Environmental drivers of coral reef carbonate production and bioerosion: a multi‐scale analysis

Abstract

The resilience of coral reefs depends on the balance between reef growth and reef breakdown, and their responses to changing environmental conditions. Across the 2500-km Hawaiian Archipelago, we quantified rates of carbonate production, bioerosion, and net accretion at regional, island, site, and within-site spatial scales and tested how these rates respond to environmental conditions across different spatial scales. Overall, there were four major outcomes from this study: (1) bioerosion rates were generally higher in the populated Main Hawaiian Islands (MHI) than the remote, protected Northwestern Hawaiian Islands (NWHI), while carbonate production rates did not vary significantly between the two regions; (2) variability in carbonate production, bioerosion, and net accretion rates was greatest at the smallest within-reef spatial scale; (3) carbonate production and bioerosion rates were associated with distinct sets of environmental parameters; and (4) the strongest correlates of carbonate production, bioerosion, and net accretion rates were different between the MHI region and the NWHI region: in the MHI, the dominant correlates were percent cover of macroalgae and herbivorous fish biomass for carbonate production and bioerosion, respectively, whereas in the NWHI, the top correlates were total alkalinity and benthic cover. This study highlights the need to understand accretion and erosion processes as well as local environmental conditions to predict net coral reef responses to future environmental changes.

Effects of submarine groundwater discharge on coral accretion and bioerosion on two shallow reef flats

“…Parrotfish biomass at outer sites in Maunalua, although low (parrotfish biomass= 0.2 ± 0.2 g m −2 at Black Point, 1.3 ± 0.5 g m −2 at Wailupe), is comparable to other open or unprotected sites on O'ahu (Williams et al ), and higher than the inshore sites included in this study, where no adult parrotfish were observed throughout the experiment (K. Lubarsky unpubl.). Indeed, the bioerosion rates at the outer sites are comparable to bioerosion rates found on reefs throughout the Hawaiian archipelago (Silbiger et al ).…”

“…This is consistent with previous studies that have noted increased bioerosion with increasing nutrients (Edinger et al ; Holmes 2000; Le Grand and Fabricius ). Studies that have assessed bioerosion rates in the Hawaiian Archipelago have found the highest bioerosion rates at Kahekili, Maui, a site with a significant influx of nutrient‐rich SGD (Prouty et al ; Silbiger et al ), indicating that the relationship between SGD and bioerosion in the current study is not a localized phenomenon.…”

“…Blocks were scanned before and after deployment using μ CT at the Multiscale CT Facility at Cornell University using an eXplore CT120 μ CT (GE Healthcare Xradia) in order to construct a three‐dimensional image of object densities in the interior and exterior of each block (Silbiger et al ; Silbiger et al ; Silbiger et al ) . μ CT analysis followed methods outlined in Silbiger et al ().…”

“…Globally, SGD makes up 6-10% of total freshwater inputs to the coastal ocean, with one-third of the global SGD component coming from large islands, particularly in the tropics (Moosdorf et al 2015). On volcanic islands like Hawai'i, for example, SGD is abundant (Dimova et al 2012;Richardson et al 2017a), can exceed river fluxes, and often makes up the largest or only source of new nutrients to the coastal ocean (Johnson et al 2008;Street et al 2008;Moosdorf et al 2015;Lee and Kim 2015). Unlike riverine inputs, which are driven by peaks in precipitation (Drupp et al 2011), SGD is driven by hydrological gradients between the subterranean estuary and the coastal ocean and discharge is often tidally modulated, leading to diurnal or semidiurnal inputs on a daily basis (Dimova et al 2012;Cyronak et al 2013;Wang et al 2014).…”

Carbonate system parameters of an algal-dominated reef along West Maui

“…Numerous efforts have been conducted along West Maui, Hawaii, USA, to characterize and quantify submarine groundwater discharge (SGD) and associated nutrient input (Dailer et al, 2010Glenn et al, 2013;Swarzenski et al, 2013Swarzenski et al, , 2016Silbiger et al, 2017), which may influence reef metabolism and community composition by changing coastal water quality. Building upon these studies, we present a comprehensive study to characterize the carbonate system parameters from the reefs in this area.…”