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The Hawaiian Archipelago

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The Hawaiian Archipelago is one of the largest and most isolated island chains in the world, and its marine ecosystems are well-studied. Research on Hawaiian mesophotic coral ecosystems (MCEs) began in the 1960s and has intensified during the past decade. In Hawai‘i, rich communities of macroalgae, corals and other invertebrates, and fishes inhabit MCEs and are associated with increased water clarity and decreasing average current strength with depth. Extensive calcified and fleshy macroalgal beds are found both in discrete patches, dense beds, and meadows over both hard and soft substrates. Several species of corals typical of shallow reefs extend to depths of ~60 m. The dominant corals below 60 m are in the genus Leptoseris, which can form extensive coral reefs spanning tens of km². Few octocoral species inhabit shallow reefs and upper MCEs (30–70 m) but are diverse at the deepest range of MCEs (>130 m). Sponges do not represent a major structural component of MCEs. Many species of fishes occur on both shallow reefs and MCEs, but MCEs harbor more endemic species (up to 100% endemism). Several new species of macroalgae, corals and other invertebrates, and fishes have recently been documented. Over 60% of the territorial waters surrounding the archipelago are protected as the Papahānaumokuākea Marine National Monument; however, no specific protections exist for MCEs. Generally, threats affecting Hawai‘i’s shallow reefs also affect MCEs to varying degrees. MCEs may be more insulated from some threats but more vulnerable than shallow reefs to others (e.g., water clarity).
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445
© Springer Nature Switzerland AG 2019
Y. Loya et al. (eds.), Mesophotic Coral Ecosystems, Coral Reefs of the World 12,
https://doi.org/10.1007/978-3-319-92735-0_25
Abstract
The Hawaiian Archipelago is one of the largest and most
isolated island chains in the world, and its marine ecosys-
tems are well-studied. Research on Hawaiian mesophotic
coral ecosystems (MCEs) began in the 1960s and has
intensied during the past decade. In Hawaii, rich com-
munities of macroalgae, corals and other invertebrates,
and shes inhabit MCEs and are associated with increased
water clarity and decreasing average current strength with
depth. Extensive calcied and eshy macroalgal beds are
found both in discrete patches, dense beds, and meadows
over both hard and soft substrates. Several species of
corals typical of shallow reefs extend to depths of ~60m.
The dominant corals below 60 m are in the genus
Leptoseris, which can form extensive coral reefs spanning
tens of km2. Few octocoral species inhabit shallow reefs
and upper MCEs (30–70m) but are diverse at the deepest
range of MCEs (>130 m). Sponges do not represent a
major structural component of MCEs. Many species of
shes occur on both shallow reefs and MCEs, but MCEs
harbor more endemic species (up to 100% endemism).
Several new species of macroalgae, corals and other
invertebrates, and shes have recently been documented.
Over 60% of the territorial waters surrounding the archi-
pelago are protected as the Papahānaumokuākea Marine
National Monument; however, no specic protections
exist for MCEs. Generally, threats affecting Hawai‘i’s
shallow reefs also affect MCEs to varying degrees. MCEs
may be more insulated from some threats but more vulner-
able than shallow reefs to others (e.g., water clarity).
Keywords
Mesophotic coral ecosystems · Hawaiian Islands · Coral
reef · Papahānaumokuākea Marine National Monument ·
Deep reef
25.1 Introduction
The islands and reefs of the Hawaiian Archipelago stretch
over 2500km across the north-central tropical Pacic Ocean.
This isolated archipelago consists of the eight Main Hawaiian
Islands (MHI) in the southeast and a linear array of mostly
uninhabited rocky islets, atolls, reefs, and seamounts com-
prising the Northwestern Hawaiian Islands (NWHI;
The Hawaiian Archipelago
HeatherL.Spalding, JoshuaM.Copus, BrianW.Bowen,
RandallK.Kosaki, KenLongenecker,
AnthonyD.Montgomery, JacquelineL.Padilla-Gamiño,
FrankA.Parrish, MelissaS.Roth, SoniaJ.Rowley,
RobertJ.Toonen, andRichardL.Pyle
H. L. Spalding (*)
Department of Botany, University of Hawaiʻi at Mānoa,
Honolulu, HI, USA
e-mail: spaldinghl@cofc.edu
J. M. Copus
Hawai‘i Institute of Marine Biology, Kāne‘ohe, HI, USA
B. W. Bowen · R. J. Toonen
Hawai‘i Institute of Marine Biology, University of Hawaiʻi at
Mānoa, Kāne‘ohe, HI, USA
R. K. Kosaki
Papahānaumokuākea Marine National Monument, National
Oceanic and Atmospheric Administration, Honolulu, HI, USA
K. Longenecker · R. L. Pyle
Bernice P.Bishop Museum, Honolulu, HI, USA
e-mail: deepreef@bishopmuseum.org
A. D. Montgomery
U.S.Fish and Wildlife Service, Pacic Islands Fish and Wildlife
Ofce, Honolulu, HI, USA
Hawaiʻi Institute of Marine Biology, University of Hawaiʻi at
Mānoa, Kāne‘ohe, HI, USA
J. L. Padilla-Gamiño
University of Washington, Seattle, WA, USA
F. A. Parrish
Pacic Islands Fisheries Science Center, National Oceanic and
Atmospheric Administration, Honolulu, HI, USA
M. S. Roth
Howard Hughes Medical Institute, Department of Plant and
Microbial Biology, University of California Berkeley,
Berkeley, CA, USA
S. J. Rowley
Department of Earth Sciences, University of Hawaiʻi at Mānoa,
Honolulu, HI, USA
25
446
Fig.25.1). The Hawaiian Archipelago spans a broad latitudi-
nal gradient, stretching from the southern tip of Hawaiʻi
Island (19° N) to Kure Atoll (28° N). Many Hawaiian reefs
are protected by local, state, and federal laws, with a wide
range of management and conservation efforts in place. The
NWHI falls within the Papahānaumokuākea Marine National
Monument (PMNM), a federally protected area larger than
all US national parks combined (>1,508,870 km2). The
PMNM is listed as a World Heritage site and includes about
10% of shallow (<30 m) coral reefs within US territorial
waters (Rohmann et al. 2005). Coral reefs within the
Hawaiian Archipelago have been extensively studied and
documented (Maragos 1977; Chave and Malahoff 1998;
Hoover 1998; Mundy 2005; Kahng and Kelley 2007;Randall
2007; Fletcher etal. 2008; Grigg etal. 2008; Jokiel 2008;
Rooney etal. 2008; Toonen etal. 2011; Selkoe etal. 2016).
Although Hawaiʻi was among the rst places where meso-
photic coral ecosystems (MCEs), or communities of light-
dependent corals and other organisms from 30–40m to over
150m depths (Hinderstein etal. 2010), were investigated,
the most intensive research within this environment has
occurred only within the past decade.
25.1.1 Research History
The rst investigations of MCEs within the Hawaiian
Archipelago were conducted in the 1960s with SCUBA
(Grigg 1965) and manned submersibles (Brock and
Chamberlain 1968; Strasburg etal. 1968). These early investi-
gations found an unexpected abundance of reef-associated
species (including hermatypic corals) at depths from 25 to
107m. These studies also revealed that many species of shes
previously believed to be restricted to shallow coral reefs also
inhabited much greater depths. In the decades that followed,
several publications reported on MCEs within the Hawaiian
Archipelago (Grigg 1976; Agegian and Abbott 1985; Maragos
and Jokiel 1985; Moftt etal. 1989; Chave and Mundy 1994;
Fig. 25.1 The Hawaiian Archipelago is composed of the eight MHI and a series of islands, atolls, and banks to the northwest called the NWHI.The
(a) NWHI are protected within the PMNM. (b) The eight MHI with the area of the ‘Au‘Au Channel enclosed in white. (c) The ‘Au‘Au Channel
between the islands of Lana‘i and Maui. MCEs within the ‘Au‘Au Channel have been extensively studied due to its gently sloping substrate and
calm waters. (d) Kaua‘i and Ni‘ihau. (e) Hawai‘i
H. L. Spalding et al.
447
Parrish and Polovina 1994; Pyle and Chave 1994), but most of
these focused on either a few species or habitats or a broad
depth range (with MCEs representing only a small portion of
the study). Beginning in the late 1980s, the advent of techni-
cal, mixed-gas diving opened up new opportunities for the
exploration of MCEs (Pyle 1996a, b, c, 1998, 2000, 2019;
Grigg et al. 2002; Parrish and Pyle 2002; Pence and Pyle
2002; Parrish and Boland 2004; Boland and Parrish 2005;
Grigg 2006). From 2004 to 2007, submersible and technical
diving surveys funded by the National Oceanic and
Atmospheric Administration (NOAA) Hawaiʻi Undersea
Research Laboratory (HURL) discovered extensive meso-
photic macroalgal assemblages around the MHI.In 2006, the
discovery of extensive MCEs with near- 100% coral cover off
Maui at 40–130m depths, coupled with interest in document-
ing MCEs in the NWHI and growing support for technical
mixed-gas diving operations among Hawaiian research insti-
tutions, led to a surge of MCE research. A series of collabora-
tive, multidisciplinary projects ensued including the
2007–2012 Deep Coral Reef Ecosystem Studies project sup-
ported by the NOAA National Centers for Coastal Ocean
Science focused on the MCEs of the ‘Au‘au Channel (located
on the submerged land bridge between the islands of Maui and
Lanaʻi; Grigg etal. 2002), the 2010–2013 study contrasting
MCEs between O‘ahu and Maui funded by the NOAA Coral
Reef Conservation Program, and annual NOAA research
cruises to PMNM beginning in 2009 (Pyle etal. 2016a).
25.2 Environmental Setting
The Hawaiian ridge spans the productivity gradient of the
Central Pacic seascape. The northern atolls are located in the
most productive waters, whereas the islands and banks in the
central region experience the seasonal southern shift of pro-
ductivity from the chlorophyll front (Polovina etal. 2001),
and the larger MHI are removed to the south where ocean
conditions are impoverished. It is unknown how the environ-
ment varies across the archipelago at mesophotic depths.
Visual surveys exploring the archipelago show there is a wide
range in the substrate composition and dominance of coral,
algae (Pyle etal. 2016a), and the associated sh assemblage
(Kane and Tissot 2017), but year-round environmental moni-
toring is lacking. Some shery studies have opportunistically
placed thermographs at mesophotic depths to characterize the
seasonal range of temperatures (Parrish and Boland 2004;
Parrish et al. 2015) but are too few to represent the wider
realm. To understand the mesophotic environment, an impor-
tant rst step is to obtain measurements of light levels, tem-
perature, salinity, oxygen, and currents at specic sites with
benthic communities that are rich with mesophotic corals and
algae. This focused study site approach would identify prior-
ity variables to form the basis for future comparative environ-
mental studies across the archipelago.
25.2.1 Auau Channel
Most of the environmental data available on Hawaiian MCEs
is from the ‘Au‘au Channel. The ‘Au‘au Channel has the most
extensive MCEs and macroalgal beds and meadows in the
MHI (Fig.25.2) and was the site of an in-depth geophysical
study (Pyle etal. 2016a). This area, in the lee of the island of
Maui, is protected from dominant trade winds and seasonal
swell (Fig.25.1). This protection, coupled with clear water,
thermal stability, and consistent water ow at 70–90m, pro-
vides an environment conducive for thriving MCEs.
