DOI: 10.5061/dryad.h44j0zpvk
title: Local human impacts interact with geography to drive benthic community depth zonation on contemporary coral reefs

description: Changes in biophysical conditions and energetic resource supply across
 depths are predicted to promote or limit the abundance of different coral
 reef benthic groups. However, the degree to which regional differences in
 biophysical processes govern and local human activities might alter
 naturally occurring depth zonation patterns remains unclear. Here we used
 2,239 reef surveys conducted between 0-30 m depth around 33 islands (18
 unpopulated and 15 populated) across the Pacific Ocean to quantify the
 percentage cover change of seven broad benthic groups. We tested whether
 natural depth zonation patterns differed across geographies (using six
 ecoregions), and whether and how local human impacts might disrupt these
 natural zonation patterns. We found benthic community depth zonation did
 not always occur. At the three ecoregions where depth zonation existed,
 there was no universal ‘natural’ zonation pattern and the benthic groups
 most responsible for driving patterns of depth zonation differed across
 geographies. We also found evidence of human-disrupted changes to benthic
 community depth zonation; patterns were inversed across depths and less
 distinct at populated compared to unpopulated islands within two
 ecoregions. We show coral reef communities are naturally highly variable,
 and that human activities can disrupt natural patterns of ecological
 organisation in contemporary ecosystems.
description: Benthic surveys were conducted at 33 islands across the
 U.S.-affiliated Pacific as part of the NOAA Coral Reef Conservation
 Program’s National Coral Reef Monitoring Program (NCRMP). At each site, to
 assess benthic cover, the mean percentage cover of benthic groups was
 quantified by taking 30 digital images of the benthos (0.7 – 1 m
 <sup>2</sup> per image) at 1-m increments along a 30 m
 transect 1 m above the benthos. At each site, a single depth stratum was
 surveyed (either shallow, mid, or deep) to maximise spatial coverage
 around each island while also quantifying depth effects for each island.
 Coral Point Count with Excel extensions (Kohler and Gill, 2006) was then
 used to overlay 10 random points onto each image (300 points per transect)
 and the benthic group under each point assigned to one of the following
 categories: scleractinian (hard) coral, crustose coralline algae (CCA);
 turf algae, including highly cropped to thick turf mats; fleshy upright
 macroalgae, Halimeda spp., (a common upright calcifying macroalga in the
  Pacific); fleshy and calcified encrusting macroalgae, and Alcyonacea
 (soft) coral. Points were pooled to generate site-level percentage cover
 estimates (~300 points per site).
description: # Local human impacts interact with geography to drive benthic community
 depth zonation on contemporary coral reefs Proceedings of The Royal
 Society: Biological Sciences DOI:
 [https://doi.org/10.5061/dryad.h44j0zpvk](https://doi.org/10.5061/dryad.h44j0zpvk) Rebecca J. Turner1*, Laura E. Richardson1, Courtney S. Couch2,3, Jessica A. Harvey1 and Gareth J. Williams1* (doi:10.1098/rspb.2024.1885). **Authors and Affiliations** 1School of Ocean Sciences, Bangor University, Menai Bridge, UK 2Cooperative Institute for Marine and Atmospheric Research, School of Ocean and Earth Science and Technology, University of Hawaii at Mānoa, Honolulu, United States 3Pacific Islands Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, Honolulu, HI, USA \**corresponding authors*: [b.turner@bangor.ac.uk](mailto:bex.turner@bangor.ac.uk), [g.j.williams@bangor.ac.uk](mailto:g.j.williams@bangor.ac.uk) ## Description of the data and file structure Benthic surveys were conducted at 33 islands across the U.S.