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concerns have also been expressed about the effects of inshore seine nets and intensive trawling activities on the seabed. For example, in some cases up to 80 of prawn trawl catch
is seagrass Msumi, pers. comm.. Seaweed farming in some areas involves removal of sea grass beds and seaweed produces a growth inhibiting substance that prevent sea grass from
growing in farmed areas. Intensive trampling on seaweed farms and adjacent areas including passages has been observed to cause physical alteration.
Another threat is destructive fishing practices like dynamite fishing. Healthy seagrass beds are located on the protected sides of coral reefs, e.g., in Mwambakuni and Mwamba
Mshingwi, the main fishing zones in the Mbegani Bay area. It is here that the dynamite fishery takes place. It is easy to collect dynamited fish on protected sides, although the loss
of uncollected fish is still high only about 50 of dead fish are collected according to Rumisha and Muhando 2007.
3.3 Coral Reefs Distribution of coral reefs
Bright sunlight and clear waters are critical to the development of coral reefs since they derive their food resources from photosynthesis. Consequently, reefs usually occur where the
seabed is shallow. The coral reef ecosystem comprises of reef-building corals as well as a vast array of other organisms that depend on habitats provided by the reef. A variety of
commercially important fish and invertebrates reside on coral reefs. Reefs protect the inshore areas from wave action and erosion, and therefore play an important role in coastal defense as
well as in determining patterns of sediment transport.
When compared with other reef sites in Tanzania, such as SongoSongo, Tanga, Mafia and Unguja, Mbegani Bay has relatively few good coral reef areas. High concentrations of coral
reefs in Mbegani Bay are found in Mwamba Kuni and Mwamba Mshingwi. Patchy and sediment stressed coral reefs are found at Mwamba Kati, Mwamba Mjini, Mwamba Poyogo,
Mwamba Tekea and Mwamba Chuma Figure 7. Those reefs that are located further away from the Ruvu River, such as Mwamba Msumeno and Maduga reefs, are in relatively better
condition.
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Figure 7 The distribution and management status of coral reefs in the Mbegani Bay area Source Muhando, 2006
The health condition of coral reefs and its associated services are influenced by many factors, some are natural and others human induced. Anthropogenic factors influencing the
distribution, and abundance as well as causing physical alteration and degradation of habitats on coral reefs in Mbegani Bay include destructive fishing practices, overfishing and to a less
extent anchor damage from tourist and fisher’s boats. The key destructive fishing practices are those involving the use of dynamite and dragnets beach seines, and various makes of nets
dragged on coral reefs and adjacent seagrass beds. Destructive fishing results in breaking of coral framework, leading to reduced reef complexity, biological productivity, carrying
capacity and biodiversity. Commercial trawling for prawns has indirect impact as it facilitates frequent resuspension of sediments which are detrimental to coral reefs.
The natural factor influencing coral reef distribution in the Mbegani Bay area is freshwater from Ruvu River that reduces salinity and carries sediments. Reef coral do not flourish
where salinity is less than 20 parts per thousand, or where the substrate is unstable or where the sedimentation rate is high Rogers, 1990; Muhando, 2003.
In 1998, a massive coral bleaching event caused extensive coral mortality in the Western Indian Ocean, including Tanzania Muhando, 1999; Wilkinson et al., 1999. Recent analysis
of coral reef recovery prospects in Chwaka Bay and adjacent areas Muhando and Mohammed, 2011 suggests that recovery after the 1998 bleaching event was poorest in areas
with chronic sedimentation problems. A similar situation is suspected in Mbegani Bay, especially on the reefs Mwamba Kati, Mwamba Mjini, Mwamba Poyogo, Mwamba Tekea
and Mwamba Chuma located near high sediment problem areas.
Ecological roles and status of coral reefs in the Mbegani Bay area
Coral reefs play very significant ecological roles as a habitat, spawning, nursery and feeding sites for a variety of organisms, including commercial fish. Consequently, they are important
fishing areas for fish stocks. The demersal fishing in the Bay is to a large extent associated and linked to coral reefs. Unfortunately, the continuing coral reef degradation results in
reduced complexity and carrying capacity. Surveys in 1997 and 2008 pers. obs clearly suggest massive degradation on Mwambakuni reefs, especially the landward protected side.
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The whole of this side was dominated by sub-massive corals, Galaxea astreata, but currently, more than 30 of reef area is covered by loose rubble, which is progressively getting
eroded. Such human influences on coral reefs and associated implications to fisheries were noticed, and alarmed fisheries officers, leading local fishers and the District to support an
initiative to protect the reefs.
Through a participation process with communities, coral reef areas that require special conservation attention in the Mbegani Bay area were selected, discussed. These were
Mwamba Kati, Mwamba Mjini, Mwamba Poyogo, Mwamba Tekea, Mwamba Chuma, Mwamba Mshingwi, Mwamba Msumeno and Mwamba Maduga. The initial proposal was
that all these should be declared as no take zones, and be managed jointly by Community- Based Fisheries Management village committees and Fisheries officers. In order to measure
management implications, it was necessary to compose a strong community based coral reef monitoring group, which was actually formed, trained and empowered to record selected reef
healthy indicators: reef benthic cover Table 2 and macro-invertebrate and reef fish Table 3 The first community based coral reef monitoring was conducted in 2005 Mbije 2005 and
repeated in 2006 Muhando, 2006. Substantial amount of information was revealed, e.g. coral benthic cover, macro-invertebrates density, and reef fish abundance.
Table 3. Reef macro-invertebrates and reef fish monitored Macro-invertebrates
Reef Fish
English Name Swahili Name
English Name Swahili
Name Sea urchin
Ulumba Goat fish
Mkundaji Cypraea
Bunda Chui Lutjanus fulviflamma,
Black spotted snappers
Kelea
Starfish Kiti cha Pweza
Blacks spotted emperor
Changudoa Brittle star
Takambe Black spotted
sweetlips Mwelea
Crown-of-thorns Kiti cha Pweza
White spotted Rabbitfish
Tasi Sea cucumber
Jongoo Parrot fishes
Pono Other gastropods
Kome Snappers
Changu Sardines
Dagaa Others
Wengineo Relatively higher live coral cover of above 25 was observed in Poyogo, Mshingwi and
Mweduga, while live coral cover in Mwamba Mjini and Kati was below 18 Fig. 8. Poor environmental conditions caused by river sediments and low visibility resulted in low coral
cover and high preference of macroalgae and seagrass beds on Mwamba Mjini and Mwamba Kati. It was suggested in 2006 that future conservation efforts be directed to conservation of
Mweduga, Mshingwi and probably Poyogo, before the others. After thorough discussions, four reefs were declared as no-take areas: Mwamba Mjini, Mwamba Poyogo, Mwamba
Mshingwi, located in Mbegani Bay and Mwamba Maduga. Proper boundaries of the no-take zones are still required.
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Community-based coral reef monitoring also revealed that most of the reef macro- invertebrates found elsewhere in Tanzania Mohammed et al., 2002 were also observed in
Mbegani Bay, however, at much lower densities Mbije 2005; Muhando, 2006. As expected, the reef invertebrate density and diversity increased for reefs located far from the
Ruvu River estuary and human centers. Mwamba mshingwi had the highest density and diversity of invertebrates.
In conclusion, the condition of coral reefs in the Mbegani Bay area is relatively poor. Coral reef management continues to face many problems related to inadequate funding to
monitoring and assessment, continued dynamite fishing, open access and weak enforcement of no-take rules, and lack of education and awareness raising efforts.
3.4 The Ruvu Delta and its influence on Mbegani Bay
