Water and sediment characteristics influence the distribution of ghost shrimps (axiidea) in the Persian and Oman Gulfs

Ghost shrimps (Crustacea: Decapoda) demonstrate remarkable levels of niche selection and habitat diversity. Due to their cryptic life style, interactions between ghost shrimp assemblages and environmental parameters that potentially shape their local distribution are poorly understood. In the present study, ghost shrimp assemblages from the Persian Gulf (PG) and the Gulf of Oman (GO) were investigated to assess the main drivers determining their assemblage structure along a wide niche type and at a large geographic scale. During three large-scale oceanographic expeditions, sediments samples for biological and physicochemical analysis were collected by box corer (0.1 m2) from 62 stations. The spatial distribution of collected samples was evaluated based on sediment parameters obtained on grain size, total organic content (TOM) and carbonate, as well as water parameters including pH, temperature, depth, dissolved oxygen, chlorophyll α and salinity. Our results indicated a biodiversity hotspot for ghost shrimp in the north-western part of PG and the eastern part of GO. Aqaballianassa ehsani is the most frequent species in this research. DistLM analysis revealed that the abundance of ghost shrimps in the region is significantly corelated with TOM and Sand. Furthermore, a step-wise regression model highlighted that each ghost shrimp species is influenced by specific environmental factors. Our findings provide new insight in niche preferences of the two Michaelcallianassa congeners. While water and sediment parameters play a crucial role in determining the habitat preference of M. persica, only sediment parameters specify the favored niche of M. indica.

The impact of salinity on a saline water insect: Contrasting survival and energy budget

Water salinity is a major driver of aquatic insects' distribution. Saline species are usually generalists with high survival and performance at both low and high salinity levels. Yet, costs of high salinity may be underestimated as these are most often measured in terms of larval life history traits, while effects of larval stressors may only be detectable when looking at physiological traits and traits in the adult stage. Here, we assessed the lethal and sublethal physiological effects of embryonic and larval exposure to a range of salinity levels in the damselfly Lestes macrostigma, both during and after metamorphosis. This species inhabits temporary freshwaters where salinity increases during the drying phase. Salinity had no effect on egg hatching success within the range 2-9.5 g/L sea salt (conductivity range 3.45-14.52 mS/cm). With increasing salinity (up to 16 g/L, 23.35 mS/cm), growth rate decreased and larvae took longer to emerge and did so at a smaller size. Larval survival to metamorphosis increased with salinity up to 8 g/L (12.45 mS/cm) and then declined at 16 g/L. Exposure to salinity in the larval stage had no effect across metamorphosis on both the adult thorax muscle mass and flight performance, and the investment in immune function. Increasing salinity in the larval stage also had no effect on the energy available but increased the energy consumption in the adult stage, resulting in a lower net energy budget. These negative sublethal effects of increasing salinity hence bridged metamorphosis and contrasted with the mortality data, suggesting that the higher mortality at the low salinity levels selected for larvae with the best body condition. Our results highlight the importance of taking into account other life-history and physiological traits, besides mortality, ideally across different life stages, to better understand and predict consequences of increasing salinization on freshwater insects.

Microhabitat distributions and species interactions of ectoparasites on the gills of cichlid fish in Lake Victoria, Tanzania

Heterogeneous exposure to parasites may contribute to host species differentiation. Hosts often harbour multiple parasite species which may interact and thus modify each other's effects on host fitness. Antagonistic or synergistic interactions between parasites may be detectable as niche segregation within hosts. Consequently, the within-host distribution of different parasite taxa may constitute an important axis of infection variation among host populations and species. We investigated the microhabitat distributions and species interactions of gill parasites (four genera) infecting 14 sympatric cichlid species in Lake Victoria, Tanzania. We found that the two most abundant ectoparasite genera (the monogenean Cichlidogyrus spp. and the copepod Lamproglena monodi) were non-randomly distributed across the host gills and their spatial distribution differed between host species. This may indicate microhabitat selection by the parasites and cryptic differences in the host-parasite interaction among host species. Relationships among ectoparasite genera were synergistic: the abundances of Cichlidogyrus spp. and the copepods L. monodi and Ergasilus lamellifer tended to be positively correlated. In contrast, relationships among morphospecies of Cichlidogyrus were antagonistic: the abundances of morphospecies were negatively correlated. Together with niche overlap, this suggests competition among morphospecies of Cichlidogyrus. We also assessed the reproductive activity of the copepod species (the proportion of individuals carrying egg clutches), as it may be affected by the presence of other parasites and provide another indicator of the species specificity of the host-parasite relationship. Copepod reproductive activity did not differ between host species and was not associated with the presence or abundance of other parasites, suggesting that these are generalist parasites, thriving in all cichlid species examined from Lake Victoria.

Spatiotemporal shifts of ammonia-oxidizing archaea abundance and structure during the restoration of a multiple pond and plant-bed/ditch wetland

Ammonia-oxidizing archaea (AOA) microorganisms have been increasingly found in aquatic and terrestrial environments. These microorganisms make vital contributions to ammonia oxidation in such systems. However, their community succession characteristics in man-made wetland ecosystems have scarcely been reported. We assessed the AOA's spatiotemporal shifts in the sediments of a constructed wetland (CW) - the Shijiuyang constructed wetland (SJY-CW) - in China from the third year (2011) to the fifth year (2013) of the CW operation. The SJY-CW is composed of a pretreatment pond, a multiple plant-bed/ditch system, and a post-treatment pond. Results showed that AOA abundance in the pre- and post-treatment ponds remained invariant through 2011-2012 and decreased in 2013, while the abundance in the plant-bed/ditch system decreased gradually with wetland operation. The AOA abundance in 2013 was one order of magnitude lower than that through 2011-2012, and the AOA abundance in the plant-bed/ditch system was generally higher than that in the pre- and post-treatment ponds from 2011 to 2013. AOA diversity showed little temporal differentiation with a slightly decreasing trend for community richness index Chao1 and diversity index Shannon H' from 2011 to 2013. The AOA community was dominated by the Nitrososphaera cluster accompanied by an increasing Nitrosopumilus cluster and Nitrososphaera sister cluster within the wetland operation. Hierarchical clustering and redundancy analysis verified the horizontal shifts of AOA communities. The shifts occurred preferentially in the central plant-bed/ditch system. The operational duration of the wetland became a key factor influencing AOA abundance and community shift in SJY-CW sediments.