Agnes Muthumbi

Meiofauna and macrofauna community structure in relation to sediment composition at the Iberian margin compared to the Goban Spur (NE Atlantic)

Meiofauna and macrofauna communities and several sediment characteristics were compared between a slope situated far from the coast (Goban Spur) and two transects across the Iberian Margin with steep slopes and close to the shore. The northern Galician transect (off La Coruna) was situated in an area subjected to wind-induced upwelling events. The western Galician transect was also subjected to upwelling, was additionally influenced by outflows of water rich in organic matter from the Ro ´as Bajas. This transect also included the Galicia Bank. Macrofauna density decreased exponentially from the shelf edge (154 m) to the abyssal plain (4951 m) and different communities occurred on the shelf, the upper- and lower slope and on the abyssal plain. Apart from two extremely low-density stations on the Iberian Margin, there were no significant differences in the meiofauna between the Goban Spur and the Iberian Margin. Along the La Coruna-transect a station where meiofaunal densities were low occurred at a depth of 1522 m, where the sediment was characterised by having a high median-grain size, ripple structures, a low C org and total N content. There were relatively high numbers of macrofaunal filter-feeders but low numbers of crustaceans, indicating a high current velocity regime. On top of the Galicia Bank (~770 m) the sediment consisted mainly of shells of pelagic foraminifers, and had low contents of Corg and N. The macrofauna was dominated by filter-feeding and carnivorous taxa. At both these stations meiofauna densities were low. Meiofauna densities and community structure differed between the Goban Spur and the Iberian Margin. Meiofauna densities on the Galician shelf were more than double those on the Goban Spur shelf. The two deep stations on the La Coruna transect and the deepest station on the Galicia Bank transect all contained meiofaunal densities that were higher than found at similar depths off the Goban Spur. The meiofaunal densities were inversely correlated with %CaCO3 content and, excluding the shelf stations, were positively correlated with both %Corg and total N at the Iberian Margin. Neither upwelling nor the enriched outflows from the rias affected the macrofauna, but meiofaunal densities were greatly enhanced.  2002 Elsevier Science Ltd. All rights reserved.

The structuring role of microhabitat type in coral degradation zones: a case study with marine nematodes from Kenya and Zanzibar

Nematode genus assemblages were identified from four locations in coral degradation zones (CDZs) along the African east coast: Watamu and Tiwi Beach (Kenya) and Matemwe and Makunduchi (Zanzibar). Three microhabitat types were distinguished: coralline sediment, coral gravel and coral fragments. Nematode community composition was comparable to that of other studies dealing with the same habitat. The presence of a common genus pool in CDZs was reflected in the considerable similarities between samples. The addition of coral fragments as a habitat for nematodes resulted in an increased importance of taxa typical for coarse sediments and large substrata. Local and regional turnover were of the same order of magnitude. The structuring effect of microhabitat type clearly overrode the effect on a local and regional scale. Differences in sediment characteristics were more important in structuring the nematode assemblages than differences between the coralline sediment and coral fragments. No effect related to the three-dimensional structure of coral fragments was found. Differences between nematode assemblages in the coralline sediment and on coral fragments were attributed to the exposed nature of the latter habitat, its large surface area and its microbial or algal cover. Differences in available food sources were reflected in nematode trophic composition.

Acantholaimus (chromadoridae:nematoda) from the Indian Ocean: description of seven species

Seven species of the Acantholaimus aredescribed. Acantholaimus vermeuleni sp.n. ischaracterised by labial and cephalic sensilla thatare located at the same level, two post amphidialsetae on the dorso-lateral side and a poorlydeveloped stoma without distinct teeth. Acantholaimus verscheldi sp.n. is characterised bya narrow elongate pharyngeal region, a long stomawith distinct teeth and short (4–7 µm) cephalicsensilla. Acantholaimus heipi sp.n. ischaracterised by a narrow elongate pharyngealregion, well developed teeth in the stoma and longcephalic sensilla (11–13 µm). Acantholaimuselegans Jensen 1988 has a narrow anteriorpharyngeal region that increases in lengthposteriorly, it has setae before and after theamphids on both sides and stoma with well developedteeth. Acantholaimus gathumai sp.n. ischaracterised by long cephalic (10–15 µm) andsomatic (8–10 µm) setae and lateraldifferentiation with fine dots (5–7 µm inwidth). Acantholaimus geraerti sp.n. has longcephalic sensilla (15–19 µm) and narrow (4–6 µm)distinct lateral differentiation. Acantholaimusinvaginatum sp.n. is characterised byvery long cephalic setae (16–21 µm), severalsetae at the pharyngeal region and wide lateraldifferentiation with fine dots, often the stoma isinvaginated.Distribution of the different species of Acantholaimus encoutered in the four transectsstudied is also described.

