Browsing by Author "Dyer, Alexei"

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    Acid-base regulation in the sea urchin Parechinus angulosus during CO₂-induced seawater acidification
    (2013) Dyer, Alexei; Lucas, Mike
    Ocean acidification is predicted to have adverse effects on the physiologies of marine organisms, particularly those that produce calcified structures. Extracellular homeostasis is considered to be critical to mediating the effects of ocean acidification. Due to their low metabolic rates and weak ability to regulate ion exchange, sea urchins are thought to be particularly weak acid-base regulators. Recent findings showing species-specific capacities for extracellular pH regulation however suggest that species currently exposed to natural CO₂ elevations, such as upwelling events, may have a higher capacity tolerate elevated CO₂. The sea urchin Parechinus angulosus currently experiences natural CO₂ variations within the Benguela upwelling system and is therefore predicted to possess the capacity to compensate moderate acid-base disturbances. Urchins were submitted to control (8.0), intermediate (7.7) and low (7.4) seawater pH treatments for 14 days to investigate the capacity to regulate extracellular acid-base status. Extracellular pH changes induced by exposure to intermediate (pH 7.7) seawater acidification were fully compensated through the accumulation of approximately 2.0 mmol l-1 of bicarbonate. The bicarbonate accumulation was only sufficient to partially compensate extracellular acid-base status during exposure to low (7.4) seawater pH. Results from acute (24 hour) exposure to low (7.4) seawater pH reveal that bicarbonate accumulation, despite being evident within 24 hours, is not sufficient to compensate extracellular pH. This study provides further support that sea urchins exposed to natural CO₂ variability possess a limited capacity to regulate extracellular acid-base disturbances. P.angulosus may therefore already be adapted to deal with a moderate reduction in seawater pH to 7.7, but lacks the iono-regulatory capacity to accumulate sufficient bicarbonate to deal with a reduction of seawater pH to 7.3. Long-term studies are needed to assess the role of acid-base regulation as a mediator of broader physiological tolerance to ocean acidification, and its consequences at the level of the whole organism.
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    Blattodea as potential indicators of Peninsula Granite Fynbos restoration following the clear-felling of pine plantations
    (2013) Dyer, Alexei
    Alien plant invasions pose a major threat to the biodiversity of the Cape Peninsula; currently facilitating the transformation of native vegetation and alien invertebrate invasions. This threat provided a motive for the removal of alien pine plantations from the lower slopes of Table Mountain, with the aim of restoring the currently endangered Peninsula Granite Fynbos vegetation. Despite some indication that native fynbos vegetation is recovering, the recovery of native invertebrate communities and their associated ecosystem function remains uncertain. Epigaeic invertebrates are easily sampled, highly abundant, responding rapidly to changes in habitat condition. This study investigates the potential of Blattodea species to be employed as ecological indicators of Peninsula Granite Fynbos restoration, along a chronosequence of recently-felled pine stands. Within 10 years of clear-felling, Blattodea communities inhabiting recovering fynbos do not appear to be very distinct in terms of species richness or composition from those inhabiting undisturbed Peninsula Granite Fynbos, indicating restoration progress. Despite the presence of endemic species among both habitat types, the abundance of the invasive Portuguese millipede (Ommatoiulus moreletii) at clear-felled sites suggests that the ecological footprint of pine still persists. The influence of pine could be reduced by implementing the follow-up clearance of alien trees and pine debris. Although an ecological indicator species was identified, its robustness needs to be tested under a range of spatial and temporal conditions.