Frontier-Tanzania Environmental Research REPORT 103 Misali Island

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Misali Island: A detailed description of the subtidal regionspreviously reported for the whole East African coast (Veron pers.comm.). Suchbiological diversity is likely to be due to its remote location, which has limitedhuman impact and sedimentation from the mainland. More importantly in terms ofbiodiversity are the strong currents around Misali, which mean that this area is alsolikely to act as an important larval source and sink for regional reefs and coastalhabitats. However, with Misali reefs receiving greater direct oceanic waters incomparison to reefs in bays and shallower waters, this may be to its detrimentduring bleaching events. Supporting this, in 1999 Mohammed et.al. (2000)recorded corals with lower levels of bleaching and mortality in sheltered andshallower waters such as Chole Bay in Mafia Island, Mnazi Bay in Mtwara,Zanzibar and Dar es Salaam. This was possibly due to night cooling, high cloudcover and rainfall reducing solar radiation and the warming of the surface water. Incontrast, Pemba dive operators were concerned in 1998 that Misali Island coralreefs may have lost their tourist potential after the bleaching event (Muhando1999).Despite the identification of Misali’s high marine biodiversity through variousshort-term surveys, it has not proven enough to ensure recent and continuedrecognition at the global level. Worldwide recognition is important in terms ofestablishing an international status of protection and sourcing funds to implementmanagement programmes and increase awareness and collaboration amongstresource users to ensure implementation of these. As such more detailedobservations would help generate a greater understanding of Misali’s marine statusand will form the basis for future management initiatives for the Pemba region.1.7.2 Benthic invertebrate censusBenthic invertebrates are important in terms of their ecological role within allsubtidal and intertidal tropical habitats. For example, molluscs form the largestgroup of fauna in the marine environment. However, these organisms are oftenoverlooked and overshadowed by the more charismatic marine vertebrates such asfish, mammals and reptiles. Given that the invertebrates are found with greatspecies diversity the conservation of this group is important in terms of maintaininglevels of biological diversity. Additionally, some species are collected in largenumbers for the marine curios trade, and in certain cases such as Charonia tritonis(Triton’s Trumpet) removal of keystone species can result in detrimental ecosystemeffects.Certain invertebrate 'indicator' species are useful in terms of analysing the status of,and threats to, the marine environment. Examples include the following…• Acanthaster planci (Crown-of-Thorns starfish) is known to predate uponscleractinian corals and can have detrimental effects on reefs when populationoutbreaks occur• Charonia tritonis is an important predator, and therefore regulator of,populations of Acanthaster planci. It is vulnerable to collection for the curiostrade in addition to other larger predatory species such as Lambis lambis(common spider conch). Declines in the markets for such species have beenFrontier-Tanzania Environmental Research Report 103 6
Misali Island: A detailed description of the subtidal regionsnoted (Marshall et. al. 2001), which indicates either a decline in the populationor in the interest of exploiting this organism• Echinoidea (sea urchins) can assist settlement of coral larvae by limitingcompetition from algae through their habitual ‘grazing’. However, if found inlarge numbers, this may indicate heavy fishing pressure on Echinoideapredators such as Labridae (wrasse) and Balistidae (triggerfish)• Holothuroidea (sea cucumbers) are essential in ingesting and recycling detritusand nutrients on and around reef areas. However, there is a large trade of ediblespecies within Tanzania, which reduces numbers found on the reef and result inimbalances within the marine environment. Landings of sea cucumber haveincreased from 324 metric tonnes in 1989 to 1,460 metric tonnes in 1995 withinTanzania (Marshall et. al. 2001)• Mollusca (shellfish) are collected for food consumption and the marine curiostrade, both locally and for export. Threatened species include the following:Tridacna sp (giant clam); various Cypraeidae (cowries); Strombidae (conchshells). Tridacna sp. are occsionally used for food but also sold to tourists asornaments. Their slow growth rate means that they are susceptible to rapidpopulation declines if collected regularly and/or intensively. The operculumcover of the Pleuroploca trapezium (tulip shell) is regularly exported to Kenyafrom Misali Island and the meat of this mollusc is eaten locally• Porifera (sponges) are important with regards to their species diversity. Thereare about 7,000 ‘valid’ species in existence within worldwide literature althoughabout 15,000 species are estimated to exist in all the world’s seas and lakes(Hooper 2000). However, the Porifera ecology in the West Indian Ocean isvirtually unknown (Barnes & Bell 2002). The vast array of species that havebeen discovered have resulted in many uses, including medicinal purposes.The rationale for the benthic invertebrate survey is to provide data on speciesexploited by local resource-users, which therefore may be threatened through themarine curios trade. It also includes certain other invertebrates such as sponges andurchins that are not collected for the curios trade but nonetheless have importantbiological or ecological values.1.7.3 Commercial fish visual censusThese surveys are designed to investigate the distribution of commerciallyimportant groups of fish species. Used in conjunction with the benthic substratadata and observations of resource-user activities within the same area, it will bepossible to investigate the effects of fishing on their distribution.Although SCUBA visual census has some limitations (e.g. disturbance of fishwithin the observed area) it does allow non-selective observations in terms of fishlength and abundance, which would not be possible if the same observations weremade at a fish-landing site.Frontier-Tanzania Environmental Research Report 103 7
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Frontier-Tanzania Environmental Research REPORT 103 Misali Island

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