Corals of the genus Porites are a locally abundant component
of the epibiont community on mangrove prop roots at
Calabash Caye, Turneffe Atoll, Belize
Zachary A Bengtsson, Kirsten M Kuhn, Anya T Battaglino, Allen S Li, Matthew N Talbot, Marzie Wafapoor, Calder J Atta, Michael B
Kowalski, Sarah P Margolis, Ekaterina A Rar, Elizabeth M Burmester, Kathryn C Lesneski, Karina Scavo, Les Kaufman, Nathan L
Stewart, John R Finnerty
Mangrove prop roots support diverse epibiont communities, but they are generally
regarded as inhospitable for corals. However, recent reports have documented corals
thriving on mangrove roots in the U.S. Virgin Islands and Cuba, and it has been proposed
that mangroves may provide a refuge from environmental conditions that trigger coral
mortality on nearby reefs. It also raises interesting questions about the potential
evolutionary significance of coral populations in mangrove forest. We investigated diverse
mangrove habitats for the presence of corals at Calabash Caye, Belize, part of a recently
designated marine reserve on Turneffe Atoll. Here we present data on the distribution, size
and morphology of 127 colonies of branching Porites found in a survey of 1858 meters of
mangrove prop roots fringing three qualitatively distinct bodies of water: a high-flow
channel, a moderate-flow creek, and a low-flow mangrove pond. The distribution of Porites
was highly clumped, with 108 colonies occurring in a 178-meter stretch of shoreline along
the high flow channel. Colony morphology varied widely, from bushy colonies with more
than 40 branch tips per 1000 cm3 of ecological volume, to spindly colonies with fewer than
10 branch tips per 1000 cm3, to new recruits that have not yet developed distinct
branches. Comparisons of the same coral-bearing roots in 2013 and 2014 revealed that
colonies can experience substantial growth in a year’s time. We also document a much
more diverse coral fauna living in the mangroves at Crooked Creek, a high flow
environment on the western edge of Turneffe Atoll. The data described here contribute to
an emerging picture of mangroves as potentially important habitat for corals, while
suggesting that different types of mangrove habitat vary in their suitability for different
species of coral. Future studies are needed to identify the critical environmental features
of mangrove habitats that support coral, to further characterize those corals that can
utilize mangrove habitat, and to investigate potential connectivity between coral
populations in mangroves and nearby reef habitats.
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Corals of the genus Porites are a locally abundant component of the epibiont
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community on mangrove prop roots at Calabash Caye, Turneffe Atoll, Belize
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Zachary A. Bengtsson1,^, Kirsten M. Kuhn1,2,^, Anya T. Battaglino2, Allen S. Li2, Matthew N.
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Talbot1,2, Marzie Wafapoor1,2, Calder J. Atta2, Michael B. Kowalski1,2, Sarah P. Margolis2,
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Ekaterina Rar2, Elizabeth M. Burmester1, Kathryn C. Lesneski1, Karina Scavo1, Les Kaufman1,2,
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Nathan L. Stewart1,2 and John R. Finnerty1,2*
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Boston University Biology Department1 and Marine Program2
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5 Cummington Mall, Boston, MA 02215
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^These authors contributed equally to this manuscript.
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*Corresponding Author:
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Telephone: 617-353-6984
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Fax: 617-353-6340
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e-mail: [email protected]
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Keywords: coral; mangrove; epibiont; Porites,
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Running Head: Coral epibionts of mangrove roots in Belize
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Abstract
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Mangrove prop roots support diverse epibiont communities, but they are generally regarded as
26
inhospitable for corals. However, recent reports have documented corals thriving on mangrove
27
roots in the U.S. Virgin Islands and Cuba, and it has been proposed that mangroves may provide
28
a refuge from environmental conditions that trigger coral mortality on nearby reefs. It also raises
29
interesting questions about the potential evolutionary significance of coral populations in
30
mangrove forest. We investigated diverse mangrove habitats for the presence of corals at
31
Calabash Caye, Belize, part of a recently designated marine reserve on Turneffe Atoll. Here we
32
present data on the distribution, size and morphology of 127 colonies of branching Porites found
33
in a survey of 1858 meters of mangrove prop roots fringing three qualitatively distinct bodies of
34
water: a high-flow channel, a moderate-flow creek, and a low-flow mangrove pond. The
35
distribution of Porites was highly clumped, with 108 colonies occurring in a 178-meter stretch of
36
shoreline along the high flow channel. Colony morphology varied widely, from bushy colonies
37
with more than 40 branch tips per 1000 cm3 of ecological volume, to spindly colonies with fewer
38
than 10 branch tips per 1000 cm3, to new recruits that have not yet developed distinct branches.
