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Biogeosciences An interactive open-access journal of the European Geosciences Union
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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 20 May 2019

Research article | 20 May 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).

Hypoxia in mangroves: occurrence and impact on valuable tropical fish habitat

Alexia Dubuc1,2, Ronald Baker3, Cyril Marchand4, Nathan J. Waltham1,2, and Marcus Sheaves1,2 Alexia Dubuc et al.
  • 1College of Science and Engineering, James Cook University, Townsville, 4810, Australia
  • 2TropWATER, Townsville, 4810, Australia
  • 3Department of Marine Sciences, University of South Alabama, Dauphin Island Sea Lab, Alabama, 36528, United States of America
  • 4Institute of Exact and Applied Sciences, University of New Caledonia, Noumea, 98800, New Caledonia

Abstract. Intertidal mangrove forests are harsh environments that can naturally experience hypoxia in association with low tide. However, we know relatively little about dissolved oxygen (DO) fluctuations and DO-induced responses by fish, although DO is a fundamental water quality parameter. This study examines DO as a potential factor regulating the utilisation of intertidal mangrove forests by fish, and consequently their value. We deployed underwater video cameras, coupled with DO and depth loggers, in a mangrove forest to record changes in fish assemblages in response to tidal variations in DO and other associated environmental parameters. Our results indicate that DO underwent extreme tidal fluctuations, reaching levels as low as 14 % saturation. As DO was identified as a significant factor to explain variability in fish assemblage composition, we further investigated fish responses to DO fluctuations. Higher taxonomic richness and frequencies of occurrence were observed once DO reached 70–80 % saturation. More detailed examination revealed species-specific responses. Three distinct patterns of mangrove utilisation in response to DO were identified, driven by apparent taxa’s behavioural DO avoidance thresholds. Most taxa did not display any behavioural avoidance, including presence at the lowest DO levels, while other taxa were not observed either below 50–60 % saturation, or below 70–80 % saturation. This implies that tidal migrations, often observed in intertidal environments, could be the result of differential DO tolerances, and not simply initiated by changes in water depth. Taxa remaining in the mangrove forest even at low DO were on average more frequently observed than the other taxa, and were mostly species commonly associated with mangrove habitats. This suggests that being adapted to withstand low DO might be an important condition to use mangrove habitats extensively. The need of being tolerant to low DO could constrain fish utilisation and explain the relatively low species richness often observed in other intertidal mangrove forests.

Alexia Dubuc et al.
Interactive discussion
Status: open (until 01 Jul 2019)
Status: open (until 01 Jul 2019)
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Alexia Dubuc et al.
Data sets

Dataset: fish assemblages and environmental parameters in Bourake. A. Dubuc

Alexia Dubuc et al.
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Short summary
Little is known about how hypoxia influences mangrove fish assemblages. In-situ video observations reveal species-specific avoidance strategies in response to developing hypoxia in a mangrove forest. Taxa commonly using mangroves could withstand hypoxia while others usually associated with reef habitats were not recorded below 70 % saturation. These results suggest that hypoxia is an important factor shaping mangrove fish assemblages and could explain the low species richness usually observed.
Little is known about how hypoxia influences mangrove fish assemblages. In-situ video...