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Changes in an East African social-ecological seagrass system: invertebrate harvesting affecting species composition and local livelihood

Published online by Cambridge University Press:  04 February 2011

Lina Nordlund ,
Johan Erlandsson ,
Maricela de la Torre-Castro  and
Narriman Jiddawi
Lina Nordlund
Affiliation:
Department of Systems Ecology, Stockholm University, S-106 91 Stockholm, Sweden ARONIA Coastal Zone Research Team, Åbo Akademi University / Novia University of Applied Sciences, 10600 Ekenäs, Finland
Johan Erlandsson
Affiliation:
ARONIA Coastal Zone Research Team, Åbo Akademi University / Novia University of Applied Sciences, 10600 Ekenäs, Finland
Maricela de la Torre-Castro
Affiliation:
Department of Systems Ecology and Stockholm Resilience Center, Stockholm University, S-106 91 Stockholm, Sweden
Narriman Jiddawi
Affiliation:
Institute of Marine sciences, University of Dar Es Salaam, P.O. Box 668, Zanzibar, Tanzania
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Abstract

Seagrass meadows support high biodiversity and are important for invertebrate harvesting activities in developing countries. The aim of this study was to estimate the social and ecological effects of invertebrate harvesting, i.e. how this exploitation may affect/has affected seagrass variables (biomass, shoot density and canopy height), macrofaunal community structure, the use and importance of these resources for the livelihood of local people over time. A multi-disciplinary approach was used, including interviews with harvesters, observations of the number/activities of invertebrate harvesters, and a biological field study in Zanzibar, Tanzania. The study showed that women/children harvest invertebrates, and they prefer large seagrass patches, high to medium shoot density, and high seagrass cover. All interviewees said they had noticed a decline in seagrass distribution over the last decade,  >20% considered it a large decline. Interviewees also reported decreased numbers of animals, but no change in the number of animal species over the last decade. The main reasons for the decline of seagrass and animals according to interviewees, are an increase in the number of harvesters, and a change in attitude, i.e. people being less careful about the intertidal zone and seagrasses. Invertebrate harvesting was found important for food security and provision of cash income. The current average catch weight was ca. 2 kg/collection day/person, and 3 kg and 5 kg, 5–10 and 30 years ago respectively according to interviewees. At present, the harvesting women earn ca 60–70% and ca 40% of what they would have if catches were the same sizes as they were 5–10 and 30 years ago respectively, according to our calculations. The field sampling within seagrass beds showed that an inaccessible/remote site had significantly higher invertebrate abundance and species richness/diversity than an exploited site (ANOVA). Multivariate statistics further revealed weak but significant differences for animal abundance and biomass between these sites. By combining findings from both interviews and field sampling this study shows that invertebrate harvesters can influence macrofaunal community structure in seagrass meadows, which in turn results in negative impacts on local harvesters’ economy and livelihood.

Keywords

BiodiversityDisturbanceHuman exploitationShellfishLocal livelihoodSeagrass bedsSocial-ecological systemsMarine protected areaZanzibarEast Africa
Type
Research Article
Information
Aquatic Living Resources , Volume 23 , Issue 4 , October 2010 , pp. 399 - 416
Copyright
© EDP Sciences, IFREMER, IRD 2011

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