Underwater Habitats Research Articles

ASSESSMENT OF A LOW-COST SIDE-SCAN SONAR FOR RIVER ESTUARY UNDERWATER IMAGING

River and estuary areas commonly exhibit complex and heterogeneous habitats. Thus, revealing the distribution of riverbed morphologies could promote the area management and habitats protection. Since the remote sensing method and manual survey are limited to use, side-scan sonar performs an expectant outcome in underwater habitat imaging. In shallow water and stream areas, low-cost side-scan sonar imaging has become a notable subject of study, yet its use in Indonesia is still limited. This study describes an investigation of the use of a recreational-grade side-scan sonar for stream underwater imaging. A visual inspection and interpretation were implemented using a free-cost sonar software. The result shows some underwater objects and debris could be portrayed perfectly and this indicates that the inexpensive sonar system is appropriate to be used in shallow water and stream areas with a non-rough sea surface. It is suggested that this system could provide a satisfactory product to the users who do not require high accuracy and high resolution of riverbed imagery.Keywords: estuary, river, underwater mapping, acoustic remote sensing, low-cost, side-scan sonar.

Changes in Individual and Team Cognition in High Stress Extreme Underwater Saturation Environment Under Intense Workload

The objective of this study was to measure potential changes in cognitive function in response to living in an extreme underwater habitat. Chronic high stress and intense workload can affect individual and team cognition. As such, associated variables were monitored during the NASA Extreme Environment Mission Operation (NEEMO) 23 mission at the Aquarius reef Base in June 2019.Individual cognition was measured on 6 subjects (2 males, 4 females) with 8 tests using a battery of cognitive assessments (Joggle Research platform), 1 day pre‐mission, at mid‐point of the mission and 1 day post‐mission. In addition, 4 cognitive tests were applied on 5 subjects (2 males, 3 females) at the beginning of Extravehicular Activities (EVA) and at the end of EVAs that lasted for ~3 to 5 hours. To monitor changes in stress level, Short Stress State Questionnaire (SSSQ) and Generalized Anxiety Disorder (GAD7) scores were collected. Effects of workload on performance were measured by NASA Task Load Index (TLX). Changes in team cognition was monitored using an assessment of cognitive process measures.There was a trend of increasing performance in individual cognition in‐habitat and post mission, compared to baseline. The NBACK test, a measure of working memory, significantly improved during the mission, compared to pre‐mission and it further improved post‐mission. The psychomotor vigilance test (PVT) results were non‐significantly lower during the mission. The Motor Praxis Task (MPT) scores decreased at the beginning of EVA and further decreased by the end of EVA. The end of EVA MPT performance was significantly lower, compared to baseline, in habitat, and post mission measurements, suggesting that long duration extravehicular activity had a significant negative effect on sensory motor speed. BART scores were significantly lower at the beginning of EVA, compared to baseline, suggesting that risk taking decreased with the start of the EVA. The PVT score was significantly lower at the end of EVA, compared to baseline, in habitat, and the beginning of EVA, suggesting that the long duration EVAs had negative effect on the ability to quickly respond to the sudden appearance of a stimuli. A trend of increasing GAD7 scores at half time of the mission and post‐mission could be observed. There were differences in NASA TLX and team cognition scores between subjects and at different time points.The present results suggests that sub‐components individual and team cognitive functions may be differently affected during this extreme environment mission. Further research is needed to isolate which cognitive functions might be altered and how these may be correlated with stress level and workload to affect mission success.Support or Funding InformationKetone Technologies LLC provided partial funding for the experiments. SIFT provided partial salary for CA.

Recent use of habitat service value for tourism and impacts on coral reefs in the target destinations in Southern Vietnam

