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AIM: The Red Sea is characterised by a unique fauna and historical periods of desiccation, hypersalinity and intermittent isolation. The origin and contemporary composition of reef‐associated taxa in this region can illuminate biogeographical principles about vicariance and the establishment (or local extirpation) of existing species. Here we aim to: (1) outline the distribution of shallow water fauna between the Red Sea and adjacent regions, (2) explore mechanisms for maintaining these distributions and (3) propose hypotheses to test these mechanisms. LOCATION: Red Sea, Gulf of Aden, Arabian Sea, Arabian Gulf and Indian Ocean. METHODS: Updated checklists for scleractinian corals, fishes and non‐coral invertebrates were used to determine species richness in the Red Sea and the rest of the Arabian Peninsula and assess levels of endemism. Fine‐scale diversity and abundance of reef fishes within the Red Sea were explored using ecological survey data. RESULTS: Within the Red Sea, we recorded 346 zooxanthellate and azooxanthellate scleractinian coral species of which 19 are endemic (5.5%). Currently 635 species of polychaetes, 211 echinoderms and 79 ascidians have been documented, with endemism rates of 12.6%, 8.1% and 16.5% respectively. A preliminary compilation of 231 species of crustaceans and 137 species of molluscs include 10.0% and 6.6% endemism respectively. We documented 1071 shallow fish species, with 12.9% endemic in the entire Red Sea and 14.1% endemic in the Red Sea and Gulf of Aden. Based on ecological survey data of endemic fishes, there were no major changes in species richness or abundance across 1100 km of Saudi Arabian coastline. MAIN CONCLUSIONS: The Red Sea biota appears resilient to major environmental fluctuations and is characterized by high rates of endemism with variable degrees of incursion into the Gulf of Aden. The nearby Omani and Arabian Gulfs also have variable environments and high levels of endemism, but these are not consistently distinct across taxa. The presence of physical barriers does not appear to explain species distributions, which are more likely determined by ecological plasticity and genetic diversity.

Very little is known about the ecology and biology of the smallest marine vertebrates, fishes in the genus Schindleria. Even though over half of named Schindleria species have been identified in the Red Sea, the collection of only very few specimens has been documented. Here, we assessed abundance patterns of nearly two thousand Red Sea long dorsal fin (LDF) adults and found evidence for putative seasonal and spatial differences, likely related to differing habitat and environmental conditions. The highest abundances were outside local seasonal temperature extremes and decoupled from peaks of coral reef fish recruitment. We also found evidence for global trends in abundances related to lunar cycles using our Red Sea data and that from a recently published large collection of specimens from the DANA Expedition (1928–1930). The abundance of adult LDF Schindleria in relation to lunar phases differed significantly, with most Schindleria caught outside the full moon, and mostly during the new moon in the Red Sea and the 3rd quarter moon in the DANA collection. We further suggest that the abundances of Schindleria at coral reefs may be related to reproductive cycles and that these cycles may be timed with the moon as back-calculations of hatch dates from otoliths from the Red Sea significantly resulted after the new moon, making Schindleria the fastest-lived coral reef fish with the shortest generation times. Schindleria could be the most numerous coral reef fish in the world, for which we encourage increased research.

Species of the gobiid genus Schindleria are among the smallest and fastest reproducing vertebrates of the oceans. We describe a new species, Schindleria qizma , from the Red Sea, Saudi Arabia. It is an extreme example of progenesis, within the already paedomorphic genus, with morphological traits clearly differentiating it from its congeners. Schindleria qizma has a unique, unflexed notochord with a straight urostyle of which the tip is inserted into the hypural cartilage, rather than the typical flexed notochord with an upturned urostyle of the other species of Schindleria . Schindleria qizma belongs to the short dorsal-fin type of Schindleria . It is further characterized by an elongated but relatively deep body; a short dorsal fin originating just slightly anterior to the anal fin (predorsal-fin length 59.4% of SL vs. preanal-fin length 60.2% of SL); a head continuously increasing in depth posteriorly with a straight dorsal profile; a short snout (18.6% of head length); large eyes (34.4% of head length); a short pectoral-radial plate (6.3% of SL); 13 dorsal-fin rays; 11 anal-fin rays; 0–2 procurrent rays (where the last procurrent ray is short, if present); an anal fin with the first anal-fin ray situated opposite the second dorsal-fin ray; toothless oral jaws; females with few (10–11, total) but very large (4.6% of SL) eggs and with a conspicuous urogenital papilla characterized by a wide urogenital opening flanked by two long, bilobed projections; a dorsally pigmented swim-bladder; blackish, iridescent eyes, capped by a silvery layer with irregular rows of black dots or blotches; and no additional external pigmentation on its body, at least in preserved specimens.

