Seasonal population dynamics and energy consumption by waterbirds in a small temperate estuary
- Hean, Jeffrey W, Craig, Adrian J F K, Richoux, Nicole B
- Authors: Hean, Jeffrey W , Craig, Adrian J F K , Richoux, Nicole B
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/456305 , vital:75501 , xlink:href="https://doi.org/10.2989/00306525.2016.1230897"
- Description: Simple measures of population dynamics and energy consumption can provide baseline information on the role of consumers in food webs, particularly for cryptic or highly-mobile species of waterbirds. We provide estimates of the seasonal population dynamics and energy consumption of waterbirds along the Kowie Estuary, South Africa. Ten census counts were conducted every month along the estuary from June 2013 to May 2014. Energy consumption and fresh-matter intake were calculated based on body-mass equations. Piscivorous birds dominated the waterbird assemblage during summer (up to 289 individuals), whereas non-migratory shorebirds were dominant at other times of the year. The total wet mass of prey items ingested by waterbirds ranged from 2.8 kg ha−1 during winter to 8.5 kg ha−1 during summer. The total energy consumption of waterbirds ranged from 12 543 kJ ha−1 during June to 33 104 kJ ha−1 during December. Shannon–Wiener diversity calculations revealed that the Kowie Estuary had a greater diversity of waterbirds than several other South African estuaries, but less diversity than many large European estuaries. Studies that incorporate census counts and energy consumption measures, although rudimentary, may provide valuable information on resource use by waterbirds in estuaries and may benefit conservation management schemes.
- Full Text:
- Date Issued: 2017
- Authors: Hean, Jeffrey W , Craig, Adrian J F K , Richoux, Nicole B
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/456305 , vital:75501 , xlink:href="https://doi.org/10.2989/00306525.2016.1230897"
- Description: Simple measures of population dynamics and energy consumption can provide baseline information on the role of consumers in food webs, particularly for cryptic or highly-mobile species of waterbirds. We provide estimates of the seasonal population dynamics and energy consumption of waterbirds along the Kowie Estuary, South Africa. Ten census counts were conducted every month along the estuary from June 2013 to May 2014. Energy consumption and fresh-matter intake were calculated based on body-mass equations. Piscivorous birds dominated the waterbird assemblage during summer (up to 289 individuals), whereas non-migratory shorebirds were dominant at other times of the year. The total wet mass of prey items ingested by waterbirds ranged from 2.8 kg ha−1 during winter to 8.5 kg ha−1 during summer. The total energy consumption of waterbirds ranged from 12 543 kJ ha−1 during June to 33 104 kJ ha−1 during December. Shannon–Wiener diversity calculations revealed that the Kowie Estuary had a greater diversity of waterbirds than several other South African estuaries, but less diversity than many large European estuaries. Studies that incorporate census counts and energy consumption measures, although rudimentary, may provide valuable information on resource use by waterbirds in estuaries and may benefit conservation management schemes.
- Full Text:
- Date Issued: 2017
The effect of different dietary microalgae on the fatty acid profile, fecundity and population development of the calanoid copepod Pseudodiaptomus hessei (Copepoda: Calanoida)
- Siqwepu, Oyama, Richoux, Nicole B, Vine, Niall G
- Authors: Siqwepu, Oyama , Richoux, Nicole B , Vine, Niall G
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/456318 , vital:75502 , xlink:href="https://doi.org/10.1016/j.aquaculture.2016.10.008"
- Description: We studied the effect of dietary microalgae on the fecundity, population development, and fatty acid profile [with focus on the essential fatty acids docosahexaenoic acid (DHA; 22:6ω3) and eicosapentaenoic acid (EPA; 20:5ω3)] of the calanoid copepod Pseudodiaptomus hessei, a potential live food for finfish larvae in aquaculture. Two mono-algal diets, the Tahitian strain of Isochrysis galbana and Rhodomonas salina, and a 50:50 binary diet of the two were fed to copepods. Wild caught copepods were used as a baseline reference point. Copepods fed I. galbana and the 50:50 binary diet had high DHA:EPA ratios and DHA content relative to those fed R. salina. The EPA content of the copepods was similar for all three diets. Copepods fed R. salina had the highest fecundity relative to those fed I. galbana and the 50:50 binary diet. The largest population was obtained when the copepods were fed I. galbana, which differed from those fed R. salina and the 50:50 binary diet. The results of this study showed that the fatty acid composition of P. hessei can be altered by changing its dietary microalgae, and that the copepod can accumulate fatty acids from its diet, especially DHA and EPA. Diet also affected fecundity and population development of P. hessei, so this species represents a potential live food candidate for marine finfish larvae as its nutritional composition and productivity can be manipulated to suit the needs of marine finfish larvae.
