Living on the edge: single-species dominance at the Pakistan oxygen minimum zone boundary

Abstract

Oxygen minimum zones (OMZs) are naturally occurring, low-oxygen water masses that create hypoxic conditions where they impinge on the seafloor. Their lower boundaries are characterised by elevated densities of hypoxia-tolerant fauna and an abundant food supply. The polychaete Linopherus sp. nov. (Amphinomidae) is the dominant taxon at the Pakistan margin (PM) lower OMZ, at near suboxic dissolved oxygen (DO) concentrations of 5 to 8 µM. We explored the response of Linopherus sp. nov. to gradients in oxygen and organic matter (OM) availability from depths of 700 to 1100 m during the inter-and late monsoon periods. Linopherus sp. nov. was present from 800 to 1000 m, and highest densities were found at 850 m. Population size structuring was evident and smaller individuals were present at depths of lowest DO concentrations. Linopherus sp. nov. showed morphological adaptation to low DO, and respiratory surface areas were significantly larger in worms at sites of lowest DO concentrations.

Uptake of algal carbon and the likely synthesis of an "essential" fatty acid by <i>Uvigerina</i> ex. gr. <i>semiornata</i> (Foraminifera) within the Pakistan margin oxygen minimum zone: evidence from fatty acid biomarker and <sup>13</sup>C tracer experiments

“…However, uptake by the polychaete Linopherus greatly exceeded that of the foraminifera when the sample from the shallower site was incubated with tracer under more oxygenated conditions, consistent with the previous experimental results of Woulds et al (2007). Jeffreys et al (2012) suggested that this polychaete may prey on foraminifera, as well as out-compete them for food, thereby keeping their densities low. Overall, these studies suggest that foraminifera are important in organic matter cycling at very low oxygen concentrations, but out-competed by metazoan macrofauna (notably polychaetes) where these are abundant outside the OMZ core.…”

“…The papers of Woulds et al (2007) and Jeffreys et al (2012) arose from a comprehensive study of carbon cycling by benthic communities during different seasons (spring inter-monsoon and late pre-monsoon, 2003) and at different water depths (140-1850 m) across the Pakistan margin OMZ (Cowie and Levin, 2009). Within the framework of this broader investigation, we focused on the calcareous foraminifera Uvigerina ex.…”

The Ecological Physiology of Earth's Second Oxygen Revolution

“…Benthic organisms have higher respiratory surface area, with respect to size or per unit mass, in waters with lower oxygen levels (Burd 1988, Lamont & Gage 2000, Jeffreys et al 2012). However, these adaptations to increase O 2 flux can increase the risk of exposure to sulfide.…”

Distribution, biology, and ecology of the deep‐water squat lobsterGalacantha diomedeae(Crustacea: Decapoda: Galatheoidea: Munidopsidae) in the Mexican Pacific

“…Still, greater densities of individuals of G. diomedeae were observed at the 1,000-1,600 m depth range, much deeper than the OMZ core Papiol et al, 2017). In areas subjected to permanent oxygen depletion, large deposits of labile organic carbon enhance proliferation of deposit feeders and burrowers in narrow bathymetric ranges just below the OMZ cores, where DO is no longer a limiting factor (Jeffreys et al, 2012;Levin, Whitcraft, Mendoza, Gonzalez, & Cowie, 2009;Méndez, 2013;Smith et al, 2000). Among decapod crustaceans, Milne-edwards 1883) have similar diets, but the former species has lower feeding intensity and replaces the latter species in deeper water (Cartes, 1993a(Cartes, , 1993b(Cartes, , 1998.…”

“…Still, greater densities of individuals of G. diomedeae were observed at the 1,000-1,600 m depth range, much deeper than the OMZ core Papiol et al, 2017). In areas subjected to permanent oxygen depletion, large deposits of labile organic carbon enhance proliferation of deposit feeders and burrowers in narrow bathymetric ranges just below the OMZ cores, where DO is no longer a limiting factor (Jeffreys et al, 2012;Levin, Whitcraft, Mendoza, Gonzalez, & Cowie, 2009;Méndez, 2013;Smith et al, 2000). Among decapod crustaceans, benthic detritivores (the squat lobster Munidopsis depressa Faxon 1893) occur at high densities and dominate the community between 800 and 1,000 m in the Gulf of California, in an environment charac- the high correlation observed between DO and T, is consistent with the observation that ectothermic animals are restricted to speciesspecific temperature ranges (Ekau, Auel, Pörtner, & Gilbert, 2010;Frederich & Pörtner, 2000;Pörtner, 2001).…”