Population Expansion of a New Invasive Coral Species - Tubastraea micranthus -
in the northern Gulf of Mexico
Paul W. Sammarco1,2, Scott A. Porter1,3, James Sinclair4, and Melissa Genazzio1,5.
1Louisiana Universities Marine Consortium (LUMCON)
8124 Hwy. 56
Chauvin, LA 70344
2Department of Oceanography and Coastal Sciences
Louisiana State University
Baton rouge, LA 70803
3Ecologic Environmental, Inc.
Houma, LA 70361
4US Department of the Interior
Bureau of Safety and Environmental Enforcement (BSEE)
1201 Elmwood Park Blvd.
New Orleans, LA 70123-2394, USA
5Center for Marine Science
University of North Carolina at Wilmington
601 S. College Rd.
Wilmington, NC 28403-5928, USA
Running Head: Distribution and Abundance of Tubastraea micranthus
Keywords: Coral, invasive species, Tubastraea micranthus, Gulf of Mexico, spread, oil
An new Indo-Pacific scleractinian coral has invaded the northern Gulf of Mexico (GOM) –
Tubastraea micranthus. It was initially observed on one oil platform (GI-93C) near the
Mississippi River. Here wWe determined whether its populations were spreading throughout the
region and whether there was evidence of rapid population expansion. We also compared
population density data with those fromat of T. coccinea, a congeneric species which
successfully invaded the western Atlantic earlier. Fourteen oil/gas platforms were assessed
down to 138 m depth (max.) using by remotely operated vehicle (ROV), digital video. Densities
in no./m2 were determined for both species, and colony size for T. micranthus. Data were
analyzed by platform and for also with respect to geographic distribution. T. micranthus
densities were highest on GI-93C and on GI-116A, SW of the Mississippi River, being
significantly higher than most other platformsinflux of recruitments. Densities declined radially
from there, suggesting this to be the epicenter of colonization. Mean colony size was highest on
MC-311A, t all colonies generally surveyed being larer than area. This platfs at the head of the
Mississippi Canyon andn, characterized by blue water instead of the turbid, lower salinity water
of other sites. This suggests that so receives blue water instead of turbid, lower salinity water,
and this speciesAlso, and /or that T. micranthus may grow betterst under blue-water conditions.
T. micranthus sSize frequency distributions of colonies for T. micranthus were generally skewed
towards 1-200 cm2 (5 cm diam.) (– sometimes >90% of the population), suggestiindicating that
most populations are potentially in an expanding explosive growth phase. T. coccinea densities
were high (range: ~50-300/m2). Its populations were also centered SW of the Mississippi River.
T. micranthus is spreading through this region and the window for its potential eradication may
be rapidly closing.
Species introductions can result in major impacts on the ecosystems (Roberts and Pullin, 2008).
This is particularly so in the marine environment, because of the ease with which their
reproductive propagules can disperse and colonize nearby habitats once they have established a
new population (Griffiths, 1991; Johnson and Carlton, 1996; Wonham et al., 2000). Examples of
rapid dispersal of introduced marine species are numerous and iInclude ude marine algae
(Chapman et al., 2006), such as Codium fragile – a Japanese cholorophyte introduced apparently
via the ballast water of ships (Trowbridge, 1998; Pederson, 2000; Williams, 2007). This species
is now common throughout much of the western Atlantic (Chapman, 1999). Another example is
Caulerpa taxifolia which was accidentally released into the Mediterranean Sea from a public
aquarium in Monaco (Williams and Smith, 2007) and is now common there. This species is now
common throughout much of the western Atlantic (Chapman, 1999). Another more recent
example is the Indo-Pacific volitan lionfish (Pterois volitans). This species was most likely
released into western Atlantic waters approximately ~10 yrs ago (Whitfield et al., 2002; Hamner
et al., 2007) and is now distributed from New York, USA south through the Caribbean and South
America (Albins and Hixon, 2011). There are hundreds to thousands of such examples of
introductions from various seas, which are reviewed in, e.g., Bax et al., (2003), Womersley
(2003; Australian algae), Zenetos et al. (2005; Mediterranean fauna), etc.
Vectors for the transport of invasive marine or freshwater species (Kerr et al., 2005)
include the ballast water of barges orf ships (Chesapeake Bay Commission, 1995; ICES,
2002), the hulls of the same (Minchin and Gollasch, 2003), transfer via towing of oil and gas
platforms to new sites (Hicks and Tunnell, 1993), accidental release of exotic species from
mariculture operations (Sapota, 2004), and deliberate release of exotics by aquarium
hobbyists (Weidema, 2000; Christmas et al., 2001; Hindar et al., 2006).
Recently there has been concern regarding invasive marine species has focused onabout
sthose pecies occurring in which have invaded the Gulf of Mexico (GOM) (Osman and
Shirley, 2007). This includes the Australian scyphozoan Phyllorhiza which colonized thise
region within the past 15 yrs (Perry and Graham, 2000), and has the ability to suppress seasonal
zooplankton populations (Graham et al., 2003; Graham and Bayha, 2008) important for
commercial fisheries. Another is the zebra mussel Dreissena polymorpha, which was originally
introduced to the Great Lakes in the mid-1980s and has since spread south through North
America (Baker et al., 2006; Dextrase and Mandrak, 2006; Ram and Pallazola, 2008) all the way
to the Mississippi River mouth (Anon., 1997; Liffman, 1997).
