Effect of the Presence of Seagrass and Nutrients on Growth Rates of Farmed Kappaphycus alvarezii and Eucheuma denticulatum(Rhodophyta)

The effects of seagrass cover and nutrients on seaweed cultivation were examined in tidal pools in Tanzania. The seaweeds Eucheuma denticulatumand Kappaphycus alvareziiwere cultivated from August 2006 - August 2007 in pools with and without seagrasses, and with and without added nutrients. Growth rates of fertilised E. denticulatumwere significantly lower in the presence of seagrasses (P <0.05) but there were no significant differences (P >0.05) in the rest of the treatments. Monthly growth was lowest during the hotter months (December-February) and heavy rains (March-May), and highest during the cooler months (June-August)

A resilience lens to explore seaweed farmers’ responses to the impacts of climate change in Tanzania

Seaweed-based mariculture is an important source of livelihoods for impoverished coastal communities in Tanzania. However, the impacts of climate change across East Africa are putting a strain on the growth of the seaweed industry. Smallholder farmers are already mobilizing strategies to cope with challenges such as disease outbreaks, but they are struggling to maintain seaweed production and derive sufficient income. A better understanding of the challenges they face and the factors inhibiting their ability to build resilience is needed to inform policies and development programmes to achieve the Sustainable Development Goals, particularly Goal 13 on Climate action and Goal 14 on Life Below Water. The global demand for seaweed is expanding rapidly. Strengthening the adaptability of seaweed production to climate change is important for farmers to rely on it as a source of livelihoods on which they can build their own resilience to climate change. Drawing on qualitative data from key informant interviews in four Tanzanian seaweed-producing areas, this paper assesses the long-term resilience capacities of seaweed farmers to respond to one of the main hazards: diseases affecting seaweed crops. While several strategies help farmers maintain their income, most of them only support resilience in the short term. The increasing pressure on marine resources and the lack of regulations for supporting an equitable and sustainable seaweed-based mariculture sector do not bode well for farmers’ long-term adaptation to climate change and environmental degradation. Seaweed farming remains a crucial source of livelihoods for poor coastal communities in Tanzania, but it does not currently lead to positive transformative changes in their socio-economic conditions. Policies aiming to support sustainable aquaculture, particularly in tropical ecosystems that are highly vulnerable to climate change, must address the existing social, economic and knowledge inequities that prevent poor communities from building their resilience

Community based aquaculture in the western Indian Ocean: Challenges and opportunities for developing sustainable coastal livelihoods

The small-fisheries social-ecological system in the western Indian Ocean (WIO) represents a typical social-ecological trap setting where very poor natural resources dependent coastal communities face local and global threats and engage in unsustainable practices of exploiting limited resources. Community-based aquaculture (CBA) has been implemented as an important alternative or supplementary income generating activity for minimizing the overdependence on marine natural resources and promoting biodiversity conservation. Despite its proliferation throughout the WIO region in recent decades, little is known about the degree to which CBA activities have contributed to achieving the objectives of breaking the cycle of poverty and environmental degradation and promoting community development and biodiversity conservation. In order to improve understanding of common challenges and to generate recommendations for best practice, we assessed the most common CBA activities practiced in the region through literature review and workshop discussion involving practitioners and key stakeholders. Findings indicated that despite favorable environmental conditions for various CBA practices, the sector remains underdeveloped, with few activities delivering the intended benefits for coastal livelihoods or conservation. Constraints included a shortage of seed and feed supplies, low investment, limited technical capacity and skills, insufficient political support, and lack of a clear strategy for aquaculture development. These are compounded by a lack of engagement of local stakeholders, with decision making often dominated by donors, development agencies, and private sector partners. Many of the region’s CBA projects are designed along unrealistically short time frames, driven by donors rather than entrepreneurs, and so are unable to achieve financial sustainability, which limits the opportunity for capacity building and longer-term development. There is little or no monitoring on ecological and socioeconomic impacts. Except for a few isolated cases, links between CBA and marine conservation outcomes have rarely been demonstrated. Realizing the potential of CBA in contributing toward food security in the WIO will necessitate concerted investment and capacity strengthening to overcome these systemic challenges in the sector. Lessons herein offer managers, scientists, and policy advisors guidance on addressing the challenges faced in building strategic development initiatives around aquaculture in developing countries

