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Seaweed farming is often depicted as a sustainable form of aquaculture, contributing to poverty reduction and financial revenues in producer countries. However, farms may negatively affect seagrasses and associated organisms (e.g. invertebrate macrofauna) with possible effects on the flow of ecosystem goods and services to coastal societies. The present study investigates the influence of a seaweed farm, and the farmed seaweed Eucheuma denticulatum in particular, on fishery catches using a traditional fishing method (“madema” basket traps) in Chwaka bay (Zanzibar, Tanzania). The results suggest that a seaweed farm, compared to a seagrass bed, had no influence on catch per unit effort (no. of individuals per catch, or catch weight) or no. of species per catch, but significantly affected catch composition (i.e. how much that was caught of which species). The two species contributing most to differences between the sites were two economically important species; the herbivorous seagrass rabbit fish Siganus sutor, which was more common in the seaweed site and is known to graze on the farmed algae; and the benthic invertebrate feeder chloral wrasse Cheilinus chlorourus, more common in the seagrass site. Compared to vegetation-free bottoms, however, the catches were 3−7 times higher, and consisted of a different set of species (ANOSIM global R > 0.4). As traps placed close to the seaweeds fished three times more fish than traps placed on sand patches within the seaweed farm, the overall pattern is attributed to the presence of submerged vegetation, whether seagrass or seaweed, probably as shelter and/or food for fish. However, qualitative differences in terms of spatial and temporal dynamics between seagrass beds with and without seaweed farms, in combination with other factors such as institutional arrangements, indicate that seaweed farms cannot substitute seagrass beds as fishing grounds.

A variety of microorganisms can evolve H2 according to the following equation:2H+ + 2e +z H2. These include strict or facultative anaerobic bacteria, aerobic bacteria, blue-green and green algae. In aerobic bacteria and in blue-green algae H2 formations are restricted to N2-fixing species. Strict and facultative anaerobic bacteria as well as green algae (Chlamydomonas, Scenedesmus, Chlorella) form the gas only under O2 exclusion in the cultures. There is no clearcut demonstration for Hrformation by mosses, ferns and higher plants. Lists of the Hrforming organisms are compiled in Mortenson and Chen I and Schlegel and Schneider2. Since the redox potential of the couple 2H+ /H2 is -413 mV at pH 7.0, a low potential reductant is required for H2-formation to proceed in the cells. The reaction is also enzyme mediated. Cells may contain 3 clearly distinguishable enzymes catalyzing either uptake or evolution of H2 under physiological conditions (for a more detailed account and the references see Bothe and Eisbrenner3).

Hydrothermal carbonization is a process in which biomass is heated in water under pressure to create a char product. With higher plants, the chemistry of the process derives primarily from lignin, cellulose and hemicellulose components. In contrast, green and blue-green microalgae are not lignocellulosic in composition, and the chemistry is entirely different, involving proteins, lipids and carbohydrates (generally not cellulose). Employing relatively moderate conditions of temperature (ca. 200 C), time (<1 h) and pressure (<2 MPa), microalgae can be converted in an energy efficient manner into an algal char product that is of bituminous coal quality. Potential uses for the product include creation of synthesis gas and conversion into industrial chemicals and gasoline; application as a soil nutrient amendment; and as a carbon neutral supplement to natural coal for generation of electrical power.