Minireviews provides an opportunity to summarize existing knowledge of selected ecological areas, with special emphasis on current topics where rapid and significant advances are occurring. Reviews should be concise and not too wide-ranging. All key references should be cited. A summary is required.
Burrow characteristics, food type, and feeding h a b~t s of the SW Atlantlc burrowing crab Chasmagnathus grdnulata were compared between ~n d i v~d u a l s living in mud flats and In Spartinadominated marshes. Burrows were shorter ( X -19.7 cm, SD = 5 8, n = 54) and more dynamlc (entrance displacement: X = 3 2 cm d-l, SD = 1 7, n = 21) in mud flats than In Spartlna-dominated areas (length X = 41 cm, SD = 12, n = 78, no entrance displacement). Sediment turnover rate was much higher in mudbetween areas, being straight, near-vert~cal tunnels in the vegetated area, but oblique (average angle to vertical = 60'. SD = 16", n = 110), and having a funnel-shape entrance and a much large]-diameter in mud flats Stomach contents also differed between habitats. Pleces of plants dominated contents in the vegetated area, while sediment (with polychaetes, diatoms, ostracods, and nematodes) d o m~n a t e d in the mud flats, lndicatlng that crabs are mainly deposit feeders In the mud flats a n d herb~vorous in the Spart~na-dominated areas. This pattern suggests that the heuristic model relatlng burrow arch~tecture to trophic modes prev~ously proposed for fossorial thalassinidean shrimps applies to individuals of a C granulata populat~on The burrow content showed higher organic content and vegetal parts in the vegetated area than in the other area. Burrows in the mud flat showed a significantly higher abundance of nematodes and ostracods. Due to their hydrodynalnic characteristics and content, burrows in the mud flats may work as passive traps for sediment and organic matter. Given the extensive intertidal area inhabited by C granulata in SW Atlantic estuanes, and the locatlon of their burrows (between marshes and the open estuary), these burrows may work as traps for detritus, thus reduclng the export rate of organic matter from marshes.
Aim To produce an inventory of south-west Atlantic saltmarshes (from latitude 31°48¢ S to 43°20¢ S) using remotely sensed images and field sampling; to quantify their total area; to describe the biogeographical variation of the main habitats characterized by dominant vascular plants, in relation to major environmental factors; to test the hypothesis of predominance of the reversal pattern in plant distribution (sedges and grasses dominate the lower, regularly inundated zones, while the upper zones are occupied by more halophytic species) previously described; and to compare these south-west Atlantic saltmarshes with others world-wide. Location South-western Atlantic saltmarshesMethods Field samples of dominant emergent plant species positioned by the global positioning system (GPS) were obtained from most coastal saltmarshes (14) between southern Brazil and northern Patagonia, Argentina. Landsat satellite images were obtained and coastal saltmarsh habitats were quantified by supervised classification, utilizing points gathered in the field.Results Three main plant species dominated the low and middle intertidal saltmarsh, Spartina alterniflora Loesel., Spartina densiflora Brong. and Sarcocornia perennis (P. Mill.) A.J. Scott. The total area of the studied coastal saltmarshes was 2133 km 2 , comprising 380 km 2 of Sp. alterniflora marsh, 366 km 2 of Sp. densiflora marsh, 746 km 2 of Sar. perennis marsh and 641 km 2 of brackish marsh (dominated by Juncus acutus L., Juncus kraussii Hochst., Scirpus maritimus L., Scirpus americanus Pers. and Phragmites australis (Cav.) Trin.). Cluster analysis showed three habitat types: saltmarshes dominated by (1) Sp. densiflora and brackish species,(2) Sp. alterniflora and Sar. perennis and (3) Sp. densiflora only. The analysis of abiotic variables showed significant differences between groups of habitats and coordinated gradients of the abiotic variables. The southwest Atlantic coast showed decreasing mean annual rainfall (1200 to 196 mm) and increasing mean tidal amplitude (< 0.5 to > 2.5 m) from latitude 31°to 43°.Main conclusions South-west Atlantic saltmarshes are globally important by virtue of their total extent. Remote sensing showed that the reversal pattern in plant distribution is not widespread. Indeed, south-west Atlantic saltmarshes are better characterized by the presence of the halophytic genera Spartina and Sarcocornia. Our results support the interpretation that south-west Atlantic saltmarshes constitute a class of temperate type (sensu Adam, 1990) with transitional characteristics between Australasian-South African saltmarshes and west Atlantic saltmarshes.
