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Sedimentary Habitats (sedimentary + habitat)

Distribution by Scientific Domains

Life Sciences	100%

Selected Abstracts

Interactions between fauna and sediment control the breakdown of plant matter in river sediments

FRESHWATER BIOLOGY, Issue 4 2010
SIMON NAVEL
Summary 1. A substantial portion of particulate organic matter (POM) is stored in the sediment of rivers and streams. Leaf litter breakdown as an ecosystem process mediated by microorganisms and invertebrates is well documented in surface waters. In contrast, this process and especially the implication for invertebrates in subsurface environments remain poorly studied. 2. In the hyporheic zone, sediment grain size distribution exerts a strong influence on hydrodynamics and habitability for invertebrates. We expected that the influence of shredders on organic matter breakdown in river sediments would be influenced strongly by the physical structure of the interstitial habitat. 3. To test this hypothesis, the influence of gammarids (shredders commonly encountered in the hyporheos) on degradation of buried leaf litter was measured in experimental systems (slow filtration columns). We manipulated the structure of the sedimentary habitat by addition of sand to a gravel-based sediment column to reproduce three conditions of accessible pore volume. Ten gammarids were introduced in columns together with litter bags containing alder leaves at a depth of 8 cm in sediment. Leaves were collected after 28 days to determine leaf mass loss and associated microbial activity (fungal biomass, bacterial abundance and glucosidase, xylosidase and aminopeptidase activities). 4. As predicted, the consumption of buried leaf litter by shredders was strongly influenced by the sediment structure. Effective porosity of 35% and 25% allowed the access to buried leaf litter for gammarids, whereas a lower porosity (12%) did not. As a consequence, leaf litter breakdown rates in columns with 35% and 25% effective porosity were twice as high as in the 12% condition. Microbial activity was poorly stimulated by gammarids, suggesting a low microbial contribution to leaf mass loss and a direct effect of gammarids through feeding activity. 5. Our results show that breakdown of POM in subsurface waters depends on the accessibility of food patches to shredders. [source]

The importance of bare marine sedimentary habitats for maintaining high polychaete diversity and the implications for the design of marine protected areas

AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 7 2009
Christopher R. S. Barrio Froján
Abstract 1.Bare intertidal sedimentary habitats have received relatively little attention compared with their neighbouring vegetated habitats. An ecological comparison of benthic faunal assemblages inhabiting tropical intertidal seagrass beds and bare sediments has been made to assess the faunal similarity between the two habitats in south-east Asia. 2.The poorly developed taxonomy of most invertebrate taxa in the region precluded the full identification of many faunal groups. Only the polychaetes , which accounted for 76% of all the macrofaunal organisms collected , were identified to the lowest possible taxonomic level, yielding 177 nominal species belonging to 35 families. Ecological analyses suggested that although each habitat had a distinct polychaete assemblage, there were few differences between habitats based on a range of calculated assemblage diversity metrics. 3.Further analyses were applied to the data to test the performance of three strategies for optimizing the selection of sites for inclusion in potential marine protected areas. Strategies were based either on the total number of species, the number of rare or endemic species, or on the level of species richness (used as a surrogate for community structure). 4.All three strategies consistently captured above average numbers of species at most levels of conservation intensity. The merits of each strategy are considered in turn. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Rhodolith bed diversity in the Gulf of California: the importance of rhodolith structure and consequences of disturbance

AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue S1 2003
D.L. Steller
Abstract 1.Rhodolith beds, unattached coralline reefs, support a high diversity and abundance of marine species from both hard and soft benthos. We used surveys in multiple shallow (3,20 m) beds in the Gulf of California to (1) examine seasonal patterns in associated floral and faunal diversity and abundance, (2) compare differences in faunal associations between rhodolith beds and adjacent sedimentary habitats, (3) examine the importance of complexity of rhodolith structure to community structure, and (4) estimate the impact of anthropogenic disturbance on rhodoliths and associated species. 2.Macroalgal richness was seasonal, and beds supported higher richness in winter (to 36 species) than summer (6,7 species), primarily due to foliose red algae. Strong seasonal variation in the abundance of dominant cover organisms was due to a shift from macroalgae and mat-forming colonial invertebrate species to microalgae. 3.The community in a rhodolith bed of high-density thalli (El Coyote average ,11000 thalli/ m,2) had higher richness (52 versus 30 species) and abundance of epibenthic and crypto- and in-faunal species compared with an adjacent sand community. Species diversity and abundance was particularly high for unique cryptofaunal organisms associated with rhodolith interstices. Cryptofauna reached average densities of 14.4 organisms/ cm,3 rhodolith, the majority of which were crustaceans, polychaetes and cnidarians along with rhodolith-specific chitons. 4.Results from sampling across a range of rhodolith morphs in the El Requeson bed (with lower average cryptofaunal densities of 2.3 organisms/ cm,3) revealed that the total organisms supported by a rhodolith significantly increased with both complexity (branching density) and space available (thallus volume). These data suggest that reducing the population size structure, structural complexity and cover of living rhodoliths could decrease species richness and abundance. 5.While disturbance is a natural feature of these free-living beds, increased anthropogenic disturbance from trawling, anchoring and changes in water quality can directly impact the bed community through substrate alteration. Commercial fishing threatens rhodolith beds in the Gulf of California by decreasing rhodolith size and increasing sedimentation and burial rates. In addition to reducing direct destruction, conservation efforts should also focus on decreasing practices that breakdown thalli. Copyright © 2003 John Wiley & Sons, Ltd. [source]