Abstract
Bathymetric distributions of photosynthetic marine invertebrate species are relatively well studied, however the importance of symbiont zonation (i.e. hosting of distinct algal endosymbiont communities over depth) in determining these depth distributions still remains unclear. Here, we assess the prevalence of symbiont zonation in tropical scleractinian corals by genotyping the Symbiodinium of the 25 most common species over a large depth range (down to 60 m) on a Caribbean reef. Symbiont depth zonation was found to be common on a reef-wide scale (11 out of 25 coral species), and a dominant feature in species with the widest depth distributions. With regards to reproductive strategy, symbiont zonation was more common in broadcasting species, which also exhibited a higher level of polymorphism in the symbiont zonation (i.e. number of different Symbiodinium profiles involved). Species with symbiont zonation exhibited significantly broader depth distributions than those without, highlighting the role of symbiont zonation in shaping the vertical distributions of the coral host. Overall, the results demonstrate that coral reefs can consist of highly structured communities over depth when considering both the coral host and their obligate photosymbionts, which probably has strong implications for the extent of connectivity between shallow and mesophotic habitats.
Highlights
Tropical scleractinian corals have been documented across a wide bathymetric range (0 to more than 100 m) within the photic2015 The Authors
As scleractinian corals depend to a great extent on photosynthesis for their energy requirements due to their obligate symbiosis with dinoflagellates from the genus Symbiodinium [8], the exponential decrease in available irradiance probably plays one of the most important roles in determining the vertical distributions of coral species [4]
Representing one of the largest genotyping efforts carried out on a single reef, this study demonstrates that coral reefs can consist of highly structured communities when taking into account both the coral host and its associated Symbiodinium
Summary
Tropical scleractinian corals have been documented across a wide bathymetric range (0 to more than 100 m) within the photic2015 The Authors. The strong environmental 2 gradients encountered across this bathymetric range are important drivers in this zonation, factors such as wave action, heterotrophic resource availability and temperature as they can differ greatly at opposite ends of the depth spectrum [4,5,6,7]. [6,12,13,14]) that can be physiologically distinct and adapted to different light conditions [15,16] Such ‘symbiont zonation’ (i.e. a bathymetric shift in associated Symbiodinium) has been observed for a range of different coral species The prevalence of ‘symbiont zonation’ on a reef-wide scale remains unknown, and it is unclear to what extent it underlies the vertical distributions of coral species
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