Key Drivers for Copepod Assemblages in a Eutrophic Coastal Brackish Lake

Exotic asphyxiation: interactions between invasive species and hypoxia

Non-indigenous species (NIS) and hypoxia (<2 mg O₂ l^-1 ) can disturb and restructure aquatic communities. Both are heavily influenced by human activities and are intensifying with global change. As these disturbances increase, understanding how they interact to affect native species and systems is essential. To expose patterns, outcomes, and generalizations, we thoroughly reviewed the biological invasion literature and compiled 100 studies that examine the interaction of hypoxia and NIS. We found that 64% of studies showed that NIS are tolerant of hypoxia, and 62% showed that NIS perform better than native species under hypoxia. Only one-quarter of studies examined NIS as creators of hypoxia; thus, NIS are more often considered passengers associated with hypoxia, rather than drivers of it. Paradoxically, the NIS that most commonly create hypoxia are primary producers. Taxa like molluscs are typically more hypoxia tolerant than mobile taxa like fish and crustaceans. Most studies examine individual-level or localized responses to hypoxia; however, the most extensive impacts occur when hypoxia associated with NIS affects communities and ecosystems. We discuss how these influences of hypoxia at higher levels of organization better inform net outcomes of the biological invasion process, i.e. establishment, spread, and impact, and are thus most useful to management. Our review identifies wide variation in the way in which the interaction between hypoxia and NIS is studied in the literature, and suggests ways to address the number of variables that affect their interaction and refine insight gleaned from future studies. We also identify a clear need for resource management to consider the interactive effects of these two global stressors which are almost exclusively managed independently.

Effects of Eutrophication on Plankton Abundance and Composition in the Gulf of Gabès (Mediterranean Sea, Tunisia)

Phytoplankton and Copepoda were investigated in the industrialized Gabès coast (Mediterranean Sea, Tunisia) to understand consequences of the Eutrophication Grade on the community composition. In the past 40 years, intensive agrochemical activities have developed in Gabès, discharging wastewater along the coast. In parallel, Gabès City has experienced a rapid demographic expansion (population: 131,000) that further increased sewage discharged into the sea. The present study was carried out in the Gulf of Gabès in March 2014. The abiotic analysis of seawater showed high concentrations of nutrients and eutrophication in all the studied fifteen stations. A growing eutrophic gradient was revealed from Zarrat to Gannouche. During this study, 42 phytoplankton taxa and 24 Copepoda taxa were identified. Bacillariophyta were the most abundant group, ranging from 67.7% to 89.2% of total phytoplankton specimens. Chaetoceros costatus, Euglena acusformis, and Thalassiosira sp. showed a positive correlation with Eutrophication Index (profited of nutrient availability). Therefore, the Shannon–Weaver diversity index of phytoplankton and Copepoda showed negative correlations with Eutrophication Index. The relatively high H′ values for phytoplankton suggest that the eutrophicated waters of Gulf of Gabès are not a hostile environment for them. Among Copepoda, Oithona similis, and Euterpina acutifrons seem to be insensible species to eutrophication.

Concentrations of trace metals in phytoplankton and zooplankton in the Gulf of Gabès, Tunisia

The concentrations of four trace metals (Cd, Cu, Pb, and Zn) were investigated for the first time in phytoplankton, zooplankton, and the seawater samples collected from the coast of Gabès, Tunisia, Mediterranean Sea. For over 40 years, this coast has witnessed significant anthropogenic impacts form fertilizer processing. Results obtained for Cd, Cu, Pb, and Zn in seawater far exceed the concentration reported for other Mediterranean coastal waters, highlighting the Gulf of Gabès as a pollution hotspot. The average metals concentration was in the order Zn > Pb > Cu > Cd in water, and phytoplankton, whereas Pb > Zn > Cu > Cd in zooplankton. The biomagnification in phytoplankton and zooplankton for Zn, Pb, Cu, and Cd was 116, 56, 38, 31, and 127, 157, 30 and 27. The biomagnification of Zn and Pb was higher in zooplankton than phytoplankton, while Cu and Cd were higher in phytoplankton.

Limno-ecological assessment of lentic ecosystems in the western Mediterranean basin (Turkey) using phytoplankton indices

Great attention has been given to freshwater ecosystems worldwide due to the increased exploitation of water resources and the degradation of water quality. This study was aimed to demonstrate the phytoplankton-stressor interactions using multivariate approaches and assess the ecological conditions of 28 sampling stations of 12 lentic ecosystems (five lakes and seven reservoirs) in the western Mediterranean basin using phytoplankton indices in dry and rainy seasons 2018. Freshwater and brackish water systems were separately ordinated by canonical correspondence analysis. The brackish ecosystems were under pressures of Ar (arsenic), N-N[Formula: see text] (nitrite), Ca (calcium), EC (electrical conductivity), Cl (chloride), B (boron), etc., whereas shallow freshwater ecosystems were associated with total organic carbon. These factors had significant effects on phytoplankton distribution among lentic ecosystems on the basin. Ecological associations of phytoplankton assemblages varied in the western Mediterranean basin during the study. Pseudanabaena catenata and Palatinus apiculatus, considered tolerant taxa, are associated with higher Ar, EC, and V (vanadium) while Desmodesmus abundans and Microcystis flos-aquae are related to total organic carbon. The modified PTI (phytoplankton trophic index) had the highest correlation coefficient value. Scores of the PTI varied from 2.02 in Çavdır Reservoir to 2.59 in Lake Kocagöl. Results of phytoplankton indices indicated that two (Gölhisar and Yazır) lakes and two (Yapraklı and Çavdır) reservoirs were classified as Good, and three lakes and five reservoirs were classified as Moderate condition. Other predicted classifications (high, poor, and bad) by phytoplankton metrics were not represented. The modified PTI could be a suitable phytoplankton metric for assessing the ecological status of lentic ecosystems in the Mediterranean system according to its highest correlation coefficient value. Overall, the results of this limno-ecological study demonstrated that responses of phytoplankton taxa to explanatory factors provide crucial ecological information about their ecology and to estimate the ecological status of lentic ecosystems.

Non-destructive genome skimming for aquatic copepods

Copepods are important ecologically and represent a large amount of aquatic biomass in both freshwater and marine systems. Despite this, the taxonomy of copepods and other meiofauna is not well understood, hampered by tiny sizes, cryptic taxa, intraspecific polymorphisms and total specimen destruction where DNA methods are employed. In this article we highlight these issues and propose a more up-to-date approach for dealing with them. Namely, we recommend non-destructive DNA extraction methods, coupled with high-throughput sequencing (HTS). Whilst DNA yields may be low, they should still be sufficient for HTS library preparation and DNA sequencing. At the same time morphological specimens can be preserved and the crucial link between morphology and DNA sequence is maintained. This is critical for an integrative taxonomy and a fuller understanding of biodiversity patterns as well as evolutionary processes in meiofauna.