The alien octocoral Carijoa riisei is a biogenic substrate multiplier in artificial Brazilian shipwrecks

Abstract

Despite the obvious negative effects caused by invasive species, some recent studies have shown that the impacts at local scale are diverse and not necessarily negative. Arborescent benthic organisms such as octocorals form three-dimensional structures capable of increasing the amount of substrate available and providing shelter for epibiont species. We investigated the role of the alien octocoral Carijoa riisei on the diversity of benthic communities in three shipwrecks on the north-eastern coast of Brazil. We expected that (a) the fauna associated with the octocoral are richer and more diverse compared to the adjacent; (b) some species are exclusively associated with C. riisei; (c) the species that are present both in the areas with and without C. riisei have a greater abundance when associated with the octocoral. For this, we compared the macrobenthic communities associated with C. riisei to those found in adjacent areas where the octocoral was absent. Our study showed that the communities associated with the octocoral were 1.5 times richer and 10 times more abundant than adjacent communities, with 29 exclusive taxa. The dominant taxa were the amphipods Ericthonius brasiliensis and Podocerus brasiliensis and polychaetes of the family Syllidae. These taxa were present in areas with presence and absence of C. riisei, but their abundance was significantly greater where the octocoral was present. Our results reinforce the idea that Carijoa riisei acts as an ecosystem engineer in coastal reefs, creating new habitats and increasing diversity at a local scale, even though it is an alien species.

Keywords: Artificial reefs; Epibiosis; Non-indigenous species; Non-native species; Octocorallia; Soft coral.

Fig. 1

Geographical localization of shipwrecks on the north-eastern coast of Brazil: Servemar X (25 m depth), Taurus (25 m depth) and Lupus (36 m depth)

Fig. 2

Carijoa riisei colonies from Servemar X shipwreck. a, b details of C. riisei colonies branching and c C. riisei in the ship’s hold. Colonies are between 15 and 25 cm in length

Fig. 3

Mean values (± SD) of univariate community attributes in relation to octocoral Carijoa riisei (CP C. riisei present, CA C. riisei absent) and Sampling events (July and December 2018)

Fig. 4

Non-metric mutidimensional scaling (nMDS) plots of the macrobenthic community structure in areas with presence (CP—blue symbols) and absence (CA—green symbols) of the octocoral Carijoa riisei. Sampling events are indicated by numbers 1 (July 2018) and 2 (December 2018). Data were Log(x + 1) transformed and were used in the calculation of Bray Curtis similarities. (Color figure online)

Fig. 5

Non-metric mutidimensional scaling (nMDS) bubble plots showing the five taxa with substantial contributions to dissimilarity between areas with presence (grey bubbles) and absence (black bubbles) of the octocoral Carijoa riisei on shipwrecks (stress = 0.18). The size of each bubble represents an untransformed abundance data