Temporal and inter-species variations in the proximate and contaminant compositions of farmed mussels, Choromytilus meridionalis and Mytilus galloprovincialis, from Saldanha Bay, South Africa

Thesis (MScAgric)--Stellenbosch University, 2018.ENGLISH ABSTRACT: Seafood is known to be a healthy source of protein, minerals and omega-3 fatty acids, but trace metal and persistent organic pollution in the ocean can threaten the health of seafood consumers through the bioaccumulation of contaminants in the marine food chain. Mussel aquaculture in Saldanha Bay creates essential local employment and provides ~1600 tonnes of seafood per annum for local consumption and export, but is threatened by the expansion of heavy industry, shipping traffic and a growing human population. Research into the impact of marine pollution in aquaculture is necessary to protect farmers and consumers, and to establish baseline data for future pollution studies. To assess temporal and inter-specific variations in the proximate and contaminant compositions of the farmed mussels from Saldanha Bay, native Choromytilus meridionalis and invasive Mytilus galloprovincialis, samples were collected from commercial mussel rafts at the centre of Small Bay at two-month intervals over two-years. Mussels were analysed for differences in morphometry, whole weights, meat weights, percentage meat yields, moisture, protein, fat, ash, trace metals (determined via ICP-MS) and a range of persistent organic pollutants (determined via GC-MS/MS), including organochlorine pesticides, polyaromatic hydrocarbons and polychlorinated biphenyls (PCBs). Significant temporal variations in whole weight, meat weight, percentage meat yield, proximate composition and contaminant compositions (Fe & As in C. meridionalis, Fe, As, Hg & Pb in M. galloprovincialis, and cis-permethrin, trans-permethrin, PCB 118 & PCB 149 in both species) were linked to changes brought on by the gametogenic cycle and storm water runoff during the winter rainfall period. Morphometrically, M. galloprovincialis was found to have a longer, wider and more ventrally flattened shell than C. meridionalis, and both species had similar moisture, protein, fat and ash contents. Species-related differences were observed for Al, Cr, Fe, Zn, Cd, Pb and PCBs 118 and 149 (higher in M. galloprovincialis), and Cu and Mn (higher in C. meridionalis). While concentrations of all persistent organic pollutants within the mussels were determined to be well below international regulatory limits, As concentrations exceeded the South African maximum limit (3mg/kg wet weight) once in each species, and Pb concentrations in M. galloprovincialis exceeded local regulations for fish (0.5mg/kg w.w.) on more than one occasion, but did not exceed EU regulatory limits for bivalves (1.5mg/kg w.w.). Overall, both farmed mussel species from Saldanha Bay were determined to be healthy sources of protein and essential trace metals for consumers, with the added benefit of low fat contents. Apart from As and Pb, the samples were relatively uncontaminated with trace metals or persistent organic pollutants and likely do not pose a significant human health risk. Additional research into pollution sources in Saldanha Bay and bivalve-specific contaminant regulations are suggested to support the future growth of the aquaculture industry in South Africa. The information from this study will be useful to farmers and consumers, and as baseline data for future research.AFRIKAANSE OPSOMMING: Seekos is bekend daarvoor dat dit 'n gesonde bron van proteïene, minerale en omega-3 vetsure is, maar die voorkoms van spoormetaal en organiese besoedeling in die oseaan kan egter die gesondheid van seekos verbruikers bedreig deur middel van bioakkumulasie van kontaminante in die mariene voedselketting. In Saldanhabaai, skep mossel-akwakultuur noodsaaklike plaaslike indiensneming en lewer ~1600 ton seekos per jaar vir plaaslike verbruik en uitvoer. Dit word egter bedreig deur die uitbreiding van swaar nywerhede, skeepsverkeer en 'n toename in die menslike bevolking. Navorsing oor die impak van mariene besoedeling in akwakultuur is noodsaaklik om ten einde boere en verbruikers te beskerm maar ook vir die bepaling van basislyn data vir toekomstige besoedelingstudies. Om die tydelike en interspesifieke variasies in die proksimale en kontaminante komposisies van die gekweekte mossels van Saldanhabaai, inheemse C. meridionalis en indringende M. galloprovincialis, te evalueer, was monsters van kommersiële mosselvlotte by die middelpunt van Kleinbaai elke twee maande geoes, oor 'n tydperk van twee jaar. Mossels was ontleed om verskille in morfometrie, heelgewig, vleisgewig, persentasie vleisopbrengs, vog, proteïen, vet, as, spoormetale (bepaal met ICP-MS) en 'n reeks organiese besoedelstowwe (bepaal met GC-MS/MS), insluitend organochlorine plaagdoders, poli-aromatiese koolwaterstowwe en poli-chloor bifenyls (PCBs) te bepaal. Beduidende tydelike variasies in heelgewig, vleisgewig, persentasie vleisopbrengs, proksimale komposisie en kontaminante komposisies (Fe en As in C. meridionalis, Fe, As, Hg en Pb in M. galloprovincialis, en cis-permetrien, trans-permetrien, PCB 118 en PCB 149 in albei spesies) was gekoppel aan veranderinge wat deur die gametogene siklus en stormwaterafloop, tydens die winterreënvalperiode, veroorsaak is. Morfometries is daar gevind dat M. galloprovincialis 'n langer, wyer en meer ventrale afgeplatte dop het as dié van C. meridionalis. Beide spesies het soortgelyke vog-, proteïen-, vet- en asinhoude gehad. Spesies-verwante verskille is waargeneem vir Al, Cr, Fe, Zn, Cd, Pb en PCBs 118 en 149 (hoër in M. galloprovincialis), en Cu en Mn (hoër in C. meridionalis). Alhoewel die konsentrasies van al die organiese besoedelstowwe binne die mossels vasgestel was om vêr onder internasionale regulatoriese perke te wees, het As konsentrasies die Suid-Afrikaanse maksimum limiet (3mg/kg natgewig) een keer in elke spesie oortref en Pb konsentrasies in M. galloprovincialis plaaslike regulasies oortref vir vis (0.5mg/kg natgewig) by meer as een geleentheid, maar dit het nie die EU-regulatoriese perke vir tweekleppiges (1.5mg/kg natgewig) oorskry nie. Algeheel was dit vasgestel dat beide gekweekte mosselspesies van Saldanhabaai gesonde bronne van proteïene en noodsaaklike spoormetale vir verbruikers is, met die addisionele voordeel van 'n lae vetinhoud. Afgesien van As en Pb, was die monsters relatief onbesmet met spoormetale of organiese besoedelstowwe en hou nie 'n gesondheidsrisiko vir die mens in nie. Daar word voorgestel dat addisionele navorsing op die besoedelings bronne in Saldanhabaai en tweekleppige-spesifieke besoedelings regulasies gedoen word om die toekomstige groei van die akwakultuurbedryf in Suid-Afrika te ondersteun. Die inligting uit hierdie studie sal nuttig wees vir boere en verbruikers, en as basislyn data vir toekomstige navorsing