Chromadoridae (Chromadorida: Nematoda) from the Indian Ocean: description of new and known species

Seventeen new and known species of the familyChromadoridae are described. The genus Dichromadora is represented by five species. Dichromadora longicaudata sp.n. is characterised bya slender body and thin long tail; Dichromadoragathuai sp.n. is characterised by a blunt anteriorend, a raised lateral alae and a gubernaculum that isserrated on the posterior end; D. loiseae sp.n.is characterised by a blunt anterior end with a raisedcollar, double bulb, spicules with a poorly developedcapitulum and seven pre-cloacal supplements; D.cucullata, Lorenzen, 1973 is characterised by lateraldifferentiation of two (four?) longitudinal rows ofdots, seven pre-cloacal supplements and spicules witha rounded capitulum that is open at the tip; D.quadripapillata sp.n. is characterised by acylindrical body with an elongate tail end, two(four?) longitudinal rows of dots, anterior pharyngealregion with two pairs of setae, spicules with poorlydeveloped capitulum and four (1+3) pre-cloacalsupplements.Hypodontolaimus genus has two species. Hypodontolaimus marleenae sp. n. has short (2 µm long)outer labial and long (18 µm long) cephalic sensilla;punctated cuticle with two longitudinal rows of dots,spicules with poorly developed capitulum and eightfine pre-cloacal supplements; Hypodontolaimusaff. angelae Inglis, 1961 is characterised by threesomatic setae at the anterior pharyngeal region, alarge hollow dorsal tooth, a well-developed posteriorpharyngeal bulb and a beak-shaped capitulum.The genus Ptycholaimellus has three species.Ptycholaimellus macrodentatus Timm, 1961 ischaracterised by a blunt anterior end, papilliformouter labial and setiform (6-8 µm long) cephalicsensilla, spicules bent at the anterior end and ashort stout gubernaculum that is sharp-pointed andhooked on the posterior end Ptycholaimelluspenninae sp.n. is characterised by a blunt anteriorend, inconspicuous labial sensilla and 5 µm longcephalic sensilla, a curved spicules with poorlydeveloped capitulum and a gubernaculum that isserrated on the posterior tip Ptycholaimellusponticus Filipjev, 1922 is characterised by bluntanterior end, poorly developed vestibulum,inconspicuous labial sensilla and 3 µm long cephalicsensilla, curved spicules with poorly developed capitulum and a simple gubernaculum. Ptycholaimellus ponticus sensu Gerlach, 1951 is givena new name, P. jenseni sp. n.The genus Trochamus Boucher and Bovée, 1971 is represented by four species. Trochamus bulbosa sp. n. is characterised by a small plump body normally thicker at the mid-body especially in gravid females,annulated and punctated cuticle with a lateral differentiation that is a raised ala, prominent labial rugae, long, slender spicules and conical cylindrical tail. Trochamus complexus Boucher, 1976 is characterised by cylindrical body swollen at the middle, annulated and punctated cuticle with a raised lateral alae, faint circular amphids, small stoma,thin slender spicules and elongate cylindrical tail.Trochamus prosoporus Blome, 1985 is characterised by rather long body (>1 mm long), with a blunt anterior end and cylindrical tail end, raised lateral alae, stoma with a large dorsal tooth, curved massive spicules and a gubernaculum with sharp posterior tip. Trochamus polki sp. n. is characterised by cylindrical body with a blunt anterior end and cylindrical tail end, raised lateral alae, prominent labial rugae, open loop-shaped amphids and in female the vagina wall is very refractive.Prochromadorella Mickoletzy, 1924 has twospecies. Prochromadorella daroae sp. n. ischaracterised by a slender body attenuating on bothends, heterogeneous cuticle without lateraldifferentiation, curved spicules with a poorlydeveloped capitulum and no pre-cloacal supplements.Prochromadorella ditlevseni (de Man, 1922),Lorenzen, 1971 is characterised by a slender body,heterogeneous cuticle without lateral differentiation,thin curved spicules and five pre-cloacalsupplements.The genus Trichromadora Kreis, 1929 isre-instated and T. longicaudata Kreis, 1929 isredescribed. It is characterised by a slender body anda long tail, cuticle with lateral differentiation ofthree longitudinal rows of dots throughout the bodylength, massive spicules with a poorly developedcapitulum and five pre-cloacal supplements.

