Two decades of carbonate budget change on shifted coral reef assemblages: are these reefs being locked into low net budget states?

Abstract

The ecology of coral reefs is rapidly shifting from historical baselines. One key-question is whether under these new, less favourable ecological conditions, coral reefs will be able to sustain key geo-ecological processes such as the capacity to accumulate carbonate structure. Here, we use data from 34 Caribbean reef sites to examine how the carbonate production, net erosion and net carbonate budgets, as well as the organisms underlying these processes, have changed over the past 15 years in the absence of further severe acute disturbances. We find that despite fundamental benthic ecological changes, these ecologically shifted coral assemblages have exhibited a modest but significant increase in their net carbonate budgets over the past 15 years. However, contrary to expectations this trend was driven by a decrease in erosion pressure, largely resulting from changes in the abundance and size-frequency distribution of parrotfishes, and not by an increase in rates of coral carbonate production. Although in the short term, the carbonate budgets seem to have benefitted marginally from reduced parrotfish erosion, the absence of these key substrate grazers, particularly of larger individuals, is unlikely to be conducive to reef recovery and will thus probably lock these reefs into low budget states.

Global declines in coral reef calcium carbonate production under ocean acidification and warming

“…S1 and S4 ). However, there is considerable natural variability in net carbonate production presently, and there are many heavily degraded reefs that already have low net carbonate production ( 33 ). To put these declines in net carbonate production rates into perspective, mean global declines in net carbonate production (e.g., SI Appendix , Fig.…”

“…However, coralline algal–dominated reefs will offer very different (or reduced) ecological services and structural complexity compared to coral-dominated reefs ( 11 ), and their capacity to produce carbonate will also be limited once ocean acidification intensifies. Conversely, their ability to support parrotfish and sea urchin bioeroders will also be reduced ( 36 – 38 ), which could therefore support slightly higher net carbonate production than equivalent coral-dominated reefs with equal gross carbonate production ( 33 ).…”

An emerging coral disease outbreak decimated Caribbean coral populations and reshaped reef functionality

“…In the absence of recovery, the ultimate consequences of coral mortality will thus be modulated by destructive forces like bioerosion or the biogenic dissolution of reef structures 47 . Although erosion rates appear to have declined in the Caribbean, erosion is becoming the primary factor controlling the carbonate budgets 48,49 . This is particularly relevant as both bioerosion rates and skeletal dissolution are thought to become pervasive when the water chemistry changes or the temperatures increase 50,51 .…”

The past, present, and future of coral reef growth in the Florida Keys

“…Census‐based carbonate budget studies, which are aimed at quantifying the biological processes that regulate reef‐framework construction and destruction, have a long history in coral‐reef research (e.g., Chave et al, 1972; Eakin, 1996; Hubbard et al, 1990; Lange et al, 2020; Perry et al, 2012). Although this approach generally does not account for the impacts of event‐driven physical erosion or chemical dissolution, it provides a valuable tool for using existing coral‐reef monitoring data to assess the present state and reconstruct temporal changes in the balance between carbonate production and bioerosion (e.g., Estrada‐Saldívar et al, 2019; Januchowski‐Hartley et al, 2017; Molina‐Hernández et al, 2020; Perry et al, 2013, 2018). These methods can also be used to identify the environmental (de Bakker et al, 2019; Eakin, 1996; Lange & Perry, 2019) and ecological drivers of changing budget states (Courtney et al, 2020; Januchowski‐Hartley et al, 2017; Molina‐Hernández et al, 2020; Perry et al, 2014, 2015) and to predict how reefs may respond to climate change and other anthropogenic disturbances in the future (Cornwall et al, 2021; Kennedy et al, 2013).…”

“…hurricane impacts (all of which primarily impacted the Lower Keys and Dry Tortugas subregions; https://coast.noaa.gov/hurri canes/), which we predicted a priori could cause significant changes on the reefs. This resulted in seven pairwise temporal comparisons that were used to evaluate: (1) the beginning versus the end of the time series (1996 vs. 2019), (2) the 1997-1998 coral-bleaching event and Hurricane Georges (Category 1) in September of 1998(1996 vs. 1999), (3) Hurricane Irene (Category 1) in October of 1999(1999 vs. 2000), (4) Hurricane Charley in August 2004 and Hurricanes Dennis, Katrina, Rita, and Wilma in July-October of 2005 (all Category 2) as well as a regional coral-bleaching event in 2005(2003 vs. 2006), (5) the January 2010 cold-water event(2009 vs. 2010), (6) the regional coral-bleaching events in2014 and 2015 (2013 vs. 2016), and(7) Hurricane Irma (Category 4) in September 2017(2017 vs. 2018). The other temporal pairwise comparisons are available on GitLab.…”