Biology and epibiont community of the red decorator crab, Schizophrys aspera, on the southern Great Barrier Reef

Abstract

Organismal symbioses are fundamental to biodiversity, evolution, and ecosystem functioning. On coral reefs, many decapod species have formed distinct epibiotic symbioses through decoration tendencies that enhance diet, camouflage, and defence. The red decorator crab, Schizophrys aspera (Majidae: Decapoda), has a broad Indo-Pacific distribution and is a successful predator of juvenile crown-of-thorns seastars (CoTS; Acanthaster sp.). However, little is known of the biology and decorating symbioses of S. aspera on the Great Barrier Reef (GBR), where CoTS pose ongoing management challenges. We characterised S. aspera and its epibiont community collected in coral rubble patches on the southern GBR. S. aspera predominantly used sponges (94 ± 1%; mean ± SE) in its decoration, with greater proportions of the carapace covered for juveniles (58 ± 5%) and females (46 ± 4%) compared to males (24 ± 4%). In short-term (8-d) experiments, S. aspera substantially reduced sponge (31%) and algal (47%) cover on rubble pieces, demonstrating its potential to alter sessile communities. The close association of S. aspera with sponges and algae likely reflects its diet and enhances camouflage and chemical defence in its coral rubble niche on the GBR. As sessile taxa are often noxious, we postulate that these symbioses may confer resilience of S. aspera to plancitoxins in its consumption of CoTS. Evaluating how epibiont diversity and biochemistry shape the habitat associations, distribution, and role of S. aspera as predator and prey may be important to understanding its ability to mediate CoTS densities on the GBR and elsewhere.