There have been Vvery few corals have successfully invaded thesions of corals to the Atlantic.
The Indo-Pacific mushroom coral Fungia scutaria was accidentally introduced intoto Discovery
Bay, Jamaica, W.I. (J. Lang, pers. comm.; P.W. Sammarco, pers. obs., 1973; Lajeunesse et al.,
2005). (The corals were held in running seawater tables for several years, and it is hypothesized
that, during the spawning seasons, planulae were released into the water and flushed into the
lagoon through the seawater discharge drain.) The Indo-Pacific sun coral, Tubastraea coccinea
(Cairns and Zibrowius, 1997) species was first introduced into Puerto Rico in 1943, and by 1948
had spread to Curacao, Netherlands Antilles (Cairns, 2000). By the late 1990s and mid 2000s,
thise species had spread to Belize and Mexico (Fenner, 1999); Venezuela, northern Gulf of
Mexico, and the Florida Keys (Fenner, 2001; Fenner and Banks, 2004; Sammarco et al., 2004;
Shearer, 2005); Brazil (Figueira de Paula and Creed, 2004); Colombia, Panama, the Bahamas,
and throughout the Lesser and Greater Antilles (Cairns, 2000; Humann and Deloach, 2002).
Tubastraea coccinea has also been observed since ---- [what year?] on deep-water [how many
meters debanks occurring at the edge of the continental shelf of the GOM. This species is now
abundant in the northern Gulf of Mexico on artificial substrata (Sammarco et al. 2004, 2007a,b,
2012a). It is present on oil/gas platforms in abundances of hundreds of thousands of colonies per
platform, with average densities reaching from 28/m2 to 300/m2. It also occurs on deep
narbonate bBanks [be more specific – are thormed o calcium caronate in the northern Gulf of
Mexico but in lower abundances (Schmahl, 2003; Hickerson et al., 2006; Schmahl and
Hickerson, 2006). It is possible that this introduction was due to a ship, barge, or ballast water,
although the details are not known. It is also possible that the oil and gas platforms, abundant in
the northern Gulf of Mexico, have acted as stepping stones for the geographic expansion of this
species in this region (Sammarco et al., 2004; Atchison, 2005; Atchison et al., 2008; Sammarco
et al., 2012a,b). It should be noted, however, that such a geographic spread was achieved
throughout most of the western Atlantic without these structures; that is, such structures were
sufficient but not necessary for the spread of this species. [add brief text on how Tubastrea were
likely introduced t
From 2000 to 2010, Sammarco et al. (2004, 2007a,b, 2008, 2012a) and SAPPorter (unpub. data)
conducted surveys via SCUBA and remotely operated vehicle (ROV) on the distribution and
abundance of scleractinian corals on 81 oil and gas platforms - in both shallow and deep water
throughout the northern Gulf of Mexico. Surveys were conducted instretched from the offshore
waters spanningoff Corpus Christi, Texas to those off Mobile, Alabama. In his surveys, SAPPorter
found a new invasive species for the Gulf of Mexico – the Indo-Pacific black sun coral species-
Tubastraea micranthus Cairns and Zibrowius 1997 (Sammarco et al., 2010) - a closely related
congener of Tubastraea coccinea. It was initially observed in 2006 on a single platform - GI-93-C
(28o32.96’N, 90o40.11’W; Fig. 1). This was , occurring near the crossing of two major safety
fairways/shipping channels southwest of the Port of New Orleans, Louisiana, near the mouth of the
Mississippi River and Port Fourchon, Louisiana.
Once a population of a new invasive species becomes established, its spread can be broad and
rapid, greatly confounding any attempt to control or eradicate it (Elton, 2000). Examples include
the invasion of the fire ant (Solenopsis invicta) into the United States (Buhs, 2004). It was
accidentally introduced into Mobile, Alabama during the 1940s and is now distributed around the
margins of the USA from the state of Washington to New Jersey, extending approximately 800
km inland. Another example is the South American coastal herbivore Nutria (Myocastor
coypus), 20 individuals of which were introduced into Avery Island, Louisiana during the
1930’s. Its populations are now distributed from Delaware to Texas, USA and reach to inland
mid-eastern states as well as those of the northwest.
An understanding of Tubastraea coccinea’s life history traits will assist in understanding some
of the potential which T. micranthus has for geographic expansion in the GOM, and allow
comparisons between the two species. T. coccinea generally has colony sizes no larger than 25
cm in diameter in the GOM, at which point it extends runners horizontally to form new ramets.
Its growth form in the Atlantic is branching but with a low profile, to a maximum of 12-15 cm.
The polyps are red or orange in color, and the corals are ahermatypic and azooxanthellate. Their
natural habitat on Indo-Pacific reefs is cryptic, and this same habitat is adopted on natural reefs
in the western Atlantic. On artificial substrata, however, the colonies are much more exposed.
With respect to T. micranthus, colony sizes are somewhat smaller (15 cm in diameter) in the
GOM. The colonies also distribute runners to form new ramets. It is also branching in habit, but
its polyps extend to a greater extent vertically, and branch as well, making the colonies often a
bit taller (up to ~ 20 cm high; Sammarco et al., 2010; Cairns, 2000). They are dark green or
black in color and are also ahermatypic and azooxanthellate. Their natural habitat on Indo-
Pacific reefs is exposed. It is not yet known what their habit will be on natural reefs in the GOM,
although they are generally exposed on oil and gas platforms there. T. micranthus’ ability to
grow well in highly exposed habitats is reason for concern, since preliminary data indicate that
this species has a strong advantage in competition for space against other sessile, benthic
epifauna (Sammarco et al., 2012c,d).