Abstract We describe a new, tiny species of Schindleria from a reef lagoon in the Red Sea off the coast of Hurghada, Egypt. Schindleria edentata , new species, belongs to the short dorsal-fin type of Schindleria , with the dorsal and anal fins of about equal length. Schindleria edentata is characterized by an elongated but relatively deep body (body depth at anal-fin origin 10.8% of SL and at 4 th anal-fin ray 10.9 % of SL); a short dorsal fin originating just slightly anterior to the anal fin (predorsal-fin length 60.9% of SL, pre-anal fin length 64.8% of SL); a stubby head with a steep frontal profile, a short snout (i.e., 23.1% of head length), and large eye (i.e., 27.7% of the head’s length); a long pectoral radial plate (length 7.6% of SL); four dorsal and four ventral procurrent caudal-fin rays increasing in length posteriorly; last procurrent ray simple without additional spine and, although the longest, not distinctly elongate; 15 dorsal-fin rays; 13 anal-fin rays; the base of the first anal-fin ray positioned below the base of the third dorsal-fin ray; upper and lower jaws toothless; in vivo with translucent body; eye black; swim bladder capped by a melanophore blotch; no pigmentation externally on body after preservation.

Coral reef fish larvae are tiny, exceedingly numerous, and hard to track. They are also highly capable, equipped with swimming and sensory abilities that may influence their dispersal trajectories. Despite the importance of larval input to the dynamics of a population, we remain reliant on indirect insights to the processes influencing larval behavior and transport. Here, we used genetic data (300 independent single nucleotide polymorphisms) derived from a light trap sample of a single recruitment event of Dascyllus abudafur in the Red Sea (N = 168 settlers). We analyzed the genetic composition of the larvae and assessed whether kinship among these was significantly different from random as evidence for cohesive dispersal during the larval phase. We used Monte Carlo simulations of similar‐sized recruitment cohorts to compare the expected kinship composition relative to our empirical data. The high number of siblings within the empirical cohort strongly suggests cohesive dispersal among larvae. This work highlights the utility of kinship analysis as a means of inferring dynamics during the pelagic larval phase. Using Monte Carlo simulations and next generation sequencing, we found strong evidence of significantly high presence of siblings within a recruiting cohort of a coral dwelling damselfish, in the Red Sea. To our knowledge our study is the first to assess the significance of kinship among new settlers thus, we provide a pipeline and computational tool to encourage similar future studies. Such information is substantial for the management of marine populations.

[...]Schindleria may be able to switch between swimming modes as shown in Fig. 1a. Specimens were collected following the local animal welfare laws, guidelines, and policies as approved by the Seychelle Bureau of Standards and the Department of Environment (Certificate No. 524). [...]we targeted a low-stress approach to capture images of the fishes in a well-illuminated bucket right at the collection site. [...]the only possible live footage was taken directly in situ from the floating dock, attracting Schindleria with a flashlight to which individuals came and left without any sign of stress or agonization. A sequence was defined as suitable for analysis when the fish performed at least one complete undulatory movement in a straight direction; and a third order polynomial regression was applied to capture the increase in the relative amplitude of the movement along the body length.

Knowledge on the early life history, ecology, and biology of marine species is crucial for future projections of the resilience of coral reef ecosystems and for adequate management strategies. A fundamental component of population dynamics is the recruitment of new individuals, and in some marine populations, this may be a limiting factor. Recruitment peaks of coral reef fishes commonly occur during the warmer months of the year in many subtropical and temperate locations worldwide. In the Red Sea, very little is known about the influence of temperature on reproductive patterns of coral reef fishes and studies on recruitment are missing. The Red Sea is one of the hottest and most isolated tropical seas in the world. We hypothesized that sea surface temperatures (SSTs) during the Red Sea’s hottest season may exceed the optimum for successful recruitment of some coral reef fishes, which therefore has to occur during other, cooler seasons, unlike recruitment among coral reef ecosystems around the world. We identified taxa among fish recruits by matching mitochondrial DNA sequences (using COI, commonly known as “barcoding”) and assessed potential biological and environmental drivers of recruitment. We studied three reefs located along a cross-shelf gradient for 12 consecutive months in the central Red Sea to capture seasonal changes in biotic and abiotic parameters along this gradient. Our results indicated that recruitment peaks did not occur during the hottest SSTs for most taxa, especially at the hottest inshore and mid-shelf reefs, and identified fish recruitment to be mainly and strongly correlated with the biomass of planktonic invertebrates. Moreover, temporal patterns of fish recruitment differed within and among taxonomic families among the reefs.

