DOI: 10.5061/dryad.08kprr4zc
title: Bleaching-driven reef community shifts drive pulses of increased reef sediment generation

description: The ecological impacts of coral bleaching on reef communities are well
 documented, but resultant impacts upon reef-derived sediment supply are
 poorly quantified. This is an important knowledge gap because these
 biogenic sediments underpin shoreline and reef island maintenance. Here we
 explore the impacts of the 2016 bleaching event on sediment generation by
 two dominant sediment producers (parrotfish and Halimeda spp.) on southern
 Maldivian reefs. Our data identifies two pulses of increased sediment
 generation in the three years since bleaching. The first occurred within
 ~6 months after bleaching as parrotfish biomass and resultant erosion
 rates increased, likely in response to enhanced food availability. The
 second pulse occurred 1-3 years post-bleaching, after further increases in
 parrotfish biomass and a major (~4-fold) increase in Halimeda spp.
 abundance. Total estimated sediment generation from these two producers
 increased from ~0.5 kg CaCO3 m-2 yr-1 (pre-bleaching; 2016) to ~3.7 kg
 CaCO3 m-2 yr-1 (post-bleaching; 2019), highlighting the strong links
 between reef ecology and sediment generation. However, the relevance of
 this sediment for shoreline maintenance likely diverges with each producer
 group, with parrotfish-derived sediment a more appropriate size-fraction
 to potentially contribute to local island shorelines.
description: Benthic cover data was collected along replicate 10 m transects
 (n= 5) in January and September 2016, March 2017 and January 2019, from
 the south-western margins of five uninhabited atoll interior reefs in
 Gaafu Dhaalu atoll, southern Maldives. All data were collected from sites
 along the outer reef flat/upper reef front (~2 m depth contour) using the
 ReefBudget methodology. Recorded groups included scleractinian corals to
 the genera and morphological level e.g., <i>Acropora</i>
 branching, <i>Porites</i> massive etc.; crustose coralline
 algae (CCA); turf algae; fleshy macroalgae; <i>Halimeda</i>
 spp.; sediment; rubble; and other benthic organisms. All data were
 collected as a function of the true 3-dimensional surface of the reefs,
 thus including cover on overhangs and vertical surfaces.
 Parrotfish abundance (ind. ha<sup>-1</sup>) was
 quantified via underwater visual census (UVC) along eight 30 m x 4 m belt
 transects in the same region of each reef in each time period, with all
 surveys completed by the same experienced observer (K.M.M.). Details on
 parrotfish species, life phase (juvenile, initial and terminal) and total
 length (in size classes of 10 cm) were recorded for each individual.
 Parrotfish biomass (kg ha<sup>-1</sup>) for each species and
 size class was then calculated using established length-weight
 relationships and multiplied by fish abundance, following the approach
 described in: Januchowski-Hartley FA, Graham NA, Wilson SK, Jennings S,
 Perry CT. (2017) Drivers and predictions of coral reef carbonate budget
 trajectories. Proc Royal Soc B. 284:20162533
 (doi.org/10.1098/rspb.2016.2533)
description: Table 1: Mean transect level cover (% cover) data for corals,
 turf and filamentous algae, and <em>Halimeda</em> from 5
 southern Maldives reef sites from Jan 2016, Sept 2016, March 2017 and Jan
 2019. Table 2: Mean transect level (n = 8) data on
 parrotfish abundance (ind./30 x 4 m belt transect) and biomass (kg
 ha<sup>-1</sup>)  from the 5 southern Maldives reef sites from
 Jan 2016, Sept 2016, March 2017 and Jan 2019