Analysis of Nutrient Enrichment on Ulva Growth

Abstract

To determine whether Ulva is nitrogen or phosphorus limited in San Juan Island oceanographic conditions, samples were cut from a single individual utilizing a cork borer and cultured in a lab environment. In addition to control conditions, five samples each were cultured in four treatments of increased nitrate (5 μM, 25 μM, 50 μM, 100 μM) and four treatments of increased phosphate (0.3125 μM, 1.5625 μM, 3.125 μM, 6.25 μM). Temperature of the treatments were kept consistent with field conditions through usage of a sea table circulating water, and light levels were kept constant (125 lx) through suspension of four fluorescent tube lights above the seatable. Samples were cultured over a period of five days, and relative growth of each treatment was measured utilizing a micrometer to determine average change in diameter on the third and fifth day. Increased nitrate treatments had higher average growth than that of increased phosphate, and both displayed significantly higher growth than that of the control. Between the two treatments, statistical significance was determined for nitrate growth conditions having higher average growth (p < 0.5). Treatments displayed moderate positive correlation between increasing nitrate levels and growth (~0.66), with almost no correlation between increasing phosphate levels and growth (~-.11). The data supports the hypothesis that Ulva growth is nitrogen limited in San Juan Island oceanographic conditions.