Frontier-Tanzania Environmental Research REPORT 103 Misali Island

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Misali Island: A detailed description of the subtidal regions3.3 BENTHIC INVERTEBRATE CENSUSData from the benthic invertebrate census surveys are represented per 1m 2 areas bymean and standard error values within taxonomic groups for each site. Kruskal-Wallistests were used to analyse whether there were significant differences between depths ateach site. 17% of all the diffferences in values tested were found to be significant (seeAppendix 6). Depths are represented separately when more than half the sites showedsignificant differences between shallow and deep surveys for each taxa analysed.Echinoidea (sea urchins) were observed in greater abundance at sites 4, 5, 6, 7 and 8 incomparison to the other sites. Site 8 was recorded with the greatest mean number ofEchinoidea, at 1.7 per 1m 2 . However, the abundance per 1m 2 quadrat varied greatly ascan be seen from the error bars in Figure 13 and the fact that 30 and 11 individualswere recorded within two separate quadrats.There were no Acanthaster planci (Crown-of-thorns starfish) observed within the810m 2 area of substrate surveyed amongst all the sites. The maximum number of otherAsteroidea (starfish) recorded per 1m 2 quadrat was 2 but the greatest average wasrecorded at site 8 as 1.5 individuals per 1m 2 (see Figure 14).Holothuroidea (sea cucumbers), both edible and non-edible, were recorded with amaximum of 2 per 1m 2 quadrat. These were recorded with the greatest abundance atsites 4, 5 and 8 and the maximum mean value for these sites was 0.15 per 1m 2 quadratat site 5 for edible Holothuroidea. The overall mean value per 1m 2 quadrat for allsurvey sites was 0.06 for edible and 0.02 for non-edible Holothuroidea. See Figure 15for mean and error bar values for Holothuroidea at each site.Ophiuroidea (brittlestars) and Crinoidea (featherstars) were found at all survey sitesexcept that no Ophiuroidea were recorded at site 6. Maximum numbers recordedwithin a 1m 2 quadrat were 25 (site 8) and 7 (site 3) for Ophiuroidea and Crinoidearespectively. See Figure 16 for mean and error bar values for Ophiuroidea andCrinoidea at each site.Gastropoda (marine snails and slugs) were observed with the largest mean abundancesat sites 4, 5 and 7 (see Figure 17) and were generally more abundant in the shallowerregions at each site. There were six Pleuroploca trapezium (tulip shells) observed inthe total 810m 2 area of substrate surveyed and these were at sites 2, 3 and 7. A total offour Charonia tritonis (Triton’s trumpet) were observed within all the invertebratesurveys, recorded at sites 1, 3 and 7.Actiniaria (sea anemones) were observed at all sites with the maximum number in anyone 1m 2 quadrat being 5. Alcyonacea (soft corals) were also observed at all sites. SeeFigure 18 for the means and standard error values for both Actiniaria and Alcyonaceaat each site.Bivalvia (bivalves) were observed predominantly at sites 3 and 8 in the shallow regions(4 – 8m depth) and site 6 in the deeper region (14 – 18m) (see Figure 19). Whenobserved, Tridacna sp. (giant clam) was recorded mainly in the shallower regions, andFrontier-Tanzania Environmental Research Report 103 30
Misali Island: A detailed description of the subtidal regionswas most abundant at sites 5, 6, 7 and 8. In total, 58 Tridacna sp. were recorded withinthe 810m 2 substrate area surveyed.Nudibranchia (nudibranchs) were separated from the other Gastropoda to assess theirindividual abundances. There were 26 of this order observed in total and theseindividuals were recorded at sites 1, 2, 5, 6, 7 and 8. There were 14 Platyhelminthes(flatworms) recorded in total, and these were observed predominantly at site 4 (10individuals) but also at sites 5, 6, 7 and 8. Sabellidae (fanworms) were most abundantat sites 2, 4 and 8, with mean values of 0.65, 0.40 and 0.31 Sabellidae per 1m 2 quadratrespectively. See Figure 20 and Figure 21 for mean and standard error values forNudibranchia, Platyhelminthes and Sabellidae observations.Crustacea (Stomatopoda (mantis shrimp), Stenopodus hispidus (Banded cleanershrimp), and Palinuridae (spiny lobsters)) were absent in most of the surveyed quadrats.The only observations of these taxa were of two Stenopodus hispidus, one each at sites1 and 7.Octopoda were not observed at any site from the 810m 2 total surveyed area between4m and 18m. However, many Octopoda have been observed during a separate study ofthe octopus fishery. Fishermen have collected such individuals from the intertidal areasurrounding Misali Island. Sepioidea (cuttlefish) and Teuthoidea (squid) wereobserved outside of the surveys (see p67).In total, the following number of Cirrhipathes (coral whips) were recorded within the810m 2 surveyed area: three at site 1; two at site 7; one each at sites 2, 6 and 8. Thetotal number of Gorgoniidae (sea fans) observed were four, which were recorded atsites 1, 4 and 5.Porifera modal values per 1m 2 quadrats are displayed in Figure 22. This phylum wasrecorded throughout the surveyed sites except at shallow depths at site 2. Maximum P6values ranged from 0 to 5, with the greatest cover by encrusting Porifera at site 1.Frontier-Tanzania Environmental Research Report 103 31
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Frontier-Tanzania Environmental Research REPORT 103 Misali Island

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