Composting the Invasive Toxic Seaweed Rugulopteryx okamurae Using Five Invertebrate Species, and a Mini-review on Composting Macroalgae

Abstract

Since 2015, the invasive alga Rugulopteryx okamurae has explosively burst into the waters of the Strait of Gibraltar with serious repercussions on marine biodiversity, tourism and the fishing industry. Its elimination entails an enormous cost for the municipalities in the area and vermicomposting is proposed as a solution, but the anti-food secondary metabolites of the algae make it unfeasible. This work analyzed for the first time the bioremediation of this toxic algae using vermicomposting (Dendrobaena veneta and Eisenia fetida), blatticomposting (Eublaberus spp. “Ivory”), mealworms (Tenebrio molitor) and black soldier fly larvae (BSFL, Hermetia illucens). Both BSFL composting and blatticomposting are viable alternatives, as the toxics in the algae do not affect the long-term survival, growth or reproduction of these invertebrates. All other tested species do not resist consumption of R. okamurae. In parallel, a synthesis of current knowledge on marine macroalgae composting has been carried out. The results of this work will allow the use of insect farms in the upwelling areas that will eliminate algae, providing fertilizers and animal proteins that will be an economic aid to the municipalities in the affected coasts of southern Mediterranean Spain. Graphical Abstract

A Concise Review on the Potential Applications of Rugulopteryx okamurae Macroalgae

“…Composting is an aerobic process ( Figure 5 ) in which organic matter is degraded by the activities of microorganisms. It is an old approach that has been gaining more attention and significance in recent years [ 10 , 36 ]. It is a process of aerobic biotransformation of organic matter, through which a product known as compost is obtained.…”

“…Invasive marine algae biomass has been used for composting and transformed into agricultural products [ 10 ], with excellent bio-fertilizing profiles [ 37 ]. The composting quality is intimately dependent on the raw materials properties, preparation methods and maturation time [ 36 ].…”

“…Additionally, because of these algae’s high terpene contents (largest fraction of volatile organic compounds, VOC), it is not easily degraded. Thus, Patón et al [ 10 ] proposed to test the bioremediation method with five different invertebrates (vermicomposting ( Dendrobaena veneta and Eisenia fetida ), blatticomposting ( Eublaberus spp. “Ivory”), mealworms ( Tenebrio molitor ) and black soldier fly larvae (BSFL, Hermetia illucens )) to identify whether invertebrate species could resist the high concentration of terpenes in this species.…”

“…Still, it should be noticed that the invasive algae are not compostable when pure. However, if combined with conditioning agents such as leftovers of garden or vegetables, they can be processed through conventional composting approaches [ 10 ].…”

“…Most studies on R. okamurae are oriented towards disseminating and monitoring the proliferation and impact of the invasive species and in identifying the causes behind its invasive character. Despite still being incipient, research on potential applications of the macroalgae is also being performed as a way of minimizing the accumulation of macroalgae residue and the costs associated with its removal and elimination from affected regions [ 10 ]. This research gives value to the residue [ 11 ], transforming a problem into an opportunity for obtaining new marketable products [ 12 ].…”