39
Comparisons of the same coral-bearing roots in 2013 and 2014 revealed that colonies can
40
experience substantial growth in a year’s time. We also document a much more diverse coral
41
fauna living in the mangroves at Crooked Creek, a high flow environment on the western edge of
42
Turneffe Atoll. The data described here contribute to an emerging picture of mangroves as
43
potentially important habitat for corals, while suggesting that different types of mangrove habitat
44
vary in their suitability for different species of coral. Future studies are needed to identify the
45
critical environmental features of mangrove habitats that support coral, to further characterize
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those corals that can utilize mangrove habitat, and to investigate potential connectivity between
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coral populations in mangroves and nearby reef habitats.
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Introduction
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Mangroves can promote the health and taxonomic richness of nearby coral reefs through a
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number of mechanisms, including stabilizing sediments, increasing water clarity, and serving as
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a nursery for juvenile fishes and invertebrates that will migrate to the reef as adults [1, 2].
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Additionally, mangrove prop roots support diverse communities of sessile epibionts, some of
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which can co-occur in nearby reef habitats [2]. For example, at seven Caribbean localities, coral
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reefs and nearby mangrove ecosystems were found to support overlapping but distinctive
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assemblages of sponges, implying that some sponge species can disperse between reef and
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mangrove [3], representing yet another mechanism whereby mangroves impact the biodiversity
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of nearby coral reefs.
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To date, the abundance and distribution of scleractinians in mangroves has received
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relatively little study [4], but based on recent published reports from the U.S. Virgin Islands [5-7]
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and Cuba [8], there is emerging evidence to suggest that mangroves could represent a significant
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habitat for corals. Rogers reported 28 coral species growing on or among mangrove prop roots in
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Hurricane Hole, St. John (Table 1) [5]. A follow-up study quantified the abundance of two reef-
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building corals — Colpophyllia natans and Diploria labrynthiformis — revealing that some
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specimens in the mangroves survived an outbreak of disease and bleaching that caused high
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mortality in nearby reef habitats [6]. Based on this finding, the authors suggested that mangroves
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may provide a refuge from conditions that promote bleaching on the reef because of differences
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in key environmental parameters e.g., shading from mangrove trees [7]. Alternatively, corals
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could become locally adapted to conditions in the mangroves. As poorly flushed mangrove
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habitats tend to experience higher temperatures than nearby reefs, mangroves could harbor
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populations of heat tolerant individuals whose larvae could replenish nearby reefs following
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heat-related coral mortality [7]. More recently, Hernández-Fernández reported 11 species of
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hermatypic corals living on mangrove roots at Jardines de la Reina National Park in Cuba, all
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inhabiting roots that were also occupied by crustose coralline algae [8].
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To evaluate the potential importance of mangroves as a habitat for corals, we conducted a
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systematic survey for corals on the prop roots of Rhizophora mangle at Calabash Caye, Turneffe
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Atoll, Belize. Here, we present data on the abundance, distribution, size, colony morphology, and
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year-to-year survival of corals along 1858 meters of mangrove prop roots fringing both banks of
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a high-flow channel, a moderate-flow creek, and a low-flow mangrove pond. In all, we found
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127 coral colonies occupying mangrove roots at Calabash, all branching members of the genus
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Porites. Their distribution was highly clustered, with 108 colonies located in a single 178-meter
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stretch of shoreline. An incipient longitudinal study of 60 randomly sampled mangrove roots at
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Calabash revealed that roots bearing corals are relatively rare, but that corals inhabiting
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mangrove roots exhibit a high survival rate over a year’s time. Given that the coral fauna we
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characterized at Calabash was substantially less diverse than that reported in the U.S. Virgin
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Islands and Cuba, we also investigated coral species richness at Crooked Creek, a high flow
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environment along the western edge of Turneffe Atoll—there, we found representatives of eight
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scleractinian genera, in contrast to the single genus we found at Calabash. We discuss the
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implications of these findings for the importance of mangroves as a coral habitat in Turneffe
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Atoll, and for the hypothesis that mangroves may represent a refuge for reef corals suffering
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from the impacts of climate change.
