Do native herbivores provide resistance to Mediterranean marine bioinvasions? A seaweed example

Abstract

Generalist herbivores in marine ecosystems are poorly examined for their potential to serve as a source of biotic resistance against algal invasion. We assessed how one of the main generalist herbivores in Mediterranean rocky reefs (the sea urchin Paracentrotus lividus) affects Lophocladia lallemandii and Caulerpa racemosa, two algal invaders with strong detrimental effects on native benthic communities. In a comparison of sea urchin gut contents to algal community composition, strong preferences were exhibited, leading to no relationship between consumption and availability. Both C. racemosa and L. lallemandi were abundant in algal assemblages (>60% occurrence), but C. racemosa (20% of diet) was consumed more than L. lallemandi (3.5%). Experimental enclosures of sea urchins (12 sea urchins * m−2) were carried out in locations where L. lallemandii was already established and C. racemosa was rare (new invasion) or abundant (established invasion). C. racemosa was negatively affected by sea urchins only when it was rare, and no effect was detected when the alga was already abundant. Results for L. lallemandi were exactly opposite: urchins limited seasonal increases in L. lallemandi in highly-invaded areas. Because of the small amount of direct consumption of L. lallemandi, its decrease in abundance may be related to the grazing of native algae where L. lallemandii is attached. Overall, our results show that high densities of native herbivores may reduce invasive algae at low densities, due to a combination of direct and indirect effects, but it has no significant effect in highly-invaded area

Under the canopy: Community-wide effects of invasive algae in Marine Protected Areas revealed by metabarcoding

“…All species have a high invasive potential and all of them are included in the black list of invasive species from IUCN (Otero et al, 2013). Both C. cylindracea and L. lallemandii were recorded for the first time in the study area in 2003 and rapidly spread to almost all benthic communities present between 0 and 45 m depth (Cebrian et al, 2011), while A. armata invasion goes back to the late 90's in the area studied (Guiry, 2017).…”

Colonization on Pinna nobilis at a marine protected area: extent of the spread of two invasive seaweeds

“…Caulerpa racemosa was recorded in the MPA in 2003 growing at 30–35 m depth, and rapidly spread to almost all benthic communities between 0 and 65 m depth. Lophocladia lallemandii was also recorded for the first time in 2003 and is currently present in nearly all habitats between 5 and 45 m depth (Cebrian et al , 2011). The fieldwork was carried out within the P. oceanica seagrass meadows in the MPA, since it is the main habitat for the bivalve P. nobilis .…”

Epiphyte assemblages of the Mediterranean seagrassPosidonia oceanica: an overview

“…Even for cases in which native herbivores feed on alien species (Cebrian et al . ), the shift from high‐diversity epiphyte assemblages to monospecific populations may influence the species composition and abundance of both grazers and mobile predators (Gestoso et al . ).…”