Browsing by Author "Robinson, Tamara B."
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- ItemBlender interstitial volume : a novel virtual measurement of structural complexity applicable to marine benthic habitats(Elsevier, 2019) Sadchatheeswara, Saachi; Moloney, Coleen L.; Branch, George M.; Robinson, Tamara B.Blender interstitial volume is a novel method that utilizes 3D modeling techniques to accurately and efficiently quantify the volume of interstitial gaps in marine benthic habitats, as well as the space provided by substrate rugosity. This method builds upon the analog methods routinely used on rocky shores and intertidal habitats, including those that measure rugosity, topography, fractals and volume. The method provides a direct Euclidean measurement and uniquely allows retrospective analysis if historical data on species composition are available. Blender interstitial volume allows users to quickly build and measure a large number of samples at no extra cost. The program for Blender is free and opensource, and requires no extra equipment Once 3D models of species are made, the entire method takes less than ten minutes to complete Blender interstitial volume is as accurate as Fractal analysis in determining structural complexity on rocky shores, but is more consistent and precise, and better at discerning differences
- ItemDistribution and impact of the alien anemone Sagartia ornata in the West Coast National Park(AOSIS Publishing, 2015-03) Robinson, Tamara B.; Swart, CheruschaSagartia ornata is an alien anemone that occurs intertidally within the West Coast National Park (WCNP). Whilst baseline distributional data was gathered in 2001, the range and abundance of this alien has not been reassessed. The present study aimed to determine the current status and distribution of this anemone, to assess its diet so as to establish the role it may play as predator and to investigate its impact on sandy-shore communities. Sagartia ornata was found to be restricted to the WCNP, where it occurred in densities of up to 508 ± 218 individuals per m2 . Within the park the distribution of this anemone had changed. Populations were recorded in Nanozostera capensis seagrass beds for the first time and this alien was absent from two areas in which it had previously occurred. Diet analysis revealed indigenous polychaetes and amphipods as the dominant prey items consumed by S. ornata. This alien was found to significantly alter sandy-shore community structure, with differences caused primarily by increases in the abundance and biomass of the tanaid Anatanais gracilis and the polychaete Orbinia angrapequensis. Additionally, invaded areas supported significantly greater invertebrate diversity, density and biomass. It is concluded that whilst this anemone negatively affects native biota, its current dependence on restricted habitats precludes widespread impacts with the park. Conservation implications: With regard to conservation implications, this invasion should be routinely monitored outside the WCNP as in its native range S. ornata occurs on rocky shores and kelp holdfasts, suggesting a potential for spread along the west coast of South Africa.
- ItemFrom Chile to the South African west coast : first reports of the Chilean stone crab Homalaspis plana (H. Milne Edwards, 1834) and the South American sunstar Heliaster helianthus (Lamarck, 1816) outside their natural ranges(Regional Euro-Asian Biological Invasions Centre, 2018-10-01) Peters, Koebraa; Robinson, Tamara B.; Grabowski, MichalThe South American multiradiate sunstar Heliaster helianthus (Lamarck, 1816) and the Chilean stone crab Homalaspis plana (H. Milne Edwards, 1834) are marine predators that, previous to this report, have no invasion history. However, during subtidal maintenance of a pier within Saldanha Bay along the South African west coast during 2015–2017, a single individual of each species was detected on the seafloor. Following this, intertidal and subtidal surveys were undertaken in surrounding natural habitats, but no further individuals were recorded. Both species are native to Chile, a region with very similar environmental conditions to the west coast of South Africa and from which other South African marine alien species originate, highlighting the connectedness between these regions and the risk for future transfers and establishment. The presence of two pathways from Chile to South Africa (shipping and aquaculture imports) and closely matching environmental conditions are likely to play a role in future successful introductions of Chilean species to the South African west coast. It is, therefore, recommended that particular attention be paid to monitoring aquaculture imports from the west coast of South America and that incoming vessels from that region be inspected upon arrival. Additionally, both H. heliaster and H. plana should be added to alien species watchlists in South Africa and other regions connected to Chile via marine vectors and which experience similar environmental conditions.
