Research Interests
The effect of DMSP in integrated algal-abalone cultivation systems
Cultivated Ulva and Gracilaria and harvested kelp (Ecklonia maximaand Laminaria pallida) are important feeds of aquacultured abalone Haliotis midae. These algae contain dimethylsulphoniopropionate (DMSP), an odour- and tasteless compound. DMSP levels are consistently high in Ulva but lower and variable in Gracilaria and kelp. Depending on algal DMSP concentrations, abalone may accumulate DMSP at high levels through feeding. A volatile breakdown product of DMSP, dimethylsulphide (DMS), is produced in abalone tissue during processing and causes repellent tastes and odours in some batches of canned meat. This is most noticeable in abalone fed Ulva. Too little dietary DMSP may also adversely affect taste and could possibly lead to reductions in growth rates.
DMSP reportedly functions as anti-oxidant in algae, and its production is mediated by environmentally induced stress that impairs algal photosynthetic performance. We aim to study these stressors in Ulva and Gracilaria cultivation systems and in kelp beds in order to understand algal DMSP production. We plan to evaluate the anti-oxidant role of DMSP through assessing chlorophyll fluorescence. This information will be used to select and produce feeds with an optimal DMSP content that will ensure the production of high-quality abalone meat. We will also validate reports of growth-promoting properties of DMSP in invertebrates, and study other physiological functions of the compound on the physiology of the abalone. This research involves collaboration with the CSIR, various abalone farms, Prof. Richard Hill at Michigan State University, and researchers at the University of Cape Town.
Marine benthic ecology
The KwaZulu-Natal coastline offers a unique range of benthic habitats that are ideally suited for experimental investigations into marine ecological processes. Competition between groups of organisms, symbiotic algal-invertebrate associations, or the importance of omnivory in food webs dynamics are areas which I find particularly fascinating. A research direction that fits well into the framework of plant-animal interactions and experimental ecology includes studies into physical damage on tropical (coral) and subtropical reefs, with the long-term goal of comparing their relative sensitivities and resilience to damage, or abilities to recover after an impact.
Stable isotope ecology
The measurement of natural abundance stable isotope signals in various ecosystem components provides a powerfully incisive means for identifying sources of natural or anthropogenic carbon (C) or nitrogen (N) entering an ecosystem, for studying its assimilation and transformation by photoautotrophs at the base of a trophic structure, and for following subsequent incorporation and transport through the food web. In some situations, it offers the only feasible tool for studying subtle changes in marine communities resulting from human impacts, but wherever possible it should be used in conjunction with other complementary forms of measurement and acquiring data. One of my main interests is the application of stable isotope measurements to problems related to marine ecosystems in order to better understand their structure and processes. Currently we have such a project in the Greater St. Lucia Wetland Park.
Experimental investigations of isotopic fractionation
Even tough stable isotopes have been used widely in the last decade to infer trophic dependencies in food web, new evidence is now challenging our usual interpretation of the measurements. In order reconcile our 'classical' understanding with the new evidence we need a detailed understanding of factors that affect isotopic fractionation (i.e. the change in ratios of the stable isotopes as they move from one trophic level to the next) in order to unravel trophic links with increased precision. This calibration can be done by doing controlled feeding experiments in order to understand how variables such as food quality and consumer organism physiologies affect isotopic fractionation.
Environmental impacts of marine pollution
Eutrophication is one of the biggest impacts on coastal marine ecosystems today. It is difficult to generalise about the effects of nutrient enrichment on the environment as it depends largely on where the impact occurs, but in a broad sense it is safe to say that the main effect is on the primary producers. Understanding sources of nutrients entering coastal water bodies via catchments has important implications for management of our natural resources. For this reason I am very interested in the biological (physiological and ecophysiological) effects of nutrient enrichment on algae, and consequent effects on other trophic levels. Particulate matter in riverine discharge is another type of pollution with potentially significant effects (increased sedimentation and turbidity) on marine ecosystems. Since some reefs along the KwaZulu-Natal coastline is susceptible to this type of impact, this research direction will also be a fruitful line of enquiry. There are many 'tools' available for studying marine pollution of which the application of stable isotopes of N and C is one of the most powerful. This work complements my interest in nutrient flow pathways discussed earlier. I am involved in a project with the CSIR that looks at marine pollutants along the KZN coastline.
