Efficacy of adapted estuarine fish-based multimetric indices as tools for evaluating ecological status of the marine environment

Estuarine environmental flow assessment based on the flow-ecological health index relation model: a case study in Yangtze River Estuary, China

Environmental flow (e-flow) is the water demand of one given ecosystem, which can become the flow regulation target for protection and restoration of river or estuarine ecosystems. In this study, an e-flow assessment based on the flow-ecological health index (EHI) relation model was conducted to improve ecosystem health of the Yangtze River Estuary (YRE). Monitoring data of hydrology, biology, and water environment in the last decades were used for the model establishment. For the description of the YRE ecosystem, an EHI system was developed by cumulative frequency distribution curves and adaption of national standards. After preprocessing original flow values into proportional flow values, the generalized additive model and Monte Carlo random sampling were used for the establishment of the flow-EHI relation model. From the model calculation, the e-flow assessment results were that, in proportional flow values, the suitable flow range was 1.05-1.35, and the optimum flow range was 1.15-1.25 (flows in Yangtze River Datong Station). For flow regulation in two crucial periods, flows of 42,630-65,545 m3/s or over 14,675 m3/s are needed for the suitable flow of YRE in summer (June-August) or January, respectively. An adaptive management framework of ecological health-based estuarine e-flow assessment for YRE was contrived due to the limitation of current established model when facing the extreme drought in summer, 2022. The methodology and framework in this study are expected to provide valuable management and data support for the sustainable development of estuarine ecosystems and to bring inspiration for further studies at even continental or global levels.

Trophic diversity and carbon sources supporting fish communities along a pollution gradient in a tropical river

Anthropogenic activities can have a great influence on water quality and in the availability of habitat and food resources, which can promote changes in the trophic diversity and carbon sources sustaining aquatic communities. The objective of this study was to evaluate if the trophic diversity and the main carbon sources sustaining fish communities change along a pollution gradient. The study was carried out at eight sites distributed along the Rio das Velhas, a Brazilian river highly impacted by anthropogenic activities, in which the discharge of domestic and industrial sewage from the Metropolitan Region of Belo Horizonte (MRBH) presents a major source of pollution. Using carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope ratios, we identified the major carbon sources/food sources of common fish species and calculated six metrics of trophic diversity. Autochthonous primary producers (algae, periphyton, and macrophytes) were the main carbon sources for all trophic guilds at all sites, but notably, sewage-derived organic matter was an additional significant carbon source to the fish community in the most polluted testing site. Here, the community was composed mainly by detritivorous and omnivorous fishes and exhibited greater ranges of carbon and nitrogen isotopic values, large total areas, high trophic diversity, small trophic redundancy, and less even distribution of trophic niches than the less polluted sites. We conclude that the trophic guilds, trophic diversity metrics, and carbon sources sustaining fish communities in the Rio das Velhas are highly influenced by the presence of pollution. Besides favoring omnivorous and detritivorous fishes, the input of sewage also provided an important food source to sustain the fish community from sites close to the MRBH.

The development of a preliminary rock reef fish multimetric index for assessing thermal and urban impacts in a tropical bay

We developed a multimetric index for assessing ecological conditions in rocky reefs areas to evaluate thermal and urban influences on fish community. Eight metrics were selected to assess thermal influence: (1) total number of species; (2) number of water column species; (3) number of transient species; (4) density of individuals with low resilience; (5) density of omnivores; (6) density of carnivores; (7) number of cryptic species; (8) density of herbivores. For urban influence, six metrics were selected: (1) total density; (2) ratio between the number of rare species and the total number of species; (3) density of individuals with heavy fishing pressure; (4) number of resident species; (5) number of cryptic species; (6) density of herbivores. This preliminary index succeed in discriminating control/impacted sites and proved to be an important tool to assess impacts that alter fish community and have potential to be used in tropical rock reef coastal areas.