- ItemFunctional responses of a cosmopolitan invader demonstrate intraspecific variability in consumer-resource dynamics(PeerJ, 2018) Howard, Brett R.; Barrios-O'Neill, Daniel; Alexander, Mhairi E.; Dick, Jaimie T. A.; Therriault, Thomas W.; Robinson, Tamara B.; Cote, Isabelle M.Background. Variability in the ecological impacts of invasive species across their geographical ranges may decrease the accuracy of risk assessments. Comparative functional response analysis can be used to estimate invasive consumer-resource dynamics, explain impact variability, and thus potentially inform impact predictions. The European green crab (Carcinus maenas) has been introduced on multiple continents beyond its native range, although its ecological impacts appear to vary among populations and regions. Our aim was to test whether consumer-resource dynamics under standardized conditions are similarly variable across the current geographic distribution of green crab, and to identify correlated morphological features. Methods. Crabs were collected from multiple populations within both native (Northern Ireland) and invasive regions (South Africa and Canada). Their functional responses to local mussels (Mytilus spp.) were tested. Attack rates and handling times were compared among green crab populations within each region, and among regions (Pacific Canada, Atlantic Canada, South Africa, and Northern Ireland). The effect of predator and prey morphology on prey consumption was investigated. Results. Across regions, green crabs consumed prey according to a Type II (hyperbolic) functional response curve. Attack rates (i.e., the rate at which a predator finds and attacks prey), handling times and maximum feeding rates differed among regions. There was a trend toward higher attack rates in invasive than in native populations. Green crabs from Canada had lower handling times and thus higher maximum feeding rates than those from South Africa and Northern Ireland. Canadian and Northern Ireland crabs had significantly larger claws than South African crabs. Claw size was a more important predictor of the proportion of mussels killed than prey shell strength. Discussion. The differences in functional response between regions reflect observed impacts of green crabs in the wild. This suggests that an understanding of consumer resource dynamics (e.g., the per capita measure of predation), derived from simple, standardized experiments, might yield useful predictions of invader impacts across geographical ranges.
- ItemMind the gap – context dependency in invasive species impacts : a case study of the ascidian Ciona robusta(Pensoft Publishers, 2017-01-04) Robinson, Tamara B.; Havenga, Brendan; Van der Merwe, Marlene; Jackson, Sue; Ruiz, GregoryENGLISH ABSTRACT: In the face of increasing invasions and limited resources, appropriate management of invasive species requires prioritisation of species for management action. This process often relies on knowledge of species specific impacts. However, as studies explicitly measuring impact of marine alien species are rare, prioritisation of management actions is often based on studies from outside the geographic area of interest. Further, few impact studies account for context dependency (e.g. seasonal variability or distinct environmental regimes), raising the question of how transferrable knowledge about the impact of a species is between invaded ranges. This study addressed this question by using the widespread invasive solitary ascidian Ciona robusta as a case study for assessing impacts across two invaded regions: South Africa and California, USA. We replicated a previously conducted experiment from California that showed that C. robusta depresses local species richness in San Francisco Bay. Our South African experiment showed no effect of C. robusta on species richness, the Shannon-Weiner diversity index or community composition, despite experiments being carried out over two years and at two depths. While these results may reflect strong density dependency in the impact of C. robusta, they serve to highlight context dependency in invasive species impacts. This suggests that until studies of impact in marine systems become common place, context dependency should be explicitly addressed as a source of uncertainty during the prioritisation of species for management action.
- ItemPatterns and traits associated with invasions by predatory marine crabs(Pensoft Publishers, 2018-08-28) Swart, Cheruscha; Visser, Vernon; Robinson, Tamara B.; Ruiz, G.Predatory crabs are considered amongst the most successful marine invasive groups. Nonetheless, most studies of these taxa have been descriptive in nature, biased towards specific species or regions and have seldom considered traits associated with invasiveness. To address this gap in knowledge, this study presents a global review of invasions by this group and applies biological trait analysis to investigate traits associated with invasion success. A total of 56 species belonging to 15 families were identified as having spread outside their native ranges. The family Portunidae supported the highest number of alien species (22). Most crabs had their origin in the North West Pacific IUCN bioregion while the Mediterranean Sea received the most species. No traits associated with successful establishment were identified, but this finding may reflect the paucity of basic biological knowledge held for many species. This lack of foundational knowledge was unexpected as crabs are large and conspicuous and likely to be well studied when compared to many other groups. Addressing this knowledge gap will be the first step towards enabling approaches like biological trait analysis that offer a means to investigate generalities in invasions.
- ItemRaising the flag on marine alien fouling species(Regional Euro-Asian Biological Invasions Centre, 2017) Peters, Koebraa; Sink, Kerry; Robinson, Tamara B.Harbours are known introduction foci of marine alien species. They act as recipients of new introductions and as sources for regional spread. We report on subtidal surveys of fouling communities from 14 harbours along the coastline of South Africa that were used to identify predictors of high alien species numbers in support of prioritisation of monitoring actions by authorities. The harbours varied in nature from large, international shipping hubs to small, regional fishing harbours and recreational marinas. Fouling assemblages were assessed using visual and scrape sampling to ensure the detection of large, mobile and small inconspicuous species. In total, 29 alien species were recorded, 15 of which were detected outside of their previously known ranges. The number of species recorded per harbour varied from five to. Results revealed that high numbers of alien species were associated with the presence of yachts and low primary productivity. Harbours which had yachts and occurred in areas with mean Chl a minimum levels lower than 0.21 mg.m⁻³ had the highest number of alien species, while harbours without yachts that were larger than 0.1km² supported the fewest alien species. These findings suggest that the presence of yachts can be used to identify harbours with high numbers of alien species, particularly in regions with low productivity. While the applicability of these findings to other regions remains to be tested, this work suggests that harbours that fall within this category could be prioritised for monitoring of marine alien species.
