Estuarine refugia and fish responses to a large anoxic, hydrogen sulphide, “black tide” event in the adjacent marine environment

The low O2avoidance strategy of the Cape silversideAtherina breviceps(Teleostei)

“…Given the effective low O 2 avoidance behaviour of A. breviceps shown in the current study, the ability of this species to survive anoxic events in the wild does not seem unreasonable and perhaps comes as no surprise. Other species, such as Liza richardsonii, that also survived the anoxic event reported by Lamberth et al (2010) may show similar behavioural responsiveness in a laboratory setting.…”

“…Lamberth et al (2010) noted a major re-distribution of this species to a large anoxic black tide event in the Berg River estuary of South Africa. The coastal anoxic black tide event led to major mortality of strictly marine species but estuarine-associated species, such as A. breviceps, re-distributed themselves up the Berg River of St. Helena Bay and therefore used the estuary as an O 2 refuge.…”

“…The cape silverside (Atherina breviceps) is a common coastal and estuarine species from South Africa and was selected as our study species of choice because this species is seen to survive low O 2 episodes in the wild (Lamberth et al 2010) but its threshold limits, in terms of behaviour, are not yet known. Using the general methodological approach of Cook et al (2011) to examine the behavioural low O 2 response of A. breviceps, we specifically set out to answer the following two questions: (1) What level of low O 2 does A. breviceps avoid when hypoxic residence time is standardised and is this avoidance threshold consistent with the known behaviour of the species in the wild (Lamberth et al 2010)?…”

“…Using the general methodological approach of Cook et al (2011) to examine the behavioural low O 2 response of A. breviceps, we specifically set out to answer the following two questions: (1) What level of low O 2 does A. breviceps avoid when hypoxic residence time is standardised and is this avoidance threshold consistent with the known behaviour of the species in the wild (Lamberth et al 2010)? (2) Does A. breviceps show an increase or decrease in swimming speed during low O 2 exposure and does their swimming behaviour have a mechanistic link with avoidance?…”

Are floating algal mats a refuge from hypoxia for estuarine invertebrates?

“…In the Berg River Estuary, a hydrogen sulfide “black tide” from the decomposition of algae, created anoxic conditions throughout the majority of the estuary leading to massive fish mortality (Lamberth, Branch & Clark, 2010). However, the authors noted that some fish capable of tolerating more variable physicochemical conditions were able to avoid the “black tide” by entering the refugium of the upper estuary (Lamberth, Branch & Clark, 2010). The upper portions of nutrient-impacted PEI estuaries are actually the reverse, with more frequent and sustained hypoxia than exists in either the outer estuary or upstream freshwater areas (Bugden et al, 2014).…”