Regarding reproduction, Tubastraea coccinea exhibited a similar broad range extension since it
was introduced in the 1940s. It is not yet known whether Tubastraea micranthus exhibits the
same population growth characteristics as its congener. Tubastraea coccinea is a single species
with a circum-tropical distribution (Cairns, 2001). It is a hermaphroditic brooder and reproduces
by producing planulae year-round (Glynn et al., 2008a). Egg development requires 6-8 wks. T.
coccinea exhibits asexual reproduction using budding, simple colony growth, and asexual
planula production (Ayre and Resing, 1986; Shearer, 2008) and runner production (Pagad, 2007).
It is considered to be a high-fecundity species and also uses sexual reproduction, producesing
gametes all year-round, even in the smallest colonies (2-10 polyps; Glynn et al., 2008a,b).
Planulae may be produced sexually or asexually (Ayre and Resing, 1986). The planular
development period is 6 wks, and the planulae settle and metamorphose within 3 days. Planular
release occurs 3-4 times per year (Hebbinghaus, 2001) from March through July, and this species
isindividuals areit is considered to possess substantialbe highly fecund (Glynn et al., 2008a,b),
with. Iformidable ts larval dispersal capabilities are formidable (Sammarco, 2012b). It is known
to withstand a variety of environmental conditions thy in othcoral species.
With respect to Tubastraea micranthus, tIf the details of its reproductionive, and dispersal
capabilities, time from release to settlement for planulae, and any obligate period that the planula
must remain in the water column prior to settlement of T. micranthus are ot yet known[?].
butwever, they are similar to those of T. coccinea, then T. micranthus former could reach
similarly high abundances similar to its congener in the western Atlantic (Sammarco et al., 2004;
Shearer, 2008). As such,That is, it is possible that there could be species could pose a potential
threat viathroua bantial massive geographic expansion of this species throughout the GOMulf
and the tropical and sub-tropical western Atlantic is poover the next 20-40 yrs.
The objectives of this study were to quantify the abundance of Tubastraea micranthus aton the
presumed initial introduction site of observation (Platform GI-93-C, see above); and to conduct
surveys on 13 other platforms in the vicinity of GI-93-C, extending to the bottom, of the
platforms, to determine whether its populations are expanding. We also assessed the direction in
which the expansion is occurring, in what types of environments it occurs, and to what degree.
Depth distribution information and competition-for-space capabilities of this species will be
Materials and Methods
The study sitesplatforms were Platform GI-93-C and 13 other platforms surrounding it within a 20
km radius (Fig. 1; Table 1). Specific platforms were chosen in consultation with the US Dept. of
the Interior - Bureau of Ocean Energy Management (BOEM). Choices were based on age and
location of the structures and availability with respect to the platform owners. . Surveys were
performed using the M/V Fling (33 m, Gulf Diving, Inc., Freeport, TX) and the R/V Acadiana (18
m, LUMCON). The study was conducted over two years, utilizing 12 days of ship-time.
TWe spent approximately two-thirds of one day were required to surveying each platform using an
We used LUMCON’s Deep Ocean Engineering Phantom S2 ROV, which has 333 m of umbilical
and is capable of surveying down to 170 m depth. We employed the techniques previously used
successfully in earlier similar surveys (Sammarco et al., 2010, 2012a). ARACAR’s SeaBotix
LBV-300 and BOEM’s similar ROV were also used as back-ups when the primary ROV
required maintenance. All units were fitted with vertical and horizontal propulsion units, site-to-
surface color video units, a topside monitor, lights, laser beams providing a spatial scale
reference, and a sample retrieval unit (fixed grab). Length of transects varied between 18m for
horizontal struts and 170 m for the deepest vertical piling. Number of transects varied between
four and seven per platform, depending upon size of the platform. Transects consisted of two to
six horizontal transects at approximately 15-18, 23-27, and ~180 m depth respectively; the
remainder of the transects were vertical. Approximately 125-585 sq m of substratum were
surveyed on each platform, depending upon the size of the platform (number of primary pilings),
depth, time available at each platform, and weather and sea conditions. We filmed continuously
down each leg and only on the outward-facing surfaces. The side of the platform sampled was
always down-current so as to insure that the ROV and/or its umbilical was not drawn into the
interior of the structure, to reduce the probability of it becoming fouled (see Sammarco et al., in
Imagery was processed using a Dell Precision 340 and T3400 desktop computers with a Pentium
4 processor and a Dell Precision M4300 Workstation fitted with a duo-core processor and
MicroSoft video imaging software. Image analysis software included Nero 7.0, VideoLAN, and
MicroSoft Windows Media Player, capable of zoom and still-image capture. Images were
analyzed at each 3 m interval within a video transect. The number of quadrats analyzed per
platform was 12-174 quadrats,, depending upon platform size and depth (see Table 1).
Data were collected for both Tubastraea micranthus and T. coccinea for comparative purposes.