- ItemA synthesis of three decades of socio-ecological change in False Bay, South Africa: setting the scene for multidisciplinary research and management(2019-08-08) Pfaff, Maya C.; Logston, Renae C.; Raemaekers, Serge J. P. N.; Hermes, Juliet C.; Blamey, Laura K.; Cawthra, Hayley C.; Colenbrander, Darryl R.; Crawford, Robert J. M.; Day, Elizabeth; du Plessis, Nicole; Elwen, Simon H.; Fawcett, Sarah E.; Jury, Mark R.; Karenyi, Natasha; Kerwath, Sven E.; Kock, Alison A.; Krug, Marjolaine; Lamberth, Stephen J.; Omardien, Aaniyah; Pitcher, Grant C.; Rautenbach, Christo; Robinson, Tamara B.; Rouault, Mathieu; Ryan, Peter G.; Shillington, Frank A.; Sowman, Merle; Sparks, Conrad C.; Turpie, Jane K.; van Niekerk, Lara; Waldron, Howard N.; Yeld, Eleanor M.; Kirkman, Stephen P.Over the past three decades, marine resource management has shifted conceptually from top-down sectoral approaches towards the more systems-oriented multi-stakeholder frameworks of integrated coastal management and ecosystem-based conservation. However, the successful implementation of such frameworks is commonly hindered by a lack of cross-disciplinary knowledge transfer, especially between natural and social sciences. This review represents a holistic synthesis of three decades of change in the oceanography, biology and human dimension of False Bay, South Africa. The productivity of marine life in this bay and its close vicinity to the steadily growing metropolis of Cape Town have led to its socio-economic significance throughout history. Considerable research has highlighted shifts driven by climate change, human population growth, serial overfishing, and coastal development. Upwelling-inducing winds have increased in the region, leading to cooling and likely to nutrient enrichment of the bay. Subsequently the distributions of key components of the marine ecosystem have shifted eastward, including kelp, rock lobsters, seabirds, pelagic fish, and several alien invasive species. Increasing sea level and exposure to storm surges contribute to coastal erosion of the sandy shorelines in the bay, causing losses in coastal infrastructure and posing risk to coastal developments. Since the 1980s, the human population of Cape Town has doubled, and with it pollution has amplified. Overfishing has led to drastic declines in the catches of numerous commercially and recreationally targeted fish, and illegal fishing is widespread. The tourism value of the bay contributes substantially to the country’s economy, and whale watching, shark-cage diving and water sports have become important sources of revenue. Compliance with fisheries and environmental regulations would benefit from a systems-oriented approach whereby coastal systems are managed holistically, embracing both social and ecological goals. In this context, we synthesize knowledge and provide recommendations for multidisciplinary research and monitoring to achieve a better balance between developmental and environmental agendas.
- ItemUse and usefulness of measures of marine endemicity in South Africa(Academy of Science of South Africa, 2015-10) Griffiths, Charles L.; Robinson, Tamara B.Numerous authors have cited numbers, or proportions, of endemic species within South(ern) African marine taxa, but comparisons between these statistics are confounded by differing definitions of regional boundaries and differences among data sets analysed. These have resulted in considerable variations in published endemicity data, even within the same taxonomic group. We tabulated and compared key endemicity statistics for regional marine taxa and explained biases in the data sets. The most comprehensive data sets available give overall marine endemicity within the national boundaries of South Africa as 28–33%, but estimates within individual taxa making up these totals vary enormously, from 0% (Aves, Mammalia) to over 90% (Polyplacophora). We also examined published data documenting localised endemicity patterns around the coastline. These consistently show the highest numbers of endemics occurring along the South Coast. There are logical biogeographical reasons to expect this trend, but endemicity rates are also inherently biased by distance from defined political boundaries and by differing sampling effort locally and in neighbouring countries. Range restriction is considered a better measure of conservation status than endemicity, although it is far less often used and yields very different patterns. Properly and consistently calculated measures of national endemicity do, however, retain significant conservation value, and the rates for South Africa marine biota are high relative to other regions globally, being exceeded only by New Zealand and Antarctica. It is important that when citing endemicity statistics, researchers and conservation managers understand the definitions used and the many constraints under which these measures are derived.