Date of Award

Spring 1982

Project Type


Program or Major


Degree Name

Doctor of Philosophy


A study was undertaken to determine if natural growth irradiance regimes influence the pigment content and/or photosynthesis-irradiance relationships of the tropical brown seaweed, Lobophora variegata. Pigment analyses were performed on samples collected from a series of depths between 9 and 49m. Chlorophyll a, chlorophyll c, and fucoxanthin were constant on a thallus weight basis, but showed small decreases when expressed in terms of thallus area. The beta-carotene content of L. variegata was much greater in shallow than in deep-water samples regardless of the pigment units employed. Experimental reduction of the light regime of the shallow population, produced a significant decrease in beta-carotene content within 2 days. In 4 days, beta-carotene had decreased by 55% on a thallus weight basis, while no significant changes were found in any of the other three pigments.

Photosynthesis-irradiance (P-I) relationships were determined in situ for Lobophora variegata populations from a series of depths between 4.6 and 36.6m. Determinations were made for each population at its native depth, as well as at the spectral regimes of several other depths. The shallowest population examined was found to have a substantially higher rate of light saturated photosynthesis (P(,max)) compared with populations from greater depths. Further reductions of P(,max) with depth were evident on a thallus area basis, but not on a thallus weight basis. The efficiency of low-light photosynthesis, indicated by the initial slope (alpha) of the P-I curve, was found to increase with depth regardless of the depth from which the L. variegata samples were collected.