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Methods
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Study sites
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In November and December of 2013 and 2014, we surveyed the mangrove roots fringing three
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contiguous bodies of water at Calabash Caye, a small mangrove on the eastern (windward) face
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of Turneffe Atoll (Fig. 1). From north to south, these sites were: (1) a mangrove pond in the
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interior of Little Calabash (17°17'18.87"N, 87°48'43.46"W); (2) the channel separating Little
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Calabash from Calabash Caye (17°17'12.88"N, 87°48'41.86"W); and (3) a narrow creek
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connecting the channel with a mangrove pond in the interior of Calabash (17°17'10.50"N,
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87°48'44.94"W). These three sites—henceforth referred to as (1) Seahorse Pond, (2) Calabash
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Channel, and (3) Calabash Creek— differed qualitatively with respect to current judged by in-
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water observers: the pond exhibited the lowest current, the channel exhibited the highest current,
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and the creek exhibited an intermediate current. At all three sites, the banks were continuously
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lined with prop roots of Rhizophora mangle, and the roots located furthest from the bank were
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densely occupied by a diverse epibiont community including macroalgae, sponges, tunicates,
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bivalves, anemones, and corals. From November 16-December 15, 2014, nine data loggers
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(HOBO Pendant® model 8K) were deployed to record hourly measurements of water
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temperature at seven locations along the survey site (Fig. 1B, a-g). We also performed visual
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surveys for corals on mangrove prop roots at Crooked Creek (17°19'45.00"N, 87°55'4.10"W), for
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comparison with the mangroves at Calabash (Fig. 1C). Crooked Creek is a high-flow channel on
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the western edge of Turneffe Atoll located approximately 12 km WNW of Calabash. The
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research was conducted under Aquatic Scientific Research Permit 000047-13 issued by the
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Belize Fisheries Department and signed by Fisheries Officer James Azueta.
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Targeted coral surveys
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In November of 2014, along three discontinuous sections of shoreline at Calabash Caye spanning
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1858 meters (Fig. 1; red lines), the mangroves were systematically inspected for the presence of
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corals by three observers who slowly snorkeled in sequence past the fringing prop roots. Each
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root that harbored at least one coral was marked above the waterline using colored zip ties, and
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its location was determined using a handheld GPS device (Garmin; GPSmap 76CSx). Every
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coral colony was photographed from above and from one side using an underwater digital
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camera (Pentax WG-10). In each photograph, a centimeter rule was held in approximately the
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same plane as the center of the coral, so that each colony’s dimensions could be estimated from
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the photographs.
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Transect-based sampling of mangrove roots
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In November 2013, we established six 30m transects along the shorelines of Calabash Channel
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and Calabash Creek (Fig. 1B; 1-6). On each transect, a unique combination of colored zip ties
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was used to mark ten mangrove prop roots at regular intervals (3, 6, 9, 12, 15, 18, 21, 24, 27 and
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30 m from the start of the transect). Video and still photography were used to record the
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macroscopic epibionts inhabiting each of these 60 marked roots. The same 60 roots were
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photographically re-sampled in November 2014. The still photos and videos were analyzed by
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five independent observers to identify corals living on the roots.
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Species identification
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Corals were identified based on gross colony morphology by observers on site and from
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photographs. In the case of the branching Porites, which proved to be the only type of coral we
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observed at Calabash, we did not attempt to identify individual colonies to species. Caribbean
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branching Porites are thought to compose a monophyletic group, but the number of species
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constituting the complex is unclear. A recent molecular phylogenetic analysis of this clade based
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on the mitochondrial control region and 10 nuclear loci failed to resolve the three nominal
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species: P. divaricata, P. furcata, and P. porites [9]. Given this uncertainty, we refer to all of
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these specimens as branching Porites, to differentiate them from sympatric crustose/massive
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congeners such as P. astreoides.
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Characterization of colony size and morphology
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The length, width, and height of each branching Porites found at Calabash Caye were measured
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on site. From these linear dimensions, the ecological volume of each colony was calculated
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according to the formula of Shaish et al. [10]. Branch tips were counted from photographs aided
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by ImageJ [11]. Branch density was then calculated by dividing the number of branch tips by the
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ecological volume.
