Differences in trophic resources and niches of two juvenile predatory species in three Pangani estuarine zones, Tanzania: stomach contents and stable isotope approaches.
Alistidia Paul Mwijage, Daniel Abel Shilla, John Ferdinand Machiwa
{"title":"Differences in trophic resources and niches of two juvenile predatory species in three Pangani estuarine zones, Tanzania: stomach contents and stable isotope approaches.","authors":"Alistidia Paul Mwijage, Daniel Abel Shilla, John Ferdinand Machiwa","doi":"10.1186/s40709-018-0084-4","DOIUrl":null,"url":null,"abstract":"<p><strong>Background: </strong>Estuaries are primary habitats that serve as feeding and nursery grounds for most juvenile marine fish. However, estuaries have been used as fishing grounds by the artisanal fishers in Tanzania. The slow-growing predatory fish at juvenile and sub-adult stages are among the most frequently caught species that functionally enhance multiple linkages of energy pathways within the food web. Stomach contents and stable isotopes (δ<sup>13</sup>C and δ<sup>15</sup>N) were used to describe the nutritional sources and trophic niches between the co-existing benthic, predatory species, <i>Carangoides chrysophrys</i> and <i>Epinephelus malabaricus</i> in the Pangani estuary, Tanzania.</p><p><strong>Results: </strong>The findings indicated significant inter-specific variations in dietary composition (PERMANOVA, <i>p</i> = 0.001, pseudo-<i>F</i> = 15.81). The prey-specific index of relative importance (%PSIRI) indicated that juvenile shrimps (%PSIRI = 51.4) and Teleostei (%PSIRI = 26.5) were the main diets of <i>C. chrysophrys</i> while brachyura (%PSIRI = 38.8), juvenile shrimps (%PSIRI = 25.6) and Teleostei (%PSIRI = 23.3) were important diets of <i>E. malabaricus</i>. The isotope mixing models indicated that the predatory fish species accumulate nutrients derived from similar autotrophic sources, microphytobenthos, seagrass and macro-algae via consumption of small fish, including clupeids and mugilids. Yet, they significantly showed different isotopic niche width with varying degree of niche overlap across the longitudinal estuary gradient. This situation was justified by the presence of basal food sources among the estuarine zones that isotopically were different.</p><p><strong>Conclusion: </strong>The reliance of both predators on clupeids and mugilid preys that are trophically linked with estuarine and marine basal food sources, is an indication of low estuarine food webs' connectivity to the fresh water related food web. This situation is most likely threatening the stability of the estuarine food web structure. Management strategies and plans in place should be cautiously implemented to ensure the balanced anthropogenic freshwater use in the catchment and fishing activities, for the maintenance of the Pangani estuarine ecosystem health.</p>","PeriodicalId":50251,"journal":{"name":"Journal of Biological Research-Thessaloniki","volume":null,"pages":null},"PeriodicalIF":1.9000,"publicationDate":"2018-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1186/s40709-018-0084-4","citationCount":"4","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Journal of Biological Research-Thessaloniki","FirstCategoryId":"99","ListUrlMain":"https://doi.org/10.1186/s40709-018-0084-4","RegionNum":3,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"2018/12/1 0:00:00","PubModel":"eCollection","JCR":"Q2","JCRName":"BIOLOGY","Score":null,"Total":0}
引用次数: 4
Abstract
Background: Estuaries are primary habitats that serve as feeding and nursery grounds for most juvenile marine fish. However, estuaries have been used as fishing grounds by the artisanal fishers in Tanzania. The slow-growing predatory fish at juvenile and sub-adult stages are among the most frequently caught species that functionally enhance multiple linkages of energy pathways within the food web. Stomach contents and stable isotopes (δ13C and δ15N) were used to describe the nutritional sources and trophic niches between the co-existing benthic, predatory species, Carangoides chrysophrys and Epinephelus malabaricus in the Pangani estuary, Tanzania.
Results: The findings indicated significant inter-specific variations in dietary composition (PERMANOVA, p = 0.001, pseudo-F = 15.81). The prey-specific index of relative importance (%PSIRI) indicated that juvenile shrimps (%PSIRI = 51.4) and Teleostei (%PSIRI = 26.5) were the main diets of C. chrysophrys while brachyura (%PSIRI = 38.8), juvenile shrimps (%PSIRI = 25.6) and Teleostei (%PSIRI = 23.3) were important diets of E. malabaricus. The isotope mixing models indicated that the predatory fish species accumulate nutrients derived from similar autotrophic sources, microphytobenthos, seagrass and macro-algae via consumption of small fish, including clupeids and mugilids. Yet, they significantly showed different isotopic niche width with varying degree of niche overlap across the longitudinal estuary gradient. This situation was justified by the presence of basal food sources among the estuarine zones that isotopically were different.
Conclusion: The reliance of both predators on clupeids and mugilid preys that are trophically linked with estuarine and marine basal food sources, is an indication of low estuarine food webs' connectivity to the fresh water related food web. This situation is most likely threatening the stability of the estuarine food web structure. Management strategies and plans in place should be cautiously implemented to ensure the balanced anthropogenic freshwater use in the catchment and fishing activities, for the maintenance of the Pangani estuarine ecosystem health.
期刊介绍:
Journal of Biological Research-Thessaloniki is a peer-reviewed, open access, international journal that publishes articles providing novel insights into the major fields of biology.
Topics covered in Journal of Biological Research-Thessaloniki include, but are not limited to: molecular biology, cytology, genetics, evolutionary biology, morphology, development and differentiation, taxonomy, bioinformatics, physiology, marine biology, behaviour, ecology and conservation.