Spatial Abundance and Colour Morphotype Densities of the Rock-Boring Sea Urchin (Echinometra lucunter) at Two Different Habitats

Abstract

The rock-boring sea urchin Echinometra lucunter is a common echinoderm found throughout the intertidal zone along the northeastern coast of, Toco, Trinidad. Sea urchin abundance, size distribution, and colour morphotypes at two sites: Pequelle Bay (SB) and Grande L’Anse (GA) were quantified using 1 m2 quadrats, accessible during extreme low tides, and in two environments, notably low and high wave action. Percent coverage of cnidarian and macroalgae were estimated in each quadrat. Sea urchin densities were 9.9–17.8 urchins/m2 in high wave action, and 25.2–60.7 urchins/m2 in low wave action environments. Size (measured as maximum sea urchin diameter) are highest between 21 and 50 mm for both black and red colour morphotypes. Black colour morphs were significantly larger than red morphs (ANOVA, F2, 175 = 5.55, p < 0.05). Sea urchins at low energy environments were significantly larger than those found in high energy environments for all years (p < 0.05). Mean hard coral, soft coral, and macroalgae cover did not show any relationship with habitat type or urchin densities. Although sea urchin abundance and distribution were variable, larger urchins were more likely to be found in low wave action environments, and smaller urchins were mostly found in the open, and exposed to high wave action.

Full text

1 23
Thalassas: An International Journal of
Marine Sciences
ISSN 0212-5919
Volume 36
Number 1
Thalassas (2020) 36:157-164
DOI 10.1007/s41208-019-00170-2
Spatial Abundance and Colour
Morphotype Densities of the Rock-Boring
Sea Urchin (Echinometra lucunter) at Two
Different Habitats
S.G.Belford

1 23
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Spatial Abundance and Colour Morphotype Densities
of the Rock-Boring Sea Urchin (Echinometra lucunter)
at Two Different Habitats
S. G. Belford
1
Received: 27 October 2018 /Revised: 28 February 2019
#Springer Nature Switzerland AG 2019
Abstract
The rock-boring sea urchin Echinometra lucunter is a common echinoderm found throughout the intertidal zone
along the northeastern coast of, Toco, Trinidad. Sea urchin abundance, size distribution, and colour morphotypes
at two sites: Pequelle Bay (SB) and Grande L’Anse (GA) were quantified using 1 m
2
quadrats, accessible during
extreme low tides, and in two environments, notably low and high wave action. Percent coverage of cnidarian
and macroalgae were estimated in each quadrat. Sea urchin densities were 9.9–17.8 urchins/m
2
in high wave
action, and 25.2–60.7 urchins/m
2
in low wave action environments. Size (measured as maximum sea urchin
diameter) are highest between 21 and 50 mm for both black and red colour morphotypes. Black colour morphs
were significantly larger than red morphs (ANOVA, F2, 175 = 5.55, p< 0.05). Sea urchins at low energy envi-
ronments were significantly larger than those found in high energy environments for all years (p< 0.05). Mean
hard coral, soft coral, and macroalgae cover did not show any relationship with habitat type or urchin densities.
Although sea urchin abundance and distribution were variable, larger urchins were more likely to be found in
low wave action environments, and smaller urchins were mostly found in the open, and exposed to high wave
action.
Keywords Colour morphotypes .Wave action environments .Sea urchin .Echinometra lucunter .Fringing reef .Southern
Caribbean
Introduction
The decline of coral reefs in the Caribbean due to
events, such as shifts in macroalgae dominance, local
point-sources of pollution, increasing sea surface tem-
peratures, overfishing, and other anthropogenic distur-
bances have been recorded over the years (Knowlton
2001;Pandolfietal.2003; Cameron and Brodeur
2007; Hughes et al. 2007; Burke et al. 2011;Perry
et al. 2015). In addition, coral bleaching events, and
disease outbreaks are becoming more frequent (Miller
et al. 2009;WeilandCróquer2009; Hoegh-Guldberg
et al. 2014; Heron et al. 2016), and recovery time be-
tween bouts is too short for full recovery (Hughes et al.
