Explore the vast range of titles available.

Determining the life-history consequences for fishes living in extreme and variable environments will be vital in predicting the likely impacts of ongoing climate change on reef fish demography. Here, we compare size-at-age and maximum body size of two common reef fish species (Lutjanus ehrenbergii and Pomacanthus maculosus) between the environmentally extreme Arabian/Persian Gulf (‘Arabian Gulf’) and adjacent comparably benign Oman Sea. Additionally, we use otolith increment width profiles to investigate the influence of temperature, salinity and productivity on the individual growth rates. Individuals of both species showed smaller size-at-age and lower maximum size in the Arabian Gulf compared to conspecifics in the less extreme and less variable environment of the Oman Sea, suggesting a life-history trade-off between size and metabolic demands. Salinity was the best environmental predictor of interannual growth across species and regions, with low growth corresponding to more saline conditions. However, salinity had a weaker negative effect on interannual growth of fishes in the Arabian Gulf than in the Oman Sea, indicating Arabian Gulf populations may be better able to acclimate to changing environmental conditions. Temperature had a weak positive effect on the interannual growth of fishes in the Arabian Gulf, suggesting that these populations may still be living within their thermal windows. Our results highlight the potential importance of osmoregulatory cost in impacting growth, and the need to consider the effect of multiple stressors when investigating the consequences of future climate change on fish demography.

Coral reefs in Arabian Gulf and Gulf of Oman waters of the United Arab Emirates (UAE) have historically been dominated by Acropora corals. By early 2021, however, extensive Acropora cover remained at only two UAE locations: the fringing reefs of Sir Bu Nair Island (SBN) (Arabian Gulf) and Khor Fakkan (KF) (Gulf of Oman). A summer 2021 marine heatwave impacted these last Acropora refugia and caused the first mass bleaching event on the UAE’s Gulf of Oman coast. Benthic surveys were conducted before, during and eight months after this event. Bleaching severity was high, with 41% of hard corals bleached in KF and 93% in SBN. Total live coral cover declined from 68% to 25% at KF and from 36% to 9% in SBN during bleaching. Acropora cover declined from 23% to 2% in KF and from 19% to 0.02% in SBN during bleaching. There was limited recovery eight months after bleaching. Community composition shifted away from Acropora toward heat-tolerant taxa, particularly Porites and Dipsastraea, with increased homogenization of coral assemblages. These last Acropora refugia could have served as valuable sources of larvae to support coral recovery elsewhere in UAE waters, highlighting the importance of conservation and restoration efforts.

Umm Al Quwain (UAQ) lagoon is a natural lagoon located in the northeastern part of the United Arab Emirates (UAE). Understanding the water circulation in the lagoon is essential for implementing the effective conservation measure to withstand future morphological changes. In this study, a two-dimensional hydrodynamics model is applied for UAQ lagoon using Delft3D-FM to investigate tide variability and currents within and on adjacent coastal lagoon region. The results show a maximum positive water level inside the lagoon of approximately 1.22 m relative to local mean sea level. Water levels within the vicinity of the lagoon range from − 0.95 to 1.22 m. Additionally, it was identified areas within the lagoon where currents increase up to 1.6 m/s due to the narrow inlet in the western entrances. However, most currents inside the lagoon are calmer varying from 0.1 to 0.4 m/s. The net residual currents indicate a system in equilibrium, as the import and export estimates are close to zero and can be considered negligible. The findings of this study provide a baseline study of the flow characteristics at UAQ lagoon and enable future broader research.

