The Effects of the Invasive Seaweed <em>Asparagopsis Armata</em> on Native Rock Pool Communities: Evidences from Experimental Exclusion

Abstract

Biological invasions represent a threat to ecosystems, through competition and habitat destruction, which may result in significant changes of the invaded community. Asparagopsis armata is a red macroalgae (Rodophyta) globally recognized as an invasive species. It is found from the intertidal to shallow subtidal areas, on rock or epiphytic, forming natural vegetation belts on exposed coasts. This study evaluated the variations on native intertidal seaweed and macroinvertebrate assemblages inhabiting rock pools with and without the presence of the invasive macroalgae A. armata. To achieve this, manipulation experiments on Atlantic (Portugal) rock pools were done. Three rock pools were maintained without A. armata by manual removal of macroalgae, and three others were not experimentally manipulated during the study period and A. armata was freely present. In this study the variations between different rock pools were assessed. Results showed different patterns in the macroalgae composition of assemblages but not for the macrobenthic communities. Ellisolandia elongata was the main algal species affected by the invasion of A. armata. Invaded pools tended to show less species richness, showing a more constant and conservative structure, with lower variation of its taxonomic composition than the pools not containing A. armata, where the variability between samples was always higher. Despite the importance of the achieved results, further data based on observation of long-term series are needed, in order to further understand more severe effects of the invader A. armata on native macroalgal assemblage.

Asparagopsis armata Exudate Cocktail: The Quest for the Mechanisms of Toxic Action of an Invasive Seaweed on Marine Invertebrates

“…Asparagopsis armata , a species of the family Bonnemaisoniaceae is a red seaweed native to western Australia, and currently is distributed throughout Europe in the Atlantic and Mediterranean basin. This seaweed is known to form specialized cells, known as vesicle or gland cells, which are sources of these halogenated products, including halomethanes, haloalkanes, haloacids, and haloketones [ 3 , 4 ], reported to have potent biological effects to protect themselves from attacks by herbivores and pathogens [ 5 , 6 ], which may ultimately influence diversity of habitats where this seaweed is present [ 7 ].…”

“…The eutrophication and the occurrence of algal blooms may result in negative ecological consequences to the aquatic ecosystem. Algal blooms of some seaweeds, such as A. armata , which are present in shallow waters, can invade several benthic environments and be present or stranded in rock pools and release high concentrations of halogenated compounds, which can be harmful and compromise inhabiting biota [ 7 , 8 ]. Limited information is available on effects of macroalgae exudates’ secondary metabolites in aquatic environments.…”

Impacts of the Invasive Seaweed Asparagopsis armata Exudate on Energetic Metabolism of Rock Pool Invertebrates

“…The pungent aroma of this alga is attributed to an essential oil that is composed mainly of bromoform with smaller amounts of other bromine-, chlorine-, and iodine-containing methane, ethane, ethanol, acetaldehydes, acetones, 2-acetoxypropanes, propenes, epoxypropanes, acroleins, and butenones, stored in vacuoles within gland cells [ 5 ]. These potent biological effects of these compounds can induce significant changes in terms of native community composition [ 6 ], including in rock pools [ 7 ], favouring A. armata in a given niche. This aggressive invasive behaviour has placed this species in the 100 “worst invasives” in the Mediterranean [ 8 ], and its rate of invasion is steadily increasing [ 9 ] threatening native biodiversity [ 10 ].…”

“…This aggressive invasive behaviour has placed this species in the 100 “worst invasives” in the Mediterranean [ 8 ], and its rate of invasion is steadily increasing [ 9 ] threatening native biodiversity [ 10 ]. Due to the enclosed environment during low-tide, rocky pools, which tend to concentrate this seaweed [ 7 , 11 ], are sites sensitive to the increase of compounds released by retained A. armata . This release may ultimately present adverse effects for other organisms such as seaweed, vertebrates or invertebrates, leading to severe consequences for coastal ecosystems [ 7 , 12 , 13 ].…”

“…Due to the enclosed environment during low-tide, rocky pools, which tend to concentrate this seaweed [ 7 , 11 ], are sites sensitive to the increase of compounds released by retained A. armata . This release may ultimately present adverse effects for other organisms such as seaweed, vertebrates or invertebrates, leading to severe consequences for coastal ecosystems [ 7 , 12 , 13 ]. To investigate potential ecological impairments caused by these compounds, key species in the structure and functioning of coastal ecosystems were used: the common prawn Palaemon elegans and the gastropod Gibbula umbilicalis .…”