The role of habitat structural complexity in shaping faunal communities has been of key interest to marine ecologists for many years, principally due to the association between increased complexity and high abundances and diversity of fauna. Despite this, macroinvertebrate assemblages within seagrasses with varying morphologies and canopy structures have seldom been compared. Algal epiphytes also contribute to the structural complexity of seagrass ecosystems, a factor often overlooked in studies on seagrass structural complexity. We used artificial seagrass units (ASUs) with varying structure to determine the relative importance of food versus structure for macroinvertebrate fauna (Experiment 1). We also tested whether the importance of different structural components of seagrasses for macroinvertebrate fauna was consistent between seagrasses (Amphibolis griffithii, Posidonia sinuosa and Cymodocea nodosa) with naturally different complexity (Experiment 2). In Experiment 1, the treatments with the combination of food and structure together had the greater density of colonizing macroinvertebrates, compared to those where either structure or food were independently tested. In Experiment 2, the density of fauna colonizing ASUs varied among complexities of ASUs, as well as seagrasses. When ASU\u27s were placed alongside A. griffithii and P. sinuosa (species which vary greatly in morphology, but little in available surface area) the highest densities of fauna were generally found on ASUs with artificial epiphytes. This suggests that small-scale variation in structure was more important than large-scale variation in canopy morphology. However, there was no difference in the total density of fauna colonizing onto ASUs placed alongside C. nodosa, which morphologically has a structure similar to P. sinuosa, but much lower surface area. We conclude from these experiments that the effect of high structural complexity in seagrasses is an important driver of macroinvertebrate density, in particular, that provided by algal epiphytes. However, the effect of structural complexity may be reduced when seagrass canopy surface area is limited
Dry, oligotrophic ecosystems are highly threatened in Europe due to massive changes in land use and eutrophication. The conservation of these xeric habitats has received much attention, whereas the ecotones between xeric habitats and other habitat types are often disregarded. One species which mainly inhabits the transition zone between pine forests and adjacent xeric habitats is the heath grasshopper, Chorthippus vagans. This species is endangered in large parts of Europe. One of the largest populations in northern Germany is found on a degraded inland dune near Hanover. This population is threatened by dense growth of deciduous trees and litter accumulation. We analyzed changes in the distribution of this population after the implementation of conservation measures (thinning out the forest and removal of leaf litter). Moreover, we examined dispersal distances of the species in order to assess its colonization potential. We also studied the microhabitat preferences of C. vagans to assess key factors influencing its local distribution. Our data show a substantial growth in population size, which might be a consequence of the conservation measures. New patches on the dune were colonized, promoting dispersal between the subpopulations. We propose that restoration of forest-dune ecotones should be considered more often in landscape planning and conservation management.
Numerous anthropogenic activities can significantly reduce the amount of light reaching seagrass habitats. Typically these result in morphological and physiological changes to the plant and associated algal epiphytes. However, the flow-on effects to seagrass-dependent fauna induced by these disturbances has yet to be examined. This study investigated the effects of different light reduction intensity (high: ~92% reduction; moderate: ~84% reduction), duration (3, 6 and 9 mo) and timing (post-winter and post-summer) on the density and biomass of macroinvertebrate epifauna within an Amphibolis griffithii seagrass ecosystem (Western Australia). There were generally lower epifauna densities and biomass within shaded seagrass plots. When moderate intensity shading was imposed at the end of winter, total density in unshaded controls was 31% lower at 3 mo, and 78% lower at 9 mo. When high intensity shading was imposed, total density was 38% lower than in controls at 3 mo, and 89% lower by 9 mo. Although densities varied, similar magnitudes of decline occurred in post-summer shaded treatments. Taxa-specific responses were variable in terms of time, rapidity and magnitude of response. Amphipod, isopod and gastropod densities generally declined in response to shading. Bivalve densities declined with shading post-summer, but not post-winter. Ostracod densities had an inconsistent response to moderate shading. Changes in epifaunal density were largely associated with declines in algal biomass, leaf variables and stem biomass, indicating food and habitat limitations. It is likely that the significant declines in epifauna observed in this experiment would have flow-on consequences to higher trophic levels. KEY WORDS: Seagrass · Disturbance · Shading · Western AustraliaResale or republication not permitted without written consent of the publisher
Marine invertebrates and macrophytes are sensitive to the toxic effects of oil. Depending on the intensity, duration and circumstances of the exposure, they can suffer high levels of initial mortality together with prolonged sublethal effects that can act at individual, population and community levels. Under some circumstances, recovery from these impacts can take years to decades. However, effects are variable because some taxa are less sensitive than others, and many factors can mitigate the degree of exposure, meaning that impacts are moderate in many cases, and recovery occurs within a few years. Exposure is affected by a myriad of factors including: type and amount of oil, extent of weathering, persistence of exposure, application of dispersants or other clean-up measures, habitat type, temperature and depth, species present and their stage of development or maturity, and processes of recolonisation, particularly recruitment. Almost every oil spill is unique in terms of its impact because of differing levels of exposure and the type of habitats, communities and species assemblages in the receiving environment. Between 1970 and February 2017, there were 51 significant oil spills in Australia. Five occurred offshore with negligible likely or expected impacts. Of the others, only 24 of the spills were studied in detail, while 19 had only cursory or no assessment despite the potential for oil spills to impact the marine environment. The majority were limited to temperate waters, although 10 of the 14 spills since 2000 were in tropical coastal or offshore areas, seven were in north Queensland in areas close to the Great Barrier Reef. All four spills that have occurred from offshore petroleum industry infrastructure have occurred since 2009. In Australia, as elsewhere, a prespill need exists to assess the risk of a spill, establish environmental baselines, determine the likely exposure of the receiving environment, and test the toxicity of the oil against key animal and plant species in the area of potential impact. Subsequent to any spill, the baseline provides a reference for targeted impact monitoring.
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