Pacific-wide pH snapshots reveal that high coral cover correlates with low, but variable pH

© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Manzello, D. P., Enochs, I. C., Carlton, R., Bruckner, A., Kolodziej, G., Dempsey, A., & Renaud, P. Pacific-wide pH snapshots reveal that high coral cover correlates with low, but variable pH. Bulletin of Marine Science, 97(1), (2021): 239-256, https://doi.org/10.5343/bms.2019.0100.Ocean acidification (OA) is impairing the construction of coral reefs while simultaneously accelerating their breakdown. The metabolism of different reef organism assemblages alters seawater pH in different ways, possibly buffering or exacerbating OA impacts. In spite of this, field data relating benthic community structure and seawater pH are sparse. We collected pH time-series data snapshots at 10 m depth from 28 different reefs (n = 13 lagoon, n = 15 fore reef) across 22 Pacific islands, spanning 31° latitude and 90° longitude. Coincident with all deployments, we measured percent cover of the benthic community. On fore reefs, high coral cover (CC) negatively correlated with mean and minimum pH, but positively correlated with pH variability. Conversely, pH minima were positively correlated to coverage of coralline and turf algae. Benthic cover did not correlate with pH in lagoonal reefs. From 0% to 100% CC, mean pH and aragonite saturation state (Ωarag) declined −0.081 and −0.51, respectively, while declines in minimum values were greater (Δmin pH = −0.164, Δmin Ωarag = −0.96). Based upon previously published relationships, the mean pH decline from 0% to 100% CC would depress coral calcification 7.7%–18.0% and increase biologically-mediated dissolution 13.5%–27.9%, with pH minima depressing dark coral calcification 14.4%–35.2% and increasing biologically-mediated dissolution 31.0%–62.2%. This spatially expansive dataset provides evidence that coral reefs with the highest coral cover may experience the lowest and most extreme pH values with OA.We thank the Khaled bin Sultan Living Ocean’s Foundation and the crew of the M/Y Golden Shadow. B Beck, J Monteiro, and many others assisted with field work. The Khaled bin Sultan Living Ocean’s Foundation supported the Global Reef Expedition. NOAA’s Coral Reef Conservation Program and Ocean Acidification Program support DP Manzello, IC Enochs, and G Kolodziej

Unprecedented early-summer heat stress and forecast of coral bleaching on the Great Barrier Reef, 2021-2022

The Great Barrier Reef (GBR) is predicted to undergo its sixth mass coral bleaching event during the Southern Hemisphere summer of 2021-2022. Coral bleaching-level heat stress over the GBR is forecast to start earlier than any previous year in the satellite record (1985-present). The National Oceanic and Atmospheric Administration (NOAA) Coral Reef Watch (CRW) near real-time satellite-based heat stress products were used to investigate early-summer sea surface temperature (SST) and heat stress conditions on the GBR during late 2021. As of 14 December 2021, values of instantaneous heat stress (Coral Bleaching HotSpots) and accumulated heat stress over a 12-week running window (Degree Heating Weeks) on the GBR were unprecedented in the satellite record. Further, 89% of GBR satellite reef pixels for this date in 2021 had a positive seven-day SST trend of greater than 0.2 degrees Celsius/week. Background temperatures (the minimum temperature over the previous 29 days) were alarmingly high, with 87% of GBR reef pixels on 14 December 2021 being greater than the maximum SST over that same 29-day period for any year from 1985-2020. The GBR is starting the 2021-2022 summer season with more accumulated heat than ever before, which could have disastrous consequences for the health, recovery, and future of this critical reef system

Seasonal Carbonate Chemistry Dynamics on Southeast Florida Coral Reefs: Localized Acidification Hotspots From Navigational Inlets

Seawater carbonate chemistry varies across temporal and spatial scales. Shallow-water environments can exhibit especially dynamic fluctuations as biological and physical processes operate on a smaller water volume relative to open ocean environments. Water was collected on a bi-monthly basis from seven sites off of southeast Florida (Miami-Dade and Broward counties), including four reefs, and three closely-associated inlets. Significant seasonal fluctuations in carbonate chemistry were observed on reef sites, with elevated pCO2 in the warmer wet season. Inlets demonstrated a more dynamic range, with periodic pulses of acidified water contributing to, on average, more advanced acidification conditions than those found at nearby reefs. Within inlet environments, there was a significant negative correlation between seawater salinity and both total alkalinity (TA) and dissolved inorganic carbon (DIC), which was in contrast to the patterns observed on reefs. Elevated TA and DIC in low salinity waters likely reflect carbonate dissolution as a result of organic matter decomposition. Together, these data highlight the important role that inlets play on shallow-water carbonate chemistry dynamics within southeast Florida waters and underscore the degree to which engineered freshwater systems can contribute to coastal acidification on localized scales

Autonomous Seawater \u3ci\u3ep\u3c/i\u3eCO\u3csub\u3e2\u3c/sub\u3e and pH Time Series From 40 Surface Buoys and the Emergence of Anthropogenic Trends