Microlaimidae (Microlaimoidea: Nematoda) from the Indian Ocean: description of nine new and known species

Nine species are described from the genera Aponema Jensen, 1978, Bolbolaimus Cobb, 1920, Calomicrolaimus Lorenzen, 1976, Ixonema Lorenzen, 1976 and Microlaimus de Man, 1880. Aponema decraemerae sp. n. is characterised by sexual dimorphism in the size of the amphids, short cephalic sensilla, spicules with a poorly developed capitulum and conical cylindrical tail with a pointed tip. Aponema mnazi sp.n. is characterised by short cephalic sensilla, head set off from the rest of the body by a fine constriction, spicules with a pointed anterior tip, one precloacal supplement located at 7 μm from the cloaca opening and a short tail with a blunt tip. Bolbolaimus bahari sp. n. is characterised by cuticular annules with fine interannular spaces, papilliform labial sensilla and short setiform cephalic ones, curved spicules with a poorly developed capitulum. Bolbolaimus abebei sp.n. is characterised by setiform outer labial and cephalic sensilla and spicules with a well-developed beak shaped capitulum. Calomicrolaimus jenseni sp. n. is characterised by an elongate cervical region, small (2 μm wide) amphids located at 44–54% of the pharyngeal length from the anterior and a conical tail with a pointed tip. Ixonema deleyi sp. n. is characterised by a small body (<400 μm long) an elongate cervical region, small (1–2 μm wide) circular amphids with rod-like corpus gelatum located at 30–45% of the pharyngeal length from the anterior. Microlaimus texianus Chitwood, 1951 is characterised by sexual dimorphism in the size of the amphids and presence of five pre-cloacal supplements. Microlaimus minutus sp. n. is characterised by a small body (< 300 μm long) that is often curved or coiled, amphids that are 55–60% cbd and located at 11–15 μm away from the anterior end and short (12–15 μm long) simple spicules. Microlaimus pwani sp.n. is characterised by prominent cuticular annules, long cephalic sensilla, amphids that are 50–55% cbd and located at 11–13 μm from the anterior end and long sausage-shaped striated sperms.

Spatial diversity of nematode and copepod genera of the coral degradation zone along the Kenyan coast, including a test for the use of higher-taxon surrogacy

The biodiversity of meiofauna in the coral degradation zone along the Kenyan coast was examined with special emphasis on the most abundant taxa, Copepoda and Nematoda. Communities from three microhabitat types (coralline sediment, coral gravel and coral fragments) at two locations (Watamu and Tiwi Beach) were analysed. The total number of meiofaunal taxa was higher than in any other tropical coral degradation zone studied so far, but lower than in a cold-water coral degradation zone. Meiofaunal community composition was mainly structured on a local scale, although microhabitat type also had an effect in Watamu. Copepod and nematode communities exhibited comparable trends in biodiversity. The coralline sediment was generally characterised by a higher genus richness than the other microhabitats, and coral fragments were consistently low in evenness. Differential susceptibility to hydrodynamic disturbance is proposed as an explanation. Coral fragments contributed considerably to the total diversity in terms of the number of nematode and copepod genera. It is therefore recommended to include this microhabitat in future biodiversity studies on tropical lagoons. Trends in bio diversity were similar for genera and families. The use of family-level identifications in fast screening and comparison of biological diversity is endorsed by this study.

