Characterization of Ulva (Ulvaceae, Chlorophyta) species cultured in commercial abalone farms in South Africa, and comparison with closely related wild species, using morpho-anatomical and molecular methods

Seaweeds are among the five marine sub-sectors of species cultured in South Africa, with Ulva species cultured at a commercial scale. In South Africa, the annual production of Ulva is approximately 2000 tonnes (wet weight), with the majority of Ulva being grown in landbased paddle raceway systems receiving abalone effluent water. Cultured Ulva is mainly used as abalone feed and for bioremediation of farm effluent water. It is not sold but rather is used either as fresh feed or dried and incorporated into formulated feeds. The main commercial abalone farms growing Ulva in paddle raceway systems in South Africa are Irvin & Johnson (I&J) Cape Abalone, Abagold, Buffeljags Abalone and Diamond Coast Aquaculture in the Western Cape province, and Wild Coast Abalone in the Eastern Cape province. The main aim of this study is to precisely identify the cultured Ulva species as their identity is not clearly understood. This will provide information on the genetic diversity in the cultured material and could enable farmers to select for a species/strain that has the desired traits such as high nutritional value, rapid growth rate, resistance to diseases, and the ability to grow vegetatively, amongst others, so that the best feed is given to abalone. Next, the cultured Ulva species will be compared with closely related seashore Ulva species and with Ulva specimens from the main farming area in Hermanus to see if they are genetically similar. Ulva specimens from these farms, nearby seashores, including the Hermanus abalone farming complex in the New Harbour were identified using morpho-anatomical and molecular methods. The molecular markers employed in this study were the plastid large subunit of Ribulose-1,5-bisphosphate carboxylase/oxygenase (rbcL), Internal Transcribed Spacer of nuclear ribosomal DNA (ITS nrDNA) and the elongation factor tufA. The 12 cultured Ulva specimens belonged in the U. lacinulata clade with weak support value of 0.57 for PP in the rbcL tree, high support value of 0.86 for PP in the ITS tree and high support value of 92% and 0.92 for BP and PP, respectively, in the tufA tree. The seashore U. capensis and farmed Ulva specimens belonged in the same large U. lacinulata clade in the rbcL tree. However, the U. capensis samples and the locally cultivated Ulva samples belonged in separate sister clades with a support value of 70% and 0.75 for BP and PP, respectively, in the ITS phylogenetic tree, and 97% and 1 for BP and PP, respectively, in the tufA phylogenetic tree. Therefore, the identity of the cultivated Ulva samples is U. lacinulata and the clade containing the U. capensis samples has now been labelled as U. uncialis as it is an older available name than U. capensis. Furthermore, the foliose U. lacinulata was also found growing attached near the inlets of the Hermanus abalone farming complex in New Harbour. There was no genetic variation within the farmed Ulva samples as they were collapsed as a single haplotype by the three molecular markers. The genetic distance between the U. uncialis and farmed U. lacinulata samples were 0.16%, 0.76% and 0.92% for the markers, rbcL, ITS and tufA, respectively. Even though the low sequence divergence between the farmed U. lacinulata and U. uncialis specimens fits within the range of variability, these two clades are separate species that are closely related. Incongruences between the molecular and morpho-anatomical identification methods were observed, as the morpho-anatomical identification method identified 9 of the 12 farmed Ulva specimens as U. lactuca and the remaining as U. rigida sensu Stegenga et al. (1997). Fewer Ulva species were resolved morphologically because of the overlap in morphological description within U. lactuca sensu Stegenga et al. (1997) and U. rigida sensu Stegenga et al. (1997). Additionally, three new records of Ulva species (U. ohnoi, U. australis and U. stenophylloides) for South African seashore specimens were molecularly identified in this study, and foliose U. compressa was recorded for the first time in the region. In this study, the molecular marker tufA, was the best marker to delimit species, as its internal clades were better supported compared to the other two markers and it was able to better separate the farmed U. lacinulata samples and the seashore U. uncialis samples into two different clades