Coral reef-based tourism has developed quickly in Southern Vietnam, taking into account the target locations namely Cu Lao Cham islands, Nha Trang bay, Ninh Thuan and Phu Quoc islands during last decade. Among them, Nha Trang bay had longer history of marine tourism, starting with inshore development and expanding to islands in and around the bay. Tourist activities in Cu Lao Cham islands and Ninh Thuan were developed in linkages with MPA development and management. Meanwhile, Phu Quoc had become a new destination and drawn huge investments for extensive development of tourism in the islands. Economic value that was brought from use of coral reefs for tourism has increased significantly. For example, the payment of entry fee to Cu Lao Cham MPA has quickly increased year by year, reaching approximately 700,000 USD in 2018 and that in Ninh Thuan around 50,000 in 2017 and up to 200,000 USD in 2018. Reclamation for infrastructure building on inshore land and islands was considered as a serious impact, resulting in loss of terrestrial and underwater habitats (e.g. loss of Melaleuca forest in Phu Quoc islands or seagrass beds and coral reefs in Nha Trang bay) and increased sediment loading to coral reefs. Overexploitation of living resources for high food and souvenir demands occurred at all areas, leading to modification of communities, poorness and uncertainty for resource recruitment. Among these tree areas, Phu Quoc waters are the most vulnerable to coral bleaching due to increased surface temperature with records of mass bleaching in 2010 and 2016. Although MPAs existed in all study areas, role of conservationists in developing coral reef tourism was significantly considerable only in Cu Lao Cham case but poor in others. Local managers and businesses should pay more attention to sustainability in order to ensure not only coral reef conservation but also long-term benefits of local communities and tourist sector itself.

Using acoustic metrics to characterize underwater acoustic biodiversity in the Southern Ocean

AbstractAcoustic metrics (AM) assist our interpretation of acoustic environments by aggregating a complex signal into a unique number. Numerous AM have been developed for terrestrial ecosystems, with applications ranging from rapid biodiversity assessments to characterizing habitat quality. However, there has been comparatively little research aimed at understanding how these metrics perform to characterize the acoustic features of marine habitats and their relation with ecosystem biodiversity. Our objectives were to 1) assess whether AM are able to capture the spectral and temporal differences between two distinct Antarctic marine acoustic environment types (i.e., pelagic vs. on‐shelf), 2) evaluate the performance of a combination of AM compared to the signal full frequency spectrum to characterize marine mammals acoustic assemblages (i.e., species richness–SR–and species identity) and 3) estimate the contribution of SR to the local marine acoustic heterogeneity measured by single AM. We used 23 different AM to develop a supervised machine learning approach to discriminate between acoustic environments. AM performance was similar to the full spectrum, achieving correct classifications for SR levels of 58% and 92% for pelagic and on‐shelf sites respectively and > 88% for species identities. Our analyses show that a combination of AM is a promising approach to characterize marine acoustic communities. It allows an intuitive ecological interpretation of passive acoustic data, which in the light of ongoing environmental changes, supports the holistic approach needed to detect and understand trends in species diversity, acoustic communities and underwater habitat quality.

Application of Hyperspectral Imaging to Underwater Habitat Mapping, Southern Adriatic Sea.

Hyperspectral imagers enable the collection of high-resolution spectral images exploitable for the supervised classification of habitats and objects of interest (OOI). Although this is a well-established technology for the study of subaerial environments, Ecotone AS has developed an underwater hyperspectral imager (UHI) system to explore the properties of the seafloor. The aim of the project is to evaluate the potential of this instrument for mapping and monitoring benthic habitats in shallow and deep-water environments. For the first time, we tested this system at two sites in the Southern Adriatic Sea (Mediterranean Sea): the cold-water coral (CWC) habitat in the Bari Canyon and the Coralligenous habitat off Brindisi. We created a spectral library for each site, considering the different substrates and the main OOI reaching, where possible, the lower taxonomic rank. We applied the spectral angle mapper (SAM) supervised classification to map the areal extent of the Coralligenous and to recognize the major CWC habitat-formers. Despite some technical problems, the first results demonstrate the suitability of the UHI camera for habitat mapping and seabed monitoring, through the achievement of quantifiable and repeatable classifications.

3D HABITAT COMPLEXITY OF CORAL REEFS IN THE NORTHWESTERN HAWAIIAN ISLANDS IS DRIVEN BY CORAL ASSEMBLAGE STRUCTURE

Abstract. Corals act as ecosystem engineers by secreting structurally complex calcium carbonate skeletons on the benthic substrate that provide habitat for a diverse array of associated reef organisms. Communities of living corals create large and dynamic benthic structures that directly affect ecological parameters such as habitat provisioning and light availability, thus influencing overall ecosystem function. Despite the important role 3D structural complexity plays in ecosystem biodiversity and productivity, the field of coral ecology has lacked accessibility to practical technology capable of quantifying 3D characteristics of underwater habitats. Advancements in the field of computer vision has led to Structure-from-Motion (SfM) photogrammetry, which provides a simple and cost-effective method for creating high-resolution and spatially accurate 3D reconstructions of natural environments. Integrating SfM approaches into coral reef research and monitoring has provided useful insight into the relationship between 3D habitat complexity and ecological processes. In this study, we examined the relationships among 2D estimates of live coral cover and several metrics of 3D habitat structural complexity among eleven long-term monitoring sites at French Frigate Shoals. Our findings show that coral assemblage structure acts as a significant driver of 3D structural complexity of coral reef habitats at this atoll. This study highlights the importance of diverse and abundant coral assemblages in supporting structurally complex coral reef habitats and provides a framework for future investigations into the ecological role of various coral morphotypes.

