Complex Residences and Sociality: How Coral Structure and Social Environment Influence Occupation Patterns in in Aquaria.

Habitat size and complexity are two of many important characteristics that can have profound effects on individual survival, growth, and reproduction. However, little is known about the influence these characteristics may have on sociality and how this may be altered in response to environmental stress. Among marine fishes, coral-dwelling gobies are highly specialized cryptobenthic fish that live almost exclusively between the branches of corals, on which they rely for survival and reproduction. The study investigated whether grouping patterns and habitat choice decisions of a facultatively social species, , were influenced by habitat complexity and size. Coral structures were 3D printed with eco-friendly polymers to create high and low complexity structures, allowing coral complexity and size to be precisely manipulated. Replicated trials consisted of three sequential 24-h treatments: (1) breeder pair only, (2) breeder pair with the addition of a subordinate, and (3) breeder pair and subordinate with a reduced size of the high complexity coral structure. All individuals were observed more frequently in the high complexity coral structure. Females chose the high complexity structure most frequently, with males and subordinates less likely to choose the high complexity structure. Breeders were more likely to occupy the high complexity coral structure even when the size of the high complexity coral structure was reduced. Breeders were observed switching more frequently in their first round (breeder pair only) compared to the latter rounds when the subordinate was added and when the coral size was reduced. Breeder males switched marginally more than breeder females. However, subordinates performed the most switches consistently throughout the two rounds they were present. These results highlight the dynamic relationship between sociality and structural complexity in a habitat specialist reef fish, with implications for our understanding of social maintenance in response to climate change and habitat loss.