Environmental and Physical Factors Affecting the Diversity and Distribution of the Ichthyoplankton in an Inverse Estuary , the Sine Saloum (Senegal)

Estuarine mangrove ecosystems are considered essential nursery grounds and feeding areas for the early life stages of many fish species, often including commercially important ones. Particularly, climate change is expected to affect and have a substantial impact on mangrove estuaries, through processes including changes in precipitation, increased temperature, and changing patterns of ocean and estuarine circulation. As a result, the inversion of the salinity gradient in several estuaries throughout the dry tropics is either underway or can be expected in the near future. Such modifications of these important estuarine environments are cause of concern because spawning and nursery grounds of fishes have requisite environmental and physical attributes. Thus, there is a strong scientific consensus that related pressing contemporary research questions regarding the early life history of fishes in these transformed estuaries should be addressed. Located in Senegal, West Africa, the Sine Saloum system is representative of estuaries where the salinity gradient has been inverted due to climatic changes in the region. Given the high overall salinity and the resulting mangrove degradation that is taking place there, its potential role (compared to a classic estuarya ) as a recruitment and nursery area for fish larvae is far to be clear. Thus, the Sine Saloum estuary is a natural and excellent choice to study how these climatic environmental transformations are affecting the ichthyoplankton community. The aim of this thesis is to gain knowledge on the environmental and physical factors affecting the Sine Saloum ichthyoplankton diversity and distribution. The survival of fish larvae is known to be influenced by complex interactions between environmental changes and tropho- and hydrodynamic processes. Consequently, I first analysed the spatial and seasonal distribution of the fish larval assemblages related to environmental parameters. Second, a field experiment measuring simultaneously vertical current profiles and larval transport were conducted to investigate the effectiveness of larval fishes in regulating transport in and out of the estuary. Lastly, stable isotope analysis was used to evaluate the contribution of the sea surface microlayer (SML) to the diet of larval and juvenile African halfbeaks (Hyporamphus picarti), one of the dominant species in the system. The summarised key findings of the thesis are: A total of 41 taxa representing 24 families and 34 genera were sampled in the estuary, which is lower than that of other tropical estuaries, providing evidences that high salinity environment may harbour a less diverse ichthyoplankton fauna. Additionally, the distributional pattern of fish larvae revealed that the total abundance and the richness in the estuary decreased from the lower to the upstream areas with salinity and water temperature as the variables that best explained the spatial and temporal differences observed. Larval fish assemblages also showed a clear vertical structure corresponding to three distinct water strata.The circulation at the entrance of the Sine Saloum estuary was characterized by the existence of a longitudinal gravitational circulation with vertical shear and net near-surface inflow into the estuarine system. This is of critical importance in the context of fish recruitment because it offers a natural path into (resp. out of) the estuarine system for organisms that would be able to maintain themselves in the upper (resp. lower) part of the water column. The distribution of the fish larvae taxa that were examined revealed depth range preferences that did not change in time, independent from tide conditions, and were consistent with the use of these pathways. From a behavioural perspective, this mechanism can be viewed as simpler than selective tidal stream transport in that it does not require the organisms to synchronise their vertical migrations with the phase of the tidal currents. By obtaining statistically distinct A 13C and A 15N isotopic signatures for the SML, its presence at the entrance of the Sine Saloum estuary was confirmed. The organisms contained in the SML presented an important food source for H. picarti larvae and juveniles, contributing to more than 70 % of their diets. These results underline the importance of the SML and the role of this estuary as a spawning and nursery habitat for H. picarti

Identifying Sumatran Peat Swamp Fish Larvae through DNA Barcoding, Evidence of Complete Life History Pattern

AbstractThe Eastern Sumatran peat swamp ecosystem is one of the most threatened and most poorly understood biotypes. Until recently, there is no scientific record concerning ichtyoplankton composition within this system and all fish's biodiversity research at this ecosystem relied on morphological diagnosis for adult stages. Two new fish records in this system, Rasbora pauciperforata and Ompok eugeneiatus were detected. Finally the authors concluded that, eleven fish species complete their life history in Eastern Sumatran peat swamp. This investigation enlarges the COI barcode database for the molecular identification of eastern Sumatran peat swamp fishes

Production, consumers' convenience, and cynical economies: The case of Uber in Buenos Aires

Based on twelve months of fieldwork into Uber's conflict in Buenos Aires, Argentina, this article examines convenience's role in the emergence of what I call cynical economies: a method and logic of production expressly organized on the awareness of a distance the very rhetoric of convenience exacerbates. For the city's middle class, convenience defined a democratizing, empowering arena of private relations away from the hierarchies and exclusions proper to the private sphere. As Uber's ratings translated consumers' experiences into a political economy for the trade, drivers organized the production of the ride knowing that whatever exceeded the immediate intelligibility of the experience could not matter in that political economy. In the process, cynical economies delegitimize complex and inherently social categories like risk, responsibility, and liability, as well as the social sphere that frames them, without offering an alternative order in return

