Harmful Algal Blooms Negatively Impact Mugil cephalus Abundance in a Temperate Eutrophic Estuary

Bornman, Eugin; Lemley, Daniel A.; Adams, Janine B.; Strydom, Nadine A.

doi:10.1007/s12237-022-01125-2

Cited by 5 publications

References 56 publications

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Variation in Larval Fish Assemblage Dynamics Associated with Harmful Algal Blooms in a Temperate Estuary, South Africa

Smit

Lemley

Bornman

et al. 2023

Estuaries and Coasts

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Eutrophication and concomitant harmful algal blooms (HABs) are on the rise globally and pose a threat to larval stages of fishes that rely on estuarine nursery habitats for growth and survival. The anthropogenically altered low inflow estuary (LIE), Sundays Estuary, South Africa, supports persistent and predictable HABs. This study investigated the effects of HABs on the environmental conditions and larval fish assemblage of this warm temperate nursery area. Sampling took place during the austral spring of 2016 and 2018 at three sites in the mesohaline zone where both larval fish abundance and HABs are known to reach maxima. Physico-chemical and phytoplankton data were collected during the day and night, while larval fishes were sampled after nightfall. Physico-chemical parameters and larval fish assemblages were compared by water column (surface and bottom) and sites within the mesohaline zone, years, and HAB intensity (hypereutrophic ≥ 2781 H. akashiwo cells•mL−1; standard ≥ 205 H. akashiwo cells•mL−1; none < 205 H. akashiwo cells•mL−1). A longer period of consecutive hypereutrophic bloom conditions was recorded during 2018 compared to 2016. Dissolved oxygen concentration was notably higher during hypereutrophic blooms (χ2 = 23.759, df = 2, P < 0.001) and reached a maximum of approximately 21 mg•L−1 during the day and 13 mg•L−1 at night. Density and similarity of estuarine resident larval assemblages were negatively correlated to supersaturated dissolved oxygen concentrations. Greater mean densities of estuarine resident larvae were recorded during hypereutrophic blooms compared to standard blooms and bloom absence and diversity was lower during 2018 when hypereutrophic bloom conditions were more persistent. These changes may have major implications for successful early development of fishes that rely on the Sundays Estuary and similar LIEs as a nursery.

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Variation in Larval Fish Assemblage Dynamics Associated with Harmful Algal Blooms in a Temperate Estuary, South Africa

Smit

Lemley

Bornman

et al. 2023

Estuaries and Coasts

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Recognizing Low-Inflow Estuaries as a Common Estuary Paradigm

Largier

2023

Estuaries and Coasts

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It has become clear that estuaries with low rates of freshwater inflow are an important but overlooked sphere of estuarine science. Low-inflow estuaries (LIEs) represent a major class of estuary long downplayed because observations do not fit well in the dominant estuary paradigm, which was developed in perennially wet climates. Rather than being rare and unusual, it is now evident that LIEs are common globally and an alternate estuary paradigm within the idea of an estuary as the place where a river meets the sea. They are found mostly in areas with arid, semi-arid, or seasonally arid climates, but LIE phenomena are also found in estuaries along mountainous coasts with small watersheds and short-tailed hydrographs. Inflows can be defined as “low” relative to basin volume, tidal mixing, evaporative losses, or wave forcing at the mouth. The focus here is on common physical phenomena that emerge in low-inflow estuaries—how low river flow is expressed in estuaries. The most common is hypersalinity (and the associated potential for inverse conditions), which develops where there is a net negative water balance. However, in small microtidal estuaries, low inflow results in mouth closure even as a positive water balance may persist, accounting for extreme stratification. Attention is also given to the longitudinal density gradient and the occurrence of thermal estuaries and inverse estuaries. Finally, ocean-driven estuaries are highlighted where marine subsidies (nutrients, particulates) dominate watershed subsidies. While climate change is altering freshwater inflow to estuaries, locally driven changes are generally more important and this presents an opportunity to restore estuaries through restoring estuarine hydrology.

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Scoping an Integrated Ecosystem Assessment for the southern Benguela: fisheries still biggest risk

Bornman,

Shannon,

Jarre

2024

ICES Journal of Marine Science

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The southern Benguela ecosystem faces complex pressures from anthropogenic activities and climate change, leading to structural and functional changes. To counter ecosystem service losses, intergovernmental marine science organizations propose integrated management. However, predictions to evaluate alternative strategies are challenging due to multifaceted sector interactions affecting ecological components. Scoping phases of Integrated Ecosystem Assessments (IEA), such as the Options for Delivering Ecosystem-Based Marine Management (ODEMM), identify priority sectors and pressures for management using linkage chains and impact risk scores. This study expands a South African-wide ODEMM assessment to investigate dependent sectors in the southern Benguela. Fishing emerged as the primary sector, exhibiting high connectance and impact risk on ecological components. Disaggregation of the fishing sector into sub-sectors and over three 21-year time periods revealed the demersal trawl and mixed species inshore trawl sectors to still have the greatest impact despite recent mitigation efforts, driven by species extraction, bycatch, and ‘incidental loss’. Research gaps, such as the effects of recreational fisheries and underwater noise, were identified and need to be addressed to improve future ecosystem assessments. Additionally, the effects of climate on long-term, ecosystem-scale variability and change need more attention in IEAs and should be incorporated into frameworks such as ODEMM.

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Harmful Algal Blooms Negatively Impact Mugil cephalus Abundance in a Temperate Eutrophic Estuary

Cited by 5 publications

References 56 publications

Variation in Larval Fish Assemblage Dynamics Associated with Harmful Algal Blooms in a Temperate Estuary, South Africa

Variation in Larval Fish Assemblage Dynamics Associated with Harmful Algal Blooms in a Temperate Estuary, South Africa

Recognizing Low-Inflow Estuaries as a Common Estuary Paradigm

Scoping an Integrated Ecosystem Assessment for the southern Benguela: fisheries still biggest risk

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