2018). Most notably, massive disease-induced sea urchin
Diadema antillarum (Philippi 1845) mortality has not
recovered after the outbreak in the early 1980s (Glynn
1984; Lessios et al. 1984).
Apart from past sea urchin mortality (Lessios et al.
1984;Hughes1994; Gardner et al. 2003), and continuing
trends in climate change, Caribbean reefs may change in a
dynamic way in the future (Raffaelli & Hawkins 1999;
Hernandez-Delgado and Suleiman-Ramos 2014). In partic-
ular, one valuable benthic organism that is important to
ecological reef processes are echinoids (Hughes 1994). In
fact, Echinometra lucunter (Linnaeus 1758) is one such
common echinoid found widely distributed throughout
the western Atlantic Ocean (Lewis and Storey 1984). In
addition, Echinometra virdis also shares common distribu-
tion in the Caribbean (Geyer & Lessios 2009), making
both species sympatric in this region.
Electronic supplementary material The online version of this article
(https://doi.org/10.1007/s41208-019-00170-2) contains supplementary
material, which is available to authorized users.
*S. G. Belford
sbelford@martinmethodist.edu
1
Division of Mathematics and Science, Martin Methodist College,
433 West Madison Street, Pulaski, TN 38478, USA
https://doi.org/10.1007/s41208-019-00170-2
Thalassas: An International Journal of Marine Sciences (2020) 36:157–164
/ Published online: 22 October 2019
Author's personal copy

Pawson (2007) stated that the Caribbean Sea alone
has a rich echinoderm diversity, with 433 echinoderm
species. Urchins have an integral impact on coral reef
communities, specifically related to their effects on al-
gae as herbivores, and as controllers of benthic commu-
nities (Carpenter 1986;Sala1997; Sanchez-Jerez et al.
2001; Rivera-Monroy et al. 2004; Cameron and Brodeur
2007; Miloslavich et al. 2010; Schultz 2010) and on
rock substrata with their bioeroding (Shiel and Foster
1986; Hughes 1994; Hendler et al. 1995). Although
much of the echinoid research has focused on
Diadema antillarum, and documenting its demise in
the early 1980s (Glynn 1984; Lessios et al. 1984;
Hughes et al. 2010), research on other echinoid species
is likely to add to current knowledge of their ecology.
E. lucunter is one such species that is common through-
out the Caribbean, and extends its range to Florida,
Brazil, and West Africa (McPherson 1969; Hendler
et al. 1995;Ebertetal.1999;Ebertetal.2008;
McClanahan & Muthiga 2013; Belford et al. 2019).
Two sub-species of E. lucunter have been identified in
the Caribbean (polypora and lucunter, McClanahan &
Muthiga 2013). Commonly found in shallow waters of
<10 m in depth, E. lucunter has an elliptical shape with
a maximum test diameter (measured as maximum sea ur-
chin diameter) of 150 mm, and approximately 100–150
spines projecting from its central test (Hendler et al.
1995; Blevins and Johnsen 2004). It is mostly found in
shallow waters, and typically lodges itself in crevices
during the day. Although Ebert et al. (2008) noted that
E. lucunter is geographically located from North
Carolina and Bermuda through the Caribbean to Brazil
and West Africa, distribution of these species follows
the general characteristics of urchins, which at best, dis-
play patchy distributions (Dumas et al. 2007), therefore it
is difficult to explain general distribution and densities.
Average densities have been reported as 11 individuals
per m
2
Pomba et al. 1990), up to 129 individuals per m
2
(Greenstein 1993), and 240 individuals per m
2
(Grunbaum et al. 1978).