Species of the gobiid genus Schindleria are among the smallest and fastest reproducing vertebrates of the oceans. We describe a new species, Schindleria qizma, from the Red Sea, Saudi Arabia. It is an extreme example of progenesis, within the already paedomorphic genus, with morphological traits clearly differentiating it from its congeners. Schindleria qizma has a unique, unflexed notochord with a straight urostyle of which the tip is inserted into the hypural cartilage, rather than the typical flexed notochord with an upturned urostyle of the other species of Schindleria. Schindleria qizma belongs to the short dorsal-fin type of Schindleria. It is further characterized by an elongated but relatively deep body; a short dorsal fin originating just slightly anterior to the anal fin (predorsal-fin length 59.4% of SL vs. preanal-fin length 60.2% of SL); a head continuously increasing in depth posteriorly with a straight dorsal profile; a short snout (18.6% of head length); large eyes (34.4% of head length); a short pectoral-radial plate (6.3% of SL); 13 dorsal-fin rays; 11 anal-fin rays; 0-2 procurrent rays (where the last procurrent ray is short, if present); an anal fin with the first anal-fin ray situated opposite the second dorsal-fin ray; toothless oral jaws; females with few (10-11, total) but very large (4.6% of SL) eggs and with a conspicuous urogenital papilla characterized by a wide urogenital opening flanked by two long, bilobed projections; a dorsally pigmented swim-bladder; blackish, iridescent eyes, capped by a silvery layer with irregular rows of black dots or blotches; and no additional external pigmentation on its body, at least in preserved specimens. Keywords: Gobiiformes , paedomorphosis, progenesis, miniaturization

We describe a new, tiny species of Schindleria from a reef lagoon in the Red Sea off the coast of Hurghada, Egypt. Schindleria edentata, new species, belongs to the short dorsal-fin type of Schindleria, with the dorsal and anal fins of about equal length. Schindleria edentata is characterized by an elongated but relatively deep body (body depth at anal-fin origin 10.8% of SL and at 4[sup.th] anal-fin ray 10.9 % of SL); a short dorsal fin originating just slightly anterior to the anal fin (predorsal-fin length 60.9% of SL, pre-anal fin length 64.8% of SL); a stubby head with a steep frontal profile, a short snout (i.e., 23.1% of head length), and large eye (i.e., 27.7% of the head's length); a long pectoral radial plate (length 7.6% of SL); four dorsal and four ventral procurrent caudal-fin rays increasing in length posteriorly; last procurrent ray simple without additional spine and, although the longest, not distinctly elongate; 15 dorsal-fin rays; 13 anal-fin rays; the base of the first anal-fin ray positioned below the base of the third dorsal-fin ray; upper and lower jaws toothless; in vivo with translucent body; eye black; swim bladder capped by a melanophore blotch; no pigmentation externally on body after preservation. Keywords: Gobiiformes , morphology, new species, paedomorphosis, progenesis

Aim To determine the impact of ecological and environmental histories on the evolution of coral reef damselfishes at two adjacent marine biogeographic suture zones. Location Indo‐West Pacific, notably including two suture zones: Socotra and Christmas and Cocos/Keeling Islands. Taxon Chromis dimidiata, Chromis margaritifer, and Chromis fieldi. Methods We utilized a combination of nuclear and mitochondrial genetic markers in addition to visual abundance survey data of these fishes. Results Despite genetic patterns consistent with incomplete lineage sorting and relatively low genetic differentiation among the three studied Chromis species, there is evidence of hybridization between C. margaritifer and C. fieldi at Christmas Island based on molecular and visual identification. Introgression appears to be spreading westwards to other C. fieldi populations based on COI haplotype comparison. Moreover, the genetic distance between C. margaritifer and C. fieldi suggests that Pleistocene sea‐level fluctuations may have contributed to allopatric divergence and secondary contact between these two closely related species. Main conclusions Our study highlights that evolutionary processes in coral reef fishes operate differently between suture zones, possibly due to different ecological and environmental predispositions regulating secondary contact of sister species. While secondary contact likely led to hybridization and introgression at Christmas and Cocos/Keeling Islands, none of those processes seem present at Socotra for the chocolate‐dipped damselfish. This difference is likely due to an environmental barrier caused by hydrodynamic regimes in the Gulf of Aden. We highlight that evolutionary processes operate differently on coral reef damselfishes at two biogeographically, adjacent marine suture zones (Socotra and Christmas and Cocos/Keeling Islands) putatively due to different ecological and environmental predispositions regulating secondary contact of sister species. Therefore, samples of the three species of “chocolate‐dipped” Chromis: Chromis dimidiata, C. fieldi, and C. margaritifer were collected within their distribution ranges (with special attention on potential hybrids), and genetically analyzed combining mitochondrial and nuclear markers. Our results include population structure of the chocolate‐dipped Chromis across the Indo‐West Pacific (including the Red Sea) and further hypothesize on putative forces behind evolutionary processes at marine suture zones.