One of the most important geophysical characteristics of
MCEs in Hawaiʻi is water clarity. Light proles taken within
one hour of high noon on calm, clear days over dense
Leptoseris spp. reefs to a maximum depth of 94m within the
Au‘au Channel and over macroalgal beds off O‘ahu to 90m
depths revealed very clear water, with a mean diffuse attenu-
ation coefcient (Ko) of 0.041±0.001m1 (Spalding 2012;
Pyle etal. 2016a). In comparison, nearby inshore areas of
West Maui had a higher Ko (and more turbid water), ranging
from 0.107m1 at 10m depth to 0.073m1 at 30m (Spalding
2012). The mean optical depths over MCEs, which corre-
spond to the midpoint (10% subsurface irradiance) and the
lower limit (1% subsurface irradiance) of the euphotic zone,
are 56 and 112 m, respectively. In general, areas with the
clearest water support the richest and most expansive MCEs
in Hawaiʻi (Pyle etal. 2016a).
Depth proles of salinity and dissolved oxygen are fairly
constant across mesophotic depths, whereas temperature
decreases variably with increasing depth (Pyle etal. 2016a).
Bottom measurements showed salinity averaged 35.05 PSU
(std 0.05) and remained constant across the habitats at differ-
ent depths. Oxygen averaged 4.84mlL1 (std 0.09), increas-
ing a tenth of a degree over the depth range sampled, while
temperature declined from 24.9°C to 21.2°C with the mean
23.3 °C (std 1.0), matching the temperature of the 80 m
depth where the richest community of Leptoseris spp. corals
were found (Pyle etal. 2016a).
The variability in water temperature across mesophotic
depths is most apparent when viewed seasonally. Water tem-
perature collected between August 2008 and July 2009 on
moorings at mesophotic depths, shallow (53 and 64m), mid-
dle (73, 84, and 93m), and deep (102, 112, and 123m) in the
Au‘au Channel, ranged from ~21°C to ~26.5°C (Fig.25.3).
A seasonal cycle was apparent throughout the water column,
with warmest temperatures from September to November
and coolest temperatures from February to May (Fig.25.3).
The temperature was consistently 2–3°C cooler at the deep
end of the sampled depth range (102–123m), with less short-
term variability and seasonal uctuation. Relatively large
(1–2°C) short-term (1day) temperature excursions occurred
at 50–75m but remained stable at the deepest site. The tem-
perature at middle depths (70–90m), where Leptoseris spp.
corals were most abundant, was the most dynamic during the
25 The Hawaiian Archipelago
448
warmest months and the most thermally stable during the
coolest months. It is unclear whether MCEs are inuenced
by tidally correlated vertical thermocline shifts.
Acoustic proler analysis indicates that the current mag-
nitude at 70–90m is 10–15cms1 with sporadic, brief pulses
>25cms1 (Pyle etal. 2016a). A clear pulsing (strengthening
and weakening) corresponded with directional changes on a
tidal frequency. At greater depths (90–110m), the ow was
almost stagnant with little tidal signal and variable direction.
These results are in stark contrast to the higher magnitude
currents (>40cms1) that occur in shallow waters subject to
daily tidally forced ows. Although there are clear differ-
ences in ow rates within these MCEs, direction of ow is
highly variable and difcult to attribute to tidal- or wind-
driven processes.
25.3 Habitat Description
MCEs in the Hawaiian Archipelago are found mostly on
gradual slopes with occasional rocky outcrops of both volca-
nic and carbonate materials. However, Kane and Tissot
(2017) describe steep slopes in some areas on the island of
Hawaiʻi. Discontinuities in the slope are common at 50–60,
80–90, and 110–120m depths. Many of these features repre-
sent ancient shorelines of rocky undercut limestone ledges or
steep sandy or limestone slopes parallel to shore (Fletcher
and Sherman 1995; Grigg etal. 2002; Rooney etal. 2008).
Gradually sloping, at-bottom areas of carbonate are mostly
covered by sand, gravel, or rhodoliths with very little coral
cover. Corals are more common on exposed rock surfaces
along rock ledges and outcrops.
In the ‘Au‘au Channel, these discontinuities are the result
of karstication and the formation of solution basins during
a low sea-level stand (Fig. 25.2). Habitats in at-bottom
areas (i.e., between discontinuities) include macroalgal
meadows (especially in the 40–90m range) and expansive
low-relief beds of interlocking branching colonies or laminar
tiers of Montipora spp. (40–60m). The 80–90m discontinu-
ity within the ‘Au‘au Channel includes a few exposed, steep
rocky walls but is otherwise dominated by beds of Leptoseris
spp. coral and mixed macroalgal beds over gently sloping
substrate.
25.4 Biodiversity
25.4.1 Macroalgae
The low-light environment of MCEs requires obligate photo-
synthetic organisms, such as algae and zooxanthellate corals,
to be highly efcient at light capture and photosynthesis.
Surprisingly, mesophotic algae are often as productive as
shallow-water algae despite the low-light environment
(Jensen etal. 1985; Littler etal. 1985, 1986). Certain groups
of algae are well adapted to growth in MCEs in general, and
are conspicuous members of the deepwater algal assem-
blage, such as the green algal genera in the Bryopsidales
0 m
1
11
1
1
4
8
8
8
8
5
53
9
77
7
6
6
6
10
10
5
1
1
8
5
9
9
1
1. Coarse sand
3. Plate Montipora
4. Branched Montipora
2. Porites compressa
6. Leptoseris fields
7. Leptoseris yabei
8. Halimeda meadows
9. Microdictyon beds
5. Limestone Ledge
10. Silty-sand basin
2
2
2
2
2
2
25 m
50 m
75 m
100 m
125
m
Fig. 25.2 Generalized diagram of the major components of MCEs in the ‘Au‘au Channel, MHI. (Reprinted from Pyle etal. 2016a)
H. L. Spalding et al.
449
(e.g., Halimeda, Codium, Caulerpa, Udotea, and
Avrainvillea). These genera are all abundant within the
Hawaiian Archipelago and form dense beds and meadows
covering tens of km2 over both hard and soft substrates.
Macroalgal communities are found in discrete patches
(separated by sand or other benthic habitats) at all mesophotic
depths in the MHI and are further described in Spalding etal.
(2019). Examples include expansive meadows of Halimeda
kanaloana Vroom in sand; beds of Halimeda distorta
(Yamada) Hillis-Colinvaux over hard substrates, as well as
monospecic beds of Distromium spp., Dictyopteris spp.,
Microdictyon spp., Caulerpa spp.; and mixed assemblages of
other macroalgal species (Fig.25.4; Spalding 2012). Some
species assemblages are restricted to specic islands, such as
dense beds of the green alga Udotea sp. (currently unde-
scribed) and the invasive species Avrainvillea amadelpha
21
22
23
24
25
26
27
Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul
Daily average water temperature (°C)Daily water temperature SD
53 m
64 m
73 m
84 m
93 m
102 m
112 m
123 m
Water Depth
a
Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul
Date (August 2008 to July 2009)
b
Fig. 25.3 Temperature data, comparing seasonal and daily uctuations at eight different depths off the ‘Au‘au Channel from August 2008 to July
2009. Graphs represent the average daily temperature (a) and the daily standard deviation (SD) (b) at each depth. The thin black line below each
depth trace in (b) represents SD=0, and the thin black line above represents SD=1; the greater the distance of the color line from the black line
below (SD=0), the more dynamic the daily temperature. SD is based on n=72 temperature values per day for data recorded at 84 and 123m, and
n=36 for other depths. (Reprinted from Pyle etal. 2016a)
25 The Hawaiian Archipelago
450
(Montagne) A.Gepp and E.S.Gepp to 90m around the south-
ern and western sides of O‘ahu. In contrast, NWHI meso-
photic macroalgal communities are dominated by beds of
Microdictyon spp. The summits of eight banks from Lisianski
to Mokumanamana Island (Necker) were also observed,
using remotely operated vehicles (ROVs), to have dense beds
of Sargassum or Dictyopteris species (Parrish and Boland
2004; collections needed for verication).
In the MHI, 72 species of frondose macroalgae have been
identied based on morphological characteristics from
MCEs, including 29 Chlorophyta, 31 Rhodophyta, and 12
Phaeophyceae (Spalding 2012; Pyle etal. 2016a). Estimates
of macroalgal diversity are likely conservative because of the
taxonomic limitations inherent in some morphological iden-
tications of algae. For instance, large-bladed green algae
(“sea lettuce”) from MCEs were all identied morphologi-
cally as the shallow-water species “Ulva lactuca.” However,
recent molecular analyses revealed that these specimens rep-
resent four undescribed species belonging to the genera Ulva
and Umbraulva, which cannot be identied using morpho-
logical characters alone; three of these species are probably
endemic to Hawaiian MCEs (Spalding et al. 2016).
Nevertheless, the methods used to identify the 72 species
were similar to current taxonomic treatments in Hawaiʻi
(Abbott 1999; Abbott and Huisman 2003; Huisman et al.
2007) allowing for comparisons with the better-known
shallow- water ora across depths. Overall, the biodiversity
of macroalgae changes with increasing depth, with more
species found at 70–100m than at 40–60 m. The most dis-
tinctive changes in diversity (i.e., the most substantial
changes in total number of species at each depth interval)
occurred at 80–90 m and 110–120 m (Pyle et al. 2016a).
Although molecular methods are needed for further com-
parison between macroalgal communities on MCEs and
shallower reefs, ~45% of the species recorded thus far are
unique to MCE environments, based on morphology.
Fig. 25.4 Representative macroalgal communities in the Hawaiian Archipelago. (a) Microdictyon spp. bed at Pearl and Hermes Atoll, NWHI at
64m. (b) Halimeda kanaloana bed at 90m in the ‘Au‘Au Channel, West Maui, MHI. (c) Dark mounds of invasive Avrainvillea amadelpha beds off
O‘ahu, MHI at 50m depth. (d) Dense bed of Udotea sp. off south O‘ahu at 50m depth. (Photo credits: (a) PMNM (b, d) HURL, and (c) H.L.Spalding)
H. L. Spalding et al.
451
25.4.2 Anthozoans
The diversity of shallow anthozoan corals is well docu-
mented in Hawaiʻi. There are approximately 66 species of
shallow scleractinian coral species (Fenner 2005), 8 species
of antipatharians (< 150 m; Wagner 2015), and approxi-
mately 5 shallow species of octocorals (Fenner 2005)
recorded from Hawai‘i. Of these species, approximately 20
scleractinian species, all 8 antipatharian species, and 14
octocoral species are found within Hawai‘i’s MCEs
(Table25.1). Despite these species being documented from
MCEs, there has been no comprehensive systematic taxo-
nomic analysis of the anthozoan species across all meso-
photic depths, and hence the complete anthozoan diversity is
unknown. Further exploration and molecular genetic studies
will likely uncover more biodiversity in MCEs.
Across the Hawaiian Archipelago, there is higher coral
cover and well-developed reef habitats at deeper depths in
the MHI than NWHI (Rooney et al. 2010). In addition to
scleractinian corals, the eight antipatharian black coral spe-
cies representing six genera are found widely distributed
throughout the Hawaiian Archipelago but appear to be less
abundant in the NWHI (Wagner 2015; Table 25.1).
