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Climate change is imposing multiple stressors on marine life, leading to a restructuring of ecological communities as species exhibit differential sensitivities to these stressors. With the ocean warming and wind patterns shifting, processes that drive thermal variations in coastal regions, such as marine heatwaves and upwelling events, can change in frequency, timing, duration, and severity. These changes in environmental parameters can physiologically impact organisms residing in these habitats. Here, we investigate the synchrony of coral and reef fish responses to environmental disturbance in the Red Sea, including an unprecedented combination of heat stress and upwelling that led to mass coral bleaching in 2015. We developed cross-dated growth chronologies from otoliths of 156 individuals of two planktivorous damselfish species,Pomacentrus sulfureusandAmblyglyphidodon flavilatus, and from skeletal cores of 48Poritesspp. coral colonies. During and immediately after the 2015 upwelling and bleaching event, damselfishes exhibited a positive growth anomaly but corals displayed reduced growth. Yet, after 2015–2016, these patterns were reversed with damselfishes showing a decline in growth and corals rebounding to pre-disturbance growth rates. Our results reveal an asynchronous response between corals and reef fish, with corals succumbing to the direct effects of heat stress, and then quickly recovering when the heat stress subsided—at least, for those corals that survived the bleaching event. Conversely, damselfish growth temporarily benefited from the events of 2015, potentially due to the increased metabolic demand from increased temperature and increased food supply from the upwelling event, before declining over four years, possibly related to indirect effects associated with habitat degradation following coral mortality. Overall, our study highlights the increasingly complex, often asynchronous, ecological ramifications of climate extremes on the diverse species assemblages of coral reefs. 

Abstract The mutualism between clownfishes (or anemonefishes) and their giant host sea anemones are among the most immediately recognizable animal interactions on the planet and have attracted a great deal of popular and scientific attention [1-5]. However, our evolutionary understanding of this iconic symbiosis comes almost entirely from studies on clownfishes— a charismatic group of 28 described species in the genusAmphiprion[2]. Adaptation to venomous sea anemones (Anthozoa: Actiniaria) provided clownfishes with novel habitat space, ultimately triggering the adaptive radiation of the group [2]. Clownfishes diverged from their free-living ancestors 25-30 MYA with their adaptive radiation to sea anemones dating to 13.2 MYA [2, 3]. Far from being mere habitat space, the host sea anemones also receive substantial benefits from hosting clownfishes, making the mutualistic and co-dependent nature of the symbiosis well established [4, 5]. Yet the evolutionary consequences of mutualism with clownfishes have remained a mystery from the host perspective. Here we use bait-capture sequencing to fully resolve the evolutionary relationships among the 10 nominal species of clownfish-hosting sea anemones for the first time (Figure 1). Using time-calibrated divergence dating analyses we calculate divergence times of less than 25 MYA for each host species, with 9 of 10 host species having divergence times within the last 13 MYA (Figure 1). The clownfish-hosting sea anemones thus diversified coincidently with clownfishes, potentially facilitating the clownfish adaptive radiation, and providing the first strong evidence for co-evolutionary patterns in this iconic partnership. 

Merten’s carpet sea anemone, Stichodactyla mertensii Brandt, 1835, is the largest known sea anemone species in the world, regularly exceeding one meter in oral disc diameter. A tropical species from the Indo-Pacific, S. mertensii drapes prominently over coral reef substrates and is a common host to numerous species of clownfishes and other symbionts throughout its range, which extends from the Red Sea through the Central Pacific Ocean. Long thought to reproduce via sexual reproduction only, recent genetic evidence suggests it may rarely reproduce asexually as well, although this process had never been confirmed through direct observation and the mechanism was yet to be described. Here, we directly observed and documented in situ asexual fragmentation via budding, in real time, by a Red Sea S. mertensii in a turbid inshore reef environment. While asexual reproduction is not unusual in sea anemones as a group, it is typically expected to be uncommon for large-bodied species. Herein, we describe S. mertensii fragmentation, provide high resolution images of the event from the Saudi Arabian coastline at multiple time points, and confirm asexual reproduction for this species. 

Abstract BackgroundThe Red Sea contains thousands of kilometers of fringing reef systems inhabited by clownfish and sea anemones, yet there is no consensus regarding the diversity of host anemone species that inhabit this region. We sought to clarify a historical record and recent literature sources that disagree on the diversity of host anemone species in the Red Sea, which contains one endemic anemonefish,Amphiprion bicinctusRüppell 1830. ResultsWe conducted 73 surveys spanning ~ 1600 km of coastline from the northern Saudi Arabian Red Sea to the Gulf of Aden and encountered seven species of host anemones, six of which hostedA. bicinctus.We revise the list of symbionts forA. bicinctusto includeStichodactyla haddoni(Saville-Kent, 1893) andStichodactyla mertensiiBrandt, 1835 which were both observed in multiple regions. We describe Red Sea phenotypic variability inHeteractis crispa(Hemprich & Ehrenberg in Ehrenberg, 1834) andHeteractis aurora(Quoy & Gaimard, 1833), which may indicate that these species hybridize in this region. We did not encounterStichodactyla gigantea(Forsskål, 1775), although the Red Sea is the type locality for this species. Further, a thorough review of peer-reviewed literature, occurrence records, and misidentified basis of record reports dating back to the early twentieth century indicate that it is unlikely thatS. giganteaoccurs in the Red Sea. ConclusionsIn sum, we present a new guide for the host anemones of the Red Sea, revise the host specificity ofA. bicinctus,and question whetherS. giganteaoccurs in the central and western Indian Ocean.