A comparison of the rates of ammonium uptake in the macroalgae species: Codium fragile (Chlorophyta), Fucus vesiculosus (Phaeophyceae), and Ulva lactuca(Chlorophyta) when exposed to varying intensities of light

Abstract

Macroalgae, also more commonly known as seaweed are classified simply as algae visible to the naked eye. Most of us only accidentally encounter seaweed a few times a year while at the beach and aren't aware of its huge importance to ourselves and aquatic ecosystems. Due to increases in human activities in recent decades nutrient loads have increased in aquatic systems leading to harmful algal blooms (HABS). These blooms can lead to toxicity of waters, and hypoxic or anoxic conditions which are the symptoms of the eutrophication cycle. The entire lack of or reduction of oxygen can cause massive fish deaths which then lead to an even greater reduction of oxygen due the decomposition process requiring large amounts of O2. Macroalgae have the ability to uptake nutrients required for growth and metabolism such as nitrogen (N) and phosphorus (P) at a rapid rate which makes them ideal candidates as bio-remediators in eutrophic waters. Eutrophication is an increase in abundance of the potentially highly toxic compound ammonium which is a normal by-product of fish metabolism, and organismal decomposition. Ammonium is normally broken down by nitrifying bacteria in an oligotrophic or mesotrophic state due to the requirement of oxygen for nitrifying bacteria to transform ammonium into nitrate, however, if hypoxic or anoxic conditions are present nitrate can convert into the dangerous compound nitrite. In aquaculture, the close proximity and high volume of live-stock can cause concentrations of ammonium to reach high which need to be removed from the system. Excess ammonium in open aquatic systems can exacerbate eutrophication, while eutrophication can exacerbate ammonium levels, therefore bio-remediators such as: certain macroalgae species tend to prefer ammonium over other forms of N due to their ability to absorb the compound without having to reduce or oxidize. In this study three species of macroalgae: Codium fragile (Chlorophyta), Fucus vesiculosus (Phaeophyceae), and Ulva lactuca (Chlorophyta) were studied for their rates of NH4+ (ammonium) uptake while exposed to three different light levels: (1) no light (0%), (2) medium light (50%), and full light (100%). Seaweeds were collected from Reed Sanctuary, incubated, placed into test tubes with known concentrations of NH4+, artificial seawater, a catalyst, reagent, and oxidizer. Seaweeds were then incubated for 30 minutes, solutions from test tubes were extracted at 0, 15, and 30-minute intervals, then measured in a spectrophotometer to compare absorbance levels to known concentration values. Results showed statistical significance for an increase in the uptake of NH4+ with the increase of light level in one trial of the species; Codium fragile for all experimental runs performed. Ulva lactuca had a slightly faster uptake rate at the 0% light level than the 50% and 100% level but statistical significance was not found. Fucus vesiculosus had a slightly higher uptake rate at 100% light exposure than the other exposure but no statistical difference was found. It is difficult to pinpoint the cause of certain species having faster uptake rates than others or why increased light availability has an effect on the uptake ability in certain species in some studies, and in other studies individual variations within the species are much more prominent.