude plants tended to be more palatable than low-latitude plants when offered to consumers in paired feeding assays in the laboratory, although assays with grasshopper consumers were less consistent than those with crab consumers, and plants in the field at low-latitude sites tended to experience greater levels of herbivore pressure than plants at high-latitude sites. Similarly, high-latitude leaf litter was more palatable than litter from low-latitude plants when offered to consumers in paired feeding assays in the laboratory. Latitudinal gradients in plant palatability and herbivore pressure may be a general phenomenon, and may contribute to latitudinal gradients in decomposition processes.

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