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Analysis of spatial distribution
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Distances between corals were estimated from GPS coordinates. Using the estimated distances
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between colonies within each contiguous stretch of shoreline, we applied the Clark-Evans test
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[12] modified for dispersion along one dimension [13] to determine if the average distance
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between nearest neighbors differed from null expectations.
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Results
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Number and distribution of corals at Calabash Caye
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Representative photographs of coral colonies on red mangrove prop roots at Calabash Caye are
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shown in Fig. 2. In all, 127 coral colonies were identified along the 1858 meters of shoreline
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surveyed at Calabash Caye (Fig. 3). All of the corals identified appeared to be branching
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members of the genus Porites. However, twenty (15.7%) of the colonies were recent recruits that
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did not yet have any branches.
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The corals exhibited a highly clustered distribution, with 85% (108/127) of the Porites
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colonies occurring on 26 prop roots in a 178-meter stretch along the north side of Calabash
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Channel (Fig. 3A, B). Single colonies were found on 9 of these roots, but multiple colonies were
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found on the other 17 roots, with as many as 18 colonies on a single root (Fig. 3B). Along the
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eastern edge of Calabash Creek and the southern side of Calabash Channel (Fig. 3A; blue line),
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corals were identified on 11 prop roots. Most of these roots bore a single coral, but three colonies
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were found on one root and five on another (Fig. 3C). Only two coral-bearing roots were found
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on the western edge of Calabash Creek (Fig. 3A; green line), each with only 1 colony per root.
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No corals were found along the 821 m of shoreline surveyed within Seahorse Pond. According to
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the Clark-Evans test, the corals along the 1110 m shoreline encompassing Seahorse Pond and the
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north side of Calabash Channel were more tightly clustered than would be expected by chance
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(p<0.001; Table 2), while those located along the 550 m shoreline encompassing the south side
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of Calabash channel and the eastern edge of Calabash Creek were not (p=0.184).
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We determined the size of the colonies using two metrics: the number of branch tips and
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the ecological volume [10]. The number of branch tips ranged from zero to 120 (mean = 9.9),
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with more than half of all corals having ≤3 branch tips (Fig. 4A). The ecological volume ranged
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from 0.25 to 8008 cm3 (mean = 366.3; Fig. 4B). The two parameters were positively correlated
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(r2=0.39; p<0.0001; Fig. 4C), but the number of branch tips varied substantially among colonies
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at higher ecological volumes. For example, the colony in Fig. 4D occupies about 73% of the
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ecological volume of the colony in Figure 4E (960 vs. 1320 cm3), but it has over 8x as many
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branch tips (65 vs. 8).
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To examine the distribution of Porites colonies by size, we divided all corals into four
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size categories based on branch number (0; 1-10; 11-40; >40) and four categories based on
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ecological volume (1-10; 10-100; 100-1000; 1000-10000 cm3; Fig. 5). Regardless of whether
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colonies were categorized according to branch number or ecological volume, the categories were
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not distributed equally among shoreline regions (for branch number: (6) = 40.05, p<0.005; for
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ecological volume: (6) = 25.49, p<0.005). Nearly all of the colonies lacking branches (19/20)
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were found in the western section of the north shore of Calabash channel (Fig. 5A, B). By
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contrast, nearly all of the colonies with >40 branches (4/5) were found in the stretch of shoreline
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encompassing the eastern bank of the creek and the southern bank of the channel (Fig. 5A, C).
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In addition to our targeted search for corals living on mangrove roots, we undertook a
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longitudinal, transect-based survey of mangrove roots at Calabash, which would allow us to
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estimate the frequency of mangrove roots bearing corals along stretches of shoreline where
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corals were observed. Of the 60 roots we surveyed in both 2013 and 2014 (labeled 1-6 in Fig.
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1B), 57 did not bear any corals in either 2013 or 2014; the roots lacking corals included 20 of 20
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roots sampled along the east bank of Calabash Creek, 20 of 20 along the south shore of Calabash
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Channel, and 17 of 20 (85%) along the north shore of Calabash Channel. In both 2013 and 2014,
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one root along the north shore of Calabash Channel was found to harbor a single coral colony
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(Fig. 6A, B), while a second root was found to harbor 4 coral colonies (Fig. 6C-E). In our 2013
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survey, we identified a single unbranched colony on root 2-7. This colony cannot be seen in the
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images recorded in 2014.