Biodiversity is declining in many local communities while also becoming increasingly homogenized across space. Experiments show that local plant species loss reduces ecosystem functioning and services, but the role of spatial homogenization of community composition and the potential interaction between diversity at different scales in maintaining ecosystem functioning remains unclear, especially when many functions are considered (ecosystem multifunctionality). We present an analysis of eight ecosystem functions measured in 65 grasslands worldwide. We find that more diverse grasslands-those with both species-rich local communities (α-diversity) and large compositional differences among localities (β-diversity)-had higher levels of multifunctionality. Moreover, α- and β-diversity synergistically affected multifunctionality, with higher levels of diversity at one scale amplifying the contribution to ecological functions at the other scale. The identity of species influencing ecosystem functioning differed among functions and across local communities, explaining why more diverse grasslands maintained greater functionality when more functions and localities were considered. These results were robust to variation in environmental drivers. Our findings reveal that plant diversity, at both local and landscape scales, contributes to the maintenance of multiple ecosystem services provided by grasslands. Preserving ecosystem functioning therefore requires conservation of biodiversity both within and among ecological communities.
Receiving coastal waters and estuaries are among the most nutrient-enriched environments on earth, and one of the symptoms of the resulting eutrophication is the proliferation of opportunistic, fast-growing marine seaweeds. Here, we used a widespread macroalga often involved in blooms, Ulva spp., to investigate how supply of nitrogen (N) and phosphorus (P), the two main potential growth-limiting nutrients, influence macroalgal growth in temperate and tropical coastal waters ranging from low- to high-nutrient supplies. We carried out N and P enrichment field experiments on Ulva spp. in seven coastal systems, with one of these systems represented by three different subestuaries, for a total of nine sites. We showed that rate of growth of Ulva spp. was directly correlated to annual dissolved inorganic nitrogen (DIN) concentrations, where growth increased with increasing DIN concentration. Internal N pools of macroalgal fronds were also linked to increased DIN supply, and algal growth rates were tightly coupled to these internal N pools. The increases in DIN appeared to be related to greater inputs of wastewater to these coastal waters as indicated by high δ15N signatures of the algae as DIN increased. N and P enrichment experiments showed that rate of macroalgal growth was controlled by supply of DIN where ambient DIN concentrations were low, and by P where DIN concentrations were higher, regardless of latitude or geographic setting. These results suggest that understanding the basis for macroalgal blooms, and management of these harmful phenomena, will require information as to nutrient sources, and actions to reduce supply of N and P in coastal waters concerned.
In this work we evaluated the effect of the burrowing crab Chasmagnathus granulata on the soil quality and on the cordgrass Spartina densiflora in a SW Atlantic coastal lagoon (Argentina, 37'32'S, 57" 19'W). Soil hardness and percolation rates were higher outside the crab inhabited area than inside, and soil profiles showed 2 different strata In areas without crabs. Crabs were associated with low soil water content, a higher variabihty In pH, and a homogeneous distribution of organic matter. Meiofaunal abundance was lower inside the area inhabited by crabs than outside. The water content of aboveground structures of S. densiflora was lower inside the crab populated areas. Leaf survival was lower inside the area inhabited by crabs than outside. In areas with new shoots (after burning by a brush flre) crabs depleted the aboveground plant structures. A caging experiment showed that crabs decreased leaf survival by herbivory. During the experiment, substrata was covered by sediment displaced by crabs, and the area showed less soil hardness and lower percolation rates than controls. Crabs decreased water content and organic matter on upper sediment layers. Meiofaunal abundance (arachnids and insects) was higher in control plots (without crabs) than in treatment plots. A field selection expenment showed that crabs decreased survival of young stems, but did not affect old stems. K11 this evidence suggests that C. granulata affects cordgrass production by herbivory on new shoots, and can change the physical characteristics of the environment, which may also indirectly affect S. densiflora production. Thus, the general belief that in Spartina marshes only a small proportion of primary production is consumed in situ may not apply to SW Atlantic Spartina marshes inhabited by crabs.
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