Studying interactions between excavating sponges and massive corals by the use of hybrid cores

Abstract

Excavating sponges often compete with reef‐building corals. To study sponge–coral interactions, we devised a design of hybrid cores that allows sponges and corals to be arranged side by side with similar size and shape, mimicking the situation of neighbouring organisms. Compared to earlier methods that attached sponge cores onto coral surfaces, hybrid cores provide an opportunity to study organism interactions under conditions more equal to the interacting partners. The use of hybrid cores was demonstrated for the excavating sponge Cliona orientalis and the massive coral Porites, which commonly interact on the Great Barrier Reef. Cliona orientalis and massive Porites were cut into half‐moon shaped explants and combined as hybrid cores under replicate conditions. After 90 days in an aquarium setting, positive growth of Cl. orientalis along with net bioerosion were observed in sponge control cores that combined Cl. orientalis with blank substrate. However, when Cl. orientalis and massive Porites were in contact in interaction cores, the sponge displayed negative growth and undetectable bioerosion, and was slightly overgrown by the coral. Cliona orientalis may have developed tissue extension beneath the living coral tissue, but growth and net calcification rates of massive Porites were apparently not affected by Cl. orientalis when comparing the interaction cores to coral control cores that combined massive Porites with blank substrate. Overall, the present work demonstrated that hybrid cores can be used to generate conditions suitable for studying sponge–coral interactions in the laboratory, which can also be applied in the field.

Using a thermistor flowmeter with attached video camera for monitoring sponge excurrent speed and oscular behaviour

“…As a bioeroder with photosymbionts, C. orientalis competes with hard corals for space (Fang et al, 2016a), and it increases its growth and bioerosion rates in response to ocean warming and ocean acidification (Fang et al, 2013a). Given potential decreases in carbonate accretion by corals (Hoegh-Guldberg et al, 2007), C. orientalis abundance may increase in the future.…”

Interannual variability and decadal stability of benthic organisms on an Indonesian coral reef

“…In particular, little is known of how algae and sponges take advantage of free substrate becoming available on the reef after coral mortality. Most research on horizontal advancement of sponges into dead substrate overgrown by algae has been carried out on clionaid bioeroding sponges in the Caribbean (López-Victoria & Zea, 2005; López-Victoria et al ., 2006), and on the Great Barrier Reef (Fang et al ., 2017). Studies considering direct competition between coral reef sponges and algae have also focused on bioeroding sponges (also mostly from the Caribbean), and have shown that macroalgae curtail sponge growth by rapidly occupying free space (González-Rivero et al ., 2011, 2012, 2016).…”

Sponge bioerosion and habitat degradation on Indonesian coral reefs

“…Of course the outcome in any competitive interaction is also jointly determined by the competitive abilities of the sponges neighbor, Vicente (1978) found that C. varians on Puerto Rican reefs was competitively superior to 13 coral species but was unable to overgrow Mycetophyllia lamarckiana, one of the most aggressive Caribbean coral species (Lang 1973). Fang et al (2017b) found similar competitive dominance by the Porites over C. orientalis using an ex situ experiment with sponge and coral cores. Competitive interactions are not limited to scleractinian corals, in the Caribbean there have been large increases in macroalgae abundance which are significant spatial competitors for bioeroding sponges.…”