In the case of T. coccinea, population densities were so high (up to hundreds per still image)
that counts were estimated visually using a log5 code system (0=1, 1=5, 2=25, 3=125, etc.),
similar to that used in the field by Williams (1982) and Halford et al. (2004) for reef fish
counts. Two laser dots of known inter-dot distance (8-12 cm, depending upon the vehicle)
within the video field of view were used to standardize for both coral density (no. corals per
unit area) and coral colony size. A transparent 10 x 10 2.54 cm grid ([total grid ara = 25.4
cm x 25.4 cm)? was this als was placed over the computer screen to assist sampling and
taking measurements. Mean densities of corals were calculated for each platform along with
standard deviations and 95% confidence limits. [range of tota
Colony size was measured for all Tubastraea micranthus colonies. . Similar data are not
presented for T. coccinea, because T. micranthus was the target organism for the study and the
objective of this study is to attempt to discern characteristics of initial population changes in the
region. It is known that T. coccinea populations are well-established in the region (Sammarco,
2012a). Colonies were assumed to be elliptical in shape, and measurements were made of the
major and minor axes. Estimated area was calculated as A = π x r1 x r2, where r1 and r2 are the
major and minor radii, respectively. Mean coral colony size was calculated for each platform
along with standard deviations and 95% confidence limits. Size-frequency diagrams were
constructed for Tubastraea micranthus colonies on each of the platforms, based on all quadrats
analyzed per platform.
All quantitative data were logged in EXCEL files and stored on the primary workstation. Data
were backed-up on a 250G Western Digital G-Book external hard-drive and , updated daily as
well as on the LUMCON computer network (, which is updated continuously).
Coral density data were analyzed by parametric tests. Analyses included ANOVA and a
posteriori Multiple Comparison Tests between Means – T-K, GT-2, and T’ tests. Basic statistics
(mean, s.d., n, range, g1 – skewness, and g2 – kurtosis) were calculated for colony size frequency
distributions. Analyses were performed using BiomStat 3.2 and 3.3 (Rohlf and Slice, 1996).
Where necessary, data were transformed by square root of (Y+ 0.5) for normalization purposes
(see Sokal and Rohlf, 1981).
Two-dimensional graphics were performed using SigmaPlot 10.0. Some data are presented
within a geographic context in three dimensions, and these were constructed using SURFER 8.0
(Golden Software, 2002). Data consisted of latitudes, longitudes, and the variate in question.
Averages were determined by kriging, a geostatisical gridding method designed for use with
irregularly spaced data, using a smoothing interpolator. We used pPoint kKriging, estimating
interpolated values of points at grid nodes and a default linear variogram without a nugget effect.
Additional details may be found in Golden Software (2002).
Data derived from analysis of ROV videos revealed that Tubastraea micranthus’ populations had
were indeed distributed outside of spread from GI-93-C on other to surrounding platforms in the
study area. Out of 14 platforms surveyed, this species was found on 9, including GI-93-C (Fig.
2). In addition, density data was highest on this platform of initial sighting, averaging
approximately 15/m2. This suggests that this site may well have been the site of original
colonizationexperienced substantial colonization from elsewhere. The platforms did not possess
the same densities of corals. ANOVAs and subsequent a posteriori tests revealed that densities
on GI-93C were significantly higher than on all other platforms except GI-116-A116A (Table
2a), which was not significantly different than GI-93C. Details regarding inter-platform
comparisons may be found in Table 2a. T. micranthus did not occur on Platforms ST-185-
A185A & B, GI-94-B, ST-81-A81A, and ST-75JA(B) (Fig. 2).
When density data were placed into a geographic context, it could be seen that Tthe peak density
of T. micranthus occurred to the southwest of the mouth of the Mississippi River (Fig. 3), next to
two major safety fairways servicing the Port of New Orleans and the Port Fourchon (Sammarco
et al., 2010). A second somewhat smaller peak in density occurredcould be seen south of GI-93-
C. This suggests that the introduction of this species may have been derived from larvae being
released from a passing ship or barge. In general, densities fell off in all directions in near
proximity to these points, with a minor peak west-southwest of the Mississippi River mouth.
Densities roseThere was a moderately rise in densities to the east of the Mississippi River.
Patterns of average colony size for Tubastraeaa. micranthus did not follow that of average
density. MThe maximum average colony size was found on Platform MC-311-A311A (Fig. 4)
and. It was significantly higher than on all other platforms (see Table 2b3 for pair-wise inter-
platform comparisons). The next largest average T. micranthus colony size was found on MC-
109A (mean = 198.6 cm2, s = 281.14, n = 47, range = 1.2 – 1,204 cm2
) , and it was significantly
higher than the average colony size on SP-87D, GI-116-A, and GI-93C. Average colony size on
almost all other platforms did was equivalent (not significantly different)other (, except on GI-
115A) versus ST-206A, and GI-93C versus SP-87-D. When these differences are placed into a
geographical context, the [obvionthree-dimensional representation of average colony size
demonstrates that colony size not only peakeds at MC-311-A311A, but it also droppeds off
evenly from that point in all directions, with no secondary peaks in that region (Fig. 5).