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Given their comparable locations on the same mangrove roots, we conclude the colonies
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found in 2013 are the same colonies identified in 2014 (Fig. 6), and therefore, it is possible to
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make inferences about change in colony shape and size in the intervening year. Among the five
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corals we can compare between years, there are colonies that appear to have lost branches and
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colonies that appear to have gained branches. In the single coral located on root 1-9 (the ninth
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root sampled on transect one) a substantial section of the colony appears to have been lost
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between 2013 and 2014 (see dashed line in Fig. 6A). By contrast, coral 1 on root 2-3 appears to
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have erupted new branches near its point of attachment with the mangrove root (compare dashed
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circles in Fig 6C and 6E).
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Species diversity of corals at Crooked Creek
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To determine whether the coral diversity on mangroves at Calabash Caye was representative of
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Turneffe Atoll, we surveyed the mangroves lining Crooked Creek, a high-flow channel on the
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western edge of Turneffe Atoll (Fig. 1C). In sharp contrast to Calabash Caye, at Crooked Creek,
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we were able to tentatively identify nine coral species in addition to branching Porites (Table 1).
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These included Porites astreoides, Dichocoenia stokesii, Orbicella faveolata and Siderastrea
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siderea (Fig. 7). Fire coral (Millepora alcicornis), a member of the cnidarian class Hydrozoa,
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was also abundant at Crooked Creek (Fig. 7) but absent from the mangroves we surveyed at
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Calabash.
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Discussion
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Mangroves are generally regarded as unsuitable habitat for scleractinians, and, as a result,
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few studies have focused on the abundance and diversity of corals living on or among mangrove
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prop roots [5, 7, 8]. There are a handful of references to corals occupying mangrove roots in
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general studies on mangrove biodiversity [14-17]. For example, in their authoritative analysis of
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mangrove epibionts at four cays off the coast of southern Belize, Farnsworth and Ellison
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included two corals among the species list in the appendix (Porites astreoides and Diploria
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strigosa), but they did not mention corals in the text [16]. In their biotic survey of the Pelican
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Cays, McIntyre et al. reported corals inhabiting mangrove roots at five sites [4]. In one mangrove
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pond, the prop roots supported a few colonies of Agaricia sp., while in another pond, a single
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large colony of Siderastrea siderea was found inhabiting mangrove roots. In three other sites,
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“corals” were listed among the members of the mangrove root community, but no species were
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identified by name [4]. In a biotic survey of Twin Cays, also in southern Belize, Rützler and co-
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workers reported corals occupying mangrove prop roots at three of 20 observation stations. The
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species identified on mangrove roots were Diploria strigosa, Porites astreoides, and P. porites
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[17].
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In contrast to these general studies of mangrove biodiversity, recent studies in St. John and
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Cuba have focused explicitly on corals. These studies have demonstrated that diverse coral
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assemblages can thrive on and among mangroves [5-8], thus raising the question of how
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important mangroves might be for particular coral species. Mangroves could prove critical to the
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long term health of certain coral populations, perhaps especially during periods of extreme
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environmental stress on nearby reef habitats [6, 7]. If this proves true, we may begin to regard
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mangroves as part of the ecological niche for some coral species [18]. Alternatively, mangroves
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may represent marginal habitat for corals with little impact on regional abundance or species’
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resilience, even for those species that occur in mangroves regularly.
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Understanding the importance of mangroves as coral habitat will require studies on coral
abundance and diversity from many more sites. Given the existing data (Table 1), it appears that
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corals are widespread on mangroves, but mangrove coral assemblages can differ substantially
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between sites. At Calabash Caye, all of the corals we identified were branching Porites,
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representing at most two nominal species (P. divaricata and P. furcata), making it the least
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diverse mangrove coral fauna so far described. The most diverse site described to date, Hurricane
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Hole, boasts 34-36 distinct species (depending upon whether P. divaricata, furcata, and porites
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prove to be valid species)[7]. Of note, the published studies from Hurricane Hole do not specify
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in every instance whether a particular species was found attached directly to mangrove prop
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roots, on the peat shelf immediately below mangrove prop roots, or on some other substratum in
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one of the mangrove lined bays and creeks that were studied [7]. This distinction is potentially
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important when identifying suitable habitat for a given species. Intermediate levels of coral
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diversity were observed at five sites in Cuba (4-9 species; [5, 7]) and at Crooked Creek, where
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we observed 10-12 different species (depending upon resolution of the branching Porites).