The Economics of Kappaphycus Seaweed Cultivation in Developing Countries: A Comparative Analysis of Farming Systems

The farming of the red seaweed Kappaphycus alvarezii and related species as raw material for the hydrocolloid carrageenan rapidly spread from the Philippines in the late 1960s to Indonesia, Tanzania, and other tropical countries around the world. Although numerous studies have documented positive socioeconomic impacts for seaweed farming, factors such as diseases and distance to export markets have led to an uneven development of the industry. Using standard budgeting techniques, this study adapted production and market data from a FAO-led global review of seaweed farming to develop comparative enterprise budgets for eight farming systems in six countries (Indonesia, the Philippines, Tanzania, India, Solomon Islands, and Mexico). Although the basic technology package is the same across countries, the study revealed large differences in the economic performance of systems due to wide variations in farm prices and the scale of operations. Although seaweed farming is a suitable activity for small-scale producers, a minimum of 2,000m of cultures lines are still necessary to ensure adequate economic returns. Greater farming plots may be needed if farm prices are well below the average farm prices paid in Indonesia and the Philippines. Policy recommendations are made to improve the economic potential of underperforming systems

Seaweed farming pressure affects seagrass and benthic macroalgae dynamics in Chwaka Bay (Zanzibar, Tanzania)

Farming of Eucheuma denticulatum is a major activity in Zanzibar affecting seagrass ecosystems primarily through shading and trampling. The aim of this study was to test the impacts of shading and trampling during seaweed farming on seagrass meadows composed by Halophila stipulacea and Thalassia hemprichii and their associated benthic macroalgae. Areas covered by these species were selected for the building of seaweed farms in three treatments: seaweed farm plots (with shading and trampling effects), trampling plots (with trampling effects only), and control plots (with no shading or trampling effects). Reduction of light within the plots was recorded over 9 weeks. Percentage cover of seagrasses and macroalgae and shoot density of seagrasses were measured over 12 weeks to assess the impact of shading and trampling by seaweed farming activities. Light was significantly reduced in the seaweed farm plots by 75 to 90% by the end of a seaweed growth cycle. H. stipulacea, despite its capacity for rapid growth, was significantly affected by the combination of shading and trampling under the seaweed farm treatment, while the climax seagrass species T. hemprichii was unaffected. Due to the decline in H. stipulacea, benthic macroalgae cover increased in the seaweed farm treatment, suggesting a change in seagrass community dynamics. In contrast, trampling had a negative effect on the benthic macroalgae as an isolated disturbance, which suggests that seagrasses are more resistant to trampling than macroalgae and would likely dominate the benthic macrophyte community under these conditions.Leibniz-Zentrum für Marine TropenforschungUniversität Bremen (DE)Deutsche Forschungsgemeinschaft (DFG

Integrated seaweed – sea cucumber farming in Tanzania

We review piloted co-culture experiments of the sea cucumber Holothuria scabra with different seaweed species in existing lagoon-based seaweed farms in Tanzania during 2011-2014. Key questions were whether stocking densities would influence growth rates of both species, and whether deposit feeders would modify organic components in the sediments. From a social perspective, we investigate if local people are readily willing to become involved in sea cucumber farming as an optional livelihood. Seaweed-specific growth rates between 0.32 and 4.1 %d−1 were reported, showing significantly higher values for those treatments combined with sea cucumbers than for the seaweed monocul- ture (F3,1=3.20, p<0.05) at Zanzibar sites. Sea cucumber growth rates ranged from 0.14 to 1.6 gd-1, and all of the studies showed that the treatments holding H. scabra at a low stocking density (average of 130 gm-2) presented a higher growth performance than when it was stocked at more than 200 gm-2. Total organic matter in sediments increased in all treat- ments over the sampling periods (p<0.05). Some 88 percent of the surveyed local people showed willingness to partici- pate in this type of mariculture for livelihood. The survey identified theft and lack of credit as the main hindrances for this activity. H. scabra is viable for lagoon co-culture with seaweed when taking into account proper stocking density, implications on total organic matter and total organic carbon in the system, and local acceptance by local people

Seaweed farming pressure affects seagrass and benthic macroalgae dynamics in Chwaka Bay (Zanzibar, Tanzania)