Despite increasing environmental variability within marine ecosystems, little is known about how coral reef fish species will cope with future climate scenarios. The Arabian/Persian Gulf is an extreme environment, providing an opportunity to study fish behaviour on reefs with seasonal temperature ranges which include both values above the mortality threshold of Indo-Pacific reef fish, and values below the optimum temperature for growth. Summer temperatures in the Gulf are comparable to those predicted for the tropical ocean by 2090–2099. Using field observations in winter, spring and summer, and laboratory experiments, we examined the foraging activity, distance from refugia and resting time of Pomacentrus trichrourus (pale-tail damselfish). Observations of fish behaviour in natural conditions showed that individuals substantially reduced distance from refugia and feeding rate and increased resting time at sub-optimal environmental temperatures in winter (average SST = 21 °C) and summer (average SST = 34 °C), while showing high movement and feeding activity in spring (average SST = 27 °C). Diet was dominated by plankton in winter and spring, while fish used both plankton and benthic trophic resources in summer. These findings were corroborated under laboratory conditions: in a replicated aquarium experiment, time away from refugia and activity were significantly higher at 28 °C (i.e. spring temperature conditions) compared to 21 °C (i.e. winter temperature conditions). Our findings suggest that P. trichrourus may have adapted to the Arabian/Persian Gulf environment by downregulating costly activity during winter and summer and upregulating activity and increasing energy stores in spring. Such adaptive behavioural plasticity may be an important factor in the persistence of populations within increasing environmentally variable coral reef ecosystems.

This paper presents a comparative study that examines the effects of the Dubai Creek extension on its hydrodynamics and water flushing dynamics. Dubai Creek (Khor Dubai) is a 24 km long artificial seawater stream located in the emirate of Dubai. The creek has experienced the impact of the rapid urbanization of Dubai and a major 13 km extension project, which connected the creek to the Arabian Gulf from the other side. In this paper, two-dimensional hydrodynamic and flushing models were created using Delft3D Flexible Mesh (2021.03) to investigate the water circulation and water quality of the creek before and after the extension. The hydrodynamic models were calibrated and validated to accurately simulate water levels and currents with correlation values close to 1 and very small RMSE and bias. Flushing models were created to simulate water renewal along the creek. The results of the flushing models showed a significant improvement in the flushing characteristics of pollutants in terms of the residence times of the extended creek (Existing Creek) model compared to the old one (Old Creek). This improvement emphasized the positive impact of the creek extension project on the local aquatic ecosystem and its overall water quality.

Marine and coastal ecosystems occupy the dynamic interface where land, water, and atmosphere interact and constantly are modified by natural events and human actions, causing the most immediate effects of environmental changes, habitat destruction, and biodiversity loss. They are rich in biodiversity and of great economic importance by providing multiple uses and resources for over half of the population currently living in coastal areas. Also, coastal wetlands (mangrove forests, salt marshes, and seagrass meadows) constitute the blue carbon ecosystems and are among the most efficiently sequesters of carbon). The pressure that marine and coastal ecosystems across the coasts of the world now face is not new and highly varied, resulting in far-reaching implications for the ocean and adjacent areas. Nevertheless, apart from the known responses of marine environments to climate changes on their functioning and structure, significant knowledge gaps on the potential effects of catastrophic natural events and intense anthropogenic stress and destruction on ecosystem dynamics are still needed, requiring new approaches to solve this problem. This Research Topic aimed to contribute to the potential responses of marine and coastal ecosystems, when subject to extreme chronic stressors or catastrophic events, either by natural or anthropogenic actions, providing a broad overview of assessment and monitoring tools from case studies from different continents.

The Persian Gulf is a semi-enclosed marine system surrounded by eight countries, many of which are experiencing substantial development. It is also a major center for the oil industry. The increasing array of anthropogenic disturbances may have substantial negative impacts on marine ecosystems, but this has received little attention until recently. We review the available literature on the Gulf’s marine environment and detail our recent experience in the United Arab Emirates (U.A.E.) to evaluate the role of anthropogenic disturbance in this marine ecosystem. Extensive coastal development may now be the single most important anthropogenic stressor. We offer suggestions for how to build awareness of environmental risks of current practices, enhance regional capacity for coastal management, and build cooperative management of this important, shared marine system. An excellent opportunity exists for one or more of the bordering countries to initiate a bold and effective, long-term, international collaboration in environmental management for the Gulf.