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Branching Porites have been reported at every mangrove site where corals have been
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systematically surveyed (Table 1), which suggests that this may among those corals most tolerant
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of the mangrove forest environment.
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With existing data we cannot ascertain definitively why some mangrove sites have high
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coral diversity, some sites have low coral diversity, and some sites are lacking corals entirely.
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The biodiversity of mangrove epibiont communities is driven by a combination of processes
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operating at different scales [16]. Key environmental parameters such as light, flow, and the
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abundance of predators can vary substantially between adjacent prop roots and even within a
275
single root.
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However, based on this study and previous studies on mangrove epibiont communities, it
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appears that flow is likely to be a major determinant of a mangrove site’s suitability for corals.
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While a detailed analysis of water flow was beyond the scope of our study, we observed a
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qualitative difference in the current between Seahorse Pond, where we found no corals, and
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Calabash Channel, where we found 85% of the corals identified in our study. Within Seahorse
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Pond, there was no perceptible current, at least none sufficient to displace a snorkeler or a small
282
buoy. The stillness of the water was further evidenced by a nearly ubiquitous layer of fine
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sediment covering the sessile epibionts on the mangrove roots, a layer that was easily dislodged
284
by the current from a passing snorkeler. By contrast, in the channel, snorkelers had to actively
285
swim against the current to maintain their positions relative to the bank, and the sessile epibionts
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inhabiting the mangrove roots were not covered in sediment. Other recent studies on low flow
287
mangrove sites are consistent with the absence of corals in the low-flow Seahorse Pond. Ruiz et
288
al. characterized more than 59,000 macroinvertebrate epibionts inhabiting prop roots in a low-
289
flow coastal mangrove pond in Mexico, and did not report a single coral specimen [19], and
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Yates et al. reported finding no corals in the most interior portion of three embayments at
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Hurricane Hole [7].
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Another factor that we suspect is impacting coral diversity in the mangroves is the fine-
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scale topography of the shoreline. Along the northern bank of Calabash Channel where we
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observed many branching Porites but no other species, there was a pronounced undercut in the
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peat bank, and the overhanging prop roots effectively shaded a habitat of mixed peat bank. By
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contrast, at Crooked Creek, the coral-bearing areas were characterized by a shallow, well-lit peat
297
bank and carbonate platform that was occupied by numerous coral colonies, some of which
298
extended from the bank to the prop roots (Fig. 7A, F). This microhabitat is similar to that
299
depicted in the photographs of mangrove corals in St. John [5, 7] and Cuba [8]. We suspect that
300
the broad, shallow, well-lit shelf observed at these sites can support a more diverse coral
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301
assemblage by providing a larger settlement area for corals and by allowing some species to
302
colonize the mangrove fringe that might not be well suited to settle and/or grow to substantial
303
size directly on the prop roots themselves.
304
To understand the importance of mangrove populations for the regional abundance of
305
corals—and whether mangroves might serve as refuges during periods of environmental stress—
306
we will require data on the growth, health, reproductive output, and temporal variability of coral
307
populations living in mangroves, as well as their relationship to populations in nearby reef
308
habitats. The current study begins to address these needs by obtaining baseline data on the size
309
and location of individual mangrove corals. By identifying a range of colony sizes, and
310
documenting the persistence of individual colonies from year-to-year, we have shown that
311
branching Porites can settle, survive, grow, and presumably reproduce in the channel and creek
312
habitats at Calabash Caye. We are in the process of acquiring additional longitudinal data (1) to
313
track the growth and survival of individual corals, (2) to determine how these life history traits
314
might be impacted by microhabitat, (3) to determine how this population fluctuates over time, (4)
315
to determine whether it is self-sustaining or requires constant immigration from adjacent “core”
316
habitats, and (5) to determine whether this site may export larvae to nearby reef and seagrass
317
habitats.
