Assessment of the Marine Environment at Malgretoute
Location
The proposed development is adjacent to the Malgretoute Beach, approximately 650m
long with a rocky shoreline at the north end and the start of the Petit Piton cliff face at
the south end. Note that the site plan shows the coastline as depicted in the 1992
topographic maps but this has receded since then, particularly in the northern half of
the beach, by as much as 10m.
The zoning plan of the Soufriere Marine Management Association shows that the area
off the beach is designated as a Yachting Area,, beach; at either end is a Fishing
Priority Area, and a Marine Reserve around Petit Piton. The seaward extent of the
SMMA boundary is presently designated as the 75m isobath.
Depth profiles
Depth profiles we determined from position and depth data gathered along transects
perpendicular to shore using a narrow-beam active sonar logging at 0.2Hz to a
Garmin GPS receiver. Profiles were generated from the 3D model developed from the
transect data in Map Maker Pro. The location of the profiles is indicated in Figure 3.
Transects were run from the shoreline to approximately the 75m isobath and show
that the slope becomes steeper progressing from north to south.
Figure 1 a. Depth profile 1, immediately north of Malgretoute beach.
Figure 1 b. Depth profile 2.
Figure 1 c. Depth profile 3, off Petit Piton.
Circulation
There are few available data on coastal currents around St. Lucia but those that are
accessible indicate that flow is primarily southward along the coast in the area of
Malgretoute, but with some local gyres with a northward component. Long-term
monitoring would be needed to describe the circulation in detail. Surface current
measurements were made by monitoring the drift of drogues with timed and
positioned with GPS. Measurements in November and December 2008 confirm the
expected pattern with the major component of circulation being southwest at speeds
of 0.1kt to 1.0kt, with the higher values recorded during the rising tide. Locations and
results of surface current measurements are indicated in Figure 2.
Figure 2. Direction and speed of measured surface currents.
Description of benthic habitats.
The distribution of main substrate types is shown in Figure 2. The study area was
treated as five zones, numbered from north to south.
Benthic community surveys were conducted with a combination of visual qualitative
surveys with photography, and quantitative methods based on photo quadrats (Kohler
and Gill, 2006). The substrate consisted of large boulders which did not permit the use
of a typical transect survey. Instead, flat boulder surfaces were selected at random and
photographed with a Nikonos V camera and 19mm (wide-angle) lens, at a distance of
approximately 1m. Images were scanned, and an area of approximately 1m2 from
each image was analysed on computer using a heads-up random point count method,
based on 100 points per quadrat. Substrate type was recorded at each point and the
data were analysed to determine the percent cover of each substrate type. Coral
species richness and relative abundance data were used to calculate the ShannonWeiner index of diversity (H’ = ∑pi ln pi). Malgretoute is one of a number of stations
monitored using the Reef Check methods (Hodgson et al. 2006). One component is
point-intercept transects whereby a 100m transect is divided into four 20m sections
and the substrate is recorded every 0.5m, to give a total of 160 points per transect.
Zone A. Rocky substrate immediately north of Malgretoute Beach.
Directly off the steep rocky shoreline the substrate consists of rocks covered by silt
and algal turf. Live corals were scarce with a few small (50 – 100mm diameter)
colonies of Porites astreoides and Diploria clivosa. There was no evidence of
recently killed corals, or older coral remnants, and it appeared that coral abundance
had not been any greater in the past few years. Some gorgonians were present but also
very sparse. Macroalgae were very abundant, but not diverse, consisting of three
species of red algae, Crouania attenuate, Liagora dendroides and L. ceranoides.
Figure 4. Zone A at 2m depth: hard substrate covered with silt and turf algae (1) and
very abundant red macroalgae (Liagora spp.) (2).
Zone B Directly off Malgretoute Beach
Adjacent to the beach is a band of rock and rubble ranging in depth from <0.5m to
>10m. As in Zone A these were covered by algal turf and silt. A few small (50 100mm diameter) colonies of the fire coral Millepora complanata and the hard corals
Porites astreoides and Diploria labyrinthiformis were noted. Gorgonians
(Pseudopterogorgia rigida) to 1m tall were common (Figure 5).