- Full Text:
- Date Issued: 2017
- Authors: Siqwepu, Oyama , Richoux, Nicole B , Vine, Niall G
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/456318 , vital:75502 , xlink:href="https://doi.org/10.1016/j.aquaculture.2016.10.008"
- Description: We studied the effect of dietary microalgae on the fecundity, population development, and fatty acid profile [with focus on the essential fatty acids docosahexaenoic acid (DHA; 22:6ω3) and eicosapentaenoic acid (EPA; 20:5ω3)] of the calanoid copepod Pseudodiaptomus hessei, a potential live food for finfish larvae in aquaculture. Two mono-algal diets, the Tahitian strain of Isochrysis galbana and Rhodomonas salina, and a 50:50 binary diet of the two were fed to copepods. Wild caught copepods were used as a baseline reference point. Copepods fed I. galbana and the 50:50 binary diet had high DHA:EPA ratios and DHA content relative to those fed R. salina. The EPA content of the copepods was similar for all three diets. Copepods fed R. salina had the highest fecundity relative to those fed I. galbana and the 50:50 binary diet. The largest population was obtained when the copepods were fed I. galbana, which differed from those fed R. salina and the 50:50 binary diet. The results of this study showed that the fatty acid composition of P. hessei can be altered by changing its dietary microalgae, and that the copepod can accumulate fatty acids from its diet, especially DHA and EPA. Diet also affected fecundity and population development of P. hessei, so this species represents a potential live food candidate for marine finfish larvae as its nutritional composition and productivity can be manipulated to suit the needs of marine finfish larvae.
- Full Text:
- Date Issued: 2017
Food preferences of the estuarine crab Sesarma catenata estimated through laboratory experiments
- Bergamino, Leandro, Richoux, Nicole B
- Authors: Bergamino, Leandro , Richoux, Nicole B
- Date: 2015
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/457256 , vital:75620 , xlink:href="https://doi.org/10.1071/MF14122"
- Description: Feeding by sesarmid crabs on plants represents an important energy pathway within some estuarine ecosystems. We examined the trophic ecology of estuarine sesarmid crabs Sesarma catenata through a series of laboratory feeding-preference experiments. Our experiments considered decomposed and mature leaves of terrestrial riparian trees, marsh plants Chenolea diffusa and Sarcocornia perennis and the marshgrass Spartina maritima as potential food items. S. catenata preferred decomposed leaves of terrestrial riparian trees, followed by decomposed and mature leaves of S. maritima. We suggest that the low carbon:nitrogen (C:N) ratios of S. maritima and high bacterial production associated with decomposed terrestrial leaves may explain the trophic behaviour of S. catenata. The faecal production by S. catenata during these experiments confirmed the preferential assimilation of decomposed material by the crabs. By combining the consumption rates with an estimated density of S. catenata within the local estuary that it inhabits, we suggest that moderate proportions of the leaf material can potentially be consumed by this species (34% of total leaf litter), leaving substantial amounts of unconsumed leaf litter that may represent an important subsidy for adjacent environments. Our results validate previously published trophic data, showing the value of linking feeding experiments with biological tracers to improve food-web models.
