Salinity Response of the Seagrass Amphibolis antarctica (Labill.) Sonder et Aschers.: an Experimental Validation of Field Results

Brief description

Viviparous seedlings of Amphibolis antarctica were collected in May 1983 from Monkey Mia, Western Australia (26° 15' S, 113° 36'E) and grown in artificial seawater cultures ranging in salinity from 35 to 65%. Leaf number and colour were recorded and seedling mortality was assessed at 7-10 day intervals.

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Maintenance and Update Frequency: notPlanned

Statement: Artificial seawater (ASP 2) was made up (Stein, 1977) with increasing weights of salts to produce salinities of 35, 42.5, 50, 57.5 and 65%o, the range
of salinities encountered in Shark Bay. Nutrient, vitamin and trace metal solutions were added to give the same final concentration in each solution, so that the only difference between treatments was the concentration of total dissolved salts. Aerated aquaria were set up in growth cabinets equipped with a mixture of incandescent and fluorescent bulbs, providing 350/~E m -2 s-1 photosynthetically
active radiation in a 12:12 light: dark cycle, and with a diel water temperature alternation of 20:15 ° C, conditions comparable to those occurring in the field during winter when seedlings are released. Each aquarium was filled with 201 of artificial seawater of known salinity. Five scrubbed plant pots were filled with acid-washed silica sand and placed in each aquarium. Viviparous seedlings were collected in May 1983 from Monkey Mia (26 ° 15' S, 113 ° 36'E), Shark Bay (see Walker, 1985, for location and salinity distributions), kept moist and cool, and returned to Perth within 24 h.

To reduce algal contamination, seedlings were rinsed in solutions of decreasing salinity to distilled
water and then in increasing salinities until the appropriate salinity was reached. Each seedling was labelled and the number of leaves present recorded before being planted (four seedlings per pot); thus 20 seedlings were placed in each aquarium. Salinities were allocated randomly within the growth cabinets. At 7-10-day intervals, leaf number and colour were recorded and any shed
leaves collected and weighed. Seedlings were assessed as "dead" when either all leaves had been shed or when all leaves were fully blackened (Biebl and McRoy, 1971 ) and no new leaves were emerging at the centre of the leaf cluster. Rates of leaf accumulation and mortality were calculated for each salinity. In an initial experiment, seedlings were collected from the drift at a site of salinity 42%o, but the salinity at which they originated is unknown. The prevailing wind direction for the region is southerly and, as tidal currents are dominated by ebb transport (Logan and Cebulski, 1970), there is little likelihood that the seedlings could have originated at a more northerly, significantly less saline site. In later work, mature seedlings were collected in situ from parental plants at two sites, one of 42%o salinity and the other of 50%0. Seedlings were used which were easily detachable and therefore close to release, and were then treated in the same way as for the initial experiment, but with salinities confined to 42.5, 50 and 57.5%o.