Invertebrate harvesting is an important livelihood in tropical settings providing income and food for numerous populations throughout the world. However, the lack of research, policy and management directed towards this livelihood hinders the analysis of time trends to evaluate invertebrate resources status. Another missing aspect is the consideration of gender analysis, i.e., the different roles and interests of men and women engaged in this activity. Based on interviews, catch assessments and inventories this multi-disciplinary study from Chwaka Bay (Zanzibar, Tanzania) shows how unregulated harvesting of invertebrates may result in sharp declines in animal abundance over a relatively short period of time (2005 to 2010), threatening the sustainability of the fishery. Specifically, the results show that catches in general, and prime target species of gastropods and bivalves in particular, had been significantly reduced in number and size. Interviews revealed gender disparities; female harvesters experienced less access to good fishing/collecting grounds and species of high value, which subsequently resulted in lower individual income. This is tightly linked to women's reproductive roles, which not only leads to limited mobility but also lessen their chances to accumulate livelihood assets (natural, physical, financial, social and human capital) thus impacting livelihood strategies. To protect invertebrate resources from overexploitation, and assure a constant flow of income and food for future generations, this case study illustrates the need for formal monitoring to assess changes in invertebrate resources, and possible ecological consequences, over time. Managers and policy-makers must also address gender to evaluate the contribution of all resource users, their capacity to cope with changing conditions, as well as specific interests.