Currently, little is known about sea urchin colour
morphotype densities and sizes in the southern
Caribbean. Lewis and Storey (1984) noted that
E. lucunter spine colour, which plays a primary role in
determining colour morphotype were significantly different
at sites, and mentioned this variability as a result of
different food sources. McPherson (1969) noted that drift
algae was the primary food source, and Hendler et al.
(1995) stated that encrusting calcareous red algae was an-
other food source, which possibly plays a role in colour
variability in sea urchins. A wider variety of algal food
availability does result in variable expression of colour
morphotypes (Lewis and Storey 1984).
Surveys on macroalgal cover on reefs show a corre-
lation with sea urchin abundance. For instance,
Cameron and Brodeur (2007) observed highest
macroalgal cover when Diadema antillarum,
Echinometra lucunter,andTripneustes ventricosus spe-
cies were absent. Additionally, surveys also have shown
predatory fishes and a lack of safe shelters to protect
sea urchins from predation, as factors that explain den-
sity and size distribution (Alvarado 2011). Safe shelters
have been reported to harbor specific sea urchin sizes:
large crevasses support larger sea urchins, and smaller
crevasses support smaller urchins (Hereu et al. 2005).
This study aims to determine patterns in abundance,
and density of sea urchin colour morphotypes across
two habitats along the coast of this southern-most re-
gion of the Caribbean Sea. The following questions
were addressed: (1) Do sea urchins show patterns in
abundance in high and low energy environments? (2)
Are there patterns in colour morphotypes abundance in
these two habitats? Finally, (3) do coral and algae cover
have any relationship between habitat type and sea ur-
chin abundance? As in Lewis and Storey (1984), I hy-
pothesize that sea urchin colour morphotypes will be
more abundant and larger at low energy environments
compared to high energy environments, because these
urchins are protected from waves by rocky outcrops.
Additionally, I predict high densities at sites due to a
lack of visible predators. As E. lucunter is a main graz-
er of algae, benthic macroalgae coverage will be quan-
tified to determine if there is a relationship with sea
urchin abundance.
Methods
Survey Sites
The northeastern coast of Trinidad adjacent to the Caribbean
Sea has numerous undeveloped patch reefs, and the only
fringing reef of Trinidad and Tobago, West Indies, which lies
on the northeastern coastal tip, located approximately 2 km
south of the Keshon Walcott Toco Lighthouse, Galera Point
(10° 50´´N, 60° 55′´ W). This fringing reef has a mixture of
sandy, rocky, and stony beaches in close vicinity of the Matura
River, which periodically has its outflow burst through its
sandy boundary during heavy rainfall. A period of low rainfall
(dry season) exists from January to late May mid-June follow-
ed by a rainy period until December. Salinity and water tem-
peratures range between 31 and 33 ppt. and 28–32 °C respec-
tively, and are relatively consistent. Tides are semidiurnal with
a maximum high tide of 2 m in open water, and > 1 m low tide
minimum.
Thalassas (2020) 36:157–164
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Fieldwork was conducted at Pequelle Bay (SB),
which is a part of Salybia Bay reef (Site 1: 10° 50′´
N, 60° 55′´ W), which is a fringing reef located ~2 km
from Galera Point, that is the most northeast point of
Trinidad (Fig. 1). The reef extends ~200 m towards the
reef crest, of which approximately 180 m is accessible
by wading during lowest low tides. The reef at Grande
L’Anse (GA), also known as Toco Bay (Site 2: 10°
50′´N,60°55′´ W) is an arrangement of underdevel-
oped patch reefs, and most of it extends ~50 m from
the shoreline, however there is a small area that ex-
tends ~80 m during lowest low tides, with ~60 m ac-
cessible from the shoreline (see Belford and Phillip
2011).
At each site, a specific rocky outcrop, only accessible
during lowest low tides was designated as an area
where sea urchins were protected from intense wave
action, that is, a low energy environment. A high ener-
gy environment was exposed to the full spectrum of
wave energy, and located close to the reef crest.
Sampling areas were no more than 250 m
2
where ran-
dom quadrats were used to collect data, with a maxi-
mum of 3 h of exposed lower intertidal zone
accessibility.