Gorgonians and soft corals are equally as sparse, with
increasing abundance and diversity at deeper depths.
However, the majority of MCEs of the NWHI have yet to be
explored, and additional diversity unique to the NWHI is
likely to be discovered.
MCEs in Hawaiʻi are often dominated by a few scleractin-
ian species occurring in distinct depth ranges (Table 25.1;
Fig.25.5). At depths of 30–60m, the dominant corals are also
commonly found on shallow reefs, including Montipora capi-
tata, Pocillopora meandrina, P. damicornis, P. eydouxi,
Pavona varians, Leptastrea purpurea, Porites compressa, and
Porites lobata (Rooney etal. 2010; Pyle etal. 2016a). Below
60 m, Leptoseris spp. form extensive reefs (Table 25.1;
Fig.25.5) with ~100% coral cover and high 3-D complexity in
some locations (Rooney etal. 2010; Pyle etal. 2016a). Other
Table 25.1 Scleractinian and antipatharian coral species in MCEs in Hawai‘i
Species 30–60m 60–100m 100–150m
Scleractinia
Leptastrea purpurea (Dana, 1846) 3
Leptoseris hawaiiensis Vaughan, 1907 3,6 6,7
Leptoseris incrustans (Quelch, 1886) 3
Leptoseris mycetoseroides Wells, 1954 3,6,12 3
Leptoseris papyracea (Dana, 1846) 12 3,6,7
Leptoseris scabra (Vaughan, 1907) 12 6,7 6
Leptoseris sp. 1 6,7 7
Leptoseris tubulifera Vaughan, 1907 6 3,6,7
Leptoseris yabei (Pillai & Scheer, 1976) 3,6,10
Montipora capitata (Dana, 1846) 3,10
Pavona sp. 1 6
Pavona varians Verrill, 1864 12 6
Pocillopora damicornis (Linnaeus, 1758) 3,10
Pocillopora grandis (=eydouxi) Dana, 1846 3
Pocillopora meandrina Dana 1846 3,10
Pocillopora molokensis Vaughan, 1907 12
Porites compressa Dana, 1846 3,12
Porites hawaiiensis Vaughan, 1907 2
Porites lobata Dana, 1846 3,10
Porites rus (Forskål, 1775) 12
Porties cf. studeri Vaughan, 1907 3,12
Antipatharia
Acanthopathes undulata (van Pesch, 1914) 8,9,11 11 8,9,11
Antipathes grandis (Verrill, 1928) 4,8,9,11 4,8,9,11 8,9,11
Antipathes griggi Opresko, 2009 8,9,11 8,9,11 9,11
Aphanipathes verticillata mauiensis Opresko etal., 2012 5,8,9,11 5,8,9,11
Cirrhipathes cf. anguina (Dana, 1846) 8,9,11 8,9,11 9
Myriopathes cf. ulex (Ellis and Solander, 1786) 8,9,11 8,9,11 8,9,11
Stichopathes echinulata Brook, 1889 8,9 8,9,11
Stichopathes? sp. 8,9,11 8,11
References: 1Fenner (2005), 2Forsman etal. (2010), 3Rooney etal. (2010), 4Wagner etal. (2010), 5Opresko et al. (2012), 6Luck et al. (2013),
7Pochon etal. (2015), 8Wagner (2015a), 9Wagner (2015b), 10Pyle etal. (2016a, b), 11Bo etal. (2019), 12A.D.Montgomery, unpublished data
25 The Hawaiian Archipelago
452
Fig. 25.5 Examples of MCE coral communities. (a) Upper MCE plating/encrusting Montipora assemblage at 50m. (b) Close-up of a plating M.
capitata. (c) Upper MCE branching Montipora assemblage at 57m (note the low rugosity habitat). (d) Close-up of a branching M. capitata. (e)
Lower MCE of monospecic aggregation of Leptoseris sp. at 75m. (f) Close-up of Leptoseris sp. (g) Lower MCE of monospecic aggregation of
L. yabei at 70m. (h) Close-up of L. yabei. (i) Transitional MCE of monospecic aggregation of Porites rus at 65m. (j) Close-up of P. rus. (Photo
credits: (ad; gj) A.D.Montgomery and (e, f) HURL)
H. L. Spalding et al.
453
species are present that are less common or absent in shallow
water (< 30m), such as Leptoseris mycetoseroides, L. papyra-
cea, L. tubulifera, L. scabra, and Porites cf. studeri. Recent
molecular work from 65 to 150m has unveiled six species of
Leptoseris, including an undescribed Leptoseris sp. 1 (Luck
et al. 2013; Pochon et al. 2015). Symbiodinium diversity in
these corals also shows depth zonation indicating niche spe-
cialization for host-Symbiodinium relationships, limiting
potential connectivity between depths (Pochon etal. 2015).
The antipatharian species have fairly broad depth ranges
(Antipathes griggi, A. grandis, and Myriopathes cf. ulex)
with some depth specialists (Stichopathes echinulata and
Acanthopathes undulata) (Wagner 2015). Typically, tropical
MCEs are dominated by gorgonian octocorals (Colin etal.
1986; Rowley 2014a, b; Sánchez et al. 2019). However,
Hawaiian MCEs are an exception possessing few or no gor-
gonians. The paucity of octocoral taxa on the shallow reefs
of Hawaiʻi compared to other regions has been well docu-
mented (Nutting 1908; Bayer 1952, 1956; Grigg and Bayer
1976; Cairns and Bayer 2008; Rowley 2014b). Yet, historic
expeditions, such as the US Fish Commission Steamer
Albatross (Nutting 1908; Bayer 1952, 1956), the “Sango
expedition” series (Grigg and Bayer 1976), and the submers-
ible Asherah (Brock and Chamberlain 1968; Strasburg etal.
1968), and recent submersible research with the HURL sub-
mersibles Pisces IV and V revealed the presence of gorgo-
nian taxa at lower MCEs throughout the Hawaiian
Archipelago (Table25.2). In particular, the Pleistocene ter-
races off west O‘ahu (at depths of 137 and 183 m) are
characterized by gorgonians within the family Coralliidae,
as well as stylasterids (Stylaster spp.) and antipatharians
(Strasburg et al. 1968). Thus in Hawaiʻi, the typical
gorgonian- dominated reefs of other tropical locations begin
to emerge at greater depths.
25.4.3 Sponges
Marine sponges are often dominant in MCEs, with both ben-
thic cover and diversity increasing with depth (up to tenfold)
in MCEs relative to shallow reefs in Palau and Chuuk
(Slattery and Lesser 2012), the Bahamas (Liddell etal. 1997;
Reed and Pomponi 1997), and the Caribbean (Slattery and
Lesser 2012). Despite being important components of the
MCE community, sponges throughout the Hawaiian
Archipelago are not well-studied. For example, surveys
throughout the ‘Au‘au Channel either showed that sponges
exist in low densities growing cryptically under rocks
(Kahng and Kelley 2007) or did not occur in more than 407
linear km of seaoor habitat (Rooney etal. 2010). However,
the latter survey denoted that the cameras used were unable
to provide high-resolution images of cryptic organisms.
Evaluating marine sponge diversity in Hawai‘i’s MCEs is
compounded by taxonomic difculties. For example, sur-
veys of Kāne‘ohe Bay, one of the best-studied coral reef
ecosystems in the world (Hunter and Evans 1995; Bahr etal.
2015), have historically reported on the order of 25 species
of sponges (De Laubenfels 1950), but a recent survey com-
bining morphological and molecular approaches suggests
that number is grossly underestimated (J.Vicente, unpubl.
data). Thus, future efforts to characterize the sponge com-
munities must involve not only quantitative observations but
also sample collections for further molecular and taxonomic
evaluation.
Table 25.2 A list of gorgonian and other notable octocoral taxa recorded throughout the Hawaiian Archipelago at mesophotic depths
Family Species Depth range (m) Location
Nidaliidae Siphonogorgia collaris Nutting, 1908 108–145 NWHI
Chrysogorgiidae Chrysogorgia sp. Duchassaing & Michelotti, 1864 85–1050 HI
Isididae Lepidisis olapa Muzik, 1978 175–665 MHI
Primnoidae Callogorgia gilberti (Nutting, 1908) 106–960 HI
Primnoidae Callogorgia formosa Kükenthal, 1907 146–750 HI
Primnoidae Candidella helminthophora (Nutting, 1908) 85–1801 MHI
Primnoidae Thouarella biserialis (Nutting, 1908) 73–426 HI
Acanthogorgiidae Acanthogorgia sp. Gray, 1857 110 MHI
Acanthogorgiidae Cyclomuricea abellata Nutting, 1908 71–335 MHI
Keroeididae Keroeides mosaica Bayer, 1956 103–388 MHI
Plexauridae Bebryce brunnea (Nutting, 1908) 71–388 HI
Plexauridae Muriceides alba (Nutting, 1908) 56 MHI
Plexauridae Psammogorgia arbuscula (Verrill, 1866) 72 MHI
Coralliidae Pleurocorallium secundum (Dana, 1846) 116–463 MHI
Melithaeidae Melithaea (Acabaria) bicolor (Nutting, 1908) 6–429 HI
Clavulariidae Carijoa riisei (Duchassaing & Michelotti, 1860) 1–120 MHI
Indeterminate n=29 specimens 77–201 HI
For location, MHI Main Hawaiian Islands, NWHI Northwestern Hawaiian Islands, and HI Hawaiian Archipelago (both MHI and NWHI). Data
sources: see Sánchez etal. (2019) and references therein
25 The Hawaiian Archipelago
454
25.4.4 Fishes
The sh fauna of the Hawaiian Archipelago is perhaps the
most thoroughly documented in the tropical Pacic, with
relatively comprehensive inventories spanning more than a
century (Jordan and Evermann 1905; Mundy 2005; Randall
2007). Pyle etal. (2016a, b) provide the most recent sum-
mary of Hawaiian MCE shes. They are not ubiquitous, but
occur in a broad array of MCE habitats, including black coral
beds (Boland and Parrish 2005), Leptoseris beds within the
Au‘au Channel (Pyle et al. 2016a), macroalgal meadows
(Langston and Spalding 2017), and limestone ledges associ-
ated with ancient sea-level stands (Brock and Chamberlain
1968). Species diversity varies among and within habitats.
For example, observations by both divers and submersibles
in the ‘Au‘au Channel noted that some areas were almost
devoid of shes, whereas others harbored high levels of both
diversity and abundance (Pyle etal. 2016a).
Modern documentation of the mesophotic sh fauna of
the NWHI began in 1902, when the Steamer Albatross con-
ducted a series of dredge hauls and trawls (Gilbert 1903;
Snyder 1904). Between 1976 and 1981, exploratory shery
surveys were conducted on the NOAA Ship Townsend
Cromwell. These surveys recorded 263 species of sh,
including many from depths beyond the range of conven-
tional SCUBA (>30m; Uchida and Uchiyama 1986). Diver-
based surveys of NWHI MCEs began in 2004, with surveys
of sh assemblages on bank tops (Parrish and Boland 2004).
