Physiological ecology of the marine alga acrocystis nana zanardini (Rhodophyta, ceramiales)

The present work was set to study how the littoral (intertidal) alga Acrocystis nana responds to different conditions of water supply under laboratory conditions in order to explain the distribution of the alga on the shore. The responses of the alga to different durations of emersion were assessed in terms of five characters: (i) Chlorophyll content (ii) total dry weight (iii) quantities of acid soluble carbon hydrates, (iv) quantities of acid in soluble materials. The underlying presumption in taking these measurements was that maximum quantities would be achieved under those conditions for which the alga is best adapted. Several aspects of the water relations of the alga were also studied in order to see how they were related to the changes in metabolic products. Field observations of the vertical distribution of A nana showed it to be absent from permanently submerged areas, being confined to areas emerged for between approximately 3 and 9 hours per tide. Laboratory studies on the metabolic products revealed that the accumulation of acid-soluble compounds and increase in weight occurred only where the alga was emerged to the air for 3 hours in every 24 hours. From these results it was concluded that the aced soluble compounds were acting as the respiratory and stress resistance components in a similar way to the ethawl-soluble compounds of the lichen Hypogymmaphysodes. Studies of water relations revealed that changes in water potential were amore valid parameters for demonstrating the close association between response and habitat than water loss rate curves. Secondly, it was evident that energy expending mechanisms operate to maintain the extra cellular sap at a lower concentration than sea-water and vacuolar sap. Thirdly, the water potential changes 3 fold, from 2.3 KJ kg 1 to 7.3 KJ kg 1 (at 30oC) on exposing A. nana to the air in the laboratory for 3 hours. From the studies of water relations it appeared that the dilute extra cellular sap was a mechanism for showing down the onset of water stress. It was also apparent that although fluctuation in water supply were indispensable for the survival of the alga, the problems of water stress and resetting which accompany the changes in water supply may threaten the survival of the alga itself to a considerable extent.