Habitat use in different life and moulting stages of Callinectes sapidus (Decapoda, Portunidae) in South Brazilian estuarine and marine environments

AbstractThe blue crab Callinectes sapidus is an important ecological and commercial species. It plays a fundamental role in the structure and function of coastal benthic food webs, with global catches of ~74,357 tons. This is the most exploited portunid species in Brazil. However, few studies about the ecology and population dynamics of C. sapidus have been published. This study aimed to analyse the preferred areas for the spatial distribution of juveniles and moulting individuals of C. sapidus in shallow areas of the Patos Lagoon estuary and the adjacent marine reproductive area, and their relation to water and sediment characteristics. Juveniles and moulting individuals preferred the embayment of the upper estuary, where the sediments are finer, with higher contents of organic matter and the presence of submerged vegetation. There was also a temporal variability in the abundance of juvenile size classes, with two marked increments of smaller individuals: (1) in late spring and summer and (2) in winter, indicating two recruitment peaks. Unusual environmental conditions in the summer of the first year, with an increase of fine sediments and organic matter, combined with low salinities in the adjacent marine area, allowed recruitment of individuals there. We suggest better attention to the embayment around the Marinheiros Island (considered here as upper estuary) for management and protection measures due to the overlapping of recruitment preferences of the blue crab, pink shrimp and fish species in this area.

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Soil properties, root responses and production of irrigated pasture on a red-brown earth after subsoil modification

Australian Journal of Experimental Agriculture ◽

10.1071/ea01076 ◽

2002 ◽

Vol 42 (4) ◽

pp. 453 ◽

Cited By ~ 10

Author(s):

S. J. Blaikie ◽

J. R. Hirth ◽

K. L. Greenwood ◽

K. A. Olsson ◽

K. E. Dellow ◽

...

Keyword(s):

Organic Matter ◽

Soil Surface ◽

First Year ◽

Initial Surface ◽

Pasture Production ◽

Physical Conditions ◽

Penetrometer Resistance ◽

Root Responses ◽

And Function ◽

Modified Soil

Soils used for growing irrigated pasture in northern Victoria have shallow (0.10-0.15 m) topsoils and dense, clay subsoils. Reducing soil limitations to root growth and function has the potential to increase pasture production. Therefore, subsoil modification treatments, comprising loosening and fragmentation of the B horizon to depths of 0.2, 0.4 and 0.6 m, the incorporation of calcium ameliorants, superphosphate and application of organic matter to the soil surface, were compared with unmodified soils and a 0.4 m deep topsoil, in a red-brown earth over a 2-year period (1994-96). Subsoil modification improved the physical condition of the soil. Air-filled porosity of the deep-modified soils (0.4 and 0.6 m deep), 24 h after irrigation, exceeded 15% at 0.1 and 0.3 m depths in both years, and was always higher than in the unmodified soils. Penetrometer resistance was markedly lower in the deep-modified subsoils in both years. Greater earthworm activity was associated with these improved soil physical conditions. However, the soil treatments did not result in greater root length or root mass beneath the pasture. In the first year, pasture yield was greater on the deep-modified soils (25-31 t DM/ha) than on the unmodified soils (19 t DM/ha). In the second year, the yield advantage of the deep-modified treatments decreased to 11%, despite the maintenance of improved soil physical conditions. In both years, pasture yields were highest where there was an initial surface application of 20 t DM/ha organic matter to a modified soil. We conclude that structural modification of the B horizon can increase pasture yields on this soil. However, further research is necessary to maintain these yield increases beyond the initial year and to develop more practical systems of soil modification.

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Water quality, substratum and biotic responses of five central Idaho (USA) streams during the first year following the Mortar Creek fire

International Journal of Wildland Fire ◽

10.1071/wf01017 ◽

2001 ◽

Vol 10 (2) ◽

pp. 185 ◽

Cited By ~ 54

Author(s):

G. Wayne Minshall ◽

James T. Brock ◽

Douglas A. Andrews ◽

Christopher T. Robinson

Keyword(s):

Organic Matter ◽

Major Ions ◽

Ecological Factors ◽

Rocky Mountain ◽

Heavy Rain ◽

Mountain Forest ◽

First Year ◽

Fine Sediments ◽

Spring Runoff ◽

Dissolved Chemicals

The Mortar Creek Fire burned 26 000 ha of mixed-conifer Rocky Mountain forest in July–August 1979. Changes in burn stream conditions were examined relative to reference streams for various ecological factors on two to six occasions, from October 1979 to August 1980. Factors included major ions and nutrients, suspended and benthic particulate matter, periphyton (algae), and macroinvertebrates. Elevated levels of most dissolved chemicals in the burn streams were evident soon after the fire and again during spring runoff. However, there were no major disruptions in the relative composition of cations (and presumably of anions also) in the burn streams during the study. Concentration (mg/L) and load (g/s) of some constituents were higher (e.g. NO 3 -N) and of others (e.g. Ca) were lower in the burn than in the reference streams during spring runoff, depending on whether they were normally under biological or geological control, respectively. Suspended sediment and particulate organic matter generally were higher in burn streams, especially during snow-melt runoff or following heavy rain storms. Benthic organic matter was higher in burn streams and was mainly charcoal, compared to the usual leaf litter found in the reference streams. Fine sediments increased and periphyton decreased in the burn streams. The fire increased the sensitivity of the burn streams to more routine smaller-scale disturbances, such as rainstorms, which had major impacts on the burn streams but not on the reference streams. The macroinvertebrate assemblage showed little direct effect from the fire but was severely altered in composition and abundance by the subsequent runoff, scouring, and channel alteration initiated by spring runoff. The burn streams showed considerable individuality in their response to fire depending on the particular set of conditions to which they were exposed.

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