Figure 5. Hard substrate typical of Zones A and B at 5m depth, showing sedimentcovered rock (1), abundant Liagora spp. (2), scattered coral recruits (Siderastrea
siderea, 3) and gorgonians (Pterogorgia rigida, 4).
Fish abundance and diversity were low in all surveys, limited to occasional small
schools of sergeant majors (Abudefduf saxatilis) and surgeonfish (Chaetodontidae ).
On the sand at the southern end of the beach a patch approximately 20m across of the
garden eel (Heteroconger halis) was noted at 5m depth. The bloom of red macroalgae
noted in Zone A continued, but with only the two Liagora species abundant (Figure
2). To the seaward side of the rocks is a sloping sand substrate.
Zone C. Shallow substrate (<8m) immediately south of Malgretoute Beach
At the south end of the beach the substrate consists of boulders extending from the
shoreline to deep water (>35m). The rock surfaces are free of the algal turf and silt
found in Zones A and B. The herbivorous long-spined sea urchin (Diadema
antillarum) was comparatively common and the substrate was dominated by
encrusting coralline algae. Macroalgae were rare. Fish abundance also increased
compared with Zones A and B, with large schools of chromis ( Chromis multilineata)
and sergeant majors and numerous parrotfish and damselfish.
Figure 6. Zone C at 4m depth. Boulders with less algal turf and more encrusting
coralline algae (1) than substrate in Zones A and B; coral recruits 50 – 100mm
diameter more common, including Diploria strigosa (2) and Siderastrea siderea (3).
Some mortality of recruits was evident but rare (4).
Figure 7. Zone C. at 8m depth. Species diversity increased with sponges and corals
becoming more abundant than in shallower water, including the barrel sponge
Xestospongia muta (1) and vase sponge Ircinia campana (5), and corals Diploria
strigosa (2) and Siderastrea siderea (4). Encrusting coralline algae common (6).
Zone D. Shallow substrate (<8m) below Petit Piton Point
Reef species diversity continued to increase southward from Zone C to Petit Piton
Point. Typical of this area of the west coast of St. Lucia the coral community is a
veneer on rock (Smith et al. 2000) and not a biogenic coral reef. Coral species
included Millepora complanata, Porites astreoides, Diploria strigosa, D. clivosa, D.
labyrinthiformis, Siderastrea siderea and Montastrea cavernosa.
Figure 8. Zone D at 2m depth. Substrate <2m has lower coral diversity and is
dominated by encrusting coralline algae.
Figure 9. Zone D at 6m depth, showing a veneer of reef species including sponges,
hard corals and gorgonians.
Figure 10. Zone D at 6m depth, showing a veneer of reef species including sponges
(1) (Spirastrella coccinea), hard corals (2) and gorgonians (3).
Fish abundance and diversity were higher than in zones A, B and C. Species included
Sergeant majors, schools of creole wrasse (Clepticus parrae) and surgeonfish, banded
butterflyfish (Chaetodon striatus), stoplight parrotfish (Sparisoma viride),yellowtail
damselfis (Microspathodon chrysurus), and yellowtail snapper (Ocyurus chrysurus).
Juveniles of many of the species were also abundant.
Table 1. Zone D Depth 5m Relative abundance of substrate classes determined from
point-intercept transects, as percent cover of substrate. Summarised from Reef Check
survey data.
Feb-2008
n=160
____________________
%
s.d.
_______
________
Oct-2007
n=160
_____________________
%
s.d.
________
________
Class.
Coral
9.4
3.75
16.3
6.29
Sponge
5.6
5.15
2.5
2.04
Macroalgae
0
5.6
3.15
Rock
68.1
7.18
60.0
7.36
Other
16.9
15.6
____________________________________________________________
Table 2. Zone D. Depth 2-5m. Relative abundance of substrate classes determined
from point intercept photo quadrat analysis. N=1450. Shannon Wiener Index for coral
= 1.03
Class
Live coral
Dead coral
Sponge
Macroalgae
Coralline algae
Other invertebrates
% substrate cover
10.8
0.07
0.76
0.14
86.28
2.00
Zone E. 10m depth, Marine Reserve Area below Petit Piton
Data from the most recent two Reef Check surveys are shown in Table 2. This is not
strictly a repeated measures method as the location of transects and the points along
them are not replicated precisely between surveys. The values therefore include the
variability between treatments and not an absolute measure of community change.
