Living on the edge: Vulnerability of coral-dependent fishes in the Gulf

Parrotfishes (Teleostei: Labridae: Scarini) of the Socotra Archipelago: Diversity and distributional biogeography, including a range extension of Scarus zufar Randall & Hoover, 1995

An updated account of the diversity of parrotfishes from the Socotra Archipelago is provided. Fourteen species are positively recorded based on underwater observations, photography and collections, including confirmations of three species which were previously only tentatively recorded: Scarus falcipinnis(Playfair, 1868), Scarus scaber Valenciennes, 1840 and Scarus tricolorBleeker, 1847. The distribution of Scarus zufar Randall & Hoover, 1995, previously known only from coastal waters of southern Oman, Pakistan and Bangladesh, is extended to the Archipelago, with Abd al-Kuri Island representing the westernmost edge of its known range. Visual records of three additional species are yet to be documented. With 1417species the Archipelago approximates the modal richness range of 1518 species for Arabian ecoregions. A species account, accompanied by photographs, provides distinctive characters, distribution details in the Arabian region, and general remarks for each species. The distributional biogeography of the family pertinent to the Socotra Archipelago and the Arabian region is analysed in the context of the Western Indian Ocean. Three main Arabian units are identified: A Red Sea unit spans the combined Red Sea ecoregions and the western Gulf of Aden; a Socotra unit covers south-eastern Arabia including the Archipelago, the eastern Gulf of Aden and southern Oman; and a Gulf unit combines the Arabian/Persian Gulf, the Gulf of Oman, and putatively central Oman. These units form a discrete pan-Arabian cluster within the wider Western Indian Ocean. The Socotra unit resembles more strongly the Gulf unit than the Red Sea unit. Parrotfishes thus contrast overall distributional patterns of reef fishes in Arabia.

Delayed recovery and host specialization may spell disaster for coral-fish mutualism

Mutualisms are prevalent in many ecosystems, yet little is known about how symbioses are affected by ecological pressures. Here, we show delayed recovery for 13 coral-dwelling goby fishes (genus Gobiodon) compared with their host Acropora corals following four consecutive cyclones and heatwaves. While corals became twice as abundant in 3 years postdisturbances, gobies were only half as abundant relative to predisturbances and half of the goby species disappeared. Although gobies primarily occupied one coral species in greater abundance predisturbances, surviving goby species shifted hosts to newly abundant coral species when their previously occupied hosts became rare postdisturbances. As host specialization is key for goby fitness, shifting hosts may have negative fitness consequences for gobies and corals alike and affect their survival in response to environmental changes. Our study is an early sign that mutualistic partners may not recover similarly from multiple disturbances, and that goby host plasticity, while potentially detrimental, may be the only possibility for early recovery.

Is the development of desalination compatible with sustainable development of the Arabian Gulf?

The development of desalination has been essential to the rapid economic development of the countries bordering the Arabian Gulf. The current production capacity of sea water desalination plants drawing water from Gulf is over 20 million m³ day^-1, which may rise to 80 million m³ day^-1 by 2050. Whilst supporting aspects of sustainable development related to water and sanitation, desalination impacts the marine environment through impingement and entrainment of organisms in intakes, and through thermal, brine and chemical discharges. This may compromise other objectives for sustainable development related to sustainable use of the oceans. Under business as usual scenarios, by 2050, the impact of individual desalination plants will combine causing a regional scale impact. Without mitigating actions to avoid the business as usual scenario, by 2050, desalination in combination with climate change, will elevate coastal water temperatures across more than 50% of the Gulf by at least 3 °C, and a volume of water equivalent to more than a third of the total volume of water between 0 and 10 m deep will pass through desalination plants each year. This will adversely impact the coastal ecosystem of the Gulf, with impacts on biodiversity, fisheries and coastal communities and may cause potential loss of species and habitats from the Gulf. Given the significant implications of these preliminary findings, and in light of the precautionary approach to management, it is recommended that mitigating options addressing behavioural, regulatory and technological change are rapidly evaluated and implemented to avoid the development of desalination in the region along a business as usual pathway, and multidisciplinary research studies should be conducted to reduce uncertainty in predictions of future impacts.

