|Spatial community structure of the hyperbenthos of Gazi Bay, Kenya|
Luhunga, B.Y. (1997). Spatial community structure of the hyperbenthos of Gazi Bay, Kenya. MSc Thesis. University of Gent, Zoology Institute, Marine Biology Section: Gent. 68 pp.
|Available in|| Author | Dataset |
- VLIZ: Archive VLIZ ARCHIVE A.THES11 
- VLIZ: Non-open access 227524
|Document type: Dissertation|
,Kenya Belgium Project, FAME, hyperbenthic fauna
Shallow tropical bays covered with seagrass beds and bordered by mangrove forests are important habitats in tropical marine ecosystems. They are among the most productive ecosystems in the world and they thus attract a lot of organisms (primary consumers). These ecosystems are used as nursery areas by juvenile fishes, crustaceans and other organisms of economic importance. Among the functional members of these ecosystems are the hyperbenthic animals. This is a group of mobile organisms that lives in the lower layers of the water column, close to the sea bottom. This fauna is potentially very important in the functioning of the marine environment. Most members of the hyperbenthos are primary consumers grazing on algae or macrophytes and others have been described as carnivores, omnivores, filter feeders, detritivores and scavengers. In turn, they are potential prey items for commercial fish stocks. Hence, they play a vital role in the aquatic food web by transferring energy from the lower to the higher trophic levels. In order to manage the tropical fishery, quantitative information on potential prey populations in terms of species composition, density, diversity and community structure are indispensable. In this study, the spatial community structure of the hyperbenthos of Gazi bay (Kenya) was investigated. The hyperbenthos was sampled with a hyperbenthic sledge in October 1994. All major seagrass beds, mangrove creeks and sand flats were covered during daytime. Also night samples were taken in selected stations. In total, 38 stations (28 stations for the day samples and 10 stations for the night samples) were sampled and analysed. The hyperbenthic fauna was sorted out and all animals present were identified to a high taxonomical level and counted. Multivariate statistical techniques (Cluster analysis, TWINSPAN and Correpondence analysis) were used to identify communities. The communities were then characterized according to density, diversity and species composition. A total of 36 taxa were encountered in this study. The dominant taxa (constituting >4% of the community) were the Amphipoda Gammaridea, Mysidacea, Gastropoda, Isopoda, zoea larvae of Brachyura, Polychaeta, larvae and early post-larvae of Pisces Teleostei and Chaetognatha for the day samples, and Mysidacea and Amphipoda Gammaridea for the night samples, Ostracoda, Copepoda, Cumacea and Natantia being locally dominant. Other important taxa (between 0.1 and 3% of the total community) were Opisthobranchia, Amphipoda Caprellidea, Nematoda, Bivalvia, Tanaidacea, Oligochaeta, juveniles and megalopae of Brachyura, Scyphozoa, juvenile Pisces Teleostei, Ascidiacea, Anthozoa and Plathelminthes. Coleoptera, Anomura, Ophiuroidea, Cephalopoda, Leptostraca, Cephalochordata, Pycnogonida, zoea larvae of shrimp, Hydrozoa, Brachyura Corystidae and unidentified eggs were rare (<0.1c /1 0 of the total community). When the day and night samples were treated separately, four communities for the day samples and 2 communities for night samples were delineated. The first community for the day samples was mainly situated in the inner western creek but also included some stations in the western part of the bay proper. It was characterized by low densities and a low number of taxa (low No ). Mysidacea were the dominant taxon and the average hyperbenthic density was around 1500 individuals per 100m2. The second community (day) was situated at the mouth region of the western creek. It was characterized by high densities and a high diversity. The hyperbenthos was dominated by Amphipoda Gammaridea, zoea larvae of Brachyura and Cumacea being subdominant. Average density in this community amounted to 7000 individuals per 100m2. The third daytime community was mainly situated in the eastern creek and the shallow areas of the eastern and central parts of the bay. It was also characterized by high densities and a high number of taxa. This community was also dominated by gammaridean amphipods, but here Isopoda and Gastropoda were subdominant. Average density was around 10000 individuals per 100m2. The fourth community (day) was found in the south-eastern part of the bay and was characterized by a high diversity and intermediate densities. This community was dominated by Amphipoda Gammaridea, all other taxa being far less important, and the average density of this community was almost 4000 individuals per 100m2. The first community for the night samples was situated at the mouth region of the western creek and the bay. It was characterized by a high number of taxa and high densities. The community was dominated by Amphipoda Gammaridea and the average density for this community was around 31000 individuals per 100m2. The second night community (night) was situated in the inner part of the western creek and was characterised by very high densities but a lower diversity. The hyperbenthos was dominated by Mysidacea; the average density for this community was in the order of 80000 individuals per 100m2.
- Counts of hyperbenthos of Gazi Bay (Kenya) sampled in October 1994, more