Most recently, mixed-gas diving using closed-circuit
rebreathers has produced quantitative documentation of
NWHI sh assemblages on MCEs (Kane et al. 2014;
Papastamatiou etal. 2015; Fukunaga et al. 2016, 2017a, b;
Kosaki etal. 2016) and a number of new species (Pyle and
Kosaki 2016; Pyle et al. 2016b). Visual diver surveys have
been supplemented with video bait stations to assess preda-
tor abundances along mesophotic depth gradients (Asher
etal. 2017a).
The remoteness of the Hawaiian Archipelago coupled
with its high volcanic islands and low carbonate atolls pro-
vides a variety of environments and opportunities for life to
settle and evolve. Endemism, therefore, is high within many
taxonomic groups including location, regional, and depth
specicity (e.g., Kosaki etal. 2016). Randall (2007) reported
612 total species of reef and shore shes occurring within the
Hawaiian Archipelago to depths of 200m. A quarter of these
species are endemic to Hawaiʻi (including Johnston Atoll),
representing one of the highest rates of reef and shore sh
endemism in the world. Pyle etal. (2016a, b) recorded 259
species on MCEs, representing 42% of all Hawaiian reef and
shore sh species. The proportion of endemic species on
MCEs is much greater than for shallow reefs, particularly in
the NWHI (Kane etal. 2014; Kosaki etal. 2016; Fig.25.6).
Only 17% of reef sh species found exclusively shallower
than 30m are Hawaiian endemics, whereas the rate of ende-
mism among reef shes found exclusively deeper than 30m
is 43%. The rate of endemism increases with depth, with
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Proportion of endemism by species
Mesophotic (40–100 m)
Shallow (1–30 m)
Hawai‘i
Maui Nui
Ni‘ihau
Nihoa
MMM
FFS
Gardner
Maro
Laysan
Lisianski
PHA
Midway
Kure
Fig. 25.6 Increase in sh endemism on MCEs across the Hawaiian Archipelago. MMM is Mokumanamana (Necker), FFS is French Frigate
Shoals, and PHA is Pearl and Hermes Atoll
H. L. Spalding et al.
455
44% endemism among shes restricted to depths greater
than 40m, 41% below 50m, 50% below 60m, and 51% for
shes found only deeper than 70m. This trend is limited to
shes inhabiting MCEs, as the rate of endemism among
shes deeper than 150m is only 14% (Mundy 2005).
The general pattern of depth stratication for shes in
Hawaiʻi reveals a broad overlap between shallow and meso-
photic reef habitats. Most (87%) of the sh species recorded
at depths greater than 30m also occur at shallower depths;
only 12% of shes recorded from MCEs are restricted to
MCEs. The most substantial faunal transitions in shes occur
in the ranges of 10–30m and 110–140m, with less substan-
tial transitions at 40–60m and 70–100m.
Despite the extensive documentation of shes in Hawaiʻi,
new species continue to be discovered, including a highly
conspicuous butterysh (Prognathodes basabei Pyle and
Kosaki 2016), two less-conspicuous species belonging to the
genera Scorpaenopsis Heckel 1839 and Suezichthys Smith
1958, and the basslet Tosanoides obama Pyle, Greene, and
Kosaki 2016 (Pyle etal. 2016b).
Near the center of the Hawaiian Archipelago,
Mokumanamana Island (23°34 N) lies almost directly on
the Tropic of Cancer. The eight remaining reefs of the NWHI
lying north of Mokumanamana are thus technically subtropical.
The composition of shallow-reef sh assemblages changes
along this gradient (Friedlander etal. 2009), with levels of
endemism increasing with latitude (Fig. 25.6). Recent
research has focused on determining whether this pattern
also exists for Hawaiian mesophotic sh assemblages.
When compared with shallow Hawaiian reef sh assem-
blages, mesophotic sh assemblages are characterized by
lower abundances of herbivores and are numerically domi-
nated by omnivorous invertivores and planktivores (Fukunaga
etal. 2016; Kane and Tissot 2017). In the NWHI, MCE sh
assemblages exhibit greater numerical dominance by
Hawaiian endemics (Fig.25.6; Kane etal. 2014; Fukunaga
etal. 2017a, b). Up to 100% endemism has been recorded in
sh assemblages at 90–100 m at Kure Atoll (Kane et al.
2014; Kosaki etal. 2016).
Tropical submergence (sensu Lowe-McConnell 1987),
whereby subtropical or temperate species are found at greater
depths at warmer tropical latitudes, may be one of the pri-
mary factors shaping the differences between mesophotic
sh assemblages of the MHI and NWHI.Many species of
shes that are found deep in the MHI are found at shallower
depths in the NWHI. For example, the butterysh
Prognathodes basabei was originally observed from a sub-
mersible at depths up to 187m in the MHI (Pyle and Chave
1994) but was not described until specimens were regularly
encountered and collected at 55–60 m in the NWHI (Pyle
and Kosaki 2016). Similarly, the angelsh Genicanthus per-
sonatus Randall, 1975 is found in the MHI at depths as great
as 175m (Randall 2007) but is routinely observed at 20m or
less in the NWHI.Several other shes in the MHI, including
the damselsh Chromis struhsakeri Randall and Swerdloff,
1973 and the wrasse Bodianus bathycapros Gomon 2006,
have been observed from submersibles at depths of up to
219 m or collected via hook and line at 302 m (Randall
2007), but had never been recorded in the NWHI until diver
surveys were conducted at 90–100 m at the northernmost
atolls, Midway and Kure Atolls (Kosaki etal. 2016). The ser-
ranids Caprodon unicolor Katayama 1975 and Epinephelus
quernus Seale 1901 are rarely observed at less than 100m in
the MHI but are frequently encountered at shallower depths
in the NWHI (Kosaki etal. 2016).
The MCEs of northwestern atolls in the NWHI (Pearl and
Hermes, Midway, and Kure Atolls) harbor several species of
shes that are not found in the MHI and which exhibit close
afnities to southern Japan. The Japanese pygmy angelsh,
Centropyge interrupta (Tanaka, 1918), is known only from
these northern atolls and southern Japan (Ralston 1981;
Mundy 2005). A recently described basslet, Tosanoides
obama, collected from 90m at Pearl and Hermes and Kure
Atolls, is most similar to two congeners found in southern
Japan (Pyle etal. 2016a).
The extent to which sh populations among geographi-
cally separated MCEs are connected, and the degree to
which subpopulations on MCEs are connected to adjacent
shallow coral reefs, is largely unknown. Increasing evidence
suggests that upper MCEs are largely an extension of shal-
low coral reef habitat; many of the organisms that occur on
Hawaiian MCEs are abundant on shallow reefs (Pyle etal.
2016a; Kahng etal. 2017). The Hawaiian endemic threespot
Chromis verater Jordan and Metz 1912 has a single continu-
ous population across shallow reefs and adjacent MCEs in
the Hawaiian Archipelago (Tenggardjaja etal. 2014). Toonen
et al. (2011) summarized population genetic data from 27
taxa (including shes and invertebrates) across the archipel-
ago and concluded that the marine fauna shares at least four
signicant barriers to dispersal (Fig.25.7). Although speci-
mens were collected on shallow reefs, at least half of the taxa
have distributions extending into MCEs. These ndings rein-
force the conclusion that population processes within MCEs
(such as uctuations in recruitment or population size) are
similar or identical to the processes on shallow reefs.
Analyses of three deep-dwelling species of snapper (genera
Etelis Cuvier in Cuvier & Valenciennes 1828 and
Pristipomoides Bleeker 1852), which occur within MCEs
and at greater depths, revealed high connectivity across the
archipelago (Gaither etal. 2011; Andrews etal. 2014). All of
these species show patterns of genetic diversity that are typi-
cal of shallow-reef shes, indicating that shes on MCEs are
not fundamentally different in terms of population history.
The preliminary conclusion from these studies is that
mesophotic shes show high connectivity with adjacent
shallow-reef cohorts, with geographic population structure
(in at least some cases) typical of shallow-reef species.
Fishes that occur both within MCEs and deeper habitats
25 The Hawaiian Archipelago
456
are highly dispersive. However, the study of connectivity
within and among MCEs is in its infancy. Due to the dif-
culties of acquiring sufcient sample sizes at mesophotic
depths, it may be years before robust patterns start to
emerge.
25.4.5 Other Biotic Components
Over 8000 currently described invertebrate species inhabit
the reefs of Hawaiʻi, but knowledge of species diversity
decreases with both body size and depth (Fautin etal. 2010).
Endemism among the shallow-water Hawaiian biota is the
highest of any tropical marine ecosystem on earth (Fautin
et al. 2010), but systematic surveys of MCE invertebrates
(other than corals) are lacking. The most detailed compari-
son of invertebrate fauna between shallow-water reefs and
MCEs in the archipelago used Autonomous Reef Monitoring
Structures (ARMS; Zimmerman and Martin 2004; Leray and
Knowlton 2015) to sample brachyuran crab communities
across a depth gradient (12, 30, 60, and 90 m) off O‘ahu.
Based on 69 morphospecies (16 families) of brachyurans
sampled via ARMS, species were highly stratied with 4–27
unique species per depth, and only ~4% of species occurring
across the entire depth range (Hurley etal. 2016). Brachyuran
communities at 30 and 60m were least dissimilar from one
another, and mesophotic depths were found to host signi-
cantly different communities at much lower total abundance
than shallow-reef communities (Hurley et al. 2016). This
stratication provides a marked contrast to the high connec-
tivity in reef shes.
25.5 Ecology
25.5.1 Macroalgae
Mesophotic macroalgal assemblages across the archipelago
are abundant, diverse, and spatially heterogeneous with com-
plex distributional patterns (Kahng and Kelley 2007; Rooney
etal. 2010; Spalding 2012). Understanding the specic eco-
logical roles of macroalgal meadows and beds in Hawaiʻi is
of importance to resource managers interested in the popula-
tion dynamics of keystone species and related organisms
inhabiting coral reefs. Although macroalgal communities
generally do not comprise major habitats for large-bodied
shes in the MHI (either on MCEs or shallow reefs), endemic
reef-associated shes were found in macroalgal (Microdictyon
spp.) beds at mesophotic depths in the NWHI (Kane etal.
2014). Cryptic shes also inhabit mesophotic algal beds
(Langston and Spalding 2017), and larger, predatory sh
such as jacks (Carangidae) have been observed foraging in
these algal beds in the MHI (Spalding 2012). Additional
studies are needed on MCEs in adjacent areas with and with-
out dense macroalgal beds or meadows to further rene the
potential role of macroalgae as mesophotic habitat for reef
shes in both the MHI and NWHI.Special attention should
be given to the morphology and species of the alga involved;
Fig. 25.7 Map of the Hawaiian Archipelago with signicant genetic breaks among 27 taxa represented as red bars between islands. For each bar,
the number of species exhibiting evidence of restricted gene ow is listed in the numerator, and the number of species with data across that geo-
graphic area is listed in the denominator. At least half of these taxa have ranges that extend into MCEs. The broad red bars at Pearl and Hermes
Atoll, and at Necker/Nihoa, indicate uncertainty about the precise location of the barrier. (Modied from Toonen etal. 2011)
H. L. Spalding et al.
457
morphological complexity (i.e., prostrate blades [e.g.,
Udotea sp.] versus upright branches [e.g., Halimeda kanalo-
ana] versus net-like attened fronds [e.g., Microdictyon
spp.]) likely inuences the quality of sh habitat. Holdfast
morphology, depth of holdfast penetration, and density
should also be considered in terms of their inuence on sedi-
ment geochemistry (Sansone etal. 2017) and the resulting
infaunal community (Fukunaga 2008).