The Creation and Perception of Underwater Built Environment or Architecture

It is obvious that the underwater architectural space is formed as the result of the contemporary human construction activity. Underwater exist built environment available to the modern man. Below the surface of the water is a space that is shaped in a way that makes an architecture. The creation of underwater space has lot of ways and methods. There are a significant desperation between the imagination of designers and the real construction made underwater. Also the problem of different perception of underwater spaces are significant problem. Human body is used to live in the air at the normal pressure of 1at, and in the environment of air. The water is not the natural environment for people so there are important differences of perception of architectural space existing below the surface. Physical conditions of underwater facilities are very different from the ground conditions and it must be considered by visionaries and concept makers to have a chance to implement them. The space of water below the surface is full of stuff which is placed or constructed by the people. Most of them are very simple construction, placed for the recreation purpose. There are dozens of futuristic visions of underwater habitats, but at present times, it is not possible to notice that designers find the way of development, which follow their imaginations. There are not exist the futuristic structures or glass domes. Most of the constructed underwater architecture is available only with the SCUBA equipment. The author as the licenced architect (since 1994) and the designer of several objects connected with water, and the instructor of the Underwater Activity Committee trying to find the purpose and the reason why the human being must (or try) to live at the enemy environment of underwater.

IMPLEMENTASI METODE RETINEX UNTUK MENINGKATKAN KUALITAS CITRA UNDERWATER

Digital imagery is a two-dimensional image process through a digital computer that is used to manipulate and modify images in various ways. Photos are examples of two-dimensional images that can be processed easily. Each photo in the form of a digital image can be processed through certain software devices. In the water environment, light factors greatly influence the results of image quality obtained. With the deepening of underwater shooting, the results obtained will be the darker the quality of the underwater image. Underwater imagery is widely used as an object in various activities such as underwater habitat mapping, underwater environment monitoring, underwater object search. Uneven lighting and colors that tend to be bluish and runny. One of the factors that influence the recognition results in pattern recognition is the quality of the image that is inputted. The image acquired from the source does not always have good quality. The process of improvement in digital images that experience interference in lighting and exposure to sunlight. The lighting repair process uses the retinex method and will compare the quality of the two methods later. Until later the results of both methods can be seen which is better. Retinex method can produce image improvement with high performance.Keywords: Digital Cintra, Underwater, Matlab Retinex Method

DNA barcoding reveals cryptic diversity of economic red algae, Pyropia (Bangiales, Rhodophyta): description of novel species from Korea

Red algal genus Pyropia that includes several commercially important species is distributed in wide regions of the world from cold temperate to tropical marine environments. Despite their practical utility, species of this genus are difficult to identify using solely morphological features because they lack reliable diagnostic characteristics. DNA barcoding using mitochondrial COI-5P marker is now well established for red algae. We explored the species diversity of the genus Pyropia in Korea based on the molecular analyses and morphological observations, and confirmed seven species including two new ones, Py. kuniedae, Py. retorta, Py. seriata, Py. tenera, Py. yezoensis, Pyropia submarina sp. nov., and Pyropia vittata sp. nov. In the DNA barcode analysis, Korean Pyropia species were clearly distinguished from other Pyropia species by 2.6 to 17.1% sequence divergences. We also uncovered cryptic species diversity in areas that are remote or not easily approachable such as Ulleung Island in the middle of east sea far from mainland or underwater habitat deeper than 10 m of Udo, Jeju. This study is verifying the probability of more biodiversity from pristine environments and providing the information that DNA barcoding is an efficient way to identify species of Pyropia, the bladed genus of the order Bangiales in Korea.

