The cultivated genus Ulva, its pests, and defence

The genus Ulva is one of the most commonly commercially cultivated seaweeds both on land in ponds and in the open sea. As a crop, its cultivation is accompanied by three pest groups: (1) diseases caused by pathogenic bacteria, algae, virii, and fungi, which cause perforations, deterioration, and decreased growth of thalli; (2) various grazers, e.g. small crustaceans, gastropods, and non-defined invertebrates, which decrease growth and damage the thalli; and (3) an epiphytic biofilm of microorganisms, which also causes damage to the end-crop decreasing its yield and value. Mitigation categories against Ulva pests may be divided into three categories: (A) pro-active human intervention by washing the infected thalli with acid, fresh water, proprietary chemicals or CO₂-saturated seawater, the use of methanolic Ulva extracts, or exudate from the green seaweed, all of which are reported to restrict pest activity; (B) using the beneficial properties of probiotic bacteria thereby eliciting antifouling activity, with selective abilities against pathogens of Ulva spp.; (C) enhancing the effects of environmental changes on pests, i.e. acidification and increased seawater temperature, which mainly decrease the grazer population and thereby their pressure. A summary of these studies is presented as a guide for rapid responses and applied management techniques for the amelioration of cultivation diseases, grazers, and harmful epiphytes affecting the foliose green alga Ulva spp.