Less is known about the role of macroalgal communities
in relation to other taxa in Hawaiʻi, such as competitive inter-
actions with coral or as habitat for other invertebrates.
Studies in deep subtidal Halimeda kanaloana meadows (to
30m depth) indicate that a variety of epibenthic and epifau-
nal invertebrates use these meadows for habitat (Fukunaga
2008). Infaunal polychaete abundances, species richness,
and diversity were higher inside the meadows than in adja-
cent unvegetated areas. The abundance of epibenthic organ-
isms were greater at deeper stations with higher densities of
plants (Fukunaga 2008), indicating that dense macroalgal
populations associated with MCEs may also host a diverse
and abundant community of invertebrates relative to unveg-
etated habitats. Macroalgae in MCEs also contain a rich
community of fungi, with 27% species overlap with Hawaiian
terrestrial ecosystems (Wainwright etal. 2017). Based on the
four genera of mesophotic algae studied, the host species had
signicantly different fungal community composition, sug-
gesting a much higher diversity of fungi may be present in
MCEs as additional host species are considered (Wainwright
et al. 2017). However, the exact nature of the algal/fungal
interactions on MCEs remains unknown.
25.5.2 Anthozoans
The distribution of coral assemblages on MCEs within the
archipelago is patchy and often consists of monospecic
coral aggregations with a few cryptic species. Little is
known about the ecology of corals on MCEs in the NWHI
given their infrequent occurrence in that region. Species
assemblages in the MHI have vertical zonation (Kahng and
Kelley 2007; Rooney et al. 2010), as well as horizontally
dispersed patchy distributions (Rooney etal. 2010). Rooney
etal. (2010) and Pyle etal. (2016a, b) reported three signi-
cant types of MCE communities: upper MCEs, branching/
plate coral MCEs, and Leptoseris MCEs (Table 25.1);
Kahng and Kelley (2007) described four distinct vertical
communities. Using a 40–150 m range for MCE habitat
(Hinderstein et al. 2010), the upper MCE is generally
accepted to be 40 to 60–70m, whereas the lower MCE hab-
itat is >60–70 m with a lower limit for scleractinians
between 130 and 150m (Kahng etal. 2010), although there
can be variability in the depth of transition from upper to
lower MCEs.
Within the upper mesophotic zone are four distinct MCE
coral communities (rening Rooney etal. 2010): (1) plating/
encrusting Montipora capitata, (2) mixed Porites species, (3)
branching M. capitata, and (4) shallow black corals
(Fig.25.5). The plating/encrusting M. capitata assemblage is
similar in species composition to shallow reefs but dominated
by plating or encrusting forms of M. capitata and is common
near the top of remnant paleo-shorelines. Mixed Porites spp.
assemblages are common near paleo-shorelines or hard-bot-
tom mounds and are very similar to shallow reefs dominated
by Porites spp. Branching Montipora assemblages are a mix-
ture of a unique nely branched form of M. capitata and mac-
roalgae (e.g., Distromium spp., Microdictyon spp., and
Caulerpa licoides), often found on at, unconsolidated sedi-
ment, where reef systems are generally not expected. There is
also a unique shallow black coral community dominated by
Antipathes griggi between 30 and 60m.
The lower mesophotic zone also has some distinct coral
assemblages and includes monospecic aggregations of
Leptoseris hawaiiensis, L. yabei, L. papyracea, or Porites
rus. These monospecic aggregations may also contain
cryptic species, but the community structure is clearly domi-
nated by a single species. The foliose, three-dimensional
colony structure of L. yabei is inhabited by sh communities.
The P. rus assemblage is a plate-forming coral community
similar to L. hawaiiensis, but P. rus is also a common shal-
low coral species. Additionally, there is a deep black coral
community dominated by A. grandis from 70 to >100m.
The physiological adaptations and mechanisms that allow
resident species to live in these low-light MCE environments
in Hawaiʻi remain largely unknown. Corals in the genus
Leptoseris, the most dominant group at 60–150m depth, are
photosynthetic, grow up to 1cmyear1 in situ (Pyle et al.
2016a), exhibit atter morphologies with increasing depth,
and possess skeletal structures that maximize light scatter
through the coral tissue (Kahng etal. 2012, 2014). How host-
Symbiodinium spp. associations inuence Leptoseris spp.
photophysiology is an important area for future investiga-
tions. The majority (~70%) of Leptoseris spp. colonies uo-
resce (Roth etal. 2015). Cyan uorescent proteins (CFP) are
dominant in shallower mesophotic corals (6585m), green
uorescent protein (GFP) are dominant in deeper corals
(96125m), and CFP and GFP are present in corals from
middle depths (8695 m). Symbiodinium spp. from corals
with and without uorescence emission have similar geno-
types, abundances, chlorophyll excitation spectra, and pho-
tosynthetic pigments, efciencies, and rates (Roth et al.
2015). Approximately 85% of the colonies have endolithic
algae; yet, their role remains unclear. Gametes in Leptoseris
spp. have not been observed, but sampling has been restricted
to a few months.
Sexual reproduction has been examined in Hawaiian
antipatharians (Wagner etal. 2011, 2012); all colonies have
25 The Hawaiian Archipelago
458
the characteristics of one sex only (gonochoric), and there is
no evidence of internal fertilization.
In the Hawaiian Archipelago, the diversity and abundance
of gorgonian corals (Table25.2) increase as temperature sta-
bilizes with increased depth (Brock and Chamberlain 1968;
Muzik 1979). Growing evidence reveals that the greatest
temperature variance and often higher nutrient levels occur
at mid-mesophotic depths (~90 m) on oceanic islands and
atolls (Hawaiʻi: Brock and Chamberlain 1968; Palau:
Wolanski etal. 2004; Colin 2001; Colin et al. 2017; Papua
New Guinea: Longenecker et al. 2019; Pohnpei: Rowley
et al. 2019). Such variance has been attributed to internal
waves exacerbated by decadal shifts (Colin etal. 2017). The
extent and source of such variance and the effects on MCE
benthic communities in the archipelago are unclear.
25.5.3 Fishes
The depth-related community structure of reef shes from
the archipelago generally conform to patterns observed
worldwide. Overall, sh abundance and herbivores decrease
with depth (Fukunaga etal. 2016; Asher etal. 2017a, b; Kane
and Tissot 2017), despite the presence of large macroalgal
meadows in MCEs (Pyle etal. 2016a; Langston and Spalding
2017). The most-abundant shes in Hawaiian MCEs are
planktivores and benthic-feeding invertivores (Fig. 25.8;
Brock and Chamberlain 1968; Parrish and Boland 2004;
Pyle et al. 2016a; Asher et al. 2017a, b; Fukunaga et al.
2017a, b; Kane and Tissot 2017).
Stable isotope analyses of the two dominant trophic
groups indicate higher trophic position for benthic-feeding
Fig. 25.8 Representative coral reef sh at 76m depth in a Leptoseris sp. reef in the ‘Au‘au Channel, West Maui. (Photo credit: HURL)
Table 25.3 Traits of mesophotic sh populations relative to shallow populations in the MHI
Species K L
Mean
LDensity L50
Annual biomass
production
Egg production
per m2Migration rate
Parupeneus multifasciatus (Quoy and Gaimard
1825)1
↓ ↓
Centropyge potteri (Jordan and Metz 1912)1 ↑ ↓
Chromis verater Jordan and Metz 1912 22 – – 3
Ctenochaetus strigosus (Bennett 1828)1 ↓ ↓
K growth coefcient, L length, L mean asymptotic length, L50 the length class in which 50% of females are expected to be mature
References: 1Pyle etal. (2016a, b), 2Winston etal. (2017), 3Tenggardjaja etal. (2014)
H. L. Spalding et al.
459
invertivores in MCEs relative to their shallow-water coun-
terparts, whereas planktivores use similar nutrient resources
and occupy similar trophic positions regardless of depth
(Bradley etal. 2016). These results suggest that plankton
are the base of the MCE food web (rather than primary
production by algae and phytoplankton as in shallow
waters) and that upwelling provides a source of nitrogen
(Bradley etal. 2016). In the NWHI, acoustic tagging and
stable isotope studies found that large apex predators such
as Galapagos sharks (Carcharhinus galapagensis) and
giant trevally (Caranx ignobilis) move regularly between
shallow reefs and MCEs, but isotopic proles indicate that
a majority of their foraging is on shallow reefs
(Papastamatiou etal. 2015). Thus, these predators may be
signicant transporters of nutrients and energy from shal-
low reefs to MCEs.
Several shes occurring in both shallow reefs and MCEs
in the Hawaiian Islands have been the subjects of detailed
life history and size-structure analyses. Although individual
life history traits vary by species (Table 25.3), biomass and
egg production were lower on MCEs typically by an order of
magnitude (Pyle etal. 2016a). The single genetic analysis of
Chromis verater available indicated high levels of connectiv-
ity between shallow reefs and MCEs, but the mean number
of migrants per generation was estimated to be higher from
shallow to deep reefs than in the reverse direction
(Tenggardjaja etal. 2014).
The introduced, invasive blue-lined snapper (Lutjanus
kasmira) is abundant on shallow reefs throughout the archi-
pelago (Gaither etal. 2010). It has not been detected between
50 and 100m in the northern half of the Hawaiian Islands up
to French Frigate Shoals (Fukunaga etal. 2017a, b). Thus,
the northernmost MCEs of the archipelago may represent an
ecosystem where native species can thrive in the absence of
invasive species.
25.5.4 Other Biotic Components
High densities of the spiny lobster Panulirus marginata Quoy
and Gaimard, 1825, were found at over 140m depth, as well
as large beds (extending up to 1500m in diameter) of the
Pinnidae bivalves Pinna muricata (Fig. 25.9; Linnaeus
1758), perhaps due to elevated nutrients (Brock and
Chamberlain 1968). Even though such P. muricata beds were
believed to have been decimated during hurricanes Iwa
(1982) and Iniki (1992) at shallow depths, recent observa-
tions reveal extensive beds below 60m depth off south Kauaʻi
(Fig. 25.9) and near Penguin Banks offshore Molokaʻi at
similar depths. Furthermore, beds of what appears to be the
invasive hydrozoan Pennaria populate hard substratum up to
107m. Increased exploration and research would further sub-
stantiate such observations and biological interactions at
depths below 100m throughout the Hawaiian Archipelago.
Fig. 25.9 Pinna muricata Linnaeus, 1758 beds at 60–65m on the south coast of Kauaʻi. (Photo credit: S.J.Rowley)
25 The Hawaiian Archipelago
460
25.6 Threats andConservation Issues
A thorough understanding of the human-mediated impacts
on MCEs is urgently needed, and biodiversity studies are a
necessary prerequisite. Cryptic species continue to emerge in
Hawaiʻi, even in well-studied groups, and this trend has
accelerated with genetic surveys (Bowen 2016; Spalding
etal. 2016). The protection status of MCEs in the archipel-
ago is geographically limited except for MCEs within the
PMNM. Within the MHI, the only MCE habitat fully
protected is the Molokini Marine Life Conservation District
(MLCD) (Fig. 25.1d) and the Old Kona Airport MLCD
(Fig.25.1b).