The method becomes more useful as an indicator of change over longer time periods.
Table 3. Zone E Depth 10m Relative abundance of substrate classes determined from
point-intercept transects, as percent cover of substrate. Summarised from Reef Check
survey data.
Feb-2008
n=160
____________________
%
s.d.
_______
________
Oct-2007
n=160
_____________________
%
s.d.
________
________
Class.
Coral
10.6
6.57
5.0
3.54
Sponge
15.6
6.67
5.0
2.89
Macroalgae
1.3
1.44
30.6
8.75
Rock
44.4
4.27
28.8
10.31
Other
28.1
30.6
____________________________________________________________
Synthesis
1. There is no particularly sensitive or critical habitat immediately north of, or directly
offshore from, Malgretoute beach. The nearshore substrate consists of rock covered
with a layer of silt and filamentous algae, with very few small colonies of hard corals
and gorgonians;
2. Immediately to the south of the beach the rocky substrate has been less impacted by
siltation, with an increase in cover of encrusting coralline algae, increasing numbers
of the herbivorous long-spined sea urchin and hard coral colonies;
3. The Marine Reserve Area below Petit Piton is characterised by large ( 5-10m
diameter) boulders supporting a more diverse assemblage of reef species, with coral
cover ranging from 10 - 16% of the top and sides of the boulders in shallow water,
and 5 – 10% at 10m depth;
4. Data on community composition are not available for greater depths but the area
below Petit Piton is considered by the SMMA to be of critical importance for the high
quality of recreational SCUBA diving that takes place there;
5. Given that coastal currents are primarily southward along the shore, any increase in
sediment load in the water at Malgretoute can be expected to impact the benthic
community in both the Fishing Priority Area and the Marine Reserve to the south of
the beach;
6. The monitoring programme of the SMMA includes two stations at Malgretoute
where data are gathered annually using the Reef Check protocol. While this method
provides valuable data on long-term changes in the status of coral reef communities, it
is not the most appropriate for rapid detection of episodic impacts, such as those that
result from significant changes in water quality, particularly sediment loading;
7. The SMMA monitoring programme at Malgretoute should be expanded to include
the following components:
 Weekly measurement of turbidity at a number of stations along the coastline,
adjacent to, and downstream from the development;
 Continuous measurement of sedimentation rate, based on a rotation of
sediment traps (i.e. settlement tubes) following the methods already in use in
the SMMA and the Canaries Anse la Raye Marine Management Area.
 Establishment of permanent photoquadrats in the Fishing Priority Area and
Marine Reserve, to be photographed every 6 – 8 weeks at least during the
construction phase of the development, and possibly post-construction
depending on the results. The quadrat photography should be analysed
using the point-count method described above. This is a very efficient
method that provides a rapid assessment of changes on community
composition, such as relative cover of live coral and other benthic species, as
well as survival and mortality of individual colonies. The number and
location of the quadrats to be decided based on a sampling design and the
resources available to the SMMA.
The expansion of the monitoring programme would provide timely information on
any changes in water quality and impacts on benthic communities that might require
additional mitigation measures, particularly the reduction of sediment runoff.
References
Kohler, K.E. and S.M. Gill. 2006. Coral Point Count with Excel extensions (CPCe):
A Visual Basic program for the determination of coral and substrate coverage using
random point count methodology. Computers and Geosciences 32(9):1259-1269.
Hodgson, G., J. Hill, W. Kiene, L. Maun, J. Mihaly, J. Liebeler, C. Shuman and R.
Torres. 2006. Reef Check instruction manual: a guide to Reef Check coral reef
monitoring. Reef Check Foundation, Pacific Palisades, California, USA. 93 pp.
Smith, A.H, M. Archibald, T. Bailey, C. Bouchon, A. Braithwaite, R. Comacho, S.
George, H. Guiste, M. Hastings, P. James, C. Jeffrey-Appleton, K. De Meyer, A.
Miller, L. Nurse, C. Petrovic and P. Phillip. 2000. Status of coral reefs in the Eastern
Caribbean, the OECS, Trinidad and Tobago, the Netherlands Antilles and the French
Caribbean. Pages 315-330 in C. Wilkinson, ed. Status of coral reefs of the world.
Australian Institute of Marine Science, Queensland, Australia.