Sampling Method
All sampling was done at the lower intertidal zone
close to the reef crest, where these sites were previous-
ly selected for surveying sea urchins. Sea urchin pop-
ulation abundance and densities were collected using
the quadrat method. A 1 m × 1 m
2
square polyvinyl
chloride (PVC) frame was randomly tossed over each
sampling area of approximately 250 m
2
(N= 120 quad-
rats per site), and all sea urchins within the quadrat
were counted, with red and black colour morphotypes
(Fig. 2) separately counted to give the total sea urchin
density per m
2
. Abundance was calculated as total sea
urchins per site/environment. Percentage cover of ben-
thic components, such as hard coral, zoanthid, coral
rubble, invertebrate, and macroalgae coverage within
each quadrat were recorded to determine if any pat-
terns existed between sea urchin densities and benthic
components.
Sea urchin colour morphotypes were randomly select-
ed from each quadrat, and a 20 cm stainless steel micro
spatula with flattened ends was used to gently pry ur-
chins from their benthic substrate. Fragments and algae
lodged between individual spines were manually re-
moved before measurements. Test diameter was mea-
sured using a hand caliper to the nearest 0.1 mm. A
digital hand-held scale was used to measure the weight
of the urchin. All measurements were completed no
longer than 45 s. for each urchin, and urchins were
returned to their aquatic habitat immediately after all
data were recorded. All measurements were done during
a short period of a few weeks in June, which provided
a brief window where turbidity and accessibility were
not an issue, hence the reason to collect data over the
time period mentioned above.
All results gathered from populations of Echinometra
lucunter were sampled at a patch and fringing reef ap-
proximately 3.5 km distance apart, along the northeast-
ern coast of Trinidad, West Indies in order to determine
Fig. 1 Map showing the location of Trinidad relative the Caribbean (left) and the study sites located on the northeastern coast of Trinidad (right)
illustrating the distance of the only marine protected area at Buccoo Reef, Tobago (see Belford and Phillip 2011)
Thalassas (2020) 36:157–164 159
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if sea urchin abundance, densities, and sizes were sim-
ilar at these reefs. Sampling was conducted during ex-
treme low tides (0.2 m depth) early June 2015, 2016,
and 2017 over a 1-week period at Pequelle Bay (SB)
reef and Grande L’Anse (GA) reef, at habitats associat-
ed with low and heavy wave action.
Data Analysis
A general linear model, such as Analysis of Variance
(ANOVA) was used to compare sea urchin test diam-
eter and weight between years, sites, colour
morphotypes (black and red), and type of environment
(low and high wave action). Test diameter data and
weight recorded were used to analyze correlation. To
test for differences in size between different habitats
and sites, data for test diameter and weight were an-
alyzed using ANOVA.
Results
In 2015 sea urchin densities at Salybia Bay (SB) were
30.5 urchins per m
2
in low wave action areas compared
to 14.9 urchins per m
2
in areas of high wave action. At
Grande L’Anse reef (GA) 58.0 sea urchins per m
2
was
recorded at low wave action areas compared to 9.9 ur-
chins per m
2
in high wave action areas. In 2016 sea
urchin densities at SB were 60.7 per m
2
in low wave
actioncomparedto17.8inhighwaveaction.Results
for GA were 53.0 urchins per m
2
in low wave action
and16.1perm
2
in areas of high wave action. For 2017
densities were 60.0 urchins per m
2
in low wave action,
and11.2urchinsperm
2
in high wave action at SB
compared to 25.2 urchins per m
2
in low wave action
and 16.2 urchins per m
2
in high wave action at GA
respectively. Altogether higher sea urchin densities were
observed in low wave action (protected), compared to
high wave action (open).
Although sea urchins were just as abundant at both
sites, black colour morphotypes were significantly more
abundant than red morphs (p< 0.05), hence also more
abundant in high versus low wave action environments.
