M. De Troch

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.

Fish communities in a tropical bay (Gazi Bay, Kenya): seagrass beds vs unvegetated areas

The fish fauna of seagrass beds and unvegetated areas in Gazi Bay (Kenya) was sampled in 9 stations with a beach seine. A total of 3601 fishes (> 95 % juveniles) was caught, comprising 75 species (40 families). The spatial patterns in the fish communities were investigated with multivariate statistical techniques. A first community occurred in the downstream part of a major river-fed creek and was characterised by a low density and diversity. These were sandy bottom stations with sparse seagrass vegetation. The dominant species of this community were Leiognathus elongatus and Bothus myriaster. A second community occurred in the upstream part of the same creek, and was characterised by a high density and diversity. Gerres acinaces and Atherinomorus duodecimalis were the dominant species. A third community occurred in the stations of the shallow part of the bay and was characterised by a high diversity but a lower density. The dominant species were Apogon thermalis and G. acinaces. Both latter communities occurred in stations with dense seagrass beds.

Spatial and temporal distribution of harpacticoid copepods in Mondego estuary

Seasonal and spatial variations in the composition and relative contribution of the harpacticoid species in the Mondego estuary (western Portugal) were studied based on a monthly sampling along a salinity gradient. These benthic harpacticoids were collected in the water column by means of a 63-mm plankton net. The influence of hydrological parameters (temperature, salinity, oxygen dissolved concentration, pH, turbidity, chlorophyll-a, total suspended solids and nutrient concentrations) was analysed by means of a redundancy data analysis. In addition, this is the first study to provide a checklist of benthic harpacticoids from this estuary. In total, 13 species plus six species not yet identified but known to belong to the genus Canuella, Microsetella, Ectinosoma, Mesochra, Harpacticus and Parapseudoleptomesochra were identified. Copepodites and adults of Euterpina acutifrons and Paronychocamptus nanus were most abundant in this harpacticoid community. While P. nanus dominated in winter and spring at upstream stations, E. acutifrons dominated more downstream. Although this species occurred along the whole salinity gradient, its highest abundances were found in the north arm of the estuary, except in autumn. This distribution may be due to the adaptability of E. acutifrons to different environments and the intermediate position between marine and estuarine conditions assigned to this species. Paraleptastacus cfr. spinicauda showed a relative occurrence of 5–10% in all stations, except at the mouth of the estuary (M). Tachidius discipes was found in low densities in Mondego estuary in spite of the large numbers of copepodites of this species in the southern arm, characterized by a high level of total suspended solids. The northern arm of the estuary was characterized by a higher numerical occurrence of harpacticoid organisms throughout the study years, with the higher densities towards the freshwater part (upstream areas). Canuella sp., Ectinosoma sp. (copepodite), Ectinosoma melaniceps, Leptocaris brevicornis, Phyllognathopus viguieri, Microsetella norvegica (copepodite) and Macrosetella gracilis (copepodite) were considered rare species. Nonetheless harpacticoid species were represented by a higher number of adults in the northern arm, and juveniles in the southern arm.

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.

Harpacticoid copepod colonization of coral fragments in a tropical reef lagoon (Zanzibar, Tanzania)

Colonization experiments were conducted in a tropical lagoon (Zanzibar Island, off the coast of Tanzania) to investigate the temporal dynamics and mode of colonization of the harpacticoid copepods community on dead coral fragments. There was fast colonization of the coral fragments attaining a substantial diversity after only two days. The ability to colonize dead coral fragments is thought to be related to the morphology and life style of different harpacticoid species. Phytal taxa (e.g. Tisbidae) were fast colonizers, reaching high abundances during the initial colonization phase. Sediment-associated and eurytopic taxa (e.g. Ameiridae, Miraciidae and Ectinosomatidae) showed lower colonization rates and became the dominant group during the later colonization phase. Most species are able to colonize the coral fragments through the water column. However, colonization along the substrate surface is also considered to be an important colonization mode, especially for sediment-associated taxa, which showed lower colonization rates when migration through the sediment was hindered.