Palm Jumeirah is the most completely developed of several man-made coastal island megaconstructions in Dubai, United Arab Emirates. The palm-shaped island, surrounded by an elliptical breakwater, was developed 7 y ago, has an overall footprint of 23 km2, of which the constructed island surface area is 7.9 km2, and is connected to shore via a 5-km-long spine from the mainland to the crescent tip. Time-series observations of hydrographic variables and currents within the interior of the development (Palm Jumeirah Lagoon) during 30 d in April–May 2008 were utilized to examine current flow, tide variability, water budget, vertical mixing, and turnover time within this megastructure. Currents within Palm Jumeirah Lagoon varied between stations; however, similar water temperatures and salinities were apparent throughout all the stations. Palm Jumeirah Lagoon tides were mixed and mainly semidiurnal, with spring and neap tidal ranges measuring 116 and 56 cm, respectively, and no difference in amplitude or phase throughout Palm Jumeirah Lagoon. There were substantial differences in water discharge between the east and west entrances, with high discharge on average exiting the eastern entrance and low discharge exiting the western entrance. These results indicate that the eastern and western halves of Palm Jumeirah Lagoon are flushed unequally and show differences in residence times (1.2 and 42 d, respectively), due to differences in tidal currents, wind influence, and variability of the bathymetric contour. Previous numerical modeling studies of water residence time within Palm Jumeirah Lagoon did not capture this difference, which could be associated with the exclusion of bathymetric variability in the previous modeling. Due to the strong shear and weak saline stratification, the water column throughout Palm Jumeirah Lagoon remained instable, with vertical mixing present during the spring-neap tidal cycle and well-mixed conditions predominating throughout the lagoon system.

In the past decade, research on climatological and seasonal circulation patterns in the Persian/Arabian Gulf has primarily relied on numerical models, with limited emphasis on in situ observations. Although these models capture large-scale circulation patterns, such as the cyclonic gyre along the Iranian coast and the influx of Indian Ocean Surface Waters through the Strait of Hormuz, our understanding of the Gulf’s local and regional oceanographic conditions remains insufficient. This gap is particularly evident around Sir Bu Nair Island (SBNI) in the central Gulf, a crucial area for coral larvae source, dispersion, and settlement patterns in southern Gulf reef communities. This study addresses this gap by investigating hydrodynamic conditions and water temperature variability near SBNI through comprehensive in situ observations conducted from 19 May to 1 July 2021. Results indicate substantial temporal variability marked by abrupt shifts in temperature and current speed/direction. Recorded water temperatures ranged from approximately 27.5°C on 20 May to a peak of about 33.5°C on 26 June. The maximum daily temperature amplitude reached ~4.0°C, observed between 24 May at 06:00h (28.5 °C) and 24 May at 11:00h (32.5 °C). Near-bottom temperatures consistently rose by approximately 4.0°C from 7 June (28.15 °C) to 16 June (32.2 °C). Water flow exhibited vertical variations, with an average near-surface current speed (~ 0.8 m/s) about twice as fast as the combined near-bottom and mid-water speed (0.3 to 0.4 m/s). Predominantly, the current direction is aligned with tidal ebb/flood flow. Analysis reveals that hydrodynamic conditions in SBNI are influenced not only by tidal currents at diurnal (~24 h) and semi-diurnal (12.5 h) periods but also by the M4 overtide driving the quarter-diurnal ebbing/flooding transport of “cold/warm” water, and to a lesser extent by “weather-band” periods (2-4 days).

Tidal influence and local morphology on circulation and salt transport are investigated in the Caeté river estuary, a well-mixed estuary along the north coast of Brazil. Velocity, temperature, and salinity data were collected in three different locations along the estuary’s main channel, over three single, 13 h tidal cycles. The aim of this study was to investigate the relationship between tidal distortion and salinity by using classical methods of comparison of three cross-channel circulation characteristics, as well as computation of salt flux and vertical mixing. Findings indicate a flood-ebb asymmetry in currents, due to the distinct funneling morphology of the estuary, with shallow marginal areas being dominant towards the estuary head, while both stratification and shear dominate near the estuary mouth. The tidal currents enhanced vertical diffusion in the mid- and lower reaches, explaining the prevailing weakly stratified conditions, while the dominant well-mixed conditions in the upper estuary are a result of a combination of stronger flood currents and negligible vertical saline gradient. The predominant downstream salt transport supports the conclusion that there is little accumulation of salt in the Caeté river estuary. In addition, findings indicate that tidal correlation and Stokes drift are important components in the upper estuary, while tidal correlation played an important role in the middle estuary, with fluvial discharge most important in the lower estuary.