STATUS OF THE MARINE ENVIRONMENT OF THE ALBION LAGOON

 

V Chineah, V Chooramum, M Nallee, Y Basant Rai, M Hurbungs, CN Paupiah, JI Mosaheb, H Terashima, A Terai and N Jayabalan

 

Albion Fisheries Research Centre

ABSTRACT

 

A study on the ecology of the Albion lagoon was made during 1997-1999 to obtain baseline information on the physico-chemical characteristics of the water, species and extent of coral cover, ichthyofauna, bacterial indicators of pollution and benthic dinoflagellates.  While the temperature of the water varied between 22.0 and 31.0 oC, salinity ranged from 8.0 to 35.4 ppt.  Though, the values of dissolved oxygen concentration (DO) and chemical oxygen demand (COD) fluctuated widely, pH values had narrow fluctuation.  The concentrations of nitrate-nitrogen and phosphate were <0.1-3.8 and <0.01-0.71 mgl-1 respectively.  The speed of the current in the lagoon ranged from 0.05 to 0.42ms-1 and the course of the current was generally southwesterly irrespective of the tides.  Coral reef monitoring indicated the existence of 20 species of corals belonging to 8 genera; of which, Acropora spp. were dominant. The fishes collected from the lagoon belonged to 87 species representing 53 genera under 23 families and 7 orders.  The number of total coliform (TC) and faecal coliform (FC) bacteria were within the guideline limits at the public beach.  The benthic dinoflagellates associated with macroalgae belonged to the genera, Gambierdiscus, Ostreopsis, Prorocentrum, Amphidinium and Coolia and their number varied between 1 and 25 cells g-1 of macroalga.

 

Keywords : lagoons, lagoon ecology, water quality, current, corals, indicator bacteria, dinoflagellates, physico-chemical indicators, Albion, Mauritius

 

INTRODUCTION

 

A thorough knowledge on the coastal zone is essential for planning sustainable development of an area.  Any damage to the coastal zone will have its resulting impact on the EEZ, the repository of valuable resources.  Information available on the seasonal distribution of water quality parameters of the lagoons of Mauritius, especially from the Albion lagoon to understand the dynamics, is scanty (Jehangeer 1978; Munbodh et al. 1988; MFMR 1998).  Hence, a comprehensive study was undertaken during 1997–1998 on the physico-chemical characteristics of the water, bacterial indicators of pollution, and benthic dinoflagellates suspected to be associated with ciguatera fish poisoning, and during May and June 1999 on the corals and fish fauna in the Albion lagoon.  The results of the study along with the current pattern investigated during 1991-1992 and subsequently during 1999 in the lagoon are reported in the paper.

 

DESCRIPTION OF THE STUDY AREA

 

The lagoon at Albion located in the western coast of Mauritius (lat. 20o12’ S; lon. 57o23’E) is enclosed by the fringing coral reef and stretches between Pointe aux Caves in the north and Pointe Moyenne in the south (Figure 1).  The length of the lagoon is about 1.8 km.  The reef situated 800m offshore runs inshore, both in the northern and southern ends enclosing an area of about 1.7 km2.  While the lagoon is shallow in most of the areas (< 2m), it is deeper in the southern end.  The tides are semidiurnal type with an amplitude of 1-1.5m.  The lagoon has two passes, a shallower one in the north and a relatively deeper one in the south were studied at 3 stations (station 1: public beach; station 2: mouth of the River Belle Eau; station 3: slipway) located in the Albion lagoon (Figure 1).

 

Figure 1 Albion lagoon

 

 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


MATERIALS AND METHODS

 

Physico-chemical parameters of the water

 

Physico-chemical parameters of the water such as surface temperature, salinity, dissolved oxygen (DO), pH, chemical oxygen demand (COD) and the nutrients, nitrate-nitrogen (NO3-N) and phosphate (PO4),  Surface water samples were collected monthly between10.00 hours and 12.00 hours irrespective of the tides during September 1997 - December 1998 using clean glass bottles.  While the temperature of water was measured to the nearest 0.5oC along with pH in situ using a portable TOA-pH meter, water samples were transported to the laboratory in an isotherm box with ice for the analysis of other parameters.  All the analyses were carried out on the same day.  Salinity of the water was estimated by Horiba-conductivity meter and dissolved oxygen by Winkler’s titration method. COD was determined using the alkaline potassium permanganate method (JIS 1995).  The concentrations of NO3-N and PO4 were quantified using a HACH DR/2000 Spectrophotometer.

