Seasonal variation in reef fish assemblages in the environmentally extreme southern Persian/Arabian Gulf

The southern Persian/Arabian Gulf experiences extreme seasonal temperature variation (> 20 °C) making it among the most hostile reef environments on Earth. Previous anecdotal evidence has suggested that seasonal temperature changes may influence regional reef fish assemblages, but to date research has been limited. To examine the influence of temperature on reef fish abundance and composition, we performed visual surveys in summer and in winter over three years at three reefs in the southern Gulf (Dhabiya, Saadiyat and Ras Ghanada). Overall abundance of fishes was 40% higher in summer than in winter, and multivariate analyses showed strong and significant differences in overall seasonal community structure, consistent at all sites and across all years. Seasonal differences were largely driven by nine of the 30 observed species, which together accounted for 70% of the divergence in community structure between summer and winter. Of these nine species, Lutjanus ehrenbergii, Lutjanus fulviflamma, Plectorhinchus sordidus and Abudefduf vaigiensis were significantly more abundant in summer, Parupeneus margaritatus and Acanthopagrus bifasciatus, were significantly more common on reefs in winter. We discuss these changes in terms of seasonal physiological and ecological constraints, and explore the implications of these changes on the functional ecology of reef fishes in this thermally variable and extreme environment.

     

Reconstructing historical baselines for the Persian/Arabian Gulf Dugong,Dugong dugon (Mammalia: Sirena)

Retrospective estimates of historic abundances and distributions of marine organisms are crucial to understanding the anthropogenic impacts on the structure and species of coastal ecosystems, especially in the case of vulnerable species such as the Dugong (Dugong dugon). The Persian/Arabian Gulf is home to the second largest Dugong population in the world, yet little is known about their current or past abundance, distribution, and ecological role. Here, we examine historical changes in dugong distribution and estimate perceived changes in their abundance. We create a ‘dugong discovery curve’ and compile global density estimates as proxies for the overall health of the population in the Gulf. We find that since 1950 dugong range may have contracted by one quarter, and despite their large population, their overall densities in the Gulf are far lower than in other areas within their range. Basic understanding of historical trajectories for Dugongs is needed in order to develop appropriate management plans and conservation targets, particularly in light of large and wide-spread coastal development projects in the region.     

Correction to: Seasonal variation in reef fish assemblages in the environmentally extreme southern Persian/Arabian Gulf

Coral Reefs - This erratum is published as citation for article in the reference list needs to be read as.     

Hydrocarbon accumulation by picocyanobacteria from the Arabian Gulf

AIMS: The objective of this work was to study picocyanobacteria in the Arabian Gulf water in relation to oil pollution. METHODS AND RESULTS: Epifluorescent microscopic counting showed that offshore water samples along the Kuwaiti coast of the Arabian Gulf were rich in picocyanobacteria which ranged in numbers between about 1 x 10(5) and 6 x 10(5) ml(-1). Most dominant was the genus Synechococcus; less dominant genera were Synechocystis, Pleurocapsa and Dermocarpella. All isolates grew well in an inorganic medium containing up to 0.1% crude oil (w/v) and could survive in the presence of up to 1% crude oil. Hydrocarbon analysis by gas liquid chromatography (GLC) showed that representative strains of the four genera had the potential for the accumulation of hydrocarbons (the aliphatic n-hexadecane, aromatic phenanthrene and crude oil hydrocarbons) from aqueous media. Electron microscopy showed that the cells of these strains appeared to store hydrocarbons in their inter thylakoid spaces. Analysis by GLC of constituent fatty acids of total lipids and individual lipid classes from representative picoplankton strains grown in the absence and presence of hydrocarbons showed, however, that the fatty acid patterns were not markedly affected by the hydrocabon substrates, meaning that the test strains could not oxidize the accumulated hydrocarbons. CONCLUSION: The Arabian Gulf is among the water bodies of the world richest in picocyanobacteria. These micro-organisms accumulate hydrocarbons from the water body, but do not biodegrade these compounds. It is assumed that hydrocarbon-utilizing bacteria that were always found associated with all picocyanobacteria in nature may carry out the biodegradation of these compounds. SIGNIFICANCE AND IMPORTANCE OF THE STUDY: The results shed light on the potential role of picocyanobacteria in controlling marine oil pollution.     

Oil-utilizing bacteria associated with fish from the Arabian Gulf

AIMS: The objectives were to count and identify the oil-utilizing bacteria associated with fish, and to study their hydrocarbon-degradation potential. METHODS AND RESULTS: The standard dilution-plate method using a medium with crude oil as a sole source of carbon and energy revealed that 10 different fish sorts from the Arabian Gulf and two from fish farms accommodated millions of oil-utilizing bacteria per square centimetre of fish surface and per gram of gills and guts. According to their 16S rRNA sequences, those bacteria were affiliated to Psychrobacter, Vibrio, Planococcus, Pseudomonas and Actinobacterium. Planktonic and benthic biomass samples from the Gulf were also rich in oil-utilizing bacteria, but with different composition. All isolates could grow on n-alkanes from C(8) to C(40) and three representative aromatics as individual sole sources of carbon and energy. Quantitative analysis of hydrocarbons by gas-liquid chromatography revealed that the biomass samples of the individual bacteria could consume crude oil, n-octadecane and phenanthrene in liquid media. CONCLUSIONS: The abundant oil-utilizing bacterial associated with fish have the potential for cleaning oily waters. SIGNIFICANCE AND IMPORTANCE OF THE STUDY: Aquatic fauna accommodates rich consortia of oil-utilizing bacteria.     