Size-specific recolonization success by coral-dwelling damselfishes moderates resilience to habitat loss

Increasing degradation of coral reef ecosystems and specifically, loss of corals is causing significant and widespread declines in the abundance of coral reef fishes, but the proximate cause(s) of these declines are largely unknown. Here, we examine specific responses to host coral mortality for three species of coral-dwelling damselfishes (Dascyllus aruanus, D. reticulatus, and Pomacentrus moluccensis), explicitly testing whether these fishes can successfully move and recolonize nearby coral hosts. Responses of fishes to localized coral loss was studied during population irruptions of coral feeding crown-of-thorns starfish, where starfish consumed 29 (34%) out of 85 coral colonies, of which 25 (86%) were occupied by coral-dwelling damselfishes. Damselfishes were not tagged or individually recognizable, but changes in the colonization of different coral hosts was assessed by carefully assessing the number and size of fishes on every available coral colony. Most damselfishes (> 90%) vacated dead coral hosts within 5 days, and either disappeared entirely (presumed dead) or relocated to nearby coral hosts. Displaced fishes only ever colonized corals already occupied by other coral-dwelling damselfishes (mostly conspecifics) and colonization success was strongly size-dependent. Despite movement of damselfishes to surviving corals, the local abundance of coral-dependent damselfishes declined in approximate accordance with the proportional loss of coral habitat. These results suggest that even if alternative coral hosts are locally abundant, there are significant biological constraints on movement of coral-dwelling damselfishes and recolonization of alternative coral habitats, such that localized persistence of habitat patches during moderate or patchy disturbances do not necessarily provide resilience against overall habitat loss.

Using vertebrate environmental DNA from seawater in biomonitoring of marine habitats

Conservation and management of marine biodiversity depends on biomonitoring of marine habitats, but current approaches are resource-intensive and require different approaches for different organisms. Environmental DNA (eDNA) extracted from water samples is an efficient and versatile approach to detecting aquatic animals. In the ocean, eDNA composition reflects local fauna at fine spatial scales, but little is known about the effectiveness of eDNA-based monitoring of marine communities at larger scales. We investigated the potential of eDNA to characterize and distinguish marine communities at large spatial scales by comparing vertebrate species composition among marine habitats in Qatar, the Arabian Gulf (also known as the Persian Gulf), based on eDNA metabarcoding of seawater samples. We conducted species accumulation analyses to estimate how much of the vertebrate diversity we detected. We obtained eDNA sequences from a diverse assemblage of marine vertebrates, spanning 191 taxa in 73 families. These included rare and endangered species and covered 36% of the bony fish genera previously recorded in the Gulf. Sites of similar habitat type were also similar in eDNA composition. The species accumulation analyses showed that the number of sample replicates was insufficient for some sampling sites but suggested that a few hundred eDNA samples could potentially capture >90% of the marine vertebrate diversity in the study area. Our results confirm that seawater samples contain habitat-characteristic molecular signatures and that eDNA monitoring can efficiently cover vertebrate diversity at scales relevant to national and regional conservation and management.

Assessment of Climate Change Impacts on Sea Surface Temperatures and Sea Level Rise—The Arabian Gulf

The Arabian Gulf is one of the regions in the world experiencing major changes due to increased economic growth rates and development practices. As a shallow water body within a hot desert, the Gulf is exposed to obvious warming in the sea surface temperatures (SST). Remotely sensed SST data were utilized to estimate decadal change in SST with a focus on coral reef locations. There is a positive trend in monthly time series SSTs, with a maximum value of about 0.7 °C/decade for the western side of the Gulf. This high trend of SST is associated with significant coral reef bleaching and it coincides with major climate/ocean interactions. Most of the Arabian countries along the Gulf have coastal developments at low-land areas of high vulnerability to sea level rise. Digital elevation models showed that there are more than 3100 km2 of coastal areas that occur at 1 m level along the Arabian countries of the Gulf. Coastal protection and conservation measures are crucial to protect low-lying coasts of urban use.

Life history traits and temporal trends of abundance of the orange-spotted trevally (Carangoides bajad) from Saudi waters of the Gulf

In this study we lay the groundwork for sustainability-oriented fisheries management, by estimating parameters the life history of orange-spotted trevally Carangoides bajad as well as trends of abundance in coral-reef habitats. We observed a new record of maximum size of 720 mm fork length. Carangoides bajad is a moderately long-lived (14 years) and slow-growing (K = 0.085 year^-1 ) carangid species, closer to a K-selection species, with higher vulnerability to fishing and lower rates of recovery when the population level is low. Growth and biological composition in terms of length and age categories do not differ between the sexes, but females become mature faster. Reproductively active months (May-August) overlapped with those from Emirati waters further south. The abundance index showed a pronounced drop during 1990-1993, possibly in connection with habitat deterioration during the Gulf War (1990-1991) oil spill. The index increased gradually from 1994 and has fluctuated close to the reference level of 1985 up to the present. Considering the findings of large-sized and old-age individuals and abundance index from coral reefs close to its level three decades back, the C. bajad stock in the western part of The Gulf appears to be in healthy exploitation status despite growing harvesting rates.