Sea urchin abundance at each site was categorized as
dominant with an average of 25 urchins or more per
quadrat, followed by average between 5 to 25 urchins
per quadrat, and low abundance at less than 5 urchins
per quadrat. Overall, for all years (2015, 2016, 2017)
sea urchins at low wave action habitat were dominant at
both sites, however sea urchins were only abundantly
average if they were found in high wave action.
Interestingly, black colour morphs were abundantly
dominant in low wave action habitat for all years, how-
ever red colour morphs showed average abundance. In
high energy wave action habitat black colour morphs
were abundantly average, whereas red colour morphs
showed low abundance.
Test diameter showed a strong correlation with sea
urchin weight at each site for all years, therefore justi-
fying these parameters as a measure of size (correlation
coefficients 2015: r = 0.91 (SB) r = 0.92 (GA); 2016: r =
0.87 (SB) r = 0.78 (GA); 2017: r = 0.72 (SB) r = 0.90
(GA)). Overall sea urchin mean test diameters (± SD)
for high wave action were 29.68 mm ± 8.03 (2015),
33.69 mm ± 6.76 (2016), and 32.11 mm ± 10.81 (2017).
Test diameter mean (± SD) for low wave action were
33.84 mm ± 12.64 (2015), 38.76 mm ± 9.24 (2016), and
38.18 mm ± 10.44 (2017). Thus urchins in low wave
energy habitat were more likely to be larger for both
colour morphotypes. Sea urchins in both habitats and
at both sites for each year were more likely to have a
test diameter ranging from 21 to 60 mm in length
(Fig. 3a-c), which is typically small (1–39 mm), and
medium (40–60 mm). However, sea urchins with the
largest test diameters (61–70 mm), which are defined
as large (61–100 mm) were more likely to be found
in areas of low wave action (see Appana et al. 2004
for size classes).
There was a significant increase in sea urchin size
amongst years for test diameter (ANOVA, F2, 321 =
8.33, p< 0.05), and weight (ANOVA, F2, 305 = 3.88,
p < 0.05). Sea urchins at sites for each year showed
significant differences in test diameter and/or weight at
PB, and GA (ANOVA, p< 0.05). Black colour morphs
had significantly larger test diameters than red morphs
(ANOVA, F2, 175 = 5.55, p < 0.05). Additionally, sea
urchins in low energy environments were significantly
larger than those found in high energy environments for
all years (t-test, p<0.05).
Mean test diameter was significantly larger for the
red colour morphed urchins in low wave action, that
is, rocky protected areas versus high wave action, or
open areas at SB in 2015 (t-test, t = 4.41, p<0.05,
Fig. 4a) and 2016 (t-test, t = 2.25, p < 0.05, Fig. 4
Fig. 2 Red and black colour morphotypes observed at Pequelle and
Grande L’Anse Bays, Toco, Trinidad
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c), and also for black colour morphs in 2016 (t-test,
t=2.67, p< 0.05, Fig. 4c). In 2017, mean test diame-
ter was significantly larger for the black colour
morphed urchins living in low wave action habitat (t-
test, t = 3.44, p< 0.05, Fig. 4e). Mean weight of red
morphs in low wave action habitat was significantly
heavier than that of red colour morphs in open habitat
at SB in 2015 (t-test, t = 4.97, p < 0.05, Fig. 4b).
Results for 2016 showed red colour morphs in rocky
habitat significantly weighed more than red colour
morphs in open habitat at GA (t-test, t = 2.17, p <
0.05, Fig. 2d). Mean weights showed no significant
increase or decrease for either colour morphs in 2017.
Both sites are dominated by 35–50% zoanthid coverage
(see Belford and Phillip 2011,2012), with scleractinian corals
maintaining 10–15% coverage throughout the reefs.
Macroalgae coverage recorded 10–15% in each year. Fish
diversity includes members represented from a variety of fam-
ilies, such as Chaetodontidae, Acanthuridae, Scombridae,
Pomacentridae, and Muraenidae.
