Physiological responses of a bloom-forming green macroalga to short-term change in salinity, nutrients, and light help explain its ecological success

Enteromorpha intestinalis is a bloom-forming species of macroalgae associated with eutrophication. The objective of this study was to investigate how this alga performs osmoregulation and nutrient uptake in order to proliferate under environmental conditions that covary with eutrophication. We quantified the response of E. intestinalis to salinity, light, and nutrients. We performed two short-term (48 h) laboratory experiments (salinity alone and salinity x nutrients x light) to examine the algal responses of tissue water, potassium (K⁺), and nutrient (NO₃^- and total N) content. Tissue water content decreased with increasing salinity, and although K⁺ concentration decreased from the initial concentration, it decreased less with increased salinity treatment demonstrating two mechanisms to withstand short-term salinity fluctuation. The salinity x nutrient x light experiment showed that, in the short term, light had an interaction with tissue K⁺. Total tissue N content was positively related to N treatment level, and light did not affect total nutrient concentration. The effect of light was present whether the nutrients were present in the tissue as inorganic or organic forms. With reduced light, we hypothesize that the assimilation of inorganic to organic N was energy limited. The ability of this alga to take up available nutrients rapidly for growth and short-term osmoregulation, even under low light and salinity levels, helps to explain the bloom potential of E. intestinalis.