Towards more sustainable coastal development in the Arabian Gulf: Opportunities for ecological engineering in an urbanized seascape

The coastlines of many Arabian cities are now dominated by structures such as seawalls, breakwaters and jetties as urbanization has expanded rapidly in the region. Coastal development has substantially degraded the mangrove forests, saltmarshes, seagrass meadows, oyster beds and coral reefs that traditionally provided invaluable ecosystem goods and services to coastal trading villages of the Arabian Gulf. Regional awareness of environmental issues is growing, however, and local governments are increasingly promoting more sustainable urban development. The use of ecological engineering approaches, along with improved environmental policies, may mitigate some past impacts, and will potentially create new development projects with greater ecological benefits for more sustainable growth in the future. In this paper, we discuss past coastal development in the Gulf, and offer advice on how ecological engineering could be used to enhance the ecological benefits of coastal infrastructure, particularly by encouraging the colonization of juvenile corals and fishes. Such approaches can encourage more sustainable development of this increasingly urbanized seascape.

Association to vegetated habitats and different vulnerability to habitat degradation for two fish species, Epinephelus areolatus (Serranidae) and Siganus canaliculatus (Siganidae), from the western Arabian Gulf

Epinephelus areolatus and Siganus canaliculatus are two species of fisheries importance associated with vegetated habitats, which are in turn threatened by human activities such as land filling. We tested their associations with vegetated habitats in the Arabian Gulf and examined essential life history traits to infer their vulnerability to the degradation of vegetated habitats. Epinephelus areolatus is found to be more abundant at deeper offshore vegetated habitats, while S. canaliculatus has higher abundance at shallow nearshore habitats. Epinephelus areolatus exhibits a longer life span, lower growth coefficient, larger size at 50% maturity, lower natural mortality, and protogynous sexual pattern, compared to Siganus canaliculatus. Accordingly, Epinephelus areolatus is expected to be more vulnerable to habitat degradation and environmental fluctuations. Different preferences in using vegetated habitats and degrees of vulnerability to habitat degradation for these two species could be further integrated to set priorities for management and conservation plans.

Population collapse dynamics in Acropora downingi, an Arabian/Persian Gulf ecosystem-engineering coral, linked to rising temperature

As in the tropical Atlantic, Acropora populations in the southern Persian/Arabian Gulf plummeted within two decades after having been ecosystem engineers on most wave-exposed reefs since the Pleistocene. Since 1996/1998 live coral cover in the Gulf declined by over 90% in many areas, primarily due to bleaching and diseases caused by rising temperatures. In the formerly dominant table-coral species A. downingi, population dynamics corresponding to disturbance regimes was quantified in three transition matrices (lower disturbance pre-1996; moderate disturbance from 1998 to 2010 and 2013 to 2017, disturbed in 1996/1998, 2010/11/12, 2017). Increased disturbance frequency and severity caused progressive reduction in coral size, cover, and population fecundity. Small size-classes were bolstered more by partial colony mortality than sexual recruitment. Some large corals had a size refuge and resisted die-back but were also lost with increasing disturbance. Matrix and biophysical larval flow models suggested one metapopulation. Southern, Arabian, populations could be connected to northern, Iranian, populations but this connectivity was lost under assumptions of pelagic larval duration at rising temperatures shortened to a third. Then, the metapopulation disintegrated into isolated populations. Connectivity required to avoid extinctions increased exponentially with disturbance frequency and correlation of disturbances across the metapopulation. Populations became unsustainable at eight disturbances in 15 years, when even highest theoretical recruitment no longer compensated mortality. This lethal disturbance frequency was 3-fold that of the moderately disturbed monitoring period and 4-fold of the preceding low-disturbance period-suggesting ongoing shortening of the disturbance-free period. Observed population collapse and environmental changes in the Gulf suggest that A. downingi is heading toward at least functional extinction mainly due to increasingly frequent temperature-induced mortality events, clearly linked to climate change.

Climate change impacts on marine biodiversity, fisheries and society in the Arabian Gulf