Ship-based time series, some now approaching over 3 decades long, are critical climate records that have dramatically improved our ability to characterize natural and anthropogenic drivers of ocean carbon dioxide (CO2) uptake and biogeochemical processes. Advancements in autonomous marine carbon sensors and technologies over the last 2 decades have led to the expansion of observations at fixed time series sites, thereby improving the capability of characterizing sub-seasonal variability in the ocean. Here , we present a data product of 40 individual autonomous moored surface ocean pCO2 (partial pressure of CO2) time series established between 2004 and 2013, 17 also include autonomous pH measurements. These time series characterie a wide range of surface ocean carbonate conditions in diffferent oceanic (17 sites), coastal (13 sites), and coral reef (10 sites) regimes. A time of trend emergence (ToE) methodology applied ot the time series that exhibit well-constrained daily to interannual variability and an estimate of decadal variability indicates that the length of sustained observations necessary to detect statistically significant anthropogenic trends varies by marine environment. The ToE estisites, and 9 to 22 years at the coral reef sites. Only two open ocean pCO2 and pH range from 8 to 15 years at the open ocean sites, 16 to 41 years at the coastal sites, and 9 to 22 years at the coral reef sites. Only two open ocean pCO2 time series, Woods Hole Oceanographic Institution Hawaii Ocean Time-series Station (WHOTS) in the subtropical North Pacific and Stratus n the South Pacific gyre, have been deployed longer than the estimated trend detection time and, for these, deseasoned monthly means show estimated anthropogenic trends of 1.9 ± 0.3 and 1.6 ± 0.3 μatm yr-1, respectively. In the future, it is possible that updates to this product will allow for the estimation of anthropogenic trends at more sites; however, the product currently provides a valuable tool in an accessible format for evaluating climatology and natural variability of surface ocean carbonate chemistry in a variety of regions. Data are available at https://doi.org/10.7289/V5DB8043 and https://www.nodc.noaa.gov/ocads/oceans/Moorings/ndp097.html (Sutton et al., 2018)

Loss of coral reef growth capacity to track future increases in sea level

Water-depths above coral reefs is predicted to increase due to global sea-level rise (SLR). As ecological degradation inhibits the vertical accretion of coral reefs, it is likely that coastal wave exposure will increase but there currently exists a lack of data in projections concerning local rates of reef growth and local SLR. In this study we have aggregated ecological data of more than 200 tropical western Atlantic and Indian Ocean reefs and calculated their vertical growth which we have then compared with recent and projected rates of SLR across different Representative Concentration Pathway (RCP) scenarios. While many reefs currently show vertical growth that would be sufficient to keep-up with recent historic SLR, future projections under scenario RCP4.5 reveal that without substantial ecological recovery many reefs will not have the capacity to track SLR. Under RCP8.5, we predict that mean water depth will increase by over half a metre by 2100 across the majority of reefs. We found that coral cover strongly predicted whether a reef could track SLR, but that the majority of reefs had coral cover significantly lower than that required to prevent reef submergence. To limit reef submergence, and thus the impacts of waves and storms on adjacent coasts, climate mitigation and local impacts that reduce coral cover (e.g., local pollution and physical damage through development land reclamation) will be necessary

Responses of Cryptofaunal Species Richness and Trophic Potential to Coral Reef Habitat Degradation

diversit

Seawater carbonate chemistry and vertical movement of stone crab larvae

Anthropogenic activities are increasing ocean temperature and decreasing ocean pH. Some coastal habitats are experiencing increases in organic runoff, which when coupled with a loss of vegetated coastline can accelerate reductions in seawater pH. Marine larvae that hatch in coastal habitats may not have the ability to respond to elevated temperature and changes in seawater pH. This study examined the response of Florida stone crab (Menippe mercenaria) larvae to elevated temperature (30°C control and 32°C treatment) and CO2-induced reductions in pH (8.05 pH control and 7.80 pH treatment). We determined whether those singular and simultaneous stressors affect larval vertical movement at two developmental stages. Geotactic responses varied between larval stages. The direction and rate of the vertical displacement of larvae were dependent on pH rather than temperature. Stage III larvae swam upwards under ambient pH conditions, but swam downwards at a faster rate under reduced pH. There was no observable change in the directional movement of Stage V larvae. The reversal in orientation by Stage III larvae may limit larval transport in habitats that experience reduced pH and could pose challenges for the northward dispersal of stone crabs as coastal temperatures warm

Micro-CT analysis of the Caribbean octocoral Eunicea flexuosa subjected to elevated pCO2

Rising anthropogenic carbon dioxide has resulted in a drop in ocean pH, a phenomenon known as ocean acidification (OA). These acidified waters have many ramifications for diverse marine biota, especially those species which precipitate calcium carbonate skeletons. The permanence of coral reef ecosystems is therefore closely related to OA stress as habitat-forming corals will exhibit reduced calcification and growth. Relatively little is known concerning the fate of other constituent taxa which may either suffer concomitant declines or be competitively favoured in acidified waters. Here, we experimentally (49 d) test the effects of next century predictions for OA (pH = 7.75, pCO2 = 1081 µatm) vs. near-present-day conditions (pH = 8.01, pCO2 = 498 µatm) on the common Caribbean octocoral Eunicea flexuosa. We measure linear extension of this octocoral and use a novel technique, high-resolution micro-computed tomography, to measure potential differences in the morphology of calcified internal skeletal structures (sclerites) in a 2 mm apical section of each branch. Despite the use of highly accurate procedures, we found no significant differences between treatments in either the growth of E. flexuosa branches or the structure of their sclerites. Our results suggest a degree of resilience to OA stress and provide evidence that this octocoral species may persist on Caribbean coral reefs, despite global change