Discussion
For the first time in Trinidad, sea urchin abundance, density,
and size in low and high wave action habitats were surveyed
over brief periods during a 3-year duration at shallow reefs
along the north-eastern coast. Both sea urchin colour morphs
were abundantly dominant in low wave action habitat, which
was similarly reported for Echinometra lucunter by Lewis and
Storey (1984). Abundance was average for black morphs and
low for red morphs in high wave action. Lawrence and Kafri
(1979) suggested that urchins in high wave action may suffer
higher mortality in general, and the dominant abundance of
sea urchins in low wave action ‘protected’habitat, may be the
result of a lack of predation from fishes, as fish predation has
been seen to cause differences in abundance and size distribu-
tion in sea urchins (Guidetti 2007;Comaetal.2011).
Black colour morphotypes had highest densities at both
sites, and this morph continued to show high densities at
low wave energy environments. Similar results were
encountered by Lawrence and Kafri (1979) illustrating greater
urchin densities in protected areas. In contrast, not all sea
urchin species show this characteristic, as Echinometra
mathaei and Echinometra oblonga aremoredominantinhigh
wave action habitat (Russo 1977). Other biota in close vicinity
to urchins were surveyed to determine if there were any pat-
terns that existed with urchin densities, however no such pat-
terns were recorded. The black colour morph made up the
dominant type on reefs, but similar differences in size and
weight were recorded for both black and red morphs in low
andhighenergyenvironments.
Although this species can reach 150 mm in size (Hendler
et al. 1995), most urchins in this study were 21–50 mm, with
largesttestdiameterreportedat51–70 mm. The densest sizes
(21–50 mm range) also were found in both low and high
energy environments, however significantly larger urchins
were found in low energy environments at both sites. Lewis
and Storey (1984) found similar results, but no mention was
made to colour morphotypes of E. lucunter, therefore this
study did reveal similar results for both colour morphs.
Appana et al. (2004) reported significantly small
Echinometra sp. (1–39 mm) dominating the reef crest (high
(a)
(b)
0
5
10
15
20
25
30
35
40
0-10 11-20 21-30 31-40 41-50 51-60 61-70
Frequency
Test Diameter (mm)
0
5
10
15
20
25
30
35
40
0-10 11-20 21-30 31-40 41-50 51-60 61-70
Frequency
Test Diameter (mm)
(c)
0
5
10
15
20
25
30
35
40
0-10 11-20. 21-30 31-40 41-50 51-60 61-70
Frequency
Test Diameter (mm)
Fig. 3 Variation in sea urchin size frequency at Pequelle Bay reef (SB =
Black bars) and Grande L’Anse reef (GA = White bars) for (a) June 2015,
N= 72 SB, 70 GA, (b)June2016,N= 58 SB, 51 GA, and (c) June 2017,
N= 24 SB, 55 GA
Thalassas (2020) 36:157–164 161
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wave action), with larger individuals (61–100 mm) absent.
Additionally, this study showed near normal distribution of
sea urchin size classes found in both habitats, which also
was reported on Fijian reefs (Appana et al. 2004).
Macroalgae cover throughout this study was considerably
low in comparison to other studies in the Caribbean, which
highlight its dynamic role on benthic communities. For exam-
ple, Olson and Steneck (2007) mentioned a significant in-
crease in macroalgae coverage coinciding with a decline in
parrotfish population in Bonaire during 2003 and 2005, which
resulted in declining reef species. However, a 2007 study stat-
ed that Bonaire reefs had improved, due to macroalgae abun-
dance of 5%, due to an increased in herbivores, such as sea
urchins.
