Abstract

Understanding how fish communities respond to different coral habitats is essential for predicting the future resilience of coral reef ecosystems. This study tested whether fish assemblages differ between hard and soft coral–dominated reef plots and among coral genera. We predicted higher fish abundance and more frequent benthic interactions in hard coral plots, and genus-specific differences in community composition, behaviour, and time spent within plots. This study examined fish species diversity, richness, abundance, behaviour, and the time spent in coral habitats. The analysis encompassed seven coral genera in an Indo-Pacific reef system. Twenty 2 × 2 m reef areas, each dominated by a specific target coral genus, were surveyed using underwater video to compare fish communities between hard and soft coral habitats, and across genera. While overall species richness did not differ significantly across coral types, fish abundance was significantly lower in soft coral–dominated habitats. Genera such as Capnella and Sclerophytum supported fewer individuals and were associated with reduced fish interactions (behaviour), possibly linked to their flexible morphology or allelopathic properties. In contrast, hard coral genera like Acropora and Heliopora supported higher fish abundance, resident fish presence, and more frequent feeding and habitat use behaviours. Species-level differences were observed, with Pomacentrus moluccensis and Chromis ternatensis more common in hard coral habitats, while Thalassoma hardwicke showed a broader association across coral types, suggesting possible habitat generalism. Time-in-plot data revealed that non-resident fish spent more time in Echinopora habitats compared to other genera, highlighting subtle but ecologically relevant patterns in habitat use. These findings underscore the importance of coral genus identity, not just coral type, in shaping reef fish communities. Habitat structure, benthic composition, and coral chemistry appear to play interconnected roles in determining fish abundance, behaviour, and habitat preferences. This research highlights the need for more fine-scale ecological assessments in reef monitoring and supports a greater need for understanding and incorporating soft coral dynamics in future conservation efforts.

Awarding Institution(s)

University of Plymouth

Supervisor

Miriam Reverter, Antony Knights

Keywords

Reef fish communities, habitat structure, fish behaviour, coral genera, reef resilience, Hard versus soft coral dominance

Document Type

Thesis

Publication Date

2026

Embargo Period

2026-03-31

Deposit Date

March 2026

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