Tropical coral reefs are highly productive ecosystems thriving in oligotrophic waters,
a phenomenon facilitated by efficient but delicate biogeochemical cycling
within reef communities. Global climate change and local stressors are driving
phase shifts from coral- to non-calcifier-dominated states in reefs worldwide, substantially
altering reef biogeochemical functioning. While major benthic players
such as coral and macroalgae have been investigated in detail regarding carbon
and nutrient dynamics, the less conspicuous “reef cryptobiome” (sensu Carvalho
et al., 2019) – comprising most of reef diversity – has only recently gained attention.
Autonomous Reef Monitoring Structures (ARMS) have recently been
developed to sample coral reef cryptobenthic communities in a non-destructive
and standardised way, allowing exploration of these often overlooked biota. Here,
16 ARMS were deployed for seven months in four distinct habitats dominated
by different benthic players (i.e., four units per habitat) in a nearshore Red
Sea coral reef to investigate the cryptobiome associated with proxies of varying
benthic states. Two of these habitats were coral-dominated, and one each
dominated by turf algae or coral rubble. To assess the biogeochemical fluxes
of pioneering cryptobenthic communities, ARMS were incubated in situ prior
to retrieval using customised chambers. Subsequently, 16S rRNA gene amplicon
and shotgun metagenomic sequencing of the ARMS sessile (i.e., encrusting)
fractions were performed to link observed fluxes with prokaryotic taxonomic and
functional profiles, particularly regarding nitrogen cycling. The results show that
the pioneering cryptobiome represents a significant source of inorganic nutrients
and that its associated microbial communities facilitate the mineralisation and
assimilation of organic matter and provide crucial genetic functional pathways
for nitrogen cycling. Functional similarities among habitats suggested functional
redundancy despite variation in bacterial community composition. Hence, the
reef cryptobiome can be considered an important biogeochemical player in coral
reefs, actively shaping the abiotic conditions within niches of the reef framework
and driving the recruitment and persistence of crytobenthic and other reef organisms.
As communities associated with the algae-dominated reef habitat were
most distinct compositionally and biogeochemically, and as non-calcifiers are becoming
more dominant in many reefs, this has implications for intensifying phase
shifts in coral reefs worldwide. Future ARMS studies will also benefit from adjustment
of sample processing and molecular protocols, resulting in higher sample
throughput and lower costs in times of increased application of ARMS.
| Identifer | oai:union.ndltd.org:kaust.edu.sa/oai:repository.kaust.edu.sa:10754/690581 |
| Date | 03 1900 |
| Creators | Daraghmeh, Nauras |
| Contributors | Daffonchio, Daniele, Carvalho, Susana, Biological and Environmental Science and Engineering (BESE) Division, Rosado, Alexandre S. |
| Source Sets | King Abdullah University of Science and Technology |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Rights | 2024-03-26, At the time of archiving, the student author of this thesis opted to temporarily restrict access to it. The full text of this thesis will become available to the public after the expiration of the embargo on 2024-03-26. |
| Relation | N/A |
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