The State of Hawai‘i’s coral reef management priorities
(2010–2020) for the MHI (State of Hawaiʻi 2010) identies
threats to coral reefs including shing pressure, recreational
overuse, land-based sources of pollution, invasive species,
climate change, and lack of awareness. Another more acute
threat is from ocean development projects such as alternative
energy infrastructure and associated cables. The gap between
scientic understanding and conservation planning has
spurred investigations for impact avoidance including pre-
dictive modeling of MCE distributions (Costa etal. 2015;
Bauer etal. 2016; Veazey etal. 2016).
While all of these threats apply to MCEs, they may
affect MCEs differently than shallow coral reefs. Fishing
pressure has not been considered a major threat to MCEs in
Hawaiʻi; however, some MCE species such as black coral,
aquarium shes, and bottomshes are targeted at meso-
photic depths. Ancillary effects of shing activities (anchor-
ing, derelict gear, or line entanglement) may pose a risk to
MCEs, but this has not been documented. Recreational
activities have begun to move deeper with advances in div-
ing technology (Parrish and Pyle 2002), but the scale of
these activities is signicantly smaller compared to shallow
coral reefs.
Land-based sources of pollution, such as sedimentation,
may represent one of the most signicant threats to the
MCEs in the MHI. Given that MCEs are characterized by
low-light levels, any decrease in water clarity may have
severe impacts to these communities (Pyle et al. 2016a).
Although there are no documented or observed impacts from
land-based sources of pollution in Hawaiʻi, this may largely
be a result of the distance from shore for most of Hawai‘i’s
MCEs, which are generally far from shore.
Invasive species impacts on coral reefs are well doc-
umented in Hawaiʻi with the majority of these impacts
focusing on introduced, invasive macroalgae in shallow
water. Two introduced species have been documented on
MCEs, the macroalga Avrainvillea amadelpha (Fig.25.4c;
Peyton 2009; Spalding 2012), and the octocoral, Carijoa
sp. (Grigg 2004). However, the signicance or long-term
impact of these two species remains uncertain.
Climate change-related effects such as increased tempera-
ture are poorly understood on Hawaiian MCEs. While MCEs
are often thought to be insulated from increased temperature
anomalies in shallow water due to their lower temperatures,
deep (>90m) MCEs may potentially be more susceptible to
increased temperatures due to their lack of exposure to high
temperature uctuations (Pyle etal. 2016a). The resiliency
of MCEs is a signicant research gap in understanding the
role MCEs play in Hawai‘i’s broader coral reef ecosystem.
Alternatively, MCEs have widely been suggested to serve as
refugia for shallow reefs. Pyle etal. (2016a, b) provided an
in-depth review of the potential for MCEs as refugia in
Hawaiʻi but concluded that the role of any potential refugia
should be assessed on a case-by-case basis and cautioned
that MCEs could be more at risk than shallower reefs.
Acknowledgments Funding and support from the NOAA National
Centers for Coastal Ocean Science (NA07NOS4780188,
NA07NOS4780187, NA07NOS478190, NA07NOS4780189), NOAA
Coral Reef Conservation Program (NA05OAR4301108,
NA09OAR4300219, HC07-11, HC08-06), NOAA’s Deep Sea Coral
Research and Technology Program, NOAA Ofce of National Marine
Sanctuaries (Papahānaumokuākea Marine National Monument), NOAA
Undersea Research Program’s Hawaiʻi Undersea Research Laboratory,
NOAA’s Ofce of Ocean Exploration and Research, National Fish and
Wildlife Foundation and the Benioff family, National Science
Foundation (DEB-1754117), State of Hawaiʻi Division of Aquatic
Resources, Hawaiʻi Coral Reef Initiative, and Dingell-Johnson Sportsh
Restoration program. We also appreciate the assistance of the ofcers
and crew of NOAA Ship Hiialakai, R/V Kaimikai-O- Kanaloa, Jason
Leonard, Brian Hauk, Keo Lopes, Kelly Gleason, Atsuko Fukunaga,
Hadley Owen, Greg McFall, and Matt Ross. This manuscript was greatly
improved by reviews from Kimberly Puglise, Yannis Papastamatiou,
Eran Brokovich, Kevin Weng, and two anonymous reviewers.
Disclaimer The scientic results and conclusions, as well as any
views or opinions expressed herein, are those of the author(s) and do
not necessarily reect the views of NOAA, the Department of
Commerce, or the US Fish and Wildlife Service.
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... The range in anthropogenic impact from the nearly pristine Northwestern Hawaiian Islands to the more heavily populated (> 1.4 million people) (https://www.populationu.com/us/hawaii-population) Main Hawaiian Islands creates a gradient for examining nitrogen dynamics in macroalgal-dominated systems (Vroom and Braun 2010;Jouffray et al. 2015;Spalding et al. 2019b) across multiple scales of depth, island/atoll, and region. Effective coral reef conservation requires establishing baselines across gradients of human impact, particularly regarding the impact of pollution and overfishing (Sandin et al. 2008). ...
... The Main Hawaiian Islands coastal reefs have a high abundance of gently sloping hard and soft-bottom habitats at mesophotic depths, while the Northwestern Hawaiian Islands reefs have steeper terrain (Rooney et al. 2010;Pyle et al. 2016;Spalding et al. 2019b). Macroalgal, coral, and fish composition within mesophotic coral ecosystems varies with depth and between the Main Hawaiian Islands and Northwestern Hawaiian Islands (Spalding et al. 2019b). ...
... The Main Hawaiian Islands coastal reefs have a high abundance of gently sloping hard and soft-bottom habitats at mesophotic depths, while the Northwestern Hawaiian Islands reefs have steeper terrain (Rooney et al. 2010;Pyle et al. 2016;Spalding et al. 2019b). Macroalgal, coral, and fish composition within mesophotic coral ecosystems varies with depth and between the Main Hawaiian Islands and Northwestern Hawaiian Islands (Spalding et al. 2019b). At 30-50 m depths, large beds of the green alga, Microdictyon setchellianum, and brown macroalgae (Dictyopteris sp. or Sargassum sp.) are present in the Northwestern Hawaiian Islands (Parrish and Boland 2004). ...
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The Hawaiian Archipelago stretches 2500 km from the Main to the Northwestern Hawaiian Islands, represents a complex gradient of oceanographic and anthropogenic drivers, and has a high abundance and diversity of native and invasive macroalgae. These photosynthetic organisms occur in intertidal to mesophotic (30–150+ m) depths and absorb nitrogen with limited fractionation associated with their physiology and source. Our goal was to examine nitrogen dynamics from shallow to mesophotic reefs using compositional patterns of two well‐characterized macroalgal tissue parameters: stable isotope ratio of nitrogen and tissue nitrogen content. We collected 813 macroalgal samples from 13 islands/atolls between 0 and 117 m depths. Within the Main Hawaiian Islands, macroalgal tissue stable N isotope ratios were higher in mesophotic depths; N content was higher in shallow depths. However, within the Northwestern Hawaiian Islands, no differences in stable N isotope ratios and N content were found between shallow and mesophotic depths. Regionally, stable N isotope ratios varied along a gradient of anthropogenic and oceanographic processes (in Main and Northwestern Hawaiian Islands, respectively), while N content reflected elevated nitrogen in the Main compared with the Northwestern Hawaiian Islands. Additionally, the invasive macroalga Avrainvillea lacerata had significantly higher N content than co‐occurring native bryopsidalean macroalgae at similar depths, and may be reshaping nutrient dynamics from shallow to mesophotic depths in the Main Hawaiian Islands. Nitrogen dynamics at mesophotic depths may be influenced by nearshore anthropogenically derived nitrogen via submarine groundwater discharge and/or inputs from deeper water within the Main Hawaiian Islands.
... Beyond coral species, the marine habitat of the Hawaiian Archipelago displays some of the highest levels of endemism worldwide, including mesophotic coral ecosystems, with 100% of fish species from deep coral reefs in the northwestern islands reported to be endemic (Kosaki et al. 2017). Endemic seaweeds (e.g., species of Ulva and Umbraulva) and sponges, of which many of the latter remain to be characterized, have also been identified in this region (Spalding et al. 2019). The terrestrial flora and fauna in the Archipelago are well-studied and given the massive radiation of taxa such as Hawaiian honeycreepers, spiders, and the "silversword alliance," a broader and more sustained evolutionary response to isolation has occurred on land (Simon 1987;Olson 2004;Patton et al. 2021). ...
... The Hawaiian chain ranges in age from 0.4 million years (Ma) for the Big Island of Hawaiʻi to 3.7 Ma for O'ahu to 5.1 million years for Kaua'i (Clague and Dalrymple 1987) (Fig. 1a). Recurrent dispersal and extinction events recorded in the fossil history of Hawaiian marine fauna (Jokiel 1987;Kay and Palumbi 1987;Spalding et al. 2019) provide an ideal testbed to ask questions about how isolation and disturbance breed innovation. It is, for example, possible that the closely related morphotypes observed in extant Montipora (e.g., Fig. 1c) and in Porites species, and other coral taxa in Hawaiʻi (Baums et al. 2012;Concepcion et al. 2014) would potentially be the "seed" for future endemics in isolated environments that did not face repeated gain and loss of habitat as is the case for the Hawaiian island chain. ...
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Degradation and loss of coral reefs due to climate change and other anthropogenic stressors has fueled genomics, proteomics, and genetics research to investigate coral stress response pathways and to identify resilient species, genotypes, and populations to restore these biodiverse ecosystems. Much of the research and conservation effort has understandably focused on the most taxonomically rich regions, such as the Great Barrier Reef in Australia and the Coral Triangle in the western Pacific. These ecosystems are analogous to tropical rainforests that also house enormous biodiversity and complex biotic interactions among different trophic levels. An alternative model ecosystem for studying coral reef biology is the relatively species poor but abundant coral reefs in the Hawaiian Archipelago that exist at the northern edge of the Indo‐Pacific coral distribution. The Hawaiian Islands are the world's most isolated archipelago, geographically isolated from other Pacific reef systems. This region houses about 80 species of scleractinian corals in three dominant genera (Porites, Montipora, and Pocillopora). Here we briefly review knowledge about the Hawaiian coral fauna with a focus on our model species, the rice coral Montipora capitata. We suggest that this simpler, relatively isolated reef system provides an ideal platform for advancing coral biology and conservation using multi‐omics and genetic tools.
... Although mode of attachment of blades was not identified, parts of blades were found entwined with species of mounding, prostrate species of Halimeda J.V. Lamouroux, which are abundant in the 'Au'Au Channel, Maui (see Spalding et al. 2019, fig. 29.1b). ...