 

Current pattern

 

The study of the current pattern in the lagoon was carried out using a set of 10 window shade drogues between May 1991 and November 1992 and again from April 1999 to June 1999.  The drogues were set on a line perpendicular to the reef at different locations 25-30m apart and the position of each of them was recorded using a Scout Master Global Positioning System (GPS) set up to display coordinates in the Universal Transverse Mercator (UTM) projection system on WGS 84 datum.  As the drogue moved with the current, the GPS positions and time were recorded.  All the points of a particular drogue were joined together to form a polyline to indicate the movement of the drogue in the lagoon.  Likewise, a series of polyline was produced for various segments from the movement of the other drogues.  The distance moved by a drogue between two consecutive points was calculated from GPS recordings and the data obtained was used to determine the velocity of the current in metre/second (ms-1).

 

Coral Ecosystem and fish fauna

 

Data on species of corals and the percentages of substrate cover for both living and non-living forms were collected during May-June 1999 at a depth of 1.5 –2.0m by diving at 6 stations (stations : A, B, C, D, E and F) in the lagoon (Figure 1). At each station, the data recordings were carried out along five 20m line intercept transects laid in parallel to the shoreline following the procedure given by English et al. (1997). The species of corals were identified in situ. At the same time, the general substrate condition was observed and the transition points between the different communities were recorded by GPS. Collected data was then extrapolated in order to constitute the zonation map (Figure 2).

 

For estimation of species composition and abundance of fish fauna of the lagoon, a total area of 12000m2 representing 2000m2 from each of the 6 stations was surveyed during the same period (May-June 1999) by Roving Diver Technique (RDT) (Schmitt and Sullivan 1996)

 

Coliform indicators

 

For the estimation of coliform indicators, water samples were collected once a month between 10h and 12h from stations 1, 2 and 3 (Figure 1) during January 1997 – December 1998 using sterile 1 litre glass bottles and kept at 4oC in the refrigerator.  The coliform indicators were quantified using the Membrane Filter Method (APHA 1995).  All the samples were processed within 6h after collection using a vacuum pump.  After incubation of membrane filters on cellulose pads saturated with BBL M-Endo broth (35 ± 0.5ºC, 24 h) the number of total coliform (TC) bacteria were estimated.  For faecal coliform (FC) bacteria the cellulose pads were saturated with the m-FC broth base, DIFCO (44.5 ± 0.5ºC, 24 h).  The presence of faecal coliform bacteria was confirmed using the EC-broth (Hi-Media) (44.5 ± 0.5ºC, 24 h).  The number of colony forming units (CFU) was calculated for 100ml of sample after 24h incubation.

 

Benthic dinoflagellates

 

The macroalgae Jania sp., Gracillaria sp., and Hypnea sp. were collected monthly between January 1997 and December 1998 from 2 locations in the lagoon to identify and quantify the benthic dinoflagellates associated with macroalgae (Figure 1).  The macroalgae were hand picked and placed in ziplock bags containing seawater and brought to the laboratory.

 

The plastic bags containing the sample were shaken vigorously to release the dinoflagellates associated with the macroalgae. The mixture was passed consecutively over 150 µm and 38 µm sieves.  The macroalgae were dried using absorbent paper and their weights were noted.  The residue on the 38 µm sieve was collected using with a jet of seawater into a beaker and the volume was brought to 50 ml.  The beaker was gently shaken and 1ml of the mixture was placed onto a Sedgewick Rafter counting cell to estimate the number of cells.  The result was expressed as number of cells number of cells per gram of macroalga.  In 1997, no quantitative estimation was effected.  The benthic dinoflagellates were identified up to generic/species level (Taylor et al. 1995).

 

RESULTS

 

Physico-chemical parameters

 

Temperature

 

Monthly variations of the surface water temperature during the period of study are provided in Figure 3.  The values ranged from 22.5 to 31.0oC in station 1, from 22.0 to 31.0oC in station 2 and from 23.0 to 30.0oC in station 3. The lowest value was recorded in station 2.