318
Branching Porites appear particularly adept at colonizing mangroves, and we suspect that
319
phenotypic plasticity is critical to their ability to tolerate a range of environments, from high
320
irradiance sites in shallow reefs, to shaded locations in the mangroves. The colony form of
321
branching corals has been shown to be strongly impacted by features of the physical
322
environment, particularly water flow and irradiance [20]. It is therefore noteworthy that our
323
study has detected substantial variation in colony form among branching Porites in the
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mangroves at Calabash, namely a 10-fold difference in the number of branch tips found in corals
325
at a similar ecological volume. At this time, we lack the data necessary to determine the relative
326
contributions of fixed genetic differences and phenotypic plasticity to the range of colony forms
327
we observed. To address this question, we are currently working to determine the genetic
328
relatedness and characterize the microhabitat of colonies exhibiting alternative morphologies.
329
We are also monitoring the development of recent recruits to document their growth patterns,
330
and how growth relates to microhabitat. Finally, we are conducting reciprocal transplants to
331
directly test the capacity for phenotypic plasticity.
332
Going forward, we hope that this study will contribute to our understanding of the
333
importance of mangrove habitats for coral resilience. Future studies will be required to determine
334
if the utilization of mangroves by corals is predictable and deterministic or stochastic. If we
335
discover that mangrove populations make important contributions to the long-term survival of
336
some coral species, and that the type of mangrove habitat utilized by these corals is predictable,
337
this information could prove vitally important to marine resource managers in the design of
338
marine protected areas.
339
340
Acknowledgments
341
This research was conducted by students and faculty participating in the Marine Semester
342
offered by the Boston University Marine Program (BUMP) and Biology Department. The
343
research was conducted at the Calabash Caye Field Station (CCFS), Environmental Research
344
Institute, University of Belize. We are grateful to the staff of BUMP (D. Brown, J. Hammer-
345
Mendez, J. Perry, and J. Scace), the staff of CCFS (M. Alamina, V. Alamina, A. Cherrington, N.
346
Craig, C. Encalada, J. Hall, J. Morey) and colleagues from UB (L. Cho-Ricketts, E. Garcia) for
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347
their technical expertise and logistical support. We are grateful to J. Azueta and I. Majil at the
348
Belize Fisheries Department for assistance in obtaining research permits. We thank J. Lang for
349
assistance in identifying corals. EAR was supported by a summer research fellowship from the
350
Undergraduate Research Opportunities Program at Boston University.
351
352
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353
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Clark PJ, Evans FC. Distance to nearest neighbor as a measure of spatial relationships in
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Clark PJ, Evans FC. Generalization of a nearest neighbor measure of dispersion for use in kdimensions. Ecology. 1979;60:316-7.
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Nagelkerken I, Blaber SJM, Bouillon S, Green P, Haywood M, Kirton LG, et al. The habitat
function of mangroves for terrestrial and marine fauna: A review. Aquat Bot. 2008;89:155-85.
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Table 1(on next page)
Species diversity of corals in mangrove habitats of the Caribbean
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Table 1. Species diversity of corals in mangrove habitats of the Caribbean
Species
Acropora palmata
Agaricia agaricites
Agaricia sp.
Cladocora arbuscula
Colpophyllia amaranthus
Colpophyllia natans
Dendrogyra cylindrus
Dichocoenia stokesii
Diploria labyrinthiformis
Eusmilia fastigiata
Favia fragum
Madracis auretenra
Manicina areolata
Meandrina meandrites
Milleopora alcicornis
Montastrea cavernosa
Mycetophillia species
Oculina diffusa
Orbicella annularis
Orbicella faveolata1
Orbicella franksi
Phyllangia americana
Porites astreoides,
Porites, branching
P. divaricata
P. furcata
P. porites
Porites colonensis
Pseudodiploria clivosa
Pseudodiploria strigosa
Scolymia cubensis
Scolymia lacera
Siderastrea radians
Siderastrea siderea
Solenastrea bournoni
Stephanocoenia intersepta
Stephanocoenia species
Tubastrea aurea
Tubastrea coccinea
TOTAL SPECIES2
HH
X
X
X
X
X
X
X
X
X
X
X
BS
LA
M-n
X
X
X
X
X
X
X
M-s
Ni
X
X
X
X
X
TC
X
X
X
X
X
X
X
CC
X
X
X
X
X
X
X
X
X
X
X
X
Ca
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
34-36
5
4-5
6-7
7-9
6-7
1-2
10-12
3
1
referred to as Montastrea faveolata; 2a range is given depending on whether branching Porites are
counted as one species or multiple species; 3not all corals found on mangrove roots in this study were
identified by species. US Virgin Islands [5]: HH=Hurricane Hole; Cuba [8]: BS=Boca Stone; LA=Las
Auras, M-n=Mariflores north, M-s=Mariflores south, Ni=Nicola; Belize: TC=Twin Cays [4];
Ca=Calabash Caye [the current study]; CC=Crooked Creek [the current study].
