Browsing by Author "Cruz, Mariana Anastácio"
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- Jellyfish, a threat or an opportunity? The non-indigenous blackfordia virginica as a potential food source for humans and aquatic organismsPublication . Cruz, Mariana Anastácio; Dias, Ester; Custódio, LuísaAnthropogenic activites such as those producing environmental changes have promoted the proliferation and establishment of non-indigenous species (NIS) in estuaries worldwide and the Guadiana estuary (Southern-Iberian Peninsula) is no exception. The extensive human development in this estuary, including river flow regulation, favoured the colonization by several NIS such as the black sea jellyfish Blackfordia virginica and more recently the blue crab Callinectes sapidus. The seasonal occurrence of B. virginica blooms have become a reason of concern due to reports of considerable economic and ecological impacts to fisheries and to the local food webs. However due to jellyfish properties, they represent an opportunity as an alternative food source for humans, while contributing to control their biomass in invaded ecosystems. Therefore, the objective of this work was to evaluate the nutritional profile of this jellyfish, testing the hypothethis that B. virginica represents an alternative and healthy food source if it follows the same composition of other known edible jellyfish. However, they may also represent a threat to the ecosystem if consumed by other NIS. Thus, the second objective of this work was to evaluate the contribution of B. virginica to the diet of opportunistic consumers in the middle Guadiana estuary, testing the hypothethis that generalist predators such as the NIS blue crab Callinectes sapidus and the indigenous green crab Carcinus maenas will benefit from B. virginica seasonal blooms by consuming this jellyfish. For the evaluation of the nutritional profile the determination of the total lipids (modified protocol of the Bligh & Dyer method), crude protein, (elementar analysis of nitrogen), ash content (incineration), fatty acids methyl esters, (gas chromatography-mass spectrometer; GC-MS), aminoacids (high pressure liquid chromatography; HPLC reverse phase), and minerals (microwave plasma – atomic emission spectrometry; MP-AES) were made. To investigate the contribution of B. virginica to the diet of the selected consumers, the presence of this jellyfish was investigated in the stomach contents of both crab species, through molecular analysis (DNA-PCR). Afterwards, its contribution to these consumers' biomass was determined using carbon (13C:13C/12C) and nitrogen (15N:15N/14N) stable isotope analysis. Results suggest that B. virginica dry biomass is mainly composed by essential minerals, and proteins rather than lipids. Blackfordia virginica composition resembled other edible jellyfish. Nonetheless the presence of cadmium, which is a toxic element, was high (3 mg/Kg) which meand they have a great potential to be used as food for humans if cadmium levels decrease. In addition, molecular analysis revealed the presence of B. virginica only in blue crab gut contents, although the Bayesian stable isotope mixing model did not show any relevant contribution to their biomass. Therefore the use of B. virginica for human consumption can represent an opportunity to decrease the abundance of this species in the ecosystem through commercial exploitation, while representing a threat if other NIS, mainly the blue crab, can take advantage of this species by consuming it.