A Commentary – Lake Tanganyika fisheries: Current constraints and the way forward

A Commentary – Lake Tanganyika fisheries: Current constraints and the way forward

Diversity of kelp holdfast-associated fauna in an Arctic fjord - inconsistent responses to glacial mineral sedimentation across different taxa

Kelp forests are complex underwater habitats that support diverse assemblages of animals ranging from sessile filter feeding invertebrates to fishes and marine mammals. In this study, the diversity of invertebrate fauna associated with kelp holdfasts was surveyed in a high Arctic glacial fjord (76 N, Hornsund, Svalbard). The effects of algal host identity (three kelp species: Laminaria digitata, Saccharina latissima and Alaria esculenta), depth (5 and 10 m) and glacier-derived disturbance (three sites with varying levels of mineral sedimentation) on faunal species richness and composition were studied based on 239 collected algal holdfasts. The species pool was mostly made up by three taxa: colonial Bryozoa and Hydrozoa, and Polychaeta. While the all-taxa species richness did not differ between depths, algal hosts and sites, the patterns varied when the two colonial sessile filter-feeding taxa were analysed alone (Hydrozoa and Bryozoa). The Hydrozoa sample species richness and average taxonomic distinctness were the highest at undisturbed sites, whereas Bryozoa species richness was higher in sediment-impacted localities, indicating relative insensitivity of this phylum to the increased level of mineral suspension in the water column. The average taxonomic distinctness of Bryozoa did not vary between sites. The species composition of kelp-associated fauna varied between sites and depths for the whole community and the most dominant taxa (Bryozoa, Hydrozoa). The high load of inorganic suspension and sedimentation did not cause pauperization of kelp holdfast-associated fauna but instead triggered the changes in species composition and shifts between dominant taxonomic groups.

Survey of Fish Behavior Analysis by Computer Vision

Assessment of the behavior or physiology of cultured fish has always been difficult due to the sampling time, differences between experimental and aquaculture conditions, and methodological bias inherent. Recent developments in computer vision technology, however, have opened possibilities to better observe fish behavior. Such technology allows for non-destructive, rapid, economic, consistent, and objective inspection tools, while providing evaluation techniques based on image analysis and processing in a wide variety of applications. “Fish”, in this study, refers to underwater vertebrate fish belonging to the Pisces class that inhabit almost all available aquatic environments. This study aims to assess current, worldwide fish behavior study methods that use cameras which utilize computer vision. The evolution of computer vision as applied to fish behavior is explored in this paper for all stages of production, from hatcheries to harvest. Computer vision technology is regarded as existing from 1973 to 2018, specifically the Elsevier database. Fish behavior and underwater habitats are explored at large, especially in aquaculture fishing. Based on the methods observed above, relevant viewpoints on the present situation are presented as well as suggestions for future research directions.

Variability of surface and underwater nocturnal spectral irradiance with the presence of clouds in urban and peri-urban wetlands.

Artificial light at night (ALAN) is an increasing phenomenon worldwide. It causes a wealth of biological and ecological effects that may eventually affect populations and ecosystems. Despite the growing concern about ALAN, little is known about the light levels species are exposed to at night, especially for wetlands and underwater habitats. We determined nocturnal irradiance in urban and peri-urban wetlands above and under water, and assessed the effect of cloud cover on the variability of ALAN across the urban gradient. Even in aquatic habitats, cloud cover could increase irradiance beyond values observed during clear full moon nights. We report a negative relationship between baseline irradiance and the increase in irradiance during overcast nights. According to this result and previous studies, we propose that the change in the variation regime of ALAN between the urban center and rural land at its periphery is a usual feature. We discuss the ecological and evolutionary implications of this spatial variation in the urban and peri-urban environment.

A resourceful and adaptable method to obtain data on the status of seagrass meadows

Coastline degradation, as well as subsequent ecosystem loss, has long been attributed to anthropogenic stress and is an all too familiar issue affecting coastal habitats. Should management and conservation efforts fail to improve the quality of coastal ecosystems and the services they provide, they may be irrevocably damaged. A significant limitation to conservation efforts is often the ability to track change in seagrass meadows due to the significant time and cost of monitoring efforts in underwater habitats. Remote sensing is often a tool used to improve our knowledge of habitat status, however, ground-truthing remote sensing results is difficult when historical data is required. We apply an innovative and resourceful approach to the attainment of data to check the status of seagrass meadows from resources that are available in many areas due to the collection of other data sets. We employ the use of underwater digital photographs originally taken for monitoring sediment movement patterns. We were successfully able to develop a method to critically and easily evaluate these photographs for habitat status, enabling the generation of a data set unable to be obtained in other ways. This method can further be utilised in a citizen science project, for other underwater digital photographs, to support the assessment of coastal submerged ecosystem habitat status.