- Full Text:
- Date Issued: 2015
- Authors: Bergamino, Leandro , Richoux, Nicole B
- Date: 2015
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/457256 , vital:75620 , xlink:href="https://doi.org/10.1071/MF14122"
- Description: Feeding by sesarmid crabs on plants represents an important energy pathway within some estuarine ecosystems. We examined the trophic ecology of estuarine sesarmid crabs Sesarma catenata through a series of laboratory feeding-preference experiments. Our experiments considered decomposed and mature leaves of terrestrial riparian trees, marsh plants Chenolea diffusa and Sarcocornia perennis and the marshgrass Spartina maritima as potential food items. S. catenata preferred decomposed leaves of terrestrial riparian trees, followed by decomposed and mature leaves of S. maritima. We suggest that the low carbon:nitrogen (C:N) ratios of S. maritima and high bacterial production associated with decomposed terrestrial leaves may explain the trophic behaviour of S. catenata. The faecal production by S. catenata during these experiments confirmed the preferential assimilation of decomposed material by the crabs. By combining the consumption rates with an estimated density of S. catenata within the local estuary that it inhabits, we suggest that moderate proportions of the leaf material can potentially be consumed by this species (34% of total leaf litter), leaving substantial amounts of unconsumed leaf litter that may represent an important subsidy for adjacent environments. Our results validate previously published trophic data, showing the value of linking feeding experiments with biological tracers to improve food-web models.
- Full Text:
- Date Issued: 2015
Trophic relationships of hake (Merluccius capensis and M. paradoxus) and sharks (Centrophorus squamosus, Deania calcea and D. profundorum) in the Northern (Namibia) Benguela Current region
- Iitembu, J A, Richoux, Nicole B
- Authors: Iitembu, J A , Richoux, Nicole B
- Date: 2015
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/457418 , vital:75636 , xlink:href="https://hdl.handle.net/10520/EJC183122"
- Description: The trophic relationships of two hake species (Merluccius capensis and M. paradoxus) and three shark species (Centrophorus squamosus, Deania calcea and D. profundorum) were investigated using nitrogen and carbon stable isotope signatures (15N and 13C) of their muscle tissues. The sharks were more enriched in 15N than the hake, an indication of the apex predator status of sharks. Among the sharks considered, C. squamosus occupied the highest trophic level and fed primarily on benthic prey. The two species of shark from the genus Deania were not different based on 15N or 13C, so they had similar diets. The 13C signatures indicated that M. capensis and sharks fed on prey derived from similar basal resources. However, there was a significant difference in 13C between M. paradoxus and all other species examined, suggesting that they occupied different feeding niches. Isotope-based populationmetrics showed narrower trophic ranges in sharks than M. capensis. Carbon and nitrogen ranges indicated that hake fed on a more diverse pool of carbon sources and had generally more enhanced trophic diversity in their feeding patterns than sharks. Among the species considered, C. squamosus occupied a unique isotopic space. Our results supported the hypothesis there are trophic overlaps among these species, but some interesting differentiation was revealed.
- Full Text:
- Date Issued: 2015
- Authors: Iitembu, J A , Richoux, Nicole B
- Date: 2015
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/457418 , vital:75636 , xlink:href="https://hdl.handle.net/10520/EJC183122"
- Description: The trophic relationships of two hake species (Merluccius capensis and M. paradoxus) and three shark species (Centrophorus squamosus, Deania calcea and D. profundorum) were investigated using nitrogen and carbon stable isotope signatures (15N and 13C) of their muscle tissues. The sharks were more enriched in 15N than the hake, an indication of the apex predator status of sharks. Among the sharks considered, C. squamosus occupied the highest trophic level and fed primarily on benthic prey. The two species of shark from the genus Deania were not different based on 15N or 13C, so they had similar diets. The 13C signatures indicated that M. capensis and sharks fed on prey derived from similar basal resources. However, there was a significant difference in 13C between M. paradoxus and all other species examined, suggesting that they occupied different feeding niches. Isotope-based populationmetrics showed narrower trophic ranges in sharks than M. capensis. Carbon and nitrogen ranges indicated that hake fed on a more diverse pool of carbon sources and had generally more enhanced trophic diversity in their feeding patterns than sharks. Among the species considered, C. squamosus occupied a unique isotopic space. Our results supported the hypothesis there are trophic overlaps among these species, but some interesting differentiation was revealed.