Composition of functional ecological guilds of the fish fauna of the internal sector of the Amazon Estuary, Pará, Brazil

The present study describes the spatial and temporal structure of the estuarine fish community in the internal sector of the Amazon Estuary. Samples were obtained in the main channels and tidal creeks of Guajará and Marajó Bays and Guamá River. A total of 41,516 fish specimens were collected, representing 136 taxa, 38 families and 12 orders. In the dry season, the mean salinity of the main channel increased along a limnic-marine gradient, between the Guamá River and the Marajó Bay. Species richness was lowest in the mouth of the Guamá River and in the right margin of the Guajará Bay. Fish species composition and environmental guilds differed markedly among areas: Migrants and Freshwater Stragglers were dominant in the Guamá River and the Guajará Bay, while Estuarine, Marine Stragglers and Migrants predominated in the Marajó Bay. However, the trophic guilds were still relatively well balanced, in functional terms. Piscivores and Zoobenthivores were the dominant feeding functional groups in all the studied areas. In this study, the assessment of the community and the use of the guild approach were efficient to describe the structure and functioning of the assemblages of estuarine fish also helping to assess the anthropogenic pressures in the area.

Measuring the ecological integrity of an industrial district in the Amazon estuary, Brazil

The aim of the present study is to provide information on the ecological integrity of an industrial district located in the estuary of Pará River (Amazon estuary), by applying a selection of fish based multimetric indices of ecosystem integrity: Abundance Biomass Comparation (ABC); Biological Health Index; Estuarine Fish Community, Transitional Fish Classification and Estuarine Biotic Integrity Indexes. To evaluate the impacts of the industrial area and cargo terminal, three areas were considered: Zone 1, (maximum impact), Zone 2 (median risk) and Zone 3 (reference area). All the biological indices used were considered to be excellent indicators of the ecological integrity of the different sectors of the study area and were especially effective for the demonstration of the critical alterations of the fish community of Zone 1 and Zone 2. The simultaneous use of different indices family, with different assumptions, did strengthen the results enhancing the confidence in the diagnostic.

Ecological quality assessment of small estuaries from the Portuguese coast based on fish assemblages indices

The importance of establishing the ecological quality of estuarine systems has been widely acknowledged and led to the development of several fish community-based multimetric indices. Nevertheless, a question rose about the accuracy of these tools when natural disturbance is acting upon the organization of the systems' communities. Four multimetric indices were used to examine their ability to differentiate the ecological status of five small estuarine systems (southern Portugal), and also to test if they reflected the level of anthropogenic pressures. Fish assemblages from Mira, Odeceixe and Aljezur (in the Southwest coast), Gilão and Bensafrim (in the South coast) estuaries were sampled seasonally for one year, and anthropogenic sources of pressure were identified and quantified. We found that although the applied indices provided information on ecological condition differentiation among systems, they are unable to explain different classes of ecological status in systems with equivalent pressure levels.

A habitat-specific fish-based approach to assess the ecological status of Mediterranean coastal lagoons

A habitat approach was promoted in the framework of ecological status assessment of transitional waters, assuming the importance of habitat heterogeneity to the overall system status. The approach was applied to the use of fish-based multimetric indices by adapting them to seagrass and marsh habitats in the Venice lagoon, Italy, through selection of appropriate metrics and reference conditions. While for marsh habitats, no clear patterns resulted, the index response for seagrass was consistent with the habitat degradation and loss recorded in the lagoon between 2002 and 2005 and with the higher habitat disturbance in southern and central lagoon sub-basins. The assessment of individual habitats is presented as a first step in the process of evaluating the overall condition of a Mediterranean lagoon environment, which should also take account of the diversity of habitats and their availability within the system to properly define an overall index of ecological status.

Development of a fish-based multimetric index to assess the ecological quality of marine habitats: the Marine Fish Community Index

In this paper the Marine Fish Community Index (MFCI) for the assessment of ecological status of marine environment is proposed. The MFCI was divided into 4 typologies: Rocky subtidal; shallow, intermediate and deep soft-bottoms. Based on the typical community associated to each typology and the DPSIR analysis performed, a set of metrics were selected and tested through a multiple correlation matrix (Pearson's coefficient) and the core ones included in the index. The MFCI was applied in all typologies and the scores obtained with each metric were analyzed. In order to test the robustness of the MFCI the final ecological value of each zone was recalculated by removing successively one metric at a time. The MFCI showed a sensitive and robust response in the ecological status assessment. Since it incorporates both functional and structural community information, the MFCI can be useful in the context of the Marine Strategy Framework Directive as well as in other contexts of conservation and sustainable management of the marine environment.