Insights into the cause of an Ulva lactuca Linnaeus bloom in the Knysna Estuary

Human, L.R.D.; Adams, Janine B.; Allanson, B. R.

doi:10.1016/j.sajb.2016.05.016

Cited by 36 publications

(19 citation statements)

References 40 publications

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“…The green tide event of 2015 caused the dieback of seagrass Zostera capensis Setch. (Allanson et al 2016;Human et al 2016b) and changed the diversity of intertidal macrofauna (Barnes 2019). Polychaete numbers increased, but small malocostracan crustaceans and microgastropods diminished to insignificant levels.…”

Section: Macroalgal Bloomsmentioning

confidence: 99%

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Nutrient enrichment as a threat to the ecological resilience and health of South African microtidal estuaries

Adams

Taljaard

Niekerk

et al. 2020

African Journal of Aquatic Science

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Journal of Aquatic Science is co-published by NISC (Pty) Ltd and Informa UK Limited (trading as Taylor & Francis Group) water and to the quality of the water concerned' (OSPAR 2003). Eutrophication is characterised by a surge in primary production in response to nutrient loading that results in a loss of submerged aquatic vegetation, oxygen depletion, harmful algal blooms, imbalanced food webs, lower biodiversity, altered biogeochemical cycling and fish-kills (Conley et al. 2009; Ferreira et al. 2011; Lemley and Adams 2019a; Van Niekerk et al. 2019a). Depending on the scale of nutrient enrichment and the type of estuary, these impacts can cause the state of an estuary to change from one dominated by macrophytes to another dominated by phytoplankton and/or macroalgae (Dahlgren and Kautsky 2004; Smith and Schindler 2009; Nunes and Adams 2014; Lemley et al. 2018c). South Africa has a range of estuary types that occur across four biogeographic regions; cool temperate, warm temperate, subtropical and tropical (Whitfield 1992; Van Niekerk et al. 2020). Nutrient enrichment is a serious concern not only in temporarily closed estuaries (e.g. Groot Brak), but also in large permanently open systems

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Section: Macroalgal Bloomsmentioning

confidence: 99%

“…Gamtoos and Sundays) and well-flushed estuarine bays (e.g. Knysna) (Snow et al 2000;Human et al 2015b;2016b;Lemley et al 2018b).…”

Section: Introductionmentioning

confidence: 99%

Nutrient enrichment as a threat to the ecological resilience and health of South African microtidal estuaries

Adams

Taljaard

Niekerk

et al. 2020

African Journal of Aquatic Science

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“…Ulva spp. have been found to displace saltmarsh vegetation (Watson et al ., ) and Z. capensis (Human et al ., ) and the available natural habitat within the Knysna Estuary is most likely decreasing.…”

Section: Discussionmentioning

confidence: 99%

Monthly population density and structure patterns of an endangered seahorse Hippocampus capensis: a comparison between natural and artificial habitats

Claassens

Hodgson

2018

Journal of Fish Biology

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This study investigated aspects of the population ecology of the endangered Knysna seahorse Hippocampus capensis within different habitat types. High densities of H. capensis were found within artificial Reno mattress habitat, within the Knysna Estuary, South Africa. Monthly surveys at three sites were conducted from October 2015 to August 2016 to compare population densities of H. capensis in this artificial habitat with natural eel grass Zostera capensis habitat. Hippocampus capensis densities varied significantly across all sites and highest population densities were consistently observed within the Reno mattress habitat. Hippocampus capensis were also found to be significantly larger within the Reno mattress habitat and pooled data showed that males were significantly larger than females. The overall sex ratio for all three sites was female biased, although this varied across seasons at two sites. The findings suggest that artificial Reno mattresses provide novel habitat for this endangered species and consideration should be given to the usefulness of these structures in future conservation actions.

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“…The development of Thesen Islands Marina with artificial habitat in the form of Reno mattress combined with the alga C. tenue has provided much needed additional habitat to H. capensis . The utilisation of additional habitat by Knysna seahorse is particularly important for the conservation of this species because the seagrass beds ( Zostera capensis ) in the Knysna estuary are increasingly threatened by eutrophication (Human et al ., ) and disturbance by bait collectors (Simon et al ., ; Claassens pers. obs.).…”

Section: Discussionmentioning

confidence: 99%

Conservation value of Codium tenue habitat for the endangered Knysna seahorse Hippocampus capensis

Villiers

Barker

Claassens

et al. 2019

Journal of Fish Biology

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We investigated the density and size structure of the endangered Knysna seahorse Hippocampus capensis in the macroalga Codium tenue at three sites in a residential marina estate in the Knysna Estuary, South Africa, over an 18 month period from March 2017 to August 2018. Seahorses were present in C. tenue throughout the year. Average (± SE) densities of 0.33 (± 0.03) and 0.23 (± 0.03) seahorses per kg of C. tenue were found for 2017 and 2018 respectively. Density did not vary across sites but varied significantly across months with a decreasing trend from summer to spring. The average (± SE) adult seahorse height was 75.16 mm (± 0.63 mm) and 69.09 mm (± 0.64 mm) and mass was 2.05 g (± 0.04 g) and 1.65 g (± 0.04 g) for males and females, respectively, and an even sex ratio was observed throughout the sampling period. Height varied across months, with significantly smaller seahorses found in June and August of 2017. Tail length was highly correlated with height and therefore can serve as a potential proxy for determining the height of H. capensis. This study showed that C. tenue is consistently utilised by Knysna seahorse and should therefore be considered an important habitat to protect and facilitate the ongoing conservation of this endangered seahorse species.

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Insights into the cause of an Ulva lactuca Linnaeus bloom in the Knysna Estuary

Cited by 36 publications

References 40 publications

Nutrient enrichment as a threat to the ecological resilience and health of South African microtidal estuaries

Nutrient enrichment as a threat to the ecological resilience and health of South African microtidal estuaries

Monthly population density and structure patterns of an endangered seahorse Hippocampus capensis: a comparison between natural and artificial habitats

Conservation value of Codium tenue habitat for the endangered Knysna seahorse Hippocampus capensis

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