Umwelt- und physikalische Faktoren, die die Diversität und Verbreitung des Ichthyoplanktons in einem "Inversem estuar", der Sine Saloum (Senegal) beeinflussen

Estuarine mangrove ecosystems are considered essential nursery grounds and feeding areas for the early life stages of many fish species, often including commercially important ones. Particularly, climate change is expected to affect and have a substantial impact on mangrove estuaries, through processes including changes in precipitation, increased temperature, and changing patterns of ocean and estuarine circulation. As a result, the inversion of the salinity gradient in several estuaries throughout the dry tropics is either underway or can be expected in the near future. Such modifications of these important estuarine environments are cause of concern because spawning and nursery grounds of fishes have requisite environmental and physical attributes. Thus, there is a strong scientific consensus that related pressing contemporary research questions regarding the early life history of fishes in these transformed estuaries should be addressed. Located in Senegal, West Africa, the Sine Saloum system is representative of estuaries where the salinity gradient has been inverted due to climatic changes in the region. Given the high overall salinity and the resulting mangrove degradation that is taking place there, its potential role (compared to a classic estuarya ) as a recruitment and nursery area for fish larvae is far to be clear. Thus, the Sine Saloum estuary is a natural and excellent choice to study how these climatic environmental transformations are affecting the ichthyoplankton community. The aim of this thesis is to gain knowledge on the environmental and physical factors affecting the Sine Saloum ichthyoplankton diversity and distribution. The survival of fish larvae is known to be influenced by complex interactions between environmental changes and tropho- and hydrodynamic processes. Consequently, I first analysed the spatial and seasonal distribution of the fish larval assemblages related to environmental parameters. Second, a field experiment measuring simultaneously vertical current profiles and larval transport were conducted to investigate the effectiveness of larval fishes in regulating transport in and out of the estuary. Lastly, stable isotope analysis was used to evaluate the contribution of the sea surface microlayer (SML) to the diet of larval and juvenile African halfbeaks (Hyporamphus picarti), one of the dominant species in the system. The summarised key findings of the thesis are: A total of 41 taxa representing 24 families and 34 genera were sampled in the estuary, which is lower than that of other tropical estuaries, providing evidences that high salinity environment may harbour a less diverse ichthyoplankton fauna. Additionally, the distributional pattern of fish larvae revealed that the total abundance and the richness in the estuary decreased from the lower to the upstream areas with salinity and water temperature as the variables that best explained the spatial and temporal differences observed. Larval fish assemblages also showed a clear vertical structure corresponding to three distinct water strata.The circulation at the entrance of the Sine Saloum estuary was characterized by the existence of a longitudinal gravitational circulation with vertical shear and net near-surface inflow into the estuarine system. This is of critical importance in the context of fish recruitment because it offers a natural path into (resp. out of) the estuarine system for organisms that would be able to maintain themselves in the upper (resp. lower) part of the water column. The distribution of the fish larvae taxa that were examined revealed depth range preferences that did not change in time, independent from tide conditions, and were consistent with the use of these pathways. From a behavioural perspective, this mechanism can be viewed as simpler than selective tidal stream transport in that it does not require the organisms to synchronise their vertical migrations with the phase of the tidal currents. By obtaining statistically distinct A 13C and A 15N isotopic signatures for the SML, its presence at the entrance of the Sine Saloum estuary was confirmed. The organisms contained in the SML presented an important food source for H. picarti larvae and juveniles, contributing to more than 70 % of their diets. These results underline the importance of the SML and the role of this estuary as a spawning and nursery habitat for H. picarti

Seasonal growth differences of larval Hyporhamphus picarti (Hemiramphidae) in the Sine Saloum estuary, Senegal

The African halfbeak Hyporhamphus picarti (Hemiramphidae) is one of the most abundant species within the ichthyoplankton community of the Sine Saloum estuary (Senegal). A year‐round occurrence of larvae suggests that the Sine Saloum is an important spawning habitat for this species. Annual fluctuations in water temperature, however, can have severe impacts on the survival probabilities of marine fish larvae. To determine whether temperature has an effect on the growth of H. picarti during its larval development, larval age at length and somatic growth rates were investigated for two contrasting spawning seasons in 2014: February (cold season, 20.8°C) and June (warm season, 26.4°C). In both months H. picarti larvae were sampled at the mouth of the Saloum River using neuston nets. Sagittal otoliths’ increments were counted to estimate the larva age at a given standard length (SL). The age of larvae ranged between 2 and 22 days, with SL of 3.86–21.68 mm, respectively. In order to describe larval age at length during the contrasting spawning seasons, two distinctive Gompertz functions were applied. Accordingly, specimens sampled in June (0.94 ± 0.17 mm per day) exhibited significantly higher somatic growth rates than those sampled in February (0.60 ± 0.06 mm per day). These findings suggest that water temperature is an important factor influencing larval growth in H. picarti. Information concerning the early life stages of H. picarti are scarce and the results of the present study may contribute to a better understanding of the species’ biology and ecology

