Water Flow in Seagrass Ecosystems - Water Motion and Productivity

Brief description

Field studies were conducted to investigate the effects of two levels of water velocity (exposure) on seagrass standing crop (biomass) and consequently community productivity. These results were then related to laboratory studies examining the physiological effects of water velocity fluctuations on seagrasses. These effects were light and water velocity on the photosynthetic rates of seagrasses and epiphytes. In addition, laboratory studies were designed to investigate the influence the role of leaf and epiphyte morphology on flow over the surface of seagrass leaves, and the rescaling of turbulence to a level which enhances nutrient uptake by the plants.

Lineage

Maintenance and Update Frequency: notPlanned

Statement: - Posidonia sinuosa standing crop studies - Several aspects of the primary production of seagrasses were studies at two sites within Shoalwater Bay: one sheltered (inshore) and one exposed (offshore). (See thumbnail) Measurements of plant density and biomass were made from these sites on seven occasions over a period of 14 months, from December 1991 to February 1993. Samples were collected in December 1991, February, April, July, October and December 1992 and February 1993. On each sampling date, a 10 m transect running parallel to the shore was randomly established through a homogeneous section of meadow at the two sites. A plastic quadrat (0.5 x 0.5 m) was used to delineate the sample area, and samples of the above-ground biomass were collected at 1 m intervals along the transect. Leaves were collected by cutting all the above-ground plant within the quadrat at sediment level by scissors. Shoots were counted at the same time as they were cut. Sampling was carried out on SCUBA or Hookah from a small boat. Samples were frozen at -20 degrees Celsius until processed in the laboratory. Seagrass biomass, as dry weight, was determined after being dried for 48 hours at 100 degrees Celsius. Crucibles were washed and preheated in a furnace (Furnance Industries) at 500 degrees Celsius for 12 hours and then weighed. 1g subsamples of each dried sample were placed in the crucibles and heated to 500 degrees Celsius for 24 hours, weighed and the resulting ash weight recorded. Additional data for mean depth, mean summer irradiance and mean summer temperature were collected for the two sites.

Statement: - Laboratory based productivity tests - A flume was designed specifically for the measurement of the physiological responses of seagrasses and algae under conditions of variable water flow. The role of water motion at an individual leaf scale was investigated with a series of laboratory flume studies of photosynthetic rates of seagrass and algae measured using an oxygen electrode. Dye visualization was used to study the significance of blade morphology on the creation of microscale turbulence at the surface of seagrass leaves.