Long-term physical, chemical and biological changes in a small, urban estuary

Viskich, M; Griffiths, C.L.; Erasmus, C; Lamberth, Stephen J.

doi:10.2989/1814232x.2015.1116466

Cited by 11 publications

(23 citation statements)

References 22 publications

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“…Orchestia gammarellus was also reported from Milnerton Lagoon (= Diep River Estuary) by Mead et al (2011) and by Viskich et al (2016) and additional collections during the course of this study confirm its presence there. The species was further discovered under vegetation and drift material on the banks of the lower reaches of the Berg River, where it was widespread and abundant.…”

Section: Orchestia Gammarellussupporting

confidence: 73%

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Disentangling the identities and distribution patterns of the introduced beachfleasOrchestia gammarellusandPlatorchestia platensis(Crustacea: Amphipoda: Talitridae) in South Africa

2016

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Two introduced beachfleas, Orchestia gammarellus and Platorchestia platensis, have been recorded from South Africa, but have been misidentified by some earlier researchers and, prior to this study, each was also known from just a few, scattered observations, such that their true distributions remained obscure. We illustrate both species to clarify the features that identify and distinguish them and determine their true distributions by re-examining historical samples and by collecting new material from estuaries and lagoons along the west and south coasts of South Africa. Adult males of O. gammarellus have slender antennae and characteristic expanded, flattened, oar-like distal segments on pereopod 7. Adult males of P. platensis have the peduncle of antenna 2 strongly swollen and have bulbous, but not flattened, distal segments on pereopod 7. Both species occur under wrack and other debris along the banks of estuaries and sheltered lagoons. Orchestia gammarellus is found only along the south-west coast, in the Berg River Estuary, Langebaan Lagoon and the Diep River Estuary. Previous records from Knysna were misidentifications of P. platensis. Platorchestia platensis is found at one west coast site, Langebaan Lagoon, but is widely distributed from Cape Point eastwards to at least Algoa Bay. Both species share the same habitats as several other native beachfleas and competitive interactions between native and introduced species merit investigation.

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Section: Orchestia Gammarellussupporting

confidence: 73%

“…Griffiths (1975 later realised that T. inaequalipes was, in fact, synonymous with O. gammarellus (and thus was an introduced, not an endemic, species). Orchestia gammarellus has subsequently been reported from the Diep River Estuary (= 'Milnerton Lagoon') in the suburbs of Cape Town by Mead et al (2011) and Viskich et al (2016).…”

mentioning

confidence: 99%

Disentangling the identities and distribution patterns of the introduced beachfleasOrchestia gammarellusandPlatorchestia platensis(Crustacea: Amphipoda: Talitridae) in South Africa

2016

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“…That said, marine estuarineopportunist Mugilidae, notably C. richardsonii, are now dominant. This species and the freshwater estuarine-opportunist O. mossambicus typically capitalize on the competitive advantage provided by eutrophication and other environmental perturbations (Lamberth et al, 2010;Viskich et al, 2016). Perhaps of more concern is the complete absence of the estuarine resident Atherina breviceps (Cape silverside) species that previously dominated catches during closed mouth conditions in the 1990s, i.e., subsequent to the WWTW becoming operational (James and Harrison, 2008).…”

Section: Discussionmentioning

confidence: 99%

Effective Management of Closed Hypereutrophic Estuaries Requires Catchment-Scale Interventions

Lemley

Lamberth

Manuel³

et al. 2021

Front. Mar. Sci.