- Full Text:
- Date Issued: 2015
Stable isotope evidence of food web connectivity by a top predatory fish (Argyrosomus japonicus: Sciaenidae: Teleostei) in the Kowie Estuary, South Africa
- Bergamino, Leandro, Dalu, Tatenda, Whitfield, Alan K, Carassou, Laure, Richoux, Nicole B
- Authors: Bergamino, Leandro , Dalu, Tatenda , Whitfield, Alan K , Carassou, Laure , Richoux, Nicole B
- Date: 2014
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/457322 , vital:75625 , xlink:href="https://doi.org/10.2989/1814232X.2014.923782"
- Description: In this study, food web connectivity within the Kowie Estuary on the south-east coast of South Africa was evidenced by the trophic behaviour of the predominantly piscivorous Argyrosomus japonicus. We examined stable isotopes of carbon (δ13C) and nitrogen (δ15N) in the dominant consumers (zooplankton, invertebrates and fishes) and food sources (particulate organic matter, epibionts and benthic microalgae) in the system. An SIAR (Stable Isotope Analysis in R) mixing model was used to interpret the possible food sources for this dominant top predatory fish. Small fishes and large epibenthic invertebrates dominated the diet of A. japonicus. Based on the contrasting diet of these prey fish and invertebrates, we propose that organic matter enters the predatory fish community via two major pathways: (1) a littoral pathway dominated by benthic microalgae production and epibionts, and (2) a channel pathway dominated by suspended particulate organic matter (including phytoplankton). We conclude that the highly mobile A. japonicus consumes both pelagic and benthic fauna from the littoral and channel zones of the estuary, thereby playing a key functional role in linking food webs. This dietary diversity may help explain the success of A. japonicus as a dominant top predator in the system, primarily by increasing the energy available to this species.
- Full Text:
- Date Issued: 2014
- Authors: Bergamino, Leandro , Dalu, Tatenda , Whitfield, Alan K , Carassou, Laure , Richoux, Nicole B
- Date: 2014
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/457322 , vital:75625 , xlink:href="https://doi.org/10.2989/1814232X.2014.923782"
- Description: In this study, food web connectivity within the Kowie Estuary on the south-east coast of South Africa was evidenced by the trophic behaviour of the predominantly piscivorous Argyrosomus japonicus. We examined stable isotopes of carbon (δ13C) and nitrogen (δ15N) in the dominant consumers (zooplankton, invertebrates and fishes) and food sources (particulate organic matter, epibionts and benthic microalgae) in the system. An SIAR (Stable Isotope Analysis in R) mixing model was used to interpret the possible food sources for this dominant top predatory fish. Small fishes and large epibenthic invertebrates dominated the diet of A. japonicus. Based on the contrasting diet of these prey fish and invertebrates, we propose that organic matter enters the predatory fish community via two major pathways: (1) a littoral pathway dominated by benthic microalgae production and epibionts, and (2) a channel pathway dominated by suspended particulate organic matter (including phytoplankton). We conclude that the highly mobile A. japonicus consumes both pelagic and benthic fauna from the littoral and channel zones of the estuary, thereby playing a key functional role in linking food webs. This dietary diversity may help explain the success of A. japonicus as a dominant top predator in the system, primarily by increasing the energy available to this species.
- Full Text:
- Date Issued: 2014
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