The mangrove forests as nursery habitats for the ichthyofauna of Mida Creek (Kenya, East Africa)

This study investigated the presumed nursery function of mangroves for the ichthyofauna in East African swamp forests, Mida Creek. The species and size composition of the fish fauna and their trophic interactions were studied for five stations. Samples were collected during 5-6 consecutive days close to spring tide in mid-July 2011. Fish were caught using different types of passive fishing gear, such as large and small fyke nets, gill nets and, additionally, beach seines. All individuals were identified to species level, measured and preserved for further analyses. Stomach content analysis was applied to provide information about their diet. Stable isotope analysis was used to detect whether the source of primary production for the higher trophic levels is mangrove-related or not. A total of 27 fish species was recorded in a catch of 938 teleost specimens. Our analyses showed that a majority of fish belonged to the zoobenthivorous/omnivorous trophic mode, since they were partially feeding on invertebrates and on various other food sources. Two species (Sphyraena barracuda and Synodus variegatus) exhibited a mixed diet, with a piscivorous preference. Results concerning the population structure suggested that the fish community of Mida mainly consists of transient species. Juveniles were numerically more abundant in the whole Creek than adults. These findings support the hypothesis of a nursery function of the mangrove forests, Mida Creek.

Chromadoridae (Chromadorida: Nematoda) from the Indian Ocean: difficulties in morphological identification of Actinonema Cobb, 1920 and Rhips Cobb, 1920

The diagnostic characteristics of ActinonemaCobb, 1920 and Rhips Cobb, 1920 are reviewed andtheir importance for genera diagnosis assessed. Threespecies of Actinonema and one species of Rhips are described. Actinonema longicaudatumSteiner, 1918 is characterised by short (2–3 µmlong) anterior sensilla, cylindrical body with arather narrow anterior end, lateral alae with inverted‘V’-patterns, wide (70–75 of cbd) double amphids andaccessory pieces composed of only the telamon which isbroad anteriorly and tapers on the posterior and along tail. Actinonema paraceltica ischaracterised by long (4–5 µm) anterior sensilla,large amphids (83–88% of cbd), lateraldifferentiation of ‘V’ pattern on each annule andaccessory pieces with telamons that have shortextensions. Actinonema smolae sp. n. ischaracterised by long and thin body, large amphidslocated close to the anterior end and six solid cones.Rhips reginae n.sp. is characterised by sixsolid cones, large (90% cbd) amphids, lateraldifferentiation of two longitudinal rows of dots anddouble jointed spicules.

Papillonema danieli gen. et sp.n. and Papillonema clavatum (Gerlach, 1957) comb.n. (Nematoda, Desmodoridae) from the Ceriops mangrove sediments of Gazi Bay, Kenya

A new genus, Papillonema gen.n., is erected to accomodate the two species P. danieli gen. et sp. n. and P. clavatum (Gerlach, 1957) comb.n. from intertidal sediments of a tropical mangrove. Papillonema gen.n. is characterized by prominent papilliform labial sensillae, an elongate muscular terminal bulb (up to 60% of pharyngeal length), and three precloacal supplements. Comments are given on the use of the terms ‘head capsule’, ‘head region’, and ‘cervical setae’.

Monitoring the effects of aquaculture effluents on benthic macroinvertebrate populations and functional feeding responses in a tropical highland headwater stream (Kenya)

Intensification of aquaculture may result in more fish culture waste being discharged into adjacent rivers and streams. Due to composition of such wastes, ecological conditions in waterbodies may be adversely affected. We determined the ecological consequences of freshwater land-based Tilapia farms on headwater streams using macroinvertebrate community attributes and functional feeding response in an upstream tributaries of a highland stream in Kenya. Nine aquaculture sites adjacent to tributaries of three headwater streams with different fish production volumes were sampled and monitored for macroinvertebrate abundance, richness, composition of Ephemeroptera, Plecoptera and Trichoptera, Oligochaetes and Chironomids (percentage Oligochaetes and Chironomids), species diversity as well as the functional feeding group responses. The total abundance of benthic macroinvertebrate consistently increased near discharge points and immediately downstream of the effluent outlets near the aquaculture farms. We observed positive correlations between macroinvertebrate attributes (except Ephemeroptera, Plecoptera and Trichoptera) with fish production at aquaculture facilities adjacent to the tributaries of the headwater streams. The proportion of Oligochaetes and Chironomids (percentage Oligochaetes and Chironomids) increased while that of Ephemeroptera, Plecoptera and Trichoptera at discharge points and downstream of the farms decreased. Also, relative abundance of scrapers and shredders decreased significantly, while significant increase of abundance was observed for deposit feeders, filter feeders and parasites with low predator population at discharge and downstream points. These consistent patterns indicated changes in ecosystem integrity and functioning, due to aquaculture effluents with particulate organic matter from fish food-derived wastes becoming a central source of energy in river benthic food webs.