Climate change–reflected in significant environmental changes such as warming, sea level rise, shifts in salinity, oxygen and other ocean conditions–is expected to impact marine organisms and associated fisheries. This study provides an assessment of the potential impacts on, and the vulnerability of, marine biodiversity and fisheries catches in the Arabian Gulf under climate change. To this end, using three separate niche modelling approaches under a ‘business-as-usual’ climate change scenario, we projected the future habitat suitability of the Arabian Gulf (also known as the Persian Gulf) for 55 expert-identified priority species, including charismatic and non-fish species. Second, we conducted a vulnerability assessment of national economies to climate change impacts on fisheries. The modelling outputs suggested a high rate of local extinction (up to 35% of initial species richness) by 2090 relative to 2010. Spatially, projected local extinctions are highest in the southwestern part of the Gulf, off the coast of Saudi Arabia, Qatar and the United Arab Emirates (UAE). While the projected patterns provided useful indicators of potential climate change impacts on the region’s diversity, the magnitude of changes in habitat suitability are more uncertain. Fisheries-specific results suggested reduced future catch potential for several countries on the western side of the Gulf, with projections differing only slightly among models. Qatar and the UAE were particularly affected, with more than a 26% drop in future fish catch potential. Integrating changes in catch potential with socio-economic indicators suggested the fisheries of Bahrain and Iran may be most vulnerable to climate change. We discuss limitations of the indicators and the methods used, as well as the implications of our overall findings for conservation and fisheries management policies in the region.

Vertical zonation and functional diversity of fish assemblages revealed by ROV videos at oil platforms in The Gulf

An assessment of vertical distribution, diel migration, taxonomic and functional diversity of fishes was carried out at offshore platforms in The (Arabian-Iranian-Persian) Gulf. Video footage was recorded at the Al Shaheen oil field between 2007 and 2014 using a remotely operated vehicle (ROV). A total of 12 822 individual fishes, from 83 taxonomic groups were recorded around the platforms. All the species identified are considered native to The Gulf, although Cyclichthys orbicularis and Lutjanus indicus were recorded for the first time in Qatari waters. Several trends were uncovered in the vertical distribution of the fish community; most species were observed between 20 and 50 m depth and fish abundance decreased towards the bottom, with the highest abundances recorded in the upper layers, i.e. down to 40 m depth. Vertical variation in fish diversity, however, was generally not accompanied by differences in vertical movements. Carnivores and invertivores were the dominant trophic groups, being found at each depth range from surface to seabed. The functional indices showed no significant differences between water depths or diel cycles. The study demonstrates that oil platforms represent a hotspot of fish diversity and interesting sites for studying fish communities, abundance and behaviour.

Abundance and composition of juvenile corals reveals divergent trajectories for coral assemblages across the United Arab Emirates

Marked shifts in the composition of coral assemblages are occurring at many locations, but it is unknown whether these are permanent shifts reinforced by patterns of population replenishment. This study examined the composition of juvenile coral assemblages across the United Arab Emirates (UAE). Densities of juvenile corals varied significantly among locations, but were highest where coral cover was highest. Juvenile coral assemblages within the Persian Gulf were dominated by Porites, while no Acropora were recorded. We expect therefore, continued declines in Acropora abundance, while observed dominance of Porites is likely to persist. In the Oman Sea, Pocillopora was the dominant juvenile coral, with Acropora and Stylophora also recorded. This study shows that taxonomic differences in replenishment are reinforcing temporal shifts in coral composition within the southern Persian Gulf, but not in the Oman Sea. Differences in environmental conditions and disturbance regimes likely explain the divergent responses between regions.

The influence of extreme winds on coastal oceanography and its implications for coral population connectivity in the southern Arabian Gulf

Using long-term oceanographic surveys and a 3-D hydrodynamic model we show that localized peak winds (known as shamals) cause fluctuation in water current speed and direction, and substantial oscillations in sea-bottom salinity and temperature in the southern Persian/Arabian Gulf. Results also demonstrate that short-term shamal winds have substantial impacts on oceanographic processes along the southern Persian/Arabian Gulf coastline, resulting in formation of large-scale (52 km diameter) eddies extending from the coast of the United Arab Emirates (UAE) to areas near the off-shore islands of Iran. Such eddies likely play an important role in transporting larvae from well-developed reefs of the off-shore islands to the degraded reef systems of the southern Persian/Arabian Gulf, potentially maintaining genetic and ecological connectivity of these geographically distant populations and enabling enhanced recovery of degraded coral communities in the UAE.

Coral reefs in the Gulf are mostly dead now, but can we do anything about it?

This article discusses two key issues: firstly, the demise of reefs in the Gulf which is happening probably more rapidly than elsewhere; and secondly, the reasons why this remains such an intractable problem. Most reasons for this decline are scientifically well understood, though clearly not by the region's managers. Several factors may cause people to ignore the problem, even though habitat loss is vastly costly to the region. About 70% of the Gulf's reefs have essentially disappeared in a few decades, and although scientific indicators confirm that this is happening, it is commonly discounted as even being a possibility. Management of human interactions with the Gulf's marine systems remains very inadequate, to the detriment of the Gulf's marine systems and its people. It is clear that this not a scientific issue any longer but rather it is a political problem and failure.