Age at length data for larval African halfbeak Hyporhamphus picarti (Hemiramphidae) in the Sine Saloum estuary, Senegal

The African halfbeak Hyporhamphus picarti (Hemiramphidae) is one of the most abundant species within the ichthyoplankton community of the Sine Saloum estuary (Senegal). A year-round occurrence of larvae suggests that the Sine Saloum is an important spawning habitat for this species. Annual fluctuations in water temperature, however, can have severe impacts on the survival probabilities of marine fish larvae. To determine whether temperature has an effect on the growth of H. picarti during its larval development, larval age at length and somatic growth rates were investigated for two contrasting spawning seasons in 2014: February (cold season, 20.8°C) and June (warm season, 26.4°C). H. picarti larvae were sampled at two stations inside the Saloum River using two vertically connected neuston nets (30 × 15 cm, 500 µm mesh size). The nets were attached to a catamaran (Hobie Cat 15), which was towed by a motorboat at a speed of two to three knots. Fish larvae were fixed immediately after the haul with a 30% ethanol/sea water solution and stored in an electric cooling box. At the laboratory, fish larvae were successively transferred to 50% and 70% ethanol. Water temperatures (°C) and salinities (practical salinity scale) were determined at each station with a multiprobe (WTW 3430). Larval standard lengths (SL ± 0.01 mm) were measured using a calibrated stereomicroscope micrometre (Stemi SV 11 and Stemi 2000-C, Zeiss). The sagittal otoliths were dissected and stored in immersion oil for several days. In order to assess the age of H. picarti larvae at a given length, otolith daily growth increments were counted (core to edge) along the otolith's largest diameter using a stereo microscope (Axioskop, Zeiss) at 200-500× magnification. Increments were counted three times by the same reader, and counter read once by an additional reader. If the results of the counts of both persons deviated by more than one increment, the respective otolith was discarded. Otolith diameter was measured using ImageJ 1.49 (Rasband, WS, US National Institutes of Health, Bethesda, MD, http://imagej.nih.gov/ij/)

Reproductive parameters of Ethmalosa fimbriata as recorded in Senegal (Atlantic coast and Sine Saloum estuary)

Little is known about the concerted influence of temperature and salinity on the fecundity of clupeid fishes. Due to a globally changing climate, both physical parameters might act as stressors, severely affecting the reproductive potential of clupeid fish populations inhabiting tropical estuaries. Differences in relative batch fecundities, the gonado-somatic index, and the condition index of bonga shad (Ethmalosa fimbriata) were analysed in individual females sampled at the Senegalese coast and inside the inverse Sine Saloum estuary, where salinity increases upstream in all seasons. Sampling took place at the Senegalese coast and inside the Saloum River from February to October 2014, during the peak of E. fimbriata's spawning season. An additional sampling campaign could be conducted in November 2016. Three different sites were sampled: Joal (Senegalese coast, 14°9.1' N; 16°51.7' W), Djifer (Saloum River's mouth, 13°57.8' N; 16°44.8' W), and Foundiougne (upstream Saloum River, 14°8.1' N; 16°28.1' W). MODIS satellite-derived (Aqua, level 2, 0.1 degrees) sea surface temperatures (https://oceancolor.gsfc.nasa.gov/) were assessed at Joal (20 km radius) and Djifer once per sampling week to enhance spatial coverage by avoiding cloud cover. As no remote sensing data for inland waters were available, the Saloum River's surface water temperatures were recorded in situ once per sampling week with a digital thermometer (ama-digit ad 15 th; precision 0.4%; accuracy 0.4%). Monthly means in MODIS satellite-derived (Aquarius, level 3, 0.5 degrees) sea surface salinities (https://oceancolor.gsfc.nasa.gov/) were used to assess the coastal ocean's salinity in a radius of 20 km around Joal. For Djifer and Foundiougne salinity was measured with a handheld refractometer (Aqua Medic; precision 0.7%, accuracy 0.2%) using a Practical Salinity Scale (PSS-78). Staging of fish was conducted macroscopically after a key by Blay Jr. & Eyeson (1982). In order to discriminate between mature females with ovaries containing fully hydrated oocytes (stage V) and females that have recently spawned (spent, stage VI) further descriptions on maturity stages in clupeid fishes were consulted (West 1990, ter Hofstede et al. 2007). Conversions of fish fork length (LF) to total length (LT) were conducted using the equation LT = 1.0007 × LF + 3.9. In order to access the nutritional status of female fish, a condition index (CI) was calculated for each individual using wet mass (WM, ±0.1 g), total length (LT, nearest mm), and b of the length-weight relationship: CI = WM x LT ^ -3.62 x 1000. The condition index (CI) and gonado-somatic index (GSI) of hydrated female spawners (Stage V) was based on the ovary-free body mss (OFBM, ±0.1 g) and the ovary mass (OM, ±0.0001 g): CI = WOF x LT ^ -3.62 x 1000; GSI = OM x OFBM ^ -1 x 100. The length-weight relationship of all sampled females across all sampling sites could be described by the following function: WM = 0.0015 x LT ^ 3.6