Abstract
Ocean acidification is a pervasive threat to coral reef ecosystems, and our understanding of the ecological processes driving patterns in tropical benthic community development in conditions of acidification is limited. We deployed limestone recruitment tiles in low aragonite saturation (Ωarag) waters during an in-situ field experiment at Puerto Morelos, Mexico, and compared them to tiles placed in control zones over a 14-month investigation. The early stages of succession showed relatively little difference in coverage of calcifying organisms between the low Ωarag and control zones. However, after 14 months of development, tiles from the low Ωarag zones had up to 70% less cover of calcifying organisms coincident with 42% more fleshy algae than the controls. The percent cover of biofilm and turf algae was also significantly greater in the low Ωarag zones, while the number of key grazing taxa remained constant. We hypothesize that fleshy algae have a competitive edge over the primary calcified space holders, coralline algae, and that acidification leads to altered competitive dynamics between various taxa. We suggest that as acidification impacts reefs in the future, there will be a shift in community assemblages away from upright and crustose coralline algae toward more fleshy algae and turf, established in the early stages of succession.
Highlights
Declining surface ocean pH is a global environmental issue likely to be deleterious for a wide range of marine organisms [1,2,3]
Five groups were comprised of calcareous organisms: including erect and crustose coralline algae (CCA), vermetid molluscs, tubicolous polychaetes, and encrusting foraminifera
The tiles from the ojos were generally dominated by fleshy algae, turf, and biofilm, while those in control conditions were dominated by CCA (Fig 3)
Summary
Declining surface ocean pH (ocean acidification) is a global environmental issue likely to be deleterious for a wide range of marine organisms [1,2,3]. Coral reef systems are expected to be susceptible to ocean acidification and may see significant declines in calcification over the 21st century due to declining aragonite saturation state (Oarag) [4,5,6]. Laboratory studies have described responses of many individual species to acidification [7,8,9], but ecosystem responses to acidification are complex [10,11]. Field studies are essential for understanding how complex assemblages of species may respond to declining pH [12,13,14,15,16,17,18,19].
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