Abstract
Associations between habitat-forming, branching scleractinian corals and damselfish have critical implications for the function and trophic dynamics of coral reef ecosystems. This study quantifies how different characteristics of reef habitat, and of coral morphology, determine whether fish occupy a coral colony. In situ surveys of aggregative damselfish–coral associations were conducted at 51 different sites distributed among 22 reefs spread along >1700 km of the Great Barrier Reef, to quantify interaction frequency over a large spatial scale. The prevalence of fish–coral associations between five damselfish (Chromis viridis, Dascyllus aruanus, Dascyllus reticulatus, Pomacentrus amboinensis and Pomacentrus moluccensis) and five coral species (Acropora spathulata, Acropora intermedia, Pocillopora damicornis, Seriatopora hystrix, and Stylophora pistillata) averaged ~30% across all corals, but ranged from <1% to 93% of small branching corals occupied at each site, depending on reef exposure levels and habitat. Surprisingly, coral cover was not correlated with coral occupancy, or total biomass of damselfish. Instead, the biomass of damselfish was two-fold greater on sheltered sites compared with exposed sites. Reef habitat type strongly governed these interactions with reef slope/base (25%) and shallow sand-patch habitats (38%) hosting a majority of aggregative damselfish-branching coral associations compared to reef flat (10%), crest (16%), and wall habitats (11%). Among the focal coral species, Seriatopora hystrix hosted the highest damselfish biomass (12.45 g per occupied colony) and Acropora intermedia the least (6.87 g per occupied colony). Analyses of local coral colony traits indicated that multiple factors governed colony usage, including spacing between colonies on the benthos, colony position, and colony branching patterns. Nevertheless, the morphological and habitat characteristics that determine whether or not a colony is occupied by fish varied among coral species. These findings illuminate the realized niche of one of the most important and abundant reef fish families and provide a context for understanding how fish–coral interactions influence coral population and community level processes.
Highlights
Reef habitat type strongly governed these interactions with reef slope/base (25%) and shallow sand-patch habitats (38%) hosting a majority of aggregative damselfish-branching coral associations compared to reef flat (10%), crest (16%), and wall habitats (11%)
Single-species groups of Pomacentrus moluccensis or Dascyllus aruanus were recorded on 80% of occupied colonies
Small-scale occupied per transect, depending on reef habitat zone and exposure
Summary
Scleractinian corals are the predominant habitat-forming organisms within coral reef ecosystems contributing to the (i) overall structure of reef habitats [1], (ii) co-existence and biodiversity of reef associated species [2,3,4], and (iii) providing critical microhabitats used by specialist species [5,6,7,8].the abundance of coral-dwelling and reef-associated species (e.g., crustaceans, sponges, bryozoans, fishes) is influenced by the abundance of habitat-forming corals [2,9], as well as by the structural complexity provided by coral-rich habitats [4,10,11,12], and the diversity of corals [13].Diversity 2019, 11, 219; doi:10.3390/d11110219 www.mdpi.com/journal/diversityImportantly, high coral cover and habitat complexity moderate predation [14] and competition [15]among reef fish species. The abundance of coral-dwelling and reef-associated species (e.g., crustaceans, sponges, bryozoans, fishes) is influenced by the abundance of habitat-forming corals [2,9], as well as by the structural complexity provided by coral-rich habitats [4,10,11,12], and the diversity of corals [13]. Corals might be a limiting resource that regulates the distribution and abundance of many reef fishes [6,19], depending on their specificity to particular coral species and their reliance on live coral habitats. Understanding this process requires intensive and broad-scale quantification of fish–coral interactions to distinguish effects of habitat types from the effects of coral cover
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