Anthropogenic forcing is spurring cyanobacterial proliferation in aquatic ecosystems worldwide. While planktonic

cyanobacterial blooms have received substantial research attention, benthic blooms of mat-forming

cyanobacteria have received considerably less attention, especially benthic mat blooms on coral reefs.

Resultingly, numerous aspects of coral reef benthic cyanobacterial bloom ecology remain unknown, including

underlying biodiversity in the mat communities. Most previous characterizations of coral reef cyanobacterial

mat composition have only considered the cyanobacterial component. Without an unbiased characterization of

full community diversity, we cannot predict whole-community response to anthropogenic inputs or effectively

determine appropriate mitigation strategies. Here, we advocate for the implementation of shotgun sequencing

techniques to study coral reef cyanobacterial mats worldwide, utilizing a case study of a coral reef benthic

cyanobacterial mat sampled from the island of Bonaire, Caribbean Netherlands. Read-based taxonomic profiling

revealed that Cyanobacteria was present at only 47.57% relative abundance in a coral reef cyanobacterial mat,

with non-cyanobacterial members of the sampled mat community, including diatoms (0.78%), fungi (0.25%), Archaea

(0.34%), viruses (0.08%), and other bacteria (45.78%), co-dominating the community.We found numerous

gene families for regulatory systems and for functional pathways (both aerobic and anaerobic). These gene families

were involved in community coordination; photosynthesis; nutrient scavenging; and the cycling of sulfur,

nitrogen, phosphorous, and iron. We also report bacteriophage (including prophage) sequences associated

with this subtidal coral reef cyanobacterial mat, which could contribute to intra-mat nutrient cycling and

bloom dynamics. Overall, our results suggest that Cyanobacteria-focused analysis of coral reef cyanobacterial

mats underestimates mat diversity and fails to capture community members possessing broad metabolic

Mangroves are effective blue carbon sinks and are the most carbon rich ecosystems on earth. However, their areal extent has declined by over one-third in recent decades. Degraded mangrove forests result in reduced carbon captured and lead to release of stored carbon into the atmosphere by CO2emission. The aim of this study was to assess changes in carbon dynamics in a gradually degrading mangrove forest on Bonaire, Dutch Caribbean. Remote sensing techniques were applied to estimate the distribution of intact and degraded mangroves. Forest structure, sediment carbon storage, sediment CO2 effluxes and dissolved organic and inorganic carbon in pore and surface waters across intact and degraded parts were assessed. On average intact mangroves showed 31% sediment organic carbon in the upper 30 cm compared to 20% in degraded mangrove areas. A loss of 1.51 MgCO2 ha−1 yr−1for degraded sites was calculated. Water samples showed a hypersaline environment in the degraded mangrove area averaging 93 which may have caused mangrove dieback. Sediment CO2 efflux within degraded sites was lower than values from other studies where degradation was caused by clearing or cutting, giving new insights into carbon dynamics in slowly degrading mangrove systems. Results of water samples agreed with previous studies where inorganic carbon outwelled from mangroves might enhance ecosystem connectivity by potentially buffering ocean acidification locally. Wetlands will be impacted by a variety of stressors resulting from a changing climate. Results from this study could inform scientists and stakeholders on how combined stresses, such as climate change with salinity intrusion may impact mangrove's blue carbon sink potential and highlight the need of future comparative studies of intact versus degraded mangrove stands.

Abstract:

Coral bleaching due to global warming currently is the largest threat to coral reefs, which may be exacerbated by altered water quality. Elevated levels of the UV filter oxybenzone in coastal waters as a result of sunscreen use have recently been demonstrated. We studied the effect of chronic oxybenzone exposure and elevated water temperature on coral health. Microcolonies of Stylophora pistillata and Acropora tenuis were cultured in 20 flow-through aquaria, of which 10 were exposed to oxybenzone at a field-relevant concentration of ~0.06 μg L−1 at 26 °C. After two weeks, half of the corals experienced a heat wave culminating at 33 °C. All S. pistillata colonies survived the heat wave, although heat reduced growth and zooxanthellae density, irrespective of oxybenzone. Acropora tenuis survival decreased to 0% at 32 °C, and oxybenzone accelerated mortality. Oxybenzone and heat significantly impacted photosynthetic yield in both species, causing a 5% and 22–33% decrease, respectively. In addition, combined oxybenzone and temperature stress altered the abundance of five bacterial families in the microbiome of S. pistillata. Our results suggest that oxybenzone adds insult to injury by further weakening corals in the face of global warming.

Keywords: Oxybenzone Benzophenone-3 Acropora tenuis Stylophora pistillata Climate change PSII yield Microbiome

Referenced in BioNews 36 article "Sunscreen increases the damaging effects of climate change on coral reefs"

Coral bleaching due to globalwarming currently is the largest threat to coral reefs,which may be exacerbated by altered water quality. Elevated levels of the UV filter oxybenzone in coastal waters as a result of sunscreen use have recently been demonstrated. We studied the effect of chronic oxybenzone exposure and elevated water temperature on coral health. Microcolonies of Stylophora pistillata and Acropora tenuis were cultured in 20 flow-through aquaria, of which 10 were exposed to oxybenzone at a field-relevant concentration of ~0.06 μg L−1 at 26 °C. After two weeks, half of the corals experienced a heat wave culminating at 33 °C. All S. pistillata colonies survived the heatwave, although heat reduced growth and zooxanthellae density, irrespective of oxybenzone. Acropora tenuis survival decreased to 0% at 32 °C, and oxybenzone accelerated mortality. Oxybenzone and heat significantly impacted photosynthetic yield in both species, causing a 5% and 22–33% decrease, respectively. In addition, combined oxybenzone and temperature stress altered the abundance of five bacterial families in the microbiome of S. pistillata. Our results suggest that oxybenzone adds insult to injury by further weakening corals in the face of global warming.