Effects of marine vessel management on the underwater acoustic environment of Glacier Bay National Park, AK

To protect the underwater acoustic environment and the marine mammals that depend upon it, Glacier Bay National Park implements marine vessel quotas, speed regulations, and routing restrictions in biologically important areas. Here, we characterize the underwater acoustic environment to quantify changes in conditions related to vessel management actions. Analysis of hourly 30-second acoustic samples obtained from a seafloor hydrophone included manual (aural and visual) identification of physical, biological, and human-made acoustic sources and measuring received sound pressure levels. A total of 10,659 30-second acoustic samples collected in 2000, 2001, 2007 and 2008 were analyzed. By quantifying the sources, occurrence, and characteristics of underwater sound we gained a new understanding of how the underwater acoustic environment relates to vessel management. For example, the occurrence of noise from large marine vessels (e.g. cruise ships) decreased despite an increase in the vessel quotas and use-days, likely due to changes in the timing of cruise ship entries. Our work documented the occurrence of biologically important humpback whale and harbor seal vocalizations; the frequency of occurrence of these vocalizations gives an indication of Glacier Bay's importance for these species and seasonality of calls documents the times of year at which a pristine acoustic environment would most benefit each species. These first descriptions of acoustic conditions in a protected coastal habitat indicate that both regulations and vessel behavior independent of regulations have discernible effects on the acoustic environment. Quantitatively describing these changes is a crucial first step toward protection of this important underwater habitat.

Diving for science ‐ science for diving: volunteer scuba divers support science and conservation in the Mediterranean Sea

Abstract Recreational diving engages 20 million people worldwide. Most of the literature refers to tropical destinations but at least 1 million dives per year take place in Mediterranean marine protected areas (MPAs). Divers may negatively affect underwater habitats. However, if effectively engaged, they can contribute to science, territorial management and more sustainable local economies. During 2006–2014, volunteers trained by the not‐for‐profit organization Reef Check Italia (RCI) completed 24 714 observations and 2417 dives in six Mediterranean countries, contributing to a dataset that supports scientific papers about climate change, rare and non‐indigenous species (NIS), and informs MPA management decision‐making. The wide range of opportunities offered by this dataset is illustrated with two examples relevant to marine conservation in the context of MPA management. They concern: (i) the spread of the NIS Caulerpa cylindracea along the Ligurian coasts, with a focus on Portofino MPA, and (ii) the distribution and abundance of protected species in the Portofino MPA. A diver‐focused survey showed that RCI volunteers are highly committed, and that participation in RCI activities has led to a better understanding of, and a sense of stewardship towards, favoured dive sites and the marine world. Knowing who volunteers are, and why they volunteer in their favourite sector, is crucial to designing citizen‐science based projects able to achieve their multiple goals. Copyright © 2016 John Wiley & Sons, Ltd.

Benthic Photo Survey: Software for Geotagging, Depth-tagging, and Classifying Photos from Survey Data and Producing Shapefiles for Habitat Mapping in GIS

Photo survey techniques are common for resource management, ecological research, and ground truthing for remote sensing but current data processing methods are cumbersome and inefficient. The Benthic Photo Survey (BPS) software described here was created to simplify the data processing and management tasks associated with photo surveys of underwater habitats. BPS is free and open source software written in Python with a QT graphical user interface. BPS takes a GPS log and jpeg images acquired by a diver or drop camera and assigns the GPS position to each photo based on time-stamps (i.e. geotagging). Depth and temperature can be assigned in a similar fashion (i.e. depth-tagging) using log files from an inexpensive consumer grade depth / temperature logger that can be attached to the camera. BPS provides the user with a simple interface to assign quantitative habitat and substrate classifications to each photo. Location, depth, temperature, habitat, and substrate data are all stored with the jpeg metadata in Exchangeable image file format (Exif). BPS can then export all of these data in a spatially explicit point shapefile format for use in GIS. BPS greatly reduces the time and skill required to turn photos into usable data thereby making photo survey methods more efficient and cost effective. BPS can also be used, as is, for other photo sampling techniques in terrestrial and aquatic environments and the open source code base offers numerous opportunities for expansion and customization.