Size-frequency diagrams were constructed for Tubastraea micranthus colonies on each of the
platforms. Size-frequency distributions of T. micranthus revealed that onIn the case of Platform
MC-109-A109A, , it could be seen that a large proportion of the colonies ( - ~60%) - were
between one and 100 cm2 in area (max. diameter = ~11 cm, ) in area (Fig. 6). CFrequencies of
smaller [larger??] average colony size category sizeies? dDecreased ifell off rapidly after this s.
nclear-sate.] This pattern of a logarithmic decrease in he frequency of average co and a heavy
reesentation of very lony sizes, heavily represented in the small colonies est size frequency, was
mimicked on all other platforms where T. micranthus occurred, particularly GI-93C and GI-
116A (Fig. 6). This is similar to the observations made in Brazil by Lages et al. (2011) and
Sampaio et al. (2012), The [what were dimensions of the largest colonies found, and the what
proportion of the population at each site reachinged thoese sizes is shown ins. It is not known
whether maximum coloy size fos species was reached here, for we are not aware odataare not
available on maximum colony sizes for Tubastraea micranthus in its native habitat[?]. ? Were
they much smaller than maximum known body sizeies? This is important, as it reveals how many
individuals had reached im
Densities of Tubastraea coccinea were much higher than those of T. micranthus, with the highest
densities in this survey reaching about 300 colonies/m2 – 20-fold higher than that of the new
invasive species (Fig. 7). The platforms had significantly different densities. Platform ST-185B
exhibited the highest concentrations of T. coccinea, which were equivalent to those on GI-116A,
but higher than on all other platforms (see Table 2c4 for pair-wise inter-platform comparisons).
Densities on GI-116A were higher than almost all other platforms. Densities on ST-206A were
approximately equivalent to most all other platforms except the above two plus MC-311A and
Interestingly, if one considers Tthe geographic distribution of T. coccinea colony density in this
region of the northern Gulf of Mexico was through three-dimensional graphing, one finds that
the distribution looks quite similar to that of the recent invader T. micranthus (Fig. 8). The major
peaks occurred southwest of the mouth of the Mississippi River, and densities decreased radially
in all directions from there.
The pattern reported here for the fact that, on the 14 platforms surveyed south of the Mississippi
River mouth, in which the highest densities of Tubastraea micranthus were found on Platform
GI-93-C, – the point of the original observation, by SAP indicates- confirmed our suspicions that
that platform had received a major influx of larvae from populations from one or more nearby
platforms. On the other hand, it may have been the is was most likely the initial point or
epicenter of colonizationut this is less likely, based on size-frequency information (see below).
by this species o. The original observation was fortuitous. The geographic pattern of
distribution of Tubastraea micranthus densities throughout the study region also supports these
former hypothessunderscores our belief that GI-93-C was the original epicenter of colonization,
with the spread being in all directions from there. The secondary peak at GI-116-A116A
suggests a similar relationship. Tubastraea micranthus is known to be able to double its colony
density in a single year (Loch et al., 2004). , however, implies that at one point or more, this
platform may have received a pulse of larvae from GI-93-C from a southerly current passing
over the latter platform.
It has been suggested that, in corals, size is a better indicator of population dynamics in corals
than age (Hughes, 1984; Goffredo and Lasker, 2006). Although size has been used often as a
target variable in colonial organisms (Grigg, 1975), colony age and size data and their impact on
calculations of current and future population growth can, however, be confounded (Grigg, 1975;
Hughes and Connell, 1987; Babcock, 1991; Chadwick-Furman, et al., 2000). Guzner et al.
(2012) have found that age structure without estimates of recruitment can be misleading due to
incomplete data. Bak and Meesters (1998) suggest that the C.V., mode, and skewness of a coral
population size-frequency distribution can provide valuable information regarding the population
dynamics of a coral population. Done (1988) and Fong and Glynn (1988) have used coral
colony size-frequency data to predict coral community recovery times after a major perturbation
such as a Crown-of-Thorns population explosion.
Data regarding the mean colony size-frequency distribution of the Tubastraea micranthus
colonies on these platforms have important implications for point of initial colonization,
definition of niche specificity, and the population dynamics of this species. Firstly, average
colony size did not peak at GI-93-C – the presumed point of original colonization; it peaked on
the MC-311-A311A and to some degree on MC-109A platform, being significantly higher than
all other survey platforms, and with average colony sizes clearly falling off in all directions from
there. A further analysis of MC-109A, however, indicated that the size-frequency distribution
was similar to those on most of the other platforms, being dominated by very small colonies. It
is possible that MC-311A could have been the initial site of colonization, since it possesses not
the most abundant largest population of T. micranthus, but the oldest colonies in this young set
of coral pons. If that were the case, and this platform were seeding the others, then the other
platforms would be expected to possess smaller sized colonies – which they do.
As another point of consideration, the currents in this region may be expected to flow from east
to west, particularly during the spawning season due to the Loop Current (Sturges and Blaha,
1976; Hamilton et al., 1999). Larvae may also have been carried by a counter-current (Wiseman
and Garvine, 1995) to the Western Boundary Current (Vidal Lorandi et al., 1999). This would
flow from the east to the north and west and could have carried larvae in that direction. Another
current from the east is that associated with the Tortugas Bank and Pulley Ridge, Florida (Jarrett
et al., 2000; Meyers et al., 2001). (See Sturges and Lugo-Fernandez, 2005 for a complete review
of currents in the GOM, including this region.) Any of these currents could have influenced
larval dispersal and settlement, and they suggest opportunities for future research in this area. In
addition, it is known that success of coral recruitment and growth may be regulated by a diverse
set of environmental factors, many of which vary in this region.