Oil-bioremediation potential of two hydrocarbonoclastic, diazotrophic Marinobacter strains from hypersaline areas along the Arabian Gulf coasts

Two halophilic, hydrocarbonoclastics bacteria, Marinobacter sedimentarum and M. flavimaris, with diazotrophic potential occured in hypersaline waters and soils in southern and northern coasts of Kuwait. Their numbers were in the magnitude of 10³ colony forming units g^?1. The ambient salinity in the hypersaline environments was between 3.2 and 3.5 M NaCl. The partial 16S rRNA gene sequences of the two strains showed, respectively, 99 and 100 % similarities to the sequences in the GenBank. The two strains failed to grow in the absence of NaCl, exhibited best growth and hydrocarbon biodegradation in the presence of 1 to 1.5 M NaCl, and still grew and maintained their hydrocarbonoclastic activity at salinities up to 5 M NaCl. Both species utilized Tween 80, a wide range of individual aliphatic hydrocarbons (C₉–C₄₀) and the aromatics benzene, biphenyl, phenanthrene, anthracene and naphthalene as sole sources of carbon and energy. Experimental evidence was provided for their nitrogen-fixation potential. The two halophilic Marinobacter strains successfully mineralized crude oil in nutrient media as well as in hypersaline soil and water microcosms without the use of any nitrogen fertilizers.     

Solea stanalandi,a new sole from the Persian Gulf

A new soleid flatfish,Solea stanalandi, is described from two specimens collected in 1–7 m in the Persian Gulf near Dhahran, Saudi Arabia. It is distinctive among species of the genus in having 57–59 dorsal rays, 46 anal rays, 104–106 pored scales in the straight portion of the lateral line to the caudal-fin base, a body depth of 2.45–2.5 in standard length, a large black spot on the outer half of the pectoral fin of the ocular side, and a similar narrower dark spot on the pectoral fin of the blind side.     

Phosphoglucose isomerase isozymes in teleostean fishes from the Arabian Gulf

Two phosphoglucose isomerases (PGI) with different electrophoretic mobilities have been found in all groups of teleostean fishes studied, with the exception of the Clupeomorpha. PGI proved to be a good taxonomic criterion to differentiate members of the Nemipteridae, Sciaenidae, Platycephalidae and Stromateidae from the other teleost families.     

Histomorphological and endocrine assessment of female Arabian carpetshark,Chiloscyllium arabicum (Elasmobranchii: Hemiscylliidae) from the Persian Gulf during annual reproductive cycle

The present study aimed at assessing the annual reproductive cycle of female Arabian carpetshark, Chiloscyllium arabicum from the Persian Gulf by a macroscopic and microscopic evaluation of the reproductive tract. The annual cycle of gonadal steroids [17β-estradiol (E2), progesterone (P4) and testosterone (T)] was also assessed in this shark. In total, 130 female C. arabicum were collected from the Bahrakan Creek (located northwest of the Persian Gulf) between January 2018 and March 2019. Females were oviparous with an external-type ovary and only one functional ovary. Five sexual maturity stages were recognized based on macroscopic and microscopic evaluation: Immature I (August–October), Immature II (November–January), Mature (February–March), Pregnant (April–May) and Spent (June–July). The structural changes in the oviducts, oviducal glands and uterus throughout the annual reproductive cycle were consistent with their roles in the egg movement, the egg capsule production and sperm storage. The plasma levels of the gonadal steroids were associated with morphological changes in the reproductive tract. E2 showed two detectable peaks during March (close to ovulation) and June (just before mating). P4 and T displayed a peak just before ovulation.     

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.     

Elasmobranchs of the Persian (Arabian) Gulf: ecology, human aspects and research priorities for their improved management

Given widespread concern about the status of elasmobranch fishes globally, information on this group in the Persian (Arabian) Gulf is reviewed comprehensively for the first time. The Arabian region may be of overlooked significance to elasmobranch biogeography, and the environmentally unique Gulf has some highly distinctive elements of biodiversity: an endemic and critically endangered rajid skate, a rarely recorded carcharhinid shark, and preliminary molecular studies which indicate intriguing levels of distinctness from conspecifics elsewhere in the Indo-Pacific. Elasmobranchs also have a long history of association with, and exploitation by, humans around the Gulf. Despite this, Gulf elasmobranchs have been poorly researched, probably due to their low esteem as food. Information is scattered through a variety of literature, and only a handful of published works have been primarily concerned with aspects relevant to management. Key areas of concern include large reported landings by Iran; the export of fins to east Asian markets (particularly through the United Arab Emirates); potentially increasing demand for elasmobranchs for pharmaceutical products and human consumption; a reported change in elasmobranch community structure along the Iranian coast; and major degradation of the Gulf’s shallow, semi-enclosed environment. Priorities for research in the near future should include: resolution of taxonomic issues; species-level monitoring and reporting of fisheries landings by all Gulf states (including the species, pathways and fisheries involved in the fin trade locally); establishing the degree of connectivity of Gulf populations to those in adjacent waterbodies; and identification of key spatio-temporal sensitivities.     