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Increased nutrient loading associated with rapid population growth is the leading cause of deteriorating water quality in urbanized estuaries globally. Small estuaries are particularly sensitive to changes when connection with the marine environment is restricted, or lost, because of high water retention. The temporarily closed Hartenbos Estuary (South Africa) is an example of how such pressures can culminate in a severely degraded ecosystem. Wastewater treatment work (WWTW) discharges introduce substantial volumes of freshwater (8,000 m3 d–1) and nutrient loads (38 kg DIN d–1 and 22 kg DIP d–1) into this estuary. This constant inflow has necessitated frequent artificial breaching (inducing alternating states) of the estuary mouth to prevent flooding of low-lying developments and, occasionally, to mitigate against extreme events such as fish kills and sewage spills. This study investigated the efficacy of artificial mouth breaching practices in eliciting responses in selected abiotic and biotic parameters. Microalgal (phytoplankton and benthic diatoms), benthic macrofauna and fish community dynamics were assessed in response to mouth state and water quality conditions using a seasonal monitoring programme. The hypereutrophic nature of the Hartenbos Estuary was highlighted by persistent high-biomass phytoplankton accumulations (>100 μg Chl-a l–1), extreme dissolved oxygen conditions (0.4–20.5 mg O2 l–1) and the predominance of harmful algal bloom (HAB) events comprising Nannochloropsis sp. and Heterosigma akashiwo. Artificial breaching of the mouth facilitated limited tidal exchange and occurred approximately bimonthly once water levels exceeded 1.9 m above mean sea level (MSL). Current pressures and management interventions have culminated in an ecosystem void of natural fluctuations and instead characterised by low diversity and shifts between undesirable states. This is highlighted by the near year-round dominance of only a few opportunistic species/groups tolerant of adverse conditions (e.g., Nannochloropsis sp., Halamphora coffeiformis, oligochaetes, estuarine round herring Gilchristella aestuaria, and southern mullet Chelon richardsonii). Therefore, catchment-scale interventions such as the diversion of WWTW discharges and restoration of hydrodynamic variability are management priorities for improving the health and biodiversity of small, closed microtidal systems such as the Hartenbos Estuary.

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“…Consequently, despite been depleted throughout their range, this component of the Palmiet fish assemblage also remained stable between the two sampling periods with none of the drastic loss of important commercial and recreational species experienced in other Western Cape estuaries (e.g. Viskich et al 2016). In addition, the complete absence of alien fish species is additional evidence of the overall stability and pristine nature of the system.…”

Section: Fish Communitymentioning

confidence: 92%

“…McQuaid and Griffiths (2014) reported massive increases in invertebrate biomass and density following the introduction of an alien, reef-building polychaete into a small urban estuary in suburban Cape Town. Similarly, Viskich et al (2016) recorded dramatic changes in salinity regime and marked declines in the numbers of both invertebrate and fish species, as well as increases in numbers of invasive species, in another nearby estuary, due largely to outfall from a sewerage plant upstream. Following on those findings, our aim here is to examine the fate of another nearby, but rural, estuary and to determine whether comparable changes in species composition have occurred in a system subject to apparently much lower levels of anthropogenic disturbance.…”

mentioning

confidence: 98%

Long-term physico-chemical and faunal changes in a small, rural South African estuary

2018

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The Palmiet Estuary is a small, rural estuary in the Western Cape that only closes briefly during dry summers. The system was previously surveyed during 1979 to 1980 and we repeated the survey in April 2015 (mouth closed) and September 2015 (mouth open). Salinity, temperature, pH and oxygen saturation were measured, and invertebrate and fish faunas surveyed. Physico-chemical characteristics have undergone little directional change, apart from an apparent increase in pH, possibly as a result of changes in land use and application of fertilisers and pesticides in the catchment. Invertebrate species richness increased from 31 to 40 species, despite lower sampling effort in 2015. Most changes were among rare species, or were readily explained by changes in mouth condition and water chemistry. We also confirmed a substantial range extension of the tropical crab, Varuna litterata, rediscovered the locally endemic amphipod, Quadrivisio aviceps, and reported several new distribution records. Gastropods had virtually disappeared from the system, whereas the previously unreported bivalve, Brachidontes virgilae, had become abundant. Overall, fish diversity dropped from 19 to 11 species, but this can largely be ascribed to differences in sampling frequency, season and mouth state. Comparisons of samples from like months showed the fish assemblage to have remained fairly stable, despite changes in inflowing water chemistry and infection of fish by the pathogenic water mould, Aphanomyces invadans. Bird abundance and diversity increased substantially. No alien invertebrate or fish species were recorded. Accordingly, in marked contrast to other smaller estuaries in the region, the Palmiet Estuary has remains in relatively good condition.

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Long-term physical, chemical and biological changes in a small, urban estuary

Cited by 11 publications

References 22 publications

Disentangling the identities and distribution patterns of the introduced beachfleasOrchestia gammarellusandPlatorchestia platensis(Crustacea: Amphipoda: Talitridae) in South Africa

Disentangling the identities and distribution patterns of the introduced beachfleasOrchestia gammarellusandPlatorchestia platensis(Crustacea: Amphipoda: Talitridae) in South Africa

Effective Management of Closed Hypereutrophic Estuaries Requires Catchment-Scale Interventions

Long-term physico-chemical and faunal changes in a small, rural South African estuary

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