 

Figure 2  Zonation map of substrate distribution in the Albion lagoon

 

 

Salinity

 

Figure. 3 shows the salinity variations of water during different months at various stations.  The minimum and maximum values recorded in station 1 were 31.3 and 35.4 ppt, in station 2 were 8.0 and 33.9 ppt, and in station 3 were 9.9 and 32.6 ppt.  The lower salinity recorded in stations 2 and 3 might be due to the fresh water inflow from the land and river runoff that diluted the lagoon water.

 

Dissolved oxygen

 

The DO values varied between 4.7 mg l-1 and 10.3 mg l-1 at station 1, between 4.0 mg l-1 and 9.5 mg l-1 at station 2 and 4.0 mg l-1 and 9.6 mg l-1 at station 3 (Figure 3).  The lower DO values were recorded in all the stations during January 1998

 

pH

 

The highest pH value (8.5) was recorded in station 1 both during January and February 1998 and the lowest value (6.8) in station  2 during July 1998.  The seasonal variation in the values of pH in all the 3 stations is shown in Figure 3.  Station 1 had consistency in the distribution of pH throughout the year excepting during July 1998 unlike in stations 2 and 3 where fluctuations were comparatively higher.

 

Chemical oxygen demand

 

The variations in the COD values during different months in the Albion lagoon are shown in Figure 3.  The values during the period of study ranged between <0.1 mg l-1 and 1.0 mg l-1,  <0.1 mg l-1 and 2.3 mg l-1, and <0.1 mg l-1 and 1.5 mg l-1 in the stations 1, 2 and 3 respectively.

 

Nitrate-nitrogen (NO3-N)

 

The nitrate-nitrogen concentration was always <0.1mg l-1 in station 1. While in station 2, the values ranged from <0.1 mg l-1 to 3.2 mg l-1; in station 3, the values recorded were between <0.1mg l-1 and 3.8 mg l-1 (Figure 3).

 

Phosphate (PO4)

 

Figure 3 shows the seasonal trend of phosphate concentrations in various stations during 1997-1998.  Among the stations, the maximum phosphate level was noted in station-2 located at the Belle Eau river mouth indicating input from land sources.  While the phosphate value ranged from <0.01 mg l-1 to 0.09 mgl-1 in station-1, stations 2 and 3 had the ranges from 0.01 mg l-1 to 0.71 mg l-1 and from 0.04 mg l-1 to 0.35 mg l-1 respectively.

 

Current pattern

 

The subsurface current within the 1m water depth showed the speed to range from 0.05ms-1 to 0.42ms-1 during flood tide and from 0.10 ms-1 to 0.23 ms-1 during ebb tide.  Table 1 shows the speed and direction of the current during different tides on the days of the drogue study.  The current showed a general flow from north to southwest  (Figure 1).

 

Table 1  Speed and direction of current during May 1991- November 1992 and April - June 1999 at different tides

 

Date

Average Speed

Net Direction

Tide

ms -1

° N

23-May-91

0.12

264

Ebb

30-May-91

0.14

231

Flood

31-May-91

0.24

262

Flood

6-Sep-91

0.16

195

Ebb

6-Sep-91

0.20

203

Ebb

22-Nov-91

0.08

185

Flood

6-Mar-92

0.13

218

Ebb

17-Apr-92

0.11

199

Ebb

14-Apr-92

0.10

220

Ebb

8-May-92

0.42

259

Flood

18-Sep-92

0.05

186

Flood

25-Sep-92

0.23

261

Ebb

30-Oct-92

0.18

244

Ebb

6-Nov-92

0.06

196

Flood

15-Apr-99

0.20

218

Ebb

16-Apr-99

0.09

305

Flood

21-May-99

0.22

156

Flood

10-Jun-99

0.20

213

Ebb

 

Coral ecosystem and fish fauna

 

Altogether 20 species of corals belonging to 8 genera have been observed in the lagoon.  They are as follows: Acropora  austera, A. nasuta, A. lutkeni, A. latistella, A. hyacinthus, A. robusta, A. cytherea, A. tenuis, A. formosa, A. danai, A. nobilis, Porites lutea, Porites sp., Pocillopora damicornis, Pocillopora sp., Montipora spp., Fungia valida, Lobophyllia sp., Goniopora sp., Millepora sp.  The zonation map of substrate distribution in the Albion lagoon is shown at Figure 2.  The percentages of substrate cover by the living and non-living forms in all the six stations are shown in Figure 4.

