Physical habitat and social conditions across a coral reef shape spatial patterns of intraspecific behavioral variation in a demersal fish

Abstract

As coral reef ecosystems decline in health worldwide, reef‐associated fishes are being impacted by changes to their coral reef habitats. While previous studies have shown coral reef structure to affect the demography of reef fishes, changes in reef conditions may also impact the behavior of reef fishes as they cope with altered habitats. In this study, we examined spatial patterns of intraspecific behavioral variation in the bicolor damselfish (Stegastes partitus) across the fringing reefs of Curaçao (Caribbean Sea), and explored how this behavioral variation associated with physical and social conditions on the reef. Principal components analysis (PCA) condensed physical parameters of the reef into principal component 1 (PC1), comprising depth, coral cover (%), rugosity, and average hole size (cm2), and principal component 2 (PC2), which represented the number of holes. PC1, but not PC2, increased spatially across the reef as the habitat transitioned from coral rubble in the shallows to live coral on the reef slope. This transition in reef structure was paralleled by changes in social conditions including decreases in bicolor damselfish density in habitats with higher PC1 values. The behavior of bicolor damselfish also varied spatially with greater aggression and more frequent shelter use in habitats with lower PC1 values. Path analysis revealed robust associations between this behavioral variation and physical habitat conditions of the reef, indicating that physical – rather than social – habitat variation is the primary determinant of these spatial patterns of intraspecific behavioral variation. Taken as a whole, this coupling between physical reef structure and behavior suggests that reef fish may show altered behaviors on coral reefs degraded by anthropogenic impacts.

Habitat-associated intraspecific variation in behavior and stress responses in a demersal coral reef fish

“…1). Schrandt et al (2011) identified distinct spatial patterns of intraspecific behavioral variation in bicolor damselfish associated with the occurrence of these 2 coral habitats at Playa Kalki. Transects (20 m in length and 3 m apart) were established on this fringing reef parallel to the shoreline, with 2 transects located in the rubble (depth range: 3.0 to 3.9 m) and 2 in live coral habitat (depth range: 5.8 to 7.9 m).…”

“…Schrandt et al (2011) identified distinct patterns of association between intra specific behavioral variation in bicolor damselfish and variation in the coral reef environment. More specifically, large (> 4 cm total length [TL]) bicolor damselfish inhabiting shallow coral rubble areas exhibited higher rates of aggression, shelter use and courtship than bicolor damselfish in areas with higher coral cover nearer the reef slope (Schrandt et al 2011). Although this previous work revealed distinct relationships between coral reef characteristics and behavior in bicolor damselfish, the physiological bases for this behavioral variation have not been examined.…”

“…In heterogeneous marine habitats such as coral reefs, it has already been established that habitat heterogeneity can lead some coral reef species, such as fishes, to exhibit intraspecific variation in behavioral and life history traits that are crucial to their population dynamics and functional roles in coral reef communities (e.g. Afonso et al 2008, Feary et al 2009, Paddack et al 2009, Schrandt et al 2011. Such habitat-associated phenotypic variation is likely to have underpinnings in the physiological stress systems.…”

“…We therefore explored whether differences in the response of the HPI axis to acute stress were present in large bicolor damselfish occupying 2 discrete types of coral reef habitat: (1) dead coral rubble, characterized by a low percentage of live coral cover substrate, and (2) live coral reef, with a comparatively high percent coral cover. Observations of the behavior of bicolor damselfish from each habitat type were first performed to confirm the behavioral differences observed previously (Schrandt et al 2011). We then collected bicolor damselfish from each habitat type and quantified changes in stressassociated mRNAs in the brain including CRH, U-I, CRH-BP, CRH-R1 and CRH-R2 following acute capture stress.…”

“…What is less commonly recognized, however, is that heterogeneity in habitat conditions can also shape the behavior and physiology of animals in ways that affect how they cope with different ecological demands. In coral reef ecosystems, for example, habitat structure varies considerably across the reef and, accordingly, relates to spa-tial variation in the behavior of reef fish (Mumby & Wabnitz 2002, Kavanagh & Olney 2006, Schrandt et al 2011. Similarly, variation in growth rate and reproductive physiological condition in coral reef fishes have also been linked to spatial variation in reef habitat structure (Pankhurst et al 2008, Feary et al 2009), indicating that a reef's physical structure can affect not only the behavioral dynamics of demersal fishes, but also the physiology underlying other traits.…”