Zoanthids have been recorded to occupy different zones
according to the nature and type of habitat. For example,
Belford and Phillip (2012) noted that Zoanthus sociatus colo-
nized stressed areas where exposure was the greatest, com-
pared to Palythoa caribaeorum colonies, which preferred less
stressed areas on the reefs. Unlike sea urchins, which can
borrow into crevasses when desiccation increases due to ex-
treme low tides, specific zoanthids may or may not occupy
high wave action areas, which become exposed for at least 3 h
during extreme low tides. Moreover, distribution of
Z. sociatus and P. caribaeorum is related to desiccation toler-
ance (Herberts 1972), whereas E. lucunter colour morph dis-
tribution does not appear to have a determining factor, except
for size being determined by low or high energy
environments.
Sea urchin distributions in this study were clumped, but
may generally be patchy, with densities varying from 0 to
100 urchins per m
2
(Dumas et al. 2007). Moderately dense
concentrations were reported in this study 30–33 urchins per
m
2
compared to 11 per m
2
(Pomba et al. 1990) and 111 ur-
chins per m
2
quadrat (this study) compared to 129 urchins
(Greenstein 1993). Even though moderate densities were re-
ported in this study, Young and Bellwood (2011) noted that
densities may be underestimated, because of urchin activity.
Higher densities are seen at night when most urchins are ac-
tive, however this study collected urchin data during the day,
and at extreme low tides, where access was readily easy at
both energy-related environments.
Both sites are generally unfished areas, therefore urchin
densities are not lost by fishing nets. No attempts were made
Fig. 4 Mean test diameter and weight for sea urchin colour morphotypes
in relation to habitat type at Salybia Bay reef (SB) and Grande L’Anse
reef (GA) are illustrated in (a) SB Rocky versus SB Open mean test
diameter in June 2015 (b) SB Rocky versus SB Open mean weight in
June 2015 (c) SB Rocky versus SB Open mean test diameter for both
colour morphs at SB in June 2016 (d) GA Rocky versus GA Open mean
weight in 2016, and (e) SB Rocky versus SB Open mean test diameter in
June 2017. Significant differences (ANOVA, p< 0.05) and error bars
indicate standard error
(a)
(b)
(c)
(d)
(e)
0
10
20
30
40
50
60
SB-Rocky
(Black)
SB-Rocky
(Red)
SB-Open
(Black)
SB-Open
(Red)
)mm(retemaiDtseTnaeM
Habitat Type
*
0
10
20
30
40
50
60
SB-Rocky
(Black)
SB-Rocky
(Red)
SB-Open
(Black)
SB-Open
(Red)
Mean Weight (g)
Habitat Type
*
0
10
20
30
40
50
60
SB-Rocky
(Black)
SB-Rocky
(Red)
SB-Open
(Black)
SB-Open
(Red)
)
m
m(r
e
temai
D
tse
T
naeM
Habitat Type
**
0
10
20
30
40
50
60
GA-Rocky
(Black)
GA-Rocky
(Red)
GA-Open
(Black)
GA-Open
(Red)
Mean Weight (g)
Habitat Type
0
10
20
30
40
50
60
SB-Rocky
(Black)
SB-Rocky
(Red)
SB-Open
(Black)
SB-Open
(Red)
)mm(retemaiDtseTnaeM
Habitat Type
*
*
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to record urchin densities at night due to the inaccessibility of
these sites, as a result of unpredictable wave action. Urchin
movement away from their shelters have been documented at
night (Carpenter 1986; Young and Bellwood 2011), therefore
this may be worth investigating in a future study.
Overall, both colour morphs distribution on reefs are too
variable to justify a specific pattern. Except for low energy
environments at Pequelle Bay in 2015, both colour morphs
showed stable densities in both environments at both sites.
Once again it should be noted that urchin numbers may be
under-represented, which may deem a night study focusing on
densities necessary.
Acknowledgements This work was supported by partial funding from
the Martin Methodist College Biology department, alumni council, and
International Studies department. Field assistants involved in some data
collection were Bradley Crye, Markeyta Bledsoe, Madeline Woods,
CalliAnna McDonald, and Douglas Dorer. Dawn A.T. Phillip is credited
for field observations that were instrumental to the development of this
manuscript.
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