Economic and environmental perspectives of end-of-life ship management

The economic feasibility and environmental impacts of three examples of end-of-life management options were analyzed with a cost–benefit analysis and an environmental life cycle assessment. The economics of ship recycling methods depend on various parameters such as the market price of reclaimed materials, ship purchase price, environmental and work safety regulation fees, labor costs, and overhead costs. Standard recycling methods are typically used in the U.S., EU, China, and Turkey. The example of recycling the USS Forrestal, showed that standard ship recycling methods can be profitable. Standard ship recycling methods must follow strict regulations, and therefore, can only release negligible amounts of hazardous substances into the environment. In addition, the reclaimed materials from standard ship recycling methods provide various life cycle environmental benefits. Substandard recycling methods, such as beaching, used in southern Asia countries, allow shipyard owners to outbid standard method recycling companies and remain profitable due to a lack of enforced environmental regulations. The non-compliance with environmental regulations, allows these substandard methods to release a large amount of harmful substances into the environment. The reefing option is neither economically viable nor completely safe for the environment, but it could improve the local economy and underwater habitats for local sea life.

Hyperbaric hyperoxia alters innate immune functional properties during NASA Extreme Environment Mission Operation (NEEMO).

Spaceflight is associated with immune dysregulation which is considered as risk factor for the performance of exploration-class missions. Among the consequences of confinement and other environmental factors of living in hostile environments, the role of different oxygen concentrations is of importance as either low (e.g. as considered for lunar or Martian habitats) or high (e.g. during extravehicular activities) can trigger immune dysfunction. The aim of this study was to investigate the impact of increased oxygen availability--generated through hyperbaricity--on innate immune functions in the course of a 14 days NEEMO mission. 6 male subjects were included into a 14 days undersea deployment at the Aquarius station (Key Largo, FL, USA). The underwater habitat is located at an operating depth of 47 ft. The 2.5 times higher atmospheric pressure in the habitat leads to hyperoxia. The collection of biological samples occurred 6 days before (L-6), at day 7 (MD7) and 11/13 (MD11/13) during the mission, and 90 days thereafter (R). Blood analyses included differential blood cell count, ex vivo innate immune activation status and inhibitory competences of granulocytes. The absolute leukocyte count showed an increase during deployment as well as the granulocyte and monocyte count. Lymphocyte count was decreased on MD7. The assessments of native adhesion molecules on granulocytes (CD11b, CD62L) indicated a highly significant cellular activation (L-6 vs. MD7/MD13) during mission. In contrast, granulocytes were more sensitive towards anti-inflammatory stimuli (adenosine) on MD13. Living in the NEEMO habitat for 14 days induced significant immune alterations as seen by an activation of adhesion molecules and vice versa higher sensitivity towards inhibition. This investigation under hyperbaric hyperoxia is important especially for Astronauts' immune competence during extravehicular activities when exposed to similar conditions.

Implications of low food availability on resource partitioning among three species of Cichlidae (Pisces: Perciformes) in a Brazilian semi-arid reservoir

AimResource partitioning has been recognized as a major driver affecting fish communities, with the potential to reduce interespecific competition. This is the result of differences in feeding apparatuses and feeding mode, location of the fish species in the water column and swimming ability, as well as type and size of prey and its availability. The present study surveys a highly limited aquatic system in semi-arid Brazil with regard to habitat and food availability, with very low diversity of fish, and poor in underwater habitat structures and prey, with the objective of understanding resource partitioning among fish species under such conditions.MethodsThree species of Cichlidae (Pisces: Perciformes) were sampled during the dry and wet seasons and had their stomach contents analyzed to evaluate food consumption. The resource partition among fish species was evaluated based on Pianka’s niche overlap index and tested for significance against null models.ResultsIt was observed a low overlap among the study species in food resource use, with individuals tending to specialize to select some food items. This is likely the result of low natural variation in abundance of specific food items associated with fish preferences (both morphological and behavioral).ConclusionsThese results support evidence that, in Brazilian semi-arid aquatic systems, coexistence of fish species seems to be enhanced by the partition of food items at specific trophic levels. Within this context, flow variability would have a key hole in fish coexistence by promoting a high diversity of aquatic habitat elements available for colonization of fish and their prey. Furthermore, food resources available to fish play an important role in this dynamics since prey foods are expected to vary in abundance as the habitat changes.