Potential health risks via consumption of six edible shellfish species collected from Piura - Peru

Scallops and their potential predators were collected in Sechura Bay and in front of the Illescas Reserved Zone (north Peru), during El Niño-Southern Oscillation (ENSO) 2016, and analyzed for the metals chromium (Cr), manganese (Mn), iron (Fe), nickel (Ni), copper (Cu), zinc (Zn), arsenic (As), cadmium (Cd) and lead (Pb). This study showed that ~20% of the molluscs exceeded the maximum residual levels (MRLs) for human consumption in inorganic As, while ~30% of the crustaceans did. For Cd, around 10% and 40% of the molluscs and the crustaceans were above the MRLs, respectively. The cephalopod Octopus mimus exhibited As concentrations, but not Cd concentrations, that exceeded the MRLs. Cr, Ni, Cu, Zn and Pb in muscle exhibited generally concentrations below the MRLs. Integrated risk indices were estimated to determine if there is a health risk for consumption. Target hazard quotients (THQs) and total hazard indices (HIs) were mostly < 1, implying no human health risk. Provisional tolerable weekly intake (PTWI) for Cd was exceeded in Bursa ventricosa at Illescas Reserved Zone. Target cancer risks (TRs) for inorganic As were always higher than the threshold (1 × 10-6), therefore an actual cancer risk is present.

Role of the source community for the recovery of seagrass associated meiofauna: a field colonisation experiment with seagrass mimics in Diani Beach, Kenya

Seagrass communities are subject to frequent disturbances that can affect the associated fauna. Seagrass loss in Kenya has been mainly due to extensive grazing by the sea urchin Tripneustes gratilla, leading to habitat fragmentation. The challenge is whether the system can recover fully and function as before. Density, diversity and community structure of meiofauna were studied to evaluate the ability of the ecosystem to recover its associated fauna. Artificial seagrass mimics were planted in natural, replanted and bare seagrass patch types. The associated meiofauna was harvested at different colonisation time intervals (min. 2 days–max. 21 days). Significantly different meiofauna densities between the patch types and the colonisation days were found whereas the harpacticoid copepod densities were only significantly affected by colonisation time. Meiofauna densities on the seagrass mimics recovered quickly in all patch types, i.e. after four days of colonisation their densities were comparable to those on natural seagrasses, but they exhibited an unstable, cyclical pattern. Initial communities consisted mainly of opportunistic non-phytal taxa. Passive and active migrations were deduced for harpacticoid copepods. We recommend the ecosystem approach as seagrass-associated meiofauna (and copepods) responded relatively quickly to new substrates, providing the surrounding (source) communities remains undisturbed.

Bioenergetics of the copepod Temora longicornis under different nutrient regimes

The copepod Temora longicornis depends on constant prey availability, but its performance also depends on how efficiently it utilizes its food sources. Our research goal was to understand copepod energy allocation in relation to diet quality. The working hypothesis was that Temora performs better on the diet whose elemental ratio is closest to its own. Diatoms (Diat) and dinoflagellates (Dino) cultured in nutrient-replete (+) and nitrogen-depleted (-) conditions were fed to the copepods. Ingestion, respiration, excretion and egg and fecal pellet production rates were measured. Carbon (C) and nitrogen (N) budgets were built to investigate differences in dietary C and N partitioning. Copepods fed nitrogen-depleted diatoms (Diat-), which had the most different C: N ratio to that of Temora longicornis, had high metabolic losses and low growth. Copepods fed nitrogen-rich dinoflagellates (Dino+) with a more similar C: N ratio to their own also had high metabolic losses, but displayed the highest investment into somatic growth and egg production. The results indicate that dinoflagellates are a better food source for T. longicornis. Furthermore, consumption of low-quality food leads to higher respiration rates and faster leakage of dissolved organic carbon from copepod fecal pellets; and egestion is a main pathway in copepods for eliminating unabsorbed and non-metabolized carbon.