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Recent investigations into the species diversity of red blades in Hawai‘i have yielded several specimens of Kallymeniaceae from Hawaiian Mesophotic Coral Ecosystems. Our combined morphological and mitochondrial COI-5P and plastid rbcL phylogenetic analyses indicated widespread cryptic diversity among those specimens commonly identified as Kallymenia sensu lato based on morphology. These analyses resolved four unique genetic lineages of Hawaiian taxa in the genus Croisettea, which are all restricted to the lower mesophotic depths (c. 60–150 m). Croisettea currently includes three described species distributed in the North Atlantic, Indian and South Pacific Oceans, and the Mediterranean Sea. Croisettea is a new genus record for the Hawaiian Islands, expanding its biogeographic range to the North Pacific. The genus has now been enlarged to include seven species comprising previously described taxa as well as four new Hawaiian taxa (C. kalaukapuae sp. nov., C. haukoaweo sp. nov., C. ohelouliuli sp. nov. and C. pakualapa sp. nov.). The known distributions of the Hawaiian Croisettea species are restricted to areas around their type localities. Although this pattern hints at a remarkable degree of endemicity, both across depth gradients in a reef area and among islands, it is also linked to a limited sampling of the group, suggesting that additional species, and more accurate distributional ranges, remain to be detected not only in Hawai‘i but also worldwide.
... In Hawai'i, MCEs have recently been described within select geographic regions in association with specific bathymetric habitat features (e.g., banks, ledges) or benthic cover (e.g., algal meadows, high coral cover) (Rooney et al., 2010;Blythe-Skyrme et al., 2013;Pyle et al., 2016). Many studies have investigated various aspects of MCE benthic habitats in the main Hawaiian Islands including coral beds, algal meadows, coral physiology, fish life histories, and fish trophic ecology (Boland and Parrish, 2005;Kahng and Kelley, 2007;Rooney et al., 2010;Blythe-Skyrme et al., 2013;Costa et al., 2015;Pochon et al., 2015;Bradley et al., 2016;Pyle et al., 2016;Spalding et al., 2016;Asher et al., 2017;Weijerman et al., 2019), with the number and spatial extent of surveys increasing in recent years (2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016)(2017)(2018) (Spalding et al., 2019). Much less is known of MCEs in the Northwestern Hawaiian Islands (NWHI) as a result of the additional logistical constraints of research at these distant locations. ...
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Mesophotic reefs (30–150 m) occur in the tropics and subtropics at depths beyond most scientific diving, thereby making conventional surveys challenging. Towed cameras, submersibles, and mixed-gas divers were used to survey the mesophotic reef fish assemblages and benthic substrates of the Au‘au Channel, between the Hawaiian Islands of Maui and Lāna‘i. Non-parametric multivariate analysis: Non-metric Multidimensional Scaling (NMDS), Hierarchical Cluster Analysis (HCA), Multi-Response Permutation Procedure (MRPP), and Indicator Species Analysis (ISA) were used to determine the association of mesophotic reef fish species with benthic substrates and depth. Between 53 and 115-m depths, 82 species and 10 genera of fish were observed together with 10 types of benthic substrate. Eight species of fish ( Apolemichthys arcuatus , Centropyge potteri, Chaetodon kleinii, Chromis leucura, Chromis verater, Forcipiger sp., Naso hexacanthus , and Parupeneus multifasciatus ) were positively associated with increasing depth, Leptoseris sp. coral cover, and hard-bottom cover, and one species ( Oxycheilinus bimaculatus ) of fish was positively associated with increasing Halimeda sp. algae cover. Fish assemblages associated with rubble were not significantly different from those associated with sand, Montipora coral beds and Leptoseris coral beds, but were distinct from fish assemblages associated with hard bottom. The patterns in the data suggested two depth assemblages, one “upper mesophotic” between 53 and 95 m and the other deeper, possibly part of a “lower mesophotic” assemblage between 96 and 115 m at the edge of the rariphotic and bottomfish complex.
... The similarity of alpha diversity is further supported by the high level of species overlap between MCE and SCR sites (84% of MCE species). The level of overlap is not unexpected since the upper MCE was targeted for this study based on previous studies that show the upper MCE to be a subset of SCR communities14,20,[40][41][42][43][44][45] . ...
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The deep reef refuge hypothesis (DRRH) postulates that mesophotic coral ecosystems (MCEs) may provide a refuge for shallow coral reefs (SCRs). Understanding this process is an important conservation tool given increasing threats to coral reefs. To establish a better framework to analyze the DRRH, we analyzed stony coral communities in American Sāmoa across MCEs and SCRs to describe the community similarity and species overlap to test the foundational assumption of the DRRH. We suggest a different approach to determine species as depth specialists or generalists that changes the conceptual role of MCEs and emphasizes their importance in conservation planning regardless of their role as a refuge or not. This further encourages a reconsideration of a broader framework for the DRRH. We found 12 species of corals exclusively on MCEs and 183 exclusively on SCRs with another 63 species overlapping between depth zones. Of these, 19 appear to have the greatest potential to serve as reseeding species. Two additional species are listed under the U.S. Endangered Species Act, Acropora speciosa and Fimbriaphyllia paradivisa categorized as an occasional deep specialist and a deep exclusive species, respectively. Based on the community distinctiveness and minimal species overlap of SCR and MCE communities, we propose a broader framework by evaluating species overlap across coral reef habitats. This provides an opportunity to consider the opposite of the DRRH where SCRs support MCEs.
... Nonetheless, the occurrence of Leptoseris species, and particularly L. glabra, is restricted to mesophotic depths. Leptoseris species are key members of the mesophotic reefs, not only in the Red Sea , but also in other regions worldwide, e.g., Hawaii (Spalding et al., 2019) and Australia (Englebert et al., 2017). A combination of the unique environmental adaptations (Fricke et al., 1987;Kahng et al., 2012), the lack of suitable competitors, and a larger potential habitat availability for settlement (MCEs comprise˜80% of coral reef habitats (Pyle and Copus, 2019;Kramer et al., 2019), may allow Leptoseris spp. to thrive in mesophotic depths and significantly contribute to its high abundance and coral living coverage. ...
Article
Full-text available
Population size structure provides information on demographic characteristics, such as growth and decline, enabling post-hoc assessment of spatial differences in susceptibility to disturbance. Nevertheless, very few studies have quantified size data of scleractinian corals along a shallow-mesophotic gradient, partly because of previously inaccessible depths. Here, we report the coral size-frequency distributions at the morphology level (six growth forms) and at the species level for ten representative locally abundant species along a broad depth gradient (5-100 m) in the Gulf of Eilat/Aqaba (GoE/A). A total of 18,865 colonies belonging to 14 families and 45 genera were recorded and measured over four reef sites. Colonies were found to be 11.2% more abundant at mesophotic (40-100 m; 55.6%) depths compared with shallow (5-30 m; 44.4%). The coral taxa exhibited heterogeneity in their size-structure, with marked differences among depths, morphological growth forms, and species. Branching and corymbose corals were more prevalent in shallow waters, while encrusting and laminar forms comprised the majority of mesophotic corals. Nevertheless, massive morphology was the most abundant growth form across all sites and depths (39%), followed by laminar (26%) and encrusting (20%). Corymbose corals (primarily Acroporidae) revealed constrained size at all depths; with the lack of small-size groups indicating populations at risk of decline. Depth-generalist species belonging to massive and laminar morphologies generally exhibited a larger colony size at the mesophotic depths, but were typified by a higher number of small colonies. Furthermore, we refute the widely and long-accepted assertion that Stylophora pistillata is the most abundant coral in the northern GoE/A, and assert that Leptoseris glabra is the one. Here, we provide a baseline for future monitoring of coral population structures, insights to recent ecological dynamics, retrospective assessment of coral community recovery following disturbances and grounds for conservation assessments and management actions.
... While shallow coral reef corals are relatively well described, mesophotic corals are poorly described in American Sāmoa. The maximum reported depth of a zooxanthellate coral is 165 m at Johnston Atoll (Kahng and Maragos 2006), and 19 of 66 coral species were reported from mesophotic depths in the Hawaiian Archipelgo (Spalding et al. 2019). Of the 51 reviewed studies that report corals from American Sāmoa, only four have reported corals from mesophotic depths (Hoffmeister 1925;Lamberts 1983;Bare et al. 2010;Montgomery et al. 2019). ...
Article
Full-text available
An annotated checklist of the stony corals (Scleractinia, Milleporidae, Stylasteridae, and Helioporidae) of American Sāmoa is presented. A total of 377 valid species has been reported from American Sāmoa with 342 species considered either present (251) or possibly present (91). Of these 342 species, 66 have a recorded geographical range extension and 90 have been reported from mesophotic depths (30-150 m). Additionally, four new species records (Acanthastreasubechinata Veron, 2000, Favitesparaflexuosus Veron, 2000, Echinophylliaechinoporoides Veron & Pichon, 1980, Turbinariairregularis Bernard, 1896) are presented. Coral species of concern include species listed under the US Endangered Species Act (ESA) and the International Union for Conservation of Nature's (IUCN) Red List of threatened species. Approximately 17.5% of the species present or possibly present are categorized as threatened by IUCN compared to 27% of the species globally. American Sāmoa has seven ESA-listed or ESA candidate species, including Acroporaglobiceps (Dana, 1846), Acroporajacquelineae Wallace, 1994, Acroporaretusa (Dana, 1846), Acroporaspeciosa (Quelch, 1886), Fimbriaphylliaparadivisa (Veron, 1990), Isoporacrateriformis (Gardiner, 1898), and Pocilloporameandrina Dana, 1846. There are two additional species possibly present, i.e., Pavonadiffluens (Lamarck, 1816) and Poritesnapopora Veron, 2000.
... Despite these limitations, some recent research on MCEs has been successfully conduced with submersibles. For example, submersibles owned and operated by the Hawaiʻi Undersea Research Laboratory at the University of Hawaiʻi (Makaliʻi, Pisces IV, and Pisces V) have conducted extensive observations on fishes within MCEs for decades (e.g., Randall et al. 1985;Colin et al. 1986;Pyle et al. 2016a;Spalding et al. 2019), including the use of rotenone and a suction device for collecting fishes. The Curasub submersible, with similar capabilities, has been used successfully and extensively for MCE research in Curaçao and Bonaire (Baldwin and Robertson 2013;Hoeksema et al. 2014;Baldwin et al. 2016;Tornabene et al. 2016b). ...
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Fishes are an important component of coral reef ecosystems, and in comparison to other marine phyla, the taxonomy of fishes is relatively robust. Some of the earliest explorations of mesophotic coral ecosystems (MCEs) involving both submersibles and rebreather diving focused on fishes. Since 1968, over 400 publications have documented fishes on MCEs, ~75% of which were published since 2011. Most fish species inhabiting MCEs belong to families and genera typical of shallow coral reefs, and many new species remain to be discovered and described. Species richness generally peaks at a depth of 30 m and declines with increasing depth. The composition of the fish communities on MCEs includes a mixture of species restricted to MCEs and species with broad depth ranges. Patterns of species turnover and composition vary depending on geographic location, ecological characteristics, and method of study. Nearly 70% of MCE fish research has occurred within the tropical western Atlantic and Hawaiʻi. Not enough is known about global distributions to infer broad biogeographical patterns, but there seems to be higher representation by endemic species and individuals on MCEs, and the eastward attenuation of diversity of shallow Pacific reefs does not appear to apply to fishes within MCEs. Analyses of nearly 900,000 occurrence records of reef fishes at depths of 1–200 m reveal patterns of diversity that are mostly consistent with controlled studies. Future work should emphasize basic exploration and documentation of diversity in under-sampled geographic regions and hypothesis-driven studies in areas where logistics facilitate MCE research.