In all cases, however, we know that the skewness of the size-frequency distributions was high
and clearly biased towards the smallest colony sizes. This pattern is similar to that described by
McNaughton and Wolf (1979) of a rapidly expanding population, where most of a population is
comprised of pre-reproductive organisms followed by reproductive ones. Such a population
would not yet be considered stable. In addition, studies of reproduction and size-structure in red
corals have shown that reproductive output increases with size (Tsounis et al., 2006). Because of
this, we hypothesize that all of the populations observed, irrespective of average size of the
colony, are in a phase of high initial population growth.
TThe environment of MC-311-A311A is different from that of GI-93-C and may also provide a
more suitable environment for growth than in the other sites. GI. GI-93-C occurs on the
continental shelf in 64 m depth of water, and it periodically receives water from the Mississippi
River plume as it meanders throughback and forth in this region. The river plume is, of course,
characterized by high turbidity, a high sediment load, high nutrients, and low salinity (Sturges
and Lugo-Fernandez, 2005; Rabalais et al., 1996). On the other hand, MC-311-A311A occurs
beyond the edge of the continental shelf, at the head of the Mississippi Canyon. It is more
frequently characterized by blue water (low turbidity, low sediment load, low nutrients - except
for upwelling events -, , and a more stable stenohaline environment; see Rabalais et al., 1996;
Weisberg and He, 2003; Green et al., 2006). Thus, one might we hypothesize that T.
micranthus grows better than does T. coccinea in a blue-water environment than a coastal one
that is, subjected to typical coastal environmental variability.
Tubastraea coccinea’s highest densities were found on ST-185-B185B and GI-116-A116A.
Both of these sites have environments similar to GI-93-C, and are subjected regularly to water
from the Mississippi River plume. This species was also commonly observed on mid-shelf
waters subjected to coastal discharge influences in the northern Gulf of Mexico, where
hermatypic (reef-building) corals were not encountered (Sammarco 2012a). This is another
indication that there may be of differences in niche specificity and preferred habitat between
these two congeners. We hypothesize that T. coccinea tolerates and perhaps thrives better in
coastal or river-influenced waters that are not as well tolerated by T. micranthus or by most other
tropical reef corals.
This observation raises an interesting point regarding potential impacts of Tubastraea
micranthus vs. T. coccinea. T. coccinea invaded the western Atlantic in the 1940s (Cairns, 2000;
Humann and DeLoach, 2002; Fenner and Banks, 2004). Since that time, it has spread as far
south as Brazil (Figueira de Paula and Creed, 2004) and as far north as the Flower Garden Banks
(Fenner, 1999, 2001; Fenner and Banks, 2004), the Florida Keys (Shearer, 2008), and platforms
in the northern Gulf of Mexico (Sammarco et al., 2012a). Tubastraea spp. in Brazil are showing
signs of expansion and disruption of native species (Lages et al., 2011; Sampaio et al., 2012).
During this period, it has become evident that populations of this species haveare able to nearly
monopolized artificial hard-bottom substrata such as offshore platforms. In no case of which we
are aware, however, has ve there been reports of this species dominateding natural, exposed coral
reef environments, despite the fact that it does has been reported to occur on these natural reefs
in the western Atlantic in both shallow and deep environments (Sammarco, 2012b; Hickerson et
We hypothesizepropose that the reason for low colony densities this deficit of colonies on natural
reefs is that T. coccinea may cannot compete well for space with the natural sessile epibenthic
fauna and flora found at least on a coral reefs it has colonized in the western Atlantic thus far. It
is also possible that coral reef, and/or there are naturally occurring predators there that
suppressng their populations when they are occur fully exposed, as has been suggestLages et al.
(2010). . On these natural reefs, the colonies observed tend to be found in their natural numbers
and ohabitat occupn the Indo-Pacific region, which areis cryptic and in low numbers, associate –
with other ahermatypic corals (cite rerences[?]). The concern here is that the natural
environment for T. micranthus in the Indo-Pacific is on the upper surfaces of reef substratum,
fully exposed (Schuhmacher, 1984; Fuzaki, 2011). If and when this species encounters a natural
Atlantic coral reef, it is possible that it is possible that may be successful at outcompeting
naturally occurring sessile epibenthic fauna and flora for space. Its degree of toxicity and degree
of palatability to predators, which could potentially control its populations, are currently
The size-frequency distributions of Tubastraea micranthus are suggest that theseindicative of a
populations may be in an a high explosive growth phase (McNaughton and Wolf, 1979). In the
case of Platform MC-109-A109A, almost 60% of the colonies are between 1 and 100 cm2 in area
or about 5 cm in diameter, while the largest size colony was 1,200 cm2, or ~40 cm in diameter.