-affiliated Pacific as part of the NOAA Coral Reef Conservation Program’s National Coral Reef Monitoring Program (NCRMP). At each site, to assess benthic cover, the mean percentage cover of benthic groups was quantified by taking 30 digital images of the benthos (0.7 – 1 m^2^ per image) at 1-m increments along a 30 m transect 1 m above the benthos. At each site, a single depth stratum was surveyed (either shallow, mid, or deep) to maximise spatial coverage around each island while also quantifying depth effects for each island. Coral Point Count with Excel extensions (Kohler and Gill, 2006) was then used to overlay 10 random points onto each image (300 points per transect) and the benthic group under each point assigned to one of the following categories: scleractinian (hard) coral, crustose coralline algae (CCA); turf algae, including highly cropped to thick turf mats; fleshy upright macroalgae, Halimeda spp., (a common upright calcifying macroalga in the  Pacific); fleshy and calcified encrusting macroalgae, and Alcyonacea (soft) coral. Points were pooled to generate site-level percentage cover estimates (~300 points per site). ## File: Turner\_et\_al\_2025\_Benthos\_2010\_2014.csv **Description:**  #### Variables * SITE: site ID of the transect * ISLAND: island of transect * METHOD: method for obtaining % cover estimates * OBS_YEAR: year of transect * REGION: region of the transect * ECOREGION: ecoregion of transect (as per Spaulding et al. 2007) * DATE: date of sampling (M/D/YYYY) * POP_STATUS: population status (U = unpopulated, P = populated) * REEF_ZONE: reef zone sampled * LATITUDE_LOV: latitude where transect undertaken (decimal degrees) * LONGITUDE_LOV: longitude where the transect was undertaken (decimal degrees) * DEPTH_BIN_NEW: depth strata of transect; shallow: 0-6 m, mid: &gt; 6-18 m, and deep: &gt; 18-30 m * CORAL_%: hard coral percentage cover * CCA_%: crustaceous coralline algae percentage cover * SC_%: soft coral percentage cover * HALIMEDA_%: *Halimeda* spp., (a common upright calcifying macroalga in the Pacific) percentage cover * MA_%: fleshy upright macroalgae percentage cover * EMA_%: fleshy and calcified encrusting macroalgae percentage cover  * TURF_%:  turf algae, including highly cropped to thick turf mats percentage cover * AVG_DEPTH_m: average depth of transect (m) - used to allocate each observation to the associated DEPTH_BIN_NEW ## File: R\_Script\_Turner\_et\_al\_2025.txt **Description:** R Script for - Local human impacts interact with geography to drive benthic community depth zonation on contemporary coral reefs. Turner et al. 2025. Proceedings of The Royal Society: Biological Sciences. Code uses data Turner_et_al_2025_Benthos_2010_2014.csv in R version 4.2.1 using packages ggplot2, tidyverse, reshape2 dplyr to produce figures 2, 4 & 5 in the manuscript. ## File: Turner\_et\_al\_primer\_2025.pwk **Description:** PRIMER v7 .pwk file containing all data used for analysis and workflow. All PERMANOVA and CAP analyses were computed using the PERMANOVA+ add-on for Primer v7. #### Variables * CORAL: hard coral percentage cover * CCA: crustaceous coralline algae percentage cover * SC: soft coral percentage cover * HALIMEDA: *Halimeda* spp., (a common upright calcifying macroalga in the Pacific) percentage cover * Macroalgae: fleshy upright macroalgae percentage cover * EMA: fleshy and calcified encrusting macroalgae percentage cover  * TURF:  turf algae, including highly cropped to thick turf mats, percentage cover The file contains PERMANOVA model design and results (table 1 in the manuscript), Pairwise model design and results (table 2 in the manuscript), and Canonical analysis of principal coordinates model design and results (figure 3 in the manuscript). References: Anderson MJ, Gorley RN, Clarke KR. 2008 PERMANOVA+ for PRIMER: Guide to software and statistical methods. PRIMER-E: Plymouth, UK. Clarke KR, Gorley RN. 2015 Getting started with PRIMER v7. PRIMER-e: plymouth, plymouth marine laboratory. **20**(1).