Emma V. Kennedy

Global warming and recurrent mass bleaching of corals

During 2015–2016, record temperatures triggered a pan-tropical episode of coral bleaching, the third global-scale event since mass bleaching was first documented in the 1980s. Here we examine how and why the severity of recurrent major bleaching events has varied at multiple scales, using aerial and underwater surveys of Australian reefs combined with satellite-derived sea surface temperatures. The distinctive geographic footprints of recurrent bleaching on the Great Barrier Reef in 1998, 2002 and 2016 were determined by the spatial pattern of sea temperatures in each year. Water quality and fishing pressure had minimal effect on the unprecedented bleaching in 2016, suggesting that local protection of reefs affords little or no resistance to extreme heat. Similarly, past exposure to bleaching in 1998 and 2002 did not lessen the severity of bleaching in 2016. Consequently, immediate global action to curb future warming is essential to secure a future for coral reefs.

Symbiodinium biogeography tracks environmental patterns rather than host genetics in a key Caribbean reef-builder, Orbicella annularis

The physiological performance of a reef-building coral is a combined outcome of both the coral host and its algal endosymbionts, Symbiodinium. While Orbicella annularis—a dominant reef-building coral in the Wider Caribbean—is known to be a flexible host in terms of the diversity of Symbiodinium types it can associate with, it is uncertain how this diversity varies across the Caribbean, and whether spatial variability in the symbiont community is related to either O. annularis genotype or environment. Here, we target the Symbiodinium-ITS2 gene to characterize and map dominant Symbiodinium hosted by O. annularis at an unprecedented spatial scale. We reveal northwest–southeast partitioning across the Caribbean, both in terms of the dominant symbiont taxa hosted and in assemblage diversity. Multivariate regression analyses incorporating a suite of environmental and genetic factors reveal that observed spatial patterns are predominantly explained by chronic thermal stress (summer temperatures) and are unrelated to host genotype. Furthermore, we were able to associate the presence of specific Symbiodinium types with local environmental drivers (for example, Symbiodinium C7 with areas experiencing cooler summers, B1j with nutrient loading and B17 with turbidity), associations that have not previously been described.

Coral bleaching in the southern inshore Great Barrier Reef: a case study from the Keppel Islands

Spatially explicit coral bleaching data can be used to improve our understanding of the causes and consequences of coral bleaching and help identify resilient reefs. In 2016, the Great Barrier Reef (GBR) experienced the most severe coral bleaching in recorded history, yet, as in previous 1998 and 2002 events, the severity and spatial extent of coral bleaching were variable. Cyclonic activity mitigated warming effects in the southern GBR, meaning corals in this region were predicted to bleach less; as a result, southern reef areas received little attention. Herein we report the effects of the 2016 warming event on southern inshore reefs around the Keppel Islands, an area of high conservation importance, with a history of environmental disturbance. Surveys of 14 reefs revealed paling of coral colonies at every site. A total of 21% of living coral, primarily Pocillopora and branching Acropora, was affected. Findings suggest that southern reefs were affected by warming, although significantly less than in the north. Records of milder bleaching help delineate variability in bleaching severity and extent across the GBR, and add to the historical record of bleaching history in the Keppel Islands, essential to understanding the complexity of exposure and recovery dynamics of the Keppel reefs.

Reduced spore germination explains sensitivity of reef-building algae to climate change stressors

Reduced seawater pH and changes in carbonate chemistry associated with ocean acidification (OA) decrease the recruitment of crustose coralline algae (CCAcf.), an important coral-reef builder. However, it is unclear whether the observed decline in recruitment is driven by impairment of spore germination, or post-settlement processes (e.g. space competition). To address this, we conducted an experiment using a dominant CCA, Porolithon cf. onkodes to test the independent and combined effects of OA, warming, and irradiance on its germination success and early development. Elevated CO2 negatively affected several processes of spore germination, including formation of the germination disc, initial growth, and germling survival. The magnitude of these effects varied depending on the levels of temperature and irradiance. For example, the combination of high CO2 and high temperature reduced formation of the germination disc, but this effect was independent of irradiance levels, while spore abnormalities increased under high CO2 and high temperature particularly in combination with low irradiance intensity. This study demonstrates that spore germination of CCA is impacted by the independent and interactive effects of OA, increasing seawater temperature and irradiance intensity. For the first time, this provides a mechanism for how the sensitivity of critical early life history processes to global change may drive declines of adult populations of key marine calcifiers.

A rapid PCR-based test for identification of fifteen British bat species

The development of a rapid method for identification of the fifteen common species of British bat is described: Barbastella barbastellus, Eptesicus serotinus, Myotis bechsteinii, Myotis daubentonii, Myotis mystacinus, Myotis nattereri, Nyctalus leisleri, Nyctalus noctula, Plecotus auritus, Plecotus austriacus, Pipistrellus nathusii, Pipistrellus pipistrellus, Pipistrellus pygmaeus,Rhinolophus ferrumequinum and Rhinolophus hipposideros. A single multiplex PCR containing five fluorescently-tagged primers and fifteen species-specific primers targeting the mitochondrial control region and genes for cytb and ND1 produces clear peaks that are unique to each species when visualised on a DNA sequencer. The multiplex also includes primers to test for PCR-amplifiable bat DNA. This method will facilitate high throughput species identification of British bats, particularly in cases where phenotypic identification is difficult.