DNA barcoding of marine fishes from Saudi Arabian waters of the Gulf

We used the cytochrome oxidase subunit I (coI) gene DNA to barcode 117 endemic Gulf and cosmopolitan Indo–West Pacific fish species belonging to 54 families and 13 orders. Novel DNA barcodes were provided for 18 fish species (Trachinocephalus sp., Nematalosa sp., Herklotsichthys lossei, Upeneus doriae, Trachurus indicus, Apogonichthyoides taeniatus, Verulux cypselurus, Favonigobius sp., Suezichthus gracilis, Sillago sp., Brachirus orientalis, Pegusa sp., Lepidotrigla bispinosa, Lepidotrigla sp., Grammoplites suppositus, Hippichthys sp., Paramonacanthus sp. and Triacanthus sp.). The species delimitation analysis, conducted with Poisson tree processes– Bayesian PTP (PTP–bPTP) and nucleotide-divergence-threshold (NDT) models), found 137 and 119 entities respectively. Overall, NDT method, neighbour-joining species tree and the prior taxonomic assessment provided similar results. Among the 54 families considered, only 10 (Ariommatidae, Ephippidae, Leiognathidae, Nemipteridae, Plotosidae, Pomacanthidae, Pomacentridae, Priacanthidae and Rachycentridae) showed the occurrence of molecular diagnostic pure characters. The DNA barcoding database developed during this study will help ichthyologists to identify and resolve the taxonomic ambiguities they may encounter with the fishes occurring in The Gulf and throughout the region.     

Alkaliphilic and halophilic hydrocarbon-utilizing bacteria from Kuwaiti coasts of the Arabian Gulf

Green animate materials from the intertidal zone of the Arabian Gulf coast accommodated more alkaliphilic and halophilic bacteria than inanimate materials. The alkaliphilic oil-utilizing bacteria, as identified by their 16S ribonucleic acid sequences, belonged to the following genera arranged in decreasing frequences: Marinobacter, Micrococcus, Dietzia, Bacillus, Oceanobacillus, and Citricoccus. The halophilic oil-utilizing bacteria belonged to the genera: Marinobacter, Georgenia, Microbacterium, Stappia, Bacillus, Isoptericola, and Cellulomonas. Most isolates could grow on a wide range of pure n-alkanes and aromatic compounds, as sole sources of carbon and energy. Quantitative gas liquid chromatographic analysis showed that individual isolates attenuated crude oil and representative pure hydrocarbons in culture. The optimum pH for most of the alkaliphilic genera was pH 10, and the optimum salinity for the halophiles ranged between 2.5 and 5% NaCl (w/v). It was concluded that as far as their microbial makeup is concerned, oily alkaline and saline intertidal areas of the Kuwaiti coasts have a self-cleaning potential.     

Prostanoid synthesis in whole blood cells from fish of the Arabian Gulf

The ability to synthesise prostaglandins and thromboxane from ¹⁴C-labelled arachidonic acid was investigated in 11 species of fish from the Arabian Gulf. Cyclooxygenase activity was assessed in washed whole blood cells. Arachidonic acid and its metabolites were extracted and separated on silicic acid columns and thin layer chromatography (silica gel G). Total capacity to convert [¹⁴C]arachidonic acid to prostanoids varied from 1 to 35% among the 11 fish species studied. Gray shark (Chiloscyllium griseum) blood cells had the highest capacity (37±0.4%) to convert arachidonate into prostanoids and two species of catfish (Arius bilineatus and A. thalassinus) exhibited greater than 10% capacity to convert [¹⁴C]arachidonate into prostanoids. The major prostanoid synthesised by the two catfish (A. bilineatus and A thalassinus) was 6-keto PGF_1α, a stable metabolite of prostacyclin, PGI₂. In contrast, A. teunispinis synthesised thromboxane B₂, a stable metabolite of thromboxane A₂. Thromboxane B₂ (TXB₂) was the major product synthesised by all three species of shark studied (Chil. griseum, Carcharhinus plumbeus, Carch. melanopterus), with 6-keto PGF_1α a minor product. Other fish studied showed a varied pattern of prostanoid synthesis. The synthesis of these prostanoids was almost completely blocked by preincubation of the whole blood cells from catfish and shark with indomethacin (0.5 μM) suggesting the involvement of cyclooxygenase-mediated prostanoid synthesis.