Contrasting hydrodynamic regimes of submerged pinnacle and emergent coral reefs

Galbraith, Gemma F., Cresswell, Benjamin J., McCormick, Mark, Bridge, Thomas C., and Jones, Geoffrey P. (2022) Contrasting hydrodynamic regimes of submerged pinnacle and emergent coral reefs. PLoS ONE, 17 (8). e0273092.

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Abstract

Hydrodynamics on coral reefs vary with depth, reef morphology and seascape position. Differences in hydrodynamic regimes strongly influence the structure and function of coral reef ecosystems. Submerged coral reefs on steep-sided, conical bathymetric features like seamounts experience enhanced water circulation as a result of interactions between currents and the abrupt physical structure. There may also be similar interactions between smaller pinnacles and regional water currents in offshore locations (crests > 10 m), while shallow reefs (crests <10 m) may be more subject to surface currents driven by wind, waves and tide. Here we tested whether coral pinnacles experienced stronger and more variable currents compared to emergent reefs at the same depth in both nearshore and offshore positions. Current speeds and temperature were monitored for 12 months at 11 reefs, representing the three different reef categories: submerged offshore pinnacles, emergent offshore reefs and emergent nearshore reefs. We found different patterns in current speeds and temperature among reef types throughout the year and between seasons. Submerged pinnacles exhibited stronger, more variable current speeds compared to both near and offshore emergent reefs. We found seasonal changes in current speeds for pinnacle and nearshore reefs but no variation in current strength on offshore reefs. Whilst instantaneous current directions did reflect the seascape position of individual sites, there was no difference in the directional variability of current speeds between reef types. Annual daily average temperatures at all reef types were not strongly seasonal, changing by less than 2 °C throughout the year. Daily temperature ranges at specific sites however, exhibited considerable variability (annual range of up to 6.5 °C), particularly amongst offshore emergent reefs which experienced the highest temperatures despite greater exposure to regional-scale circulation patterns. Additionally, we found a consistent mismatch between satellite sea surface temperatures and in-situ temperature data, which was on average 2 °C cooler throughout the annual study period. Our results suggest that distinct hydrodynamic processes occur on smaller submerged structures that are physically analogous to seamounts. Our findings highlight important nuances in environmental processes that occur on morphologically distinct coral reef habitats and these are likely to be important drivers for the community dynamics of organisms that inhabit these reefs.

Item ID: 76149
Item Type: Article (Research - C1)
ISSN: 1932-6203
Related URLs:
Copyright Information: © 2022 Galbraith et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funders: Australian Research Council (ARC), ARC Centre of Excellence for Coral Reef Studies
Projects and Grants: ARC DP190103056
Research Data: https://zenodo.org/record/6558786#.Ysxkh3bMI2w, https://github.com/gfgalbraith/kimbe_currentmeters
Date Deposited: 05 Oct 2022 00:26
FoR Codes: 31 BIOLOGICAL SCIENCES > 3103 Ecology > 310305 Marine and estuarine ecology (incl. marine ichthyology) @ 10%
37 EARTH SCIENCES > 3708 Oceanography > 370801 Biological oceanography @ 30%
37 EARTH SCIENCES > 3708 Oceanography > 370803 Physical oceanography @ 60%
SEO Codes: 18 ENVIRONMENTAL MANAGEMENT > 1805 Marine systems and management > 180502 Assessment and management of pelagic marine ecosystems @ 50%
28 EXPANDING KNOWLEDGE > 2801 Expanding knowledge > 280111 Expanding knowledge in the environmental sciences @ 50%
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