The decomposition of estuarine macrophytes under different temperature regimes

The Great Brak Estuary is a temporarily open/closed system situated along the warm temperate coast of the Western Cape, South Africa. The estuary is subject to a variety of anthropogenic impacts (e.g. freshwater abstraction and sewage discharge) that increases its susceptibility to prolonged  periods of mouth closure, eutrophication, and ultimately the formation of macroalgal blooms. The aim of this study was to determine the  decomposition characteristics of the most dominant submerged  macrophyte and macroalgal species in the Great Brak Estuary. Laboratory experiments were conducted to determine the effect of different  temperature regimes on the rate of decomposition of 3 macrophyte  species and the extent of inorganic nutrients released. The results  demonstrated that anaerobic decomposition of Zostera capensis, Ruppia  cirrhosa, and Cladophora glomerata resulted in high levels of inorganic  nutrient release over the 28-day study period. Ammonium (NH4+) was the dominant form of dissolved inorganic nitrogen (DIN) released during the decomposition process for all three species. The low levels of total  oxidised nitrogen (nitrate and nitrite) released during decomposition were attributed to the inhibition of nitrification by heterotrophic bacteria under anoxic conditions. The relative levels of dissolved inorganic phosphorus (DIP) released were lower than that observed for DIN, and peaked early on in the experimental period (ca. 7 days), thereafter stabilising or  decreasing. The DIP levels were explained, in part, by the varying nutrient requirements and limitations of each species (e.g. nitrogen-limited). The release of inorganic nutrients was greatest at higher temperatures (i.e. 25°C and 30°C), due to the reduced bacterial activity experienced at lower temperatures (i.e. 15°C). Ultimately, estuarine health deteriorates during macroalgal blooms, and therefore it is important to implement mitigation measures, such as artificial mouth breaching and plant harvesting, in order to minimise or reverse the effects of eutrophication.Keywords: Great Brak Estuary, decomposition, temperature, inorganic nutrient release, Cladophora glomerata, Zostera capensis, Ruppia cirrhos

An endangered seahorse selectively chooses an artificial structure

The development of a residential marina estate within the Knysna estuary, South Africa, introduced Reno mattresses (horizontal wire cages filled with rocks) as a novel habitat for the endangered Knysna seahorse Hippocampus capensis. Consistently high seahorse densities on these artificial structures, despite the availability of seagrass habitat, begged the question of whether this habitat was chosen by the seahorse in preference to natural vegetation. An in situ habitat choice experiment was conducted which focused on the choice made by adult H. capensis between natural vegetation (Zostera capensis) and artificial (Reno mattress) habitat within a choice chamber. Seahorses were significantly more likely to move away from Z. capensis onto a Reno mattress structure or remain on this structure. This study concludes that higher H. capensis densities on Reno mattresses within Thesen Islands Marina are owing to some positive feature of this habitat and the underlying processes responsible for the choice made by this species (additional food, holdfasts, protection) can now be investigated

Realism or idealism? Corporate social responsibility and the employee stakeholder in the global fast-food industry

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