We are unaware of what the maximum size for this species is in its natural environment, but
available images indicate that it is on the order of one meter. (ref[?]; determine whet. In
addition, the size-frequency distributions were highly consistent from platform to platform; thus,
highthis explosive aspectt of population growth is occurring on across all of the newly colonized
platforms. It is possible that Alternately, the similarpatterns of all these populations may indicate
that they all have reached a mature, stable size structurestructure, but such is unlikely, given the
assumed ti of the introduction. s impossible to tell the difference unlample populations at
various points in time] The shape of this single-point size-frequency distribution is similar to that
of a “wide-based pyramid”, described by human demographers to be indicative of human
populations with a high growth rate and low doubling times and Oertel, 196
, e.g., T. coccinea, where there is more data. Are there data on temporal changes in T. coccinea
through time after invasion? ]. TwoOne factors limiting our interpretations of population
growth are firstly, of density and size-frequency data is that they represent only one sampling
point in time. Having a temporal data sequence would maddress som whether these populationss
are stable or dynamic. From other studies of expanding populations, howeverns ([gen refnd
coral refs?]), we assume at this point in time that they are dynamic. Sncy data is in itself
limiting. Nonetheless, we offer these explanatory hypotheses for consideration. Having a
temporal sequence would more easily address some these hypotheses.
India, China, and Indonesia (Miller, 2000).
A problem with your analysis is that you have measured the new invaders at only one point in
time, and so have only static data on both population density and body size patterns.]
We believe that we have confirmed–e data presented here suggestindicate that Tubastraea
micranthus has appears to hhas successfully invaded the northern GOMulf of Mexico and mayis
exhibiting signs of producing rapidly expanding its populations in thise region. Its congener, T.
coccinea, has already demonstrated a strong formidable capability for geographic range
extensionies in this area. Preliminary data on depth distribution and competitive abilities
(Sammarco et al., work in progress) give cause for further concern about the invasion of T.
micranthus. [We believet awa a suggest that T. micranthus has the ability for extensive
geographic expansion in the western Atlantic Ocean if left unchecked. Complete eradication of
introduced marine species is possible, but such can be difficult, and eradication efforts must be
swift and complete if they are to be effective (Fitzhugh and Rouse, 1999). In thatis case, it is
possible that[we believe that the window for action may ae is closing rapidly. If introduced
populations are left unchecked for too long, the new speciesy newly introduced populations will
become well integrated into its target the invaded?original community, creating a new
community structure and stable equilibrium, with defining a new f set of ecological interactions
[betweenamong species (Mooney and Cleland, 2001; Krushelnycky and Gillespie, 2008). In that
case, eradication may actually create more problems than it solves (Bergstrom et al., 2009;
Casey, 2009). At this point, we stand at a branch in the decision-making road regarding
eradication of Tubastraea micranthus. Thriefly tell the reader: at what stage do any decisions
currently exist regarding eradication, within the management agencies responsible for Gulf
ecological health, such as your funding agencies listed below? In your experience, or in the lite
We express our deep-felt thanksa to the following for their topside assistance in the field:
LUMCON - C. Sevin, T. Widgeon, M. Wike; M/V Fling – B. Allen, K. Bush, K. Dies, M.
McReynold, B. Oldham, M. Spurgeon, J. Tyler; NASA/US Air Force – D. Perrenod; Others – M.
Gaskill. For their financial support of the project, we extend our thanks to the Bureau of Ocean
Energy Management (BOEM), US Department of Interior through the Louisiana State University
Coastal Marine Institute (CMI) program, under the direction of L. Rouse and S. Welsh, under
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Figure 1. Map of the north-central Gulf of Mexico showing locations of the 14 offshore oil
and gas platforms studied. Platform GI-93-C (triangle) represents the site of first
sighting of Tubastraea micranthus (Sammarco et al., 2010).
Figure 2. Density of Tubastraea micranthus on 14 offshore oil/gas platforms in the northern
Gulf of Mexico. Densities shown in no./m2 with 95% confidence limits.
Densities are highly significantly different from each other (p < 0.001, one-way
ANOVA). Data transformed via square-root of (Y + 0.5) for purposes of
normalization (see Sokal and Rohlf, 1985). See Table 2a for details of inter-
platform comparisons. See Table 1 for sample sizes.
Figure 3. Geographic distribution of the density of Tubastraea micranthus in the northern
Gulf of Mexico, south of the Mississippi River mouth. Note the primary peak (at
GI-93C, the presumed location of initial invasion), the secondary peak (at GI-
116A) indicating a strong southerly spread, and the dissipation of density radially
from these points. Numnbers represent study platforms. See Table 1 for platform
Figure 4. Mean colony size of Tubastraea micranthus in the northern Gulf of Mexico, south
of the Mississippi River mouth. Note that the largest average colony sizes are
found on MC-311A, a potential original site of colonization and one a site which
occurs in blue water within the Mississippi Canyon, unlike many of the other
sites. Significant difference between colony sizes on different platforms (p <
0.001, one-way ANOVA; see Table 2b for detailed comparisons). Data
transformed by square root (Y + 0.5) for normalization purposes. See Table 1 for
Figure 5. Geographic distribution of the mean colony size of Tubastraea micranthus in the
northern Gulf of Mexico, south of the Mississippi River mouth. Note the primary
peak (at MC-311A, within the Mississippi Canyon) and how average colony size
decreases radially from that point, indicating that this site might possess the best
environmental conditions for growth for this species. Numbers represent study
platforms. See Table 1 for platform names.