The biology of commercially important macroalgal species
Several species of economically valuable macroalgae are found along the South African coastline. The most important ones are Ecklonia maxima, Laminaria pallida, Graciliaria gracilis, Gelidium pristoides, Gelidium abbotiorum and Gelidium pteridifolium. Gracilaria has received much research attention in South Africa over the last 15 years in terms of its cultivation in land-based and open-water aquaculture systems. This genus is probably also the most widely research Rhodophyte genus in the world. The other species mentioned above are generally not suitable for cultivation, either because of economic or biological constraints. We also have several other macroalgal species that might be of possible economic importance since they do contain useable quantities of hydrocolloids (carrageenan and agar): Gigartina polycarpa, Sarcothalia stiriata, Aeodes orbitosa, Mazzaella capensis, Gelidium vittatum (formerly Suhria vittata) and Carpoblepharis flaccida. In order to diversify the number of species used commercially in South Africa, research into the biology of these species are needed. The biomass of these species along the coastline is generally too low to allow harvesting, so cultivation is the only option. Specific issues that need to be addressed include: a) studies of their environmental tolerances; b) studies into the chemical characterization of their hydrocolloids; c) selecting strains that can be propagated vegetatively; d) understanding biological and physical factors that might affect their growth during cultivation; and e) understanding the economics of seaweed cultivation. There is also scope for developing initiatives that would allow us to add value to already exploited algal resources, such as manufacturing artificial feeds that include macroalgae for use in invertebrate or fish cultivation.
Recent Publications
Anderson RJ, Bolton JJ, Smit AJ, Gillespie R, Rotmann KWG, Critchley AT (2006) The Seaweed Resources of South Africa. In: Seaweed Resources 1.0 (Critchley AT, Ohno M, Largo D, eds.), ETI BioInformatics, The Netherlands.
Botes L, Smit AJ, Cook PA (2003) The potential threat of algal blooms to the abalone (Haliotis midae) mariculture industry situated around the South African coast. Harmful Algal Blooms 2: 247-259.
Gartner A, Lavery P, Smit AJ (2002) Using the δ15N values of different functional forms of macroalgae and filter-feeders to reveal temporal and spatial patterns in sewage distribution. Marine Ecology Progress Series 235: 63-73.
Rothmann MD, Anderson RJ, Smit AJ (in press) The effect of kelp (Ecklonia maxima) harvesting on kelp population structure, growth rate and recruitment in South Africa. Journal of Aplied Phycology
Smit AJ (2001) Source identification in marine ecosystems: food web studies using δ13C and δ15N. In: (Unkovich MJ, Pate JS, McNeil AM, Gibbs J, eds.), Stable Isotope Techniques in the Study of Biological Processes and Functioning of Ecosystems, Kluwer Academic Publishers.
Smit AJ (2004) Medical and pharmaceutical applications of seaweed natural products. A review. Journal of Applied Phycology 16: 245-262.
Smit AJ (2006) Bioactivity and pharmacology of seaweed natural products. In: Seaweed Resources 1.0 (Critchley AT, Ohno M, Largo D, eds.), ETI BioInformatics, The Netherlands.
Smit AJ, Brearley A, Hyndes GA, Lavery PS, Walker DI (2006) δ15N and δ13C analysis of a Posidonia sinuosa seagrass bed in Western Australia. Aquatic Botany 84: 277-282
Smit AJ, Brearley A, Hyndes GA, Lavery PS, Walker DI (2005) Carbon and nitrogen stable isotope analysis of an Amphibolis griffithii seagrass bed. Estuarine, Coastal and Shelf Science 65: 545-556
Smit AJ, Fourie AM, Robertson BL, du Preez DR (2003) Control of the herbivorous isopod, Paridotea reticulata, in tank cultures of Gracilaria gracilis. Aquaculture 217: 385-393
Vanderklift MA, Kendrick GA, Smit AJ (2006) Differences in trophic position among sympatric sea urchin species. Estuarine, Coastal and Shelf Science 66: 291-297
Dr AJ Smit
Qualifications
B.Sc. (University of Port Elizabeth)
B.Sc. Hons. (University of Port Elizabeth)
M.Sc. (University of Port Elizabeth)
Ph.D (University of Cape Town)
Modules taught
BIOL214 - Invertebrate Diversity and Ecology
BIOL231H2 - Marine Environment
BIOL781HC - Marine Biodiversity
BIOL231H2 - Marine Environment
BIOL781HC - Marine Biodiversity
BIOD340 - Marine Science
Links
Marine Biology
Presentations
