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

Abstract

<p><strong>Abstract.</strong> 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.</p>

Competing with each other: Fish isotopic niche in two resource availability contexts

“…Complex substrates act as ecosystem engineers, essential in recycling carbon by retaining sediments, thus trapping nutrients (Van Oevelen et al, 2009). In addition, reef proximity influences the ichthyofauna composition of other coastal biomes, such as mangroves (Dubuc et al, 2019). Both threats should be addressed simultaneously, as habitat degradation and climate change go hand in hand.…”

The influence of physicochemical environment on the distribution and abundance of mangrove gastropods in Ngurah Rai Forest Park Bali, Indonesia

“…Measurements of DO were carried out to analyze changes in biological and chemical processes in the waters. DO concentration will be high if there is a process of photosynthesis and otherwise DO will below if there is an oxidation process of organic matter and respiration by organisms (Dubuc et al 2019;Mitra 2019). DO concentration in waters plays a role in the oxidation and reduction of organic and inorganic materials.…”

Struktur Dan Sebaran Vegetasi Mangrove Berdasarkan Kualitas Lingkungan Biofisik Di Taman Hutan Raya Ngurah Rai Bali

“…Oksigen terlarut (DO) merupakan indikator kualitas lingkungan perairan yang sangat penting bagi organisme laut. Kandungan DO dibutuhkan dalam proses respirasi dan metabolisme yang selanjutnya menghasilkan energi untuk perkembangbiakan organisme laut (Dubuc et al, 2019). Hasil pengukuran kandungan DO pada stastiun penelitian berkisar antara 2,85 -4,18 mg/l.…”