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Mesophotic gorgonian corals comprise a polyphyletic group of octocorals mostly with a proteinaceous branching axial skeleton. Dense assemblages of gorgonian corals usually dominate the seascape in mesophotic coral ecosystems (MCEs). In this chapter, we review the mesophotic gorgonian coral biodiversity, followed by a synthesis of the ecological implications of inhabiting this environment, as well as the threats that these communities face. MCEs include ~87 gorgonian corals genera distributed worldwide, where the Indo-Pacific (65) is almost twice as diverse as the Caribbean and Gulf of Mexico (37) and Brazil (23), whereas the Tropical Eastern Pacific has only eight genera. We discuss several predictions on the nature of mesophotic gorgonian corals in areas such as microbial endosymbiosis to understand the health, ecology, and evolution of these assemblages. A notable colonization of shallow-water species into MCEs in the Caribbean suggests that colonizing deeper environments promotes ecological divergence. MCEs are not immune to the influence of natural events such as tropical storms and/or anthropogenic encroachment from coastal development, pollution, global climate change, ocean acidification, and overfishing; yet, gorgonian corals, in general, appear resilient to many of these threats.
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Macroalgae in mesophotic coral ecosystems are generally understudied compared to corals and fishes yet may be more abundant than coral-dominated reefs given their lower depth limits (> 200 m) and ability to grow over soft and hard bottom habitats. These assemblages are abundant and diverse globally, with changing species composition with increasing depth. Ubiquitous macroalgal assemblages include the red algal rhodolith beds and nongeniculate and Peyssonneliales assemblages; green algal Halimeda beds, meadows, and bioherms and Caulerpa spp. beds; and brown algal Lobophora spp. or Distromium spp. beds, Sargassum spp., and kelps. The use of molecular techniques is elucidating macroalgal diversity and rates of endemism, and molecular data and phylogenetic analyses often show strong cryptic diversity or pseudodiversity when compared with morphoanatomical analyses. Mesophotic macroalgae are important as habitat and may serve as seedbanks or refugia for ecosystem resilience following environmental stress. Invasive algal blooms may be deleterious, particularly with the removal of native herbivores or increasing nutrients. Geomorphologically, calcified species such as rhodoliths and Halimeda spp. are significant global producers of calcium carbonate. Abiotic factors influencing the abundance and distribution of mesophotic macroalgae include temperature, water clarity, nutrients, and currents. In general, threats include rhodolith mining, oil spills, sedimentation, ocean acidification, invasive species, bottom trawling, and eutrophication. The impacts of global warming at mesophotic depths are unknown. Future studies should focus on collections for molecular analyses to evaluate population-level dynamics and connectivity between shallow and mesophotic depths and in situ manipulations to determine competitive interactions and ecophysiological processes in these low-light environments.
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The mesophotic coral ecosystems (MCEs) of the Senyavin Islands (Pohnpei Island, and neighboring atolls Ant and Pakin) in the Federated States of Micronesia have received little research attention until recent years. These vibrant, environmentally dynamic ecosystems harbor a reservoir of biodiversity, with species and interactions new to science. Depths of ≥90 m have up to 20 °C annual variance. A strong El Niño event in 2016 resulted in a bloom-forming cyanobacteria smothering the upper MCEs of Pohnpei (25–65 m). Conditions persisted into 2017 with extensive coral bleaching and reef degradation with associated smothering by bloom-forming cyanobacteria and algae in the shallows. The initial bloom signature of 2016 at depth may, therefore, serve as a projected indicator of shallow reef health. Of the 160 reef-building scleractinian corals reported, 28 spanned the full depth range (0–45 m). Differences in irradiance due to geomorphology, as well as reef health, determined the depth transition between two primary benthic groups: photosynthetic scleractinians and filter-feeding azooxanthellate gorgonians, 60 m on low-relief atoll reefs and 45 m at high-relief walls and degraded reefs. Of the 109 gorgonian corals reported, 19 spanned the full depth range (0–140 m) with 70 morphospecies specific to lower mesophotic depths. Similarly, fish assemblages partitioned between shallow and mesophotic depths, characterized by herbivores and planktivores, respectively. Continuously growing marine resource exploitation and terrestrial runoff are heavily influencing reef health. The MCEs of Pohnpei are, thus, unique, yet vulnerable to the exacerbating stresses of man.
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The Bluestriped Snapper, Lutjanus kasmira (Forsskål, 1775), was intentionally introduced to the island of O'ahu between 1955 and 1961. It quickly spread throughout the Hawaiian Islands and became highly abundant in reef slope and spur and groove habitats. Here, we investigated the distribution of L. kasmira on shallow and mesophotic reefs of the Northwestern Hawaiian Islands (NWHI) using fish survey data collected from 2007 to 2016. L. kasmira was recorded at all islands or atolls of NWHI except for Gardner Pinnacles, Maro Reef, and Laysan Island—the middle region of the NWHI. It was most abundant at French Frigate Shoals and Nihoa at the southern end of the NWHI. On mesophotic reefs, L. kasmira was not observed at any locations north of French Frigate Shoals, except for one individual at Lisianski Island at an upper mesophotic depth. Small-bodied individuals were found more frequently at greater depths. L. kasmira was often observed along with Mulloidichthys vanicolensis (Valenciennes, 1831), Chromis acares Randall and Swerdloff, 1973, and Naso hexacanthus (Bleeker, 1855) on shallow-water reefs. The present study indicates the potential effects of habitat types and water temperature in the vertical and horizontal distribution of L. kasmira in the NWHI and the possibility of differential utilization of resources by adults and juveniles.
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Coral reefs are among the most biodiverse and productive ecosystems on the planet. However, our understanding of these ecosystems and their inhabitants has primarily been gleaned from shallow-water studies (<40 m), while light-dependent corals and the ecosystems they support extend much deeper (e.g., 150 m in some locations). In recent decades, coral reef ecosystems have substantially declined globally due to direct and indirect anthropogenic activities that differentially impact shallow-water habitats. This decline has led to the suggestion that surface-oriented stressors and disturbances may be mediated by depth. The role of deeper coral reef ecosystems, called mesophotic coral ecosystems (MCEs), as refugia for shallow-water species has fueled new investigations into this realm facilitated in part by advances in diving technology and remote observation platforms. The increasing access to these poorly studied ecosystems is revealing new insights into the biodiversity of MCEs as well as that of shallow coral reefs. The upper mesophotic community is largely an extension of the shallow-water coral reef community, much of the flora and fauna are shared across these depths. However, there is a transition with increasing depth to a lower mesophotic community dominated by flora and fauna that are largely endemic to this zone. Investigations are also expanding depth and geographic ranges for many species, and new species are being discovered regularly in MCEs. However, caution must be taken when generalizing due to the geographically and numerically limited nature of these studies.
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Mesophotic coral ecosystems are an almost entirely unexplored and undocumented environment that likely contains vast reservoirs of undescribed biodiversity. Twenty-four macroalgae samples, representing four genera, were collected from a Hawaiian mesophotic reef at water depths between 65 and 86 m in the ‘Au‘au Channel, Maui, Hawai‘i. Algal tissues were surveyed for the presence and diversity of fungi by sequencing the ITS1 gene using Illumina technology. Fungi from these algae were then compared to previous fungal surveys conducted in Hawaiian terrestrial ecosystems. Twenty-seven percent of the OTUs present on the mesophotic coral ecosystem samples were shared between the marine and terrestrial environment. Subsequent analyses indicated that host species of algae significantly differentiate fungal community composition. This work demonstrates yet another understudied habitat with a moderate diversity of fungi that should be considered when estimating global fungal diversity.
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Effective exploration of mesophotic coral ecosystems (MCEs) has been limited primarily by available technology. Although research targeting MCEs led to the development of the first electronically controlled, closed-circuit rebreather in the late 1960s to the early 1970s, it wasn’t until the 1990s that the technology was utilized extensively for MCE research. Over the years, diving techniques and technologies have gradually advanced from conventional SCUBA to open-circuit, mixed-gas diving to closed-circuit rebreathers, each progressively increasing diver safety and bottom time at depth. Over the past decade, the application of closed-circuit rebreathers for use in MCE research has increased dramatically, enabling research activities that are impractical or impossible using other technologies. When conducting advanced diving operations to study MCEs, many logistical and practical considerations must be taken into account. Trained and experienced divers and support personnel are required and must have access to appropriate equipment. Contingencies both during dives (e.g., bailout options) and in response to emergencies must be clearly defined and understood. Insights and guidelines for conducting MCE research using rebreathers are recommended based on over three decades of field experience. As scientific diving programs at more institutions continue to establish support for advanced technical diving operations, the application of this approach to MCE research will help scientists conduct work efficiently and safely.
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Papua New Guinea (PNG) hosts a unique range of geological features and is located in the Coral Triangle, the world center of marine biodiversity. However, working in PNG poses considerable logistical challenges in addition to those typically associated with mesophotic coral ecosystem (MCE; light-dependent reefs from 30 to ~150 m) research. Although its MCEs are poorly documented, they are likely extensive. Water temperatures at 90 m (23.3–26.3 °C) are cooler and less variable annually than those at 15 m (24.2–31.0 °C) but tend to be more variable on a daily basis and are within the range necessary to support coral growth. Limited studies have documented at least 213 coral species (40% of PNG’s coral fauna) and 73 sponge species (14% of PNG’s sponge fauna) at mesophotic depths. MCE fish communities are generally composed of taxa typical of shallow coral reefs; however these appear to be less abundant at mesophotic depths. Because biological surveys have been conducted in only a few locations, checklists of PNG’s mesophotic species are likely to grow with additional research. The major threat to PNG’s MCEs is likely terrigenous sediment associated with the country’s chief industries of forestry, mining, and agriculture. However, the effects of global climate change, i.e., warmwater coral bleaching, have also been observed at mesophotic depths.
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About 63% of the known antipatharian genera occur at mesophotic depths (30–150 m), with the majority extending into the deep sea. Along the continental shelf and offshore sites, antipatharians tend to increase in diversity and abundance with depth, reaching a peak at mesophotic depths due to favorable environmental factors enhancing their settlement and growth and biotic factors associated with lower levels of competition for space. A review of taxonomic and ecological studies for shallow and mesophotic antipatharians is presented for four regionally based case studies, three in the tropics (1) Central Indo-Pacific, plus adjacent sections of the Western Indo-Pacific, (2) Eastern Indo-Pacific (primarily Hawaiʻi), and (3) the Caribbean Sea) and one at temperate latitudes in the Mediterranean Sea and adjacent sections of the Northeast Atlantic. The mesophotic fauna is mainly represented by the families Antipathidae, Aphanipathidae, and Myriopathidae. The most diverse community is found in the Central/Western Indo-Pacific, followed by the Caribbean Sea. The tropical antipatharians are represented by shallow species that extend their distribution into the upper mesophotic zone (30–60 m), while the temperate antipatharians consist of deepwater (> 150 m) species that extend upward into the lower part of the mesophotic zone. Black corals in mesophotic coral ecosystems can be habitat-forming components of benthic assemblages on hard substratum. They have an enormous potential for hidden biodiversity and play an important ecological role for the broader marine ecosystem. The threats to antipatharians consist of demersal fishing activities and coral harvesting, which may be highly destructive to these poorly understood systems.