Browsing by Author "Wright, Amy G"

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    Drivers of burrow symbiont distribution in a softsediment system: host abundance or burrow trophic environment?
    (2013) Wright, Amy G; Pillay, Deena
    The Langebaan Lagoon sandflats are dominated by the burrowing activities of thalassinid shrimps. Their burrows are home to various burrow symbionts including a commensal shrimp (Betaeus jucundus), a six-legged crab (Spiroplax spiralis) and a scaleworm (Antinoe lactea). Little work has been conducted on these burrow symbionts, and the mechanisms influencing their abundance and distribution are unknown. To test whether host abundance or the burrow trophic environment (i.e. food availability) is the dominant force shaping patterns of burrow symbiont distribution, samples of host and symbiont abundances as well as chlorophyll-a and extracellular polymeric substance (EPS) measurements were taken from three sites in Langebaan Lagoon over spring and autumn. Clear signals emerged in contradiction of the hypothesis that burrow symbiont abundances peak in areas associated with high abundances of hosts. Host abundances peaked at Bottelary (10.18 counts/site ± 1.02 SE), a site where recreational activities and thalassinid shrimp bait collection are prohibited. In contrast, peak B. jucundus abundance (6.56 counts/site ± 0.37 SE) occurred at Oesterval during September – the muddy sediment of the site resulted in high sedimentary food retention and the September spring phytoplankton bloom resulted in peak chlorophylla (234.12 mg chl-a/g sediment ± 42.74 SE) and EPS (0.13 mg EPS/g sediment ± 0.008 SE) concentrations. Regression analyses confirmed that food availability was the best explanation of the patterns observed in B. jucundus distributions, over and above that of host distributions. S. spiralis and A. lactea did not show this pattern, the result of the low counts of these species in the collected samples or their reliance on food sources different to those depended on by B. jucundus. These results are of consequence in changing the way we think about symbiont distributions relative to that of the hosts, in that the two may not be linked directly, but rather influenced by larger scale trophic changes such as the availability of food within the burrow.
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    Resolution of the Marthasterias Taxonomic "Disar-star"
    (2013) Wright, Amy G; Griffiths, Charles L
    Marthasterias glacialis is a sea-star found in the cool-temperate waters of the north-eastern Atlantic as well as along the south-western tip of Africa. The South African Marthasterias population is comprised of two distinct morphotypes, a smooth, spineless rarispina form and a spiny africana form. These distinct morphotypes have been variably described as separate species, subspecies or forma by various authors over the last century. To test whether these two morphotypes are separate species, or part of a single distinct South African clade, 78 Marthasterias individuals were collected from the Cape Peninsula of South Africa. Morphological comparisons were carried out between individuals of the two forms and the results showed no significant clustering of samples. This indicates that there is no morphological separation of the forms into distinct species. The africana and rarispina forms were also shown to be genetically indistinguishable, using both a mitochondrial COI sequence and a nucleic ITS1 gene. The COI and ITS sequences of the South African specimens were also compared to that from European specimens, and the p-value distances of 4% and 3% respectively show a significant distinction between the two clades. The South African Marthasterias is thus genetically distinct from the European M. glacialis, and as such, Marthasterias africana sp. nov. will be formally described as a new species elsewhere. M. glacialis has a spine armament pattern of a series of three regular rows of spines down the length of each arm, whilst Marthasterias africana sp. nov. is either covered in many irregularly-spaced spines, or has an extraordinarily bare surface of only two spine rows per arm. M. africana sp. nov. may also have an actinal spine simulating the presence of a third inferomarginal spine. This work resolves a century of taxonomic dispute, separation and amalgamation of the two forms and establishes that will for part of a single, uniquely South African, Marthasterias species that is distinct from the European M. glacialis.