Figure 6. Size-frequency distribution of colonies of Tubastraea micranthus on three
platforms in the northern Gulf of Mexico, near the Mississippi River mouth –MC-
109A (top), GI-93C (bottom left), and GI-116A (bottom right). Examplary of
distributions found on all platforms. Note the abundant over-representation of
smaller-sized colonies, potentially indicating high explosive population growth
with low doubling times. Platform MC-109A: Mean = 198.6 cm2, s.d. = 281.14,
ni = 47, g1 = 1.92, g2 = 3.36. Platform GI-116A: Mean = 34.7 cm2, s.d. = 45.60,
ni = 24, g1 = 2.74, g2 = 8.23. Platform GI-93C: Mean = 33.5 cm2, s.d. = 94.18, ni
= 472, g1 = 7.19, g2 = 63.11.
Figure 7. Density of Tubastraea coccinea in the northern Gulf of Mexico on 14 platforms
off the mouth of the Mississippi River. Densities shown in no./m2 with 95%
confidence limits. Densities are highly significantly different from each other (p
< 0.001, one-way ANOVA). Data transformed via square-root of (Y + 0.5) for
purposes of normalization (see Sokal and Rohlf, 1985). See Table 2c4 for details
of inter-platform comparisons. See Table 1 for sample sizes.
Figure 8. Geographic distribution of the density of Tubastraea coccinea in the northern
Gulf of Mexico, south of the Mississippi River mouth. Note the primary peak (at
ST-185B and GI-116A), exhibiting a distribution pattern similar to that of T.
micranthus. Also note the dissipation of density radially from these points.
Numbers represent study platforms. Platform names given in Table 1.
Table 1. List of 14 platforms in the northern Gulf of Mexico, near the mouth of the
Mississippi River, video-surveyed by ROV for the ahermatypic invasive Indo-
Pacific corals Tubastraea micranthus and T. coccinea. Platform number, name,
owner, and latitude and longitude of geographic location, and number of quadrats
analyzed per platform provided.
Table 2. (a) Summary of results of a posteriori multiple comparisons of means tests
performed on mean colony densities of Tubastraea micranthus on 14 oil/gas
platforms in the northern Gulf of Mexico. T’, T-K, and GT-2 tests were used.
Results of pairwise comparisons shown. Platforms are shown in order of density,
high to low. An asterisk denotes a significant difference between coral densities
on two given platforms. (b)
Table 3. Summary of results of a posteriori multiple comparisons of means tests
performed on average colony sizes of Tubastraea micranthus on 14 oil/gas
platforms in the northern Gulf of Mexico. T’, T-K, and GT-2 tests were used.
Results of pairwise comparisons shown. Platforms are shown in order of average
colony size, high to low. An asterisk denotes a significant difference between
coral colony sizes on two given platforms.(c) Summary of results
Table 4. Summary of results of a posteriori multiple comparisons of means tests
performed on mean colony densities of Tubastraea coccinea on 14 oil/gas
platforms in the northern Gulf of Mexico. T’, T-K, and GT-2 tests were used.
Results of pairwise comparisons shown. Platforms are shown in order of density,
high to low. An asterisk denotes a significant difference between coral densities
on two given platforms.
Mean Density by Platform
Mean Density (per m
Mean Colony Size by Platform
Mean Colony Size (cm
Mean Density by Platform
Mean Density (per m
Code Owner Latitude Longitude
GI-90A-1 Apache Corp. 28.575144 -90.072429
GI-90A-2 Apache Corp. 28.575144 -90.072429
GI-93C Apache Corp. 28.548886 -90.068677
GI-115A Walter Oil & Gas Corporation 28.3076123 -90.0219665
GI-116A Apache Corp. 28.30928306 -90.07054334
MC-109A Stone Energy Corporation 28.86467752 -88.93079054
MC-311A Apache Corp. 28.642636 -89.794241
SP-87D Apache Corp. 28.72001853 -89.43078669
SP-89B Apache Corp. 28.680464 -89.387596
JA(B) Stone Energy Corporation 28.76955709 -90.74085664
ST-81A Stone Energy Corporation 28.78656092 -90.42747823
Black Elk Energy Offshore Operations,
LLC 28.495501 -90.203098
Black Elk Energy Offshore Operations,
LLC 28.47493 -90.235942
ST-206A Apache Corp. 28.45372522 -90.38341283
Platform Number of
r Code Owner Latitude Longitude Quadrats
1 GI-90A-1 Apache Corp. 28.575144 -90.072429 23
2 GI-90A-2 Apache Corp. 28.575144 -90.072429 129
3 GI-93C Apache Corp. 28.548886 -90.068677 125
4 GI-115A Walter Oil & Gas Corporation 28.3076123 -90.0219665 44
5 GI-116A Apache Corp. 28.30928306
6 MC-109A Stone Energy Corporation 28.86467752
7 MC-311A Apache Corp. 28.642636 -89.794241 174
8 SP-87D Apache Corp. 28.72001853
9 SP-89B Apache Corp. 28.680464 -89.387596 90
JA(B) Stone Energy Corporation 28.76955709
11 ST-81A Stone Energy Corporation 28.78656092
Black Elk Energy Offshore Operations,
LLC 28.495501 -90.203098 87
Black Elk Energy Offshore Operations,
LLC 28.47493 -90.235942 22
14 ST-206A Apache Corp. 28.45372522
GI-93C * * * * * * * * * * *
GI-116A * * * *
B89B SP-87D GI-
116A GI-93C GI-90A GI-115A
MC-311A * * * * * * * *
MC-109A * * *
ST-185B * * * * * * * * * * * *
* * * * * * * * * *
MC-311A * * * *
ST-185A * *