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Table 2(on next page)
Clark-Evans analysis of dispersion
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Table 2. Clark-Evans analysis of dispersion
Shoreline
N. Channel1
S. Channel2
Corals Span
108
1100m
14
550m
RA
1.66 m
10.00 m
RE
5.09 m
16.18 m
RA/RE
0.33
0.62
σRE
0.49
3.92
C
6.99
1.57
p
<0.001
0.116
1
includes Seahorse pond; 2includes eastern shore of Calabash Creek; RA = actual mean
nearest-neighbor distance; RE = expected mean nearest-neighbor distance; σRE = the
standard error of the mean distance to nearest neighbor in a randomly distributed
population with a known density; c= the standard variate of the normal curve
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1
Overhead view of study sites
(A) The locations of mangrove roots that were inspected for the presence of corals are shown
for (B) Calabash Caye and (C) Crooked Creek. At Calabash Caye, the survey area was divided
between three discontinuous stretches of mangrove: (1) the shoreline of Seahorse Pond
which is contiguous with the northern shoreline of Calabash Channel; (2) the eastern edge of
Calabash Creek which is contiguous with the southern shore of Calabash Channel; (3) the
western edge of Calabash Creek. In panel B, the white diamonds labeled a-g indicate the
approximate locations of temperature loggers, and the white lines labeled 1-6 indicate the
approximate locations of 30m transects. In panel C, the red lines indicate the shoreline that
was surveyed for corals.
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2
Representative photographs of Porites inhabiting prop roots
The images depict a specimen that has not yet developed any branches (A) as well as larger
colonies with eight (B) or more than 20 (C) branches. A 5-cm scale bar is shown in each
photograph.
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3
Plot of coral locations
(A) Along three stretches of shoreline (yellow, blue, and green lines), we identified 40 prop
roots bearing corals (circles). (B-D) The graphs indicated the number of corals found at each
point along the three transects.
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4
Coral dimensions
(A) Number of corals with a given number of branches. (B) Number of corals with a given
ecological volume. (C) Linear regression of branch number versus ecological volume.
Photographs of two of the individual corals represented in this plot (red circles) are shown (DE).
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5
Geographic distribution of coral size classes at Calabash
(A) All corals along three stretches of shoreline (B-D) were placed into one of four size
categories based upon the number of branch tips and one of four size categories based upon
ecological volume. The pie charts indicate the proportion (and number) of corals in each size
category for branch tips and for ecological volume for each stretch of shoreline. The same
color scheme is used as in Fig. 3.
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6
Visual comparison of the same coral colonies in 2013 and 2014
The single coral observed on mangrove root 1-9 is shown in 2013 (A) and 2014 (B). The
corresponding sections of the coral colony are given the same number in each panel (1-3).
The arrow indicates what appears to be the identical sponge species in the same location
relative to the colony in both photographs. The dashed line in (A) indicates a region of the
colony that was lost between 2014 and 2014 (B). The five corals observed on root 2-3 are
shown for both 2013 (C, D) and 2014 (E). The presumed correspondence between colonies,
based on their relative locations along the root, is indicated by the numbering (1-5). The
dashed circles on colony 1 in 2013 (C) indicate protuberances near the base of the colony
that appear to be located in the same relative positions as the bases of two erupting
branches in 2014 (E). The asterisks (C, D) indicate branches that have experienced breakage.
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7
Coral diversity at Crooked Creek
Representative photos of corals observed at Crooked Creek. (A) PA: Porites astreiodes; (B)
bP: branching Porites; DS: Dichocoenia stokesii; (C) PA: Porites astreiodes; (D) OF: Orbicella
faveolata; SS: Siderastrea siderea; (E) MA: Milleopora alcicornis (a hydrozoan); (F) DS:
Dichocoenia stokesii;
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