The biology of Australian seagrasses

Seagrasses are angiosperms which have ventured into the marine environment, where they produce totally submerged flowers which are pollinated under water. They occur in many regions of the world,but the following account is concerned primarily with studies on the biology of these plants in Australian waters. It also attempts to contrast some of the features displayed by the seagrasses with those of more familiar terrestrial plants

A Standard format for Les Houches event files

A standard file format is proposed to store process and event information, primarily output from parton-level event generators for further use by general-purpose ones. The information content is identical with what was already defined by the Les Houches Accord five years ago, but then in terms of Fortran commonblocks. This information is embedded in a minimal XML-style structure, for clarity and to simplify parsing

The loss of seagrasses in Cockburn Sound, Western Australia. I. The time course and magnitude of seagrass decline in relation to industrial development

The areas of seagrass meadows in Cockburn Sound, a marine embayment in Western Australia, were estimated from historical aerial photographs supplemented by ground surveys, studies on meadows in adjoining areas, and coring for rhizome remains. Ten species of seagrasses with different habitat tolerances are recorded for the area, with Posidonia sinuosa Cambridge et Kuo forming the most extensive meadows. It is estimated that from 1954 to 1978 the meadow area was reduced from some 4200 to 900 ha. Based on measurements of aboveground productivity at several sites, this represents a reduction of leaf detritus production from 23 000 to 4000 t (dry wt.) y−1. The major loss of seagrass occurred during a period of industrial development on the shore, and the discharge of effluents rich in plant nutrients

Ultrastructure of the seagrass rhizoshere

Bacterial colonies, fungi and other micro-organisms occur in the rhizosphere and peripheral root tissues of seagrasses of the genus, Posidonia. Fungi penetrate the epidermal cells and lyse the thick polysaccharide materials in the walls of the hypodermal cells. A suberin lamella in the wall of the hypodermal cell is more resistant but fungi and bacteria occur both within the lumen of hypodermal cells and in cortical cells adjacent to the hypodermis. It is suggested that these micro-organisms in the rhizosphere and peripheral root tissues may be involved in nutrient uptake and nitrogen fixation into seagrasses

Nutrient accumulation in the fruits of two species of seagrass, Posidonia australis and Posidonia sinuosa

The accumulation is described of N, P, K, S, Ca, Mg, Na, Fe, Zn, Mn and Cu in the developing pericarp and seed of two species of seagrass. Both species showed essentially the same patterns, which resemble those of herbaceous terrestrial plants. There was a close relation between dry matter and nutrient accumulation. N, P, K, Fe, Zn, Mn and Cu accumulated in the fruit against large concentration gradients, with discrimination against Na. Seeds accumulated N, P and trace elements to a greater extent than pericarps and other plant parts; P was apparently retrieved from pericarps to a greater extent than other elements. Calculations were made of the losses of these elements from seagrass meadows in shed fruits

The nitrogen and phosphorus nutrition of developing plants of two seagrasses, Posidonia australis and Posidonia sinuosa

The depletion of dry matter, N and P from seeds of Posidonia australis Hook. f. and Posidonia sinuosa Cambridge et Kuo during germination and seedling establishment is described. Seeds of both species showed essentially the same patterns of depletion, which resembled those of terrestrial plants. Seed reserves of N and P were retrieved with an apparent efficiency of ca. 95%, and linear relationships existed between the loss of these nutrients and dry matter from seeds during the first nine months of seedling growth. The distribution of dry matter, N and P amongst plant parts of both species was very similar. Leaves were major sinks for N and P during the first two years of plant development. Leaves contained the highest concentrations of N and rhizomes the highest levels of P. All seedling parts accumulated N and P against large concentration gradients. The environment contributed 100–150 mg N and 17–25 mg P m−2 to seedlings during their two years of growth. In 5-year-old plants, leaf bases contained important reserves of P, and 30–40% of the plant's N and P was associated with dead and morinund tissue. Leaf bases lost 84% of their N and 95% of their P during senescence

Chemistry, agriculture and the environment

SIGLEAvailable from British Library Document Supply Centre- DSC:91/14340(Chemistry) / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Guideline use in non-design disciplines

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The loss of seagrass in Cockburn Sound, Western Australia. II. Possible causes of seagrass decline

This paper examines possible reasons for the extensive loss of seagrass in Cockburn Sound following industrial development. Transplanted seedlings survived poorly in Cockburn Sound compared with an adjoining embayment. Altered temperature, salinity, sedimentation and water movement do not explain the death of seagrass over wide areas, and there is no evidence for a role of pathogens. Oil refinery effluent reduced seagrass growth in aquaria at concentrations similar to those at the point of discharge, but could not account for the widespread deterioration observed in the field. Severe grazing by sea urchins was observed on meadows already under stress and does not appear to be a primary cause of decline; caged, transplanted seedlings also deteriorated. Increased light attenuation by phytoplankton blooms may have affected the ddepth to which seagrasses could survive, but would have had little significant effect in shallow water; marked phytoplankton blooms were recorded only after extensive seagrass decline had taken place. Light reduction by enhanced growth of epiphytes and loose-lying blankets of filamentous algae in nutrient enriched waters is suggested as the most likely cause of decline. Heavy epiphyte fouling was consistently observed on seagrasses in deteriorating meadows, as well as on declining, transplanted seedlings, and is known to significantly impair photosynthesis in other systems. Extensive seagrass decline coincided with the discharge of effluents rich in plant nutrients