Farming of Eucheuma denticulatum is a major activity in Zanzibar affecting seagrass ecosystems primarily through shading and trampling. The aim of this study was to test the impacts of shading and trampling during seaweed farming on seagrass meadows composed by Halophila stipulacea and Thalassia hemprichii and their associated benthic macroalgae. Areas covered by these species were selected for the building of seaweed farms in three treatments: seaweed farm plots (with shading and trampling effects), trampling plots (with trampling effects only), and control plots (with no shading or trampling effects). Reduction of light within the plots was recorded over 9 weeks. Percentage cover of seagrasses and macroalgae and shoot density of seagrasses were measured over 12 weeks to assess the impact of shading and trampling by seaweed farming activities. Light was significantly reduced in the seaweed farm plots by 75 to 90% by the end of a seaweed growth cycle. H. stipulacea, despite its capacity for rapid growth, was significantly affected by the combination of shading and trampling under the seaweed farm treatment, while the climax seagrass species T. hemprichii was unaffected. Due to the decline in H. stipulacea, benthic macroalgae cover increased in the seaweed farm treatment, suggesting a change in seagrass community dynamics. In contrast, trampling had a negative effect on the benthic macroalgae as an isolated disturbance, which suggests that seagrasses are more resistant to trampling than macroalgae and would likely dominate the benthic macrophyte community under these conditions

Growth performance of the sea cucumber Holothuria scabra and the seaweed Eucheuma denticulatum: integrated mariculture and effects on sediment organic characteristics

Deposit-feeding sea cucumbers play a key role in marine ecosystems through bioturbation, burrowing and feeding on organic matter in marine sediments. Many deposit-feeding holothurians have therefore been recommended for integrated multitrophic aquaculture systems (IMTA). We set up an integrated mariculture system of sea cucumber Holothuria scabra and seaweed Eucheuma denticulatum in Bweleo, Unguja Island of Zanzibar, Tanzania, to investigate the effect of stocking density on the growth and survival of culture species, total organic matter (TOM) and total organic carbon (TOC) content in the sediment. Treatments that included a fixed stocking density (500 g, ca. 200 g m-2) of E. denticulatum and 4 sea cucumber stocking densities (monoculture, low, medium and high density; 0, 150 ± 5, 236 ± 24, 345 ± 48 g m-2, mean ± SD) of medium-sized H. scabra (114 ± 37 g) were established. Stocking density of H. scabra did not influence survival of either species. Seaweed cultured under high stocking density of H. scabra had a higher specific growth rate of 2.33% d-1 than that cultured at the medium or low densities or without sea cucumbers. Sea cucumbers cultured at low stocking density had a higher mean growth rate of 0.80 g d-1 compared to those cultured at medium or high densities. TOM and TOC in sediments decreased over the experimental period at medium sea cucumber stocking density, while at low and high stocking densities, organic matter accumulated. The study demonstrates that the integration of E. denticulatum and H. scabra at 200 g m-2 enhances seaweed growth and can reduce organic matter content in the sediments

A review of Kappaphycus farming: prospects and constraints

A review of Kappaphycus (broadly including Eucheuma) farming is presented, including the current possibilities and challenges with the goal of contributing to sustainable mariculture management practices

Health problems related to algal bloom among seaweed farmers in coastal areas of Tanzania

There is a scarcity of research-based data on the factors associated with skin irritation due to algal blooms in seaweed farming. Changes in temperature with an increase in nutrients levels lead to the growth of harmful algal blooms, which produce many active metabolites, some of which induce toxic responses in human including skin irritation. The objective of this study was to identify health problems experienced by seaweed farmers and the seasons when they occur, and how these are treated. A cross-sectional study design was used to gather data using structured questionnaire, focus group discussions and key informant interviews. The study was conducted between June and August 2015, in six villages, two from Mainland, and four from Zanzibar Islands, Tanzania. Study revealed that seaweed more than 50% of farmers experienced skin irritation problem, followed by 30.4% who had eye related problems, and only 19.6% had respiratory disorders as the most serious. Hot season, which is associated with algal blooms, was the period with the highest occurrence of skin irritation. No specific medication was used to treat the health problems reported. In some severely affected areas, farmers could not tend to their farms for months, a situation which affected their income. It is suggested that the findings from this study would reduce this knowledge gap and motivate stakeholders especially the policy makers to implement measures, which reduce the health problems observed due to algal blooms in the seaweed farmers.publishedVersio