Effect of the temperature in biological interactions between the coral Tubastraea coccinea and the sponge Darwinella sp. in Arraial do Cabo, RJ

Abstract

The invasive cup coral Tubastraea coccinea, originary from the Pacific, was introduced in Brazil in the 80s. Today it can be found in many sites along the Brazilian Coast. Tubastraea coccinea has a great competitive ability and may overgrow weaker opponents due to chemical and physical defenses. At Arraial do Cabo, located in Southeast Brazil, the sponge Darwinella sp. is commonly found near T. coccinea. To evaluate if these species have any effect on each other’s growth, in situ experiments were performed. The first experiment, using artificial plates, was conducted at the Instituto de Estudos do Mar Almirante Paulo Moreira testing area, located at Cabo Frio Island. Colonies of T. coccinea and Darwinella sp. were fixed to PVC plates in 8 different treatments: 1) only Darwinella sp.(control 1); 2) only T. coccinea (control 2); 3) Darwinella sp. with T. coccinea mimic (0 cm- distance); 4) Darwinella sp. with T. coccinea mimic (2 cm-distance); 5) T. coccinea with Darwinella sp. mimic (0 cm-distance); 6) T. coccinea with Darwinella sp.mimic (2cm- distance); 7) T. coccinea with Darwinella sp. (0 cm-distance); 8) T. coccinea with Darwinella sp.(2cm-distance). At the second experiment, conducted on the natural substrate, three treatments were replicated: 1) only Darwinella sp.(control 1); 2) only T. coccinea (control 2); 3) T. coccinea with Darwinella sp. (0 cm). At the third experiment, the allelopathic effect of the crude extract of T. coccinea on growth of Darwinella sp. was tested. Our results demonstrated that there were no significant differences on growth of Darwinella and Tubastraea between the different treatments along time on artificial plates and on natural substrate. Likewise, the crude extract of T. coccinea did not inhibit the sponge’s growth. However, variations on Darwinella sp. growth were observed through time, probably due to the occurrence of low water temperature events, since Arraial do Cabo is a region under strong influence of upwelling. Thus, the data obtained showed that the growth of both species (Darwinella sp. and T. coccinea) is not affected (negatively or positively) by the presence of the other. Temperature variations in the Cabo Frio upwelling region seem to be more important in control the dynamics of these species populations than the biological interactions.