 

Figure 3  Physico chemical parameters

 

 

At station A, the seagrass Halodule uninervis, represented the maximum cover (40%).  At station B, which was close to the pass, although rubble contributed to 39% of the substrate, massive Porites were  evenly scattered (11%). At station C, Acropora sp was dominant (48%). At station D, macroalgae and turf algae together constituted 35% of the substrate cover.  At station E, the dominant biota was seagrass (43%) while at station F, the main feature was sandy bottom (23%) with regular patches of macroalgae (23%), branching corals (12%).

 

Figure 4 Subtrate cover at Albion Lagoon

 

 

Abbreviations

AA

Algal assemblage

CM

Coral massive

R

Rubble

ACB

Acropora branching

CMR

Coral mushroom

S

Sand

ACT

Acropora tabulate

CS

Submassive coral

SG

Combined patches of SG-S,H & F

CA

Coraline algae

DC

Dead coral

SG-H

Seagrass Halodule

CB

Coral branching

DT

Dead coral tabulate

SG-F

Seagrass Halophila

CE

Coral encrusting

MA

Macroalgae

SG-S

Seagrass Syringodium

CF

Coral foliose

OT

Others

TA

Turf Algae

 

The species composition of fish occurring in the lagoon is given in Annex 1.  87 species of fishes belonging to 53 genera and 23 families under 7 orders indicate the richness in fish faunal diversity.

 

Coliform indicators

 

Tables 2 and 3 show the load of TC and FC bacteria in the waters of Albion lagoon.  In station 1, while the TC counts varied from 10 to 100 CFU/100ml during 1997, a wider range in their distribution (<1-235 CFU/100ml) was observed in 1998.  The values of FC also had a similar trend during both years.  In general, a higher load of indicator bacteria was discernible during 1998.

 

The estimated TC and FC colony forming units per 100 ml showed the highest levels in station 2 with an average of 1459 and 458 during 1997 and 1073 and 351 during 1998 respectively.  During 1997, the maximum value of TC was recorded in June (3,233) and the minimum was recorded in November (600).  The densities of TC and FC were comparatively lesser during 1998 with a minimum of 85 and 17 respectively in August, and a maximum of 2535 and 1570 respectively in May.

 

Table 2  Variation of TC and FC level at different stations in the Albion Lagon - Year 1997

 

Month

Station 1

Station 2

Station 3

TC

FC

TC

FC

TC

FC

January

51

48

2900

1400

610

75

February

10

7

1017

437

390

30

June

33

33

3233

433

116

73

August

100

20

1133

82

218

20

September

40

32

333

167

57

45

October

87

33

NS

NS

13

10

November

48

40

600

290

163

96

December

100

5

1000

400

200

40

Average

59

27

1459

458

221

49

NS:  Not Sampled

 

 

Table 3  Variation of TC and FC level at different stations in the Albion Lagon - Year 1998

 

Month

Station 1

Station 2

Station 3

TC

FC

TC

FC

TC

FC

January

40

37

600

400

100

37

February

75

50

725

300

368

145

March

125

75

625

250

275

30

May

51

42

2535

1570

808

189

June

<   1

<   1

1750

100

100

30

August

<   1

<   1

85

17

40

8

September

100

27

2000

470

100

32

October

235

70

1235

170

200

<   1

November

200

167

170

100

170

100

December

100

50

1000

135

170

70

Average

81

52

1073

351

233

64

 

In station 3, during 1997, the minimum and maximum TC values (CFU/100ml) in the water were 13 in October and 610 in January. The minimum and maximum FC values (CFU/100ml) were 10 in October and 96 in November.  However, during 1998, the TC load varied from 40 in August to 808 in May and the FC population ranged from <1 in October to 189 in May respectively.

 

Benthic dinoflagellates

 

The monthly distribution of the benthic dinoflagellates during 1997 and 1998 in the Albion lagoon are provided in Tables 4 and 5 respectively.  Five species of dinoflagellates namely Gambierdiscus toxicus, Ostreopsis sp., Prorocentrum sp., Amphidinium sp. and Coolia sp. were recorded.  During, January and February 1998, no dinoflagellate was recorded in the lagoon.

Table 4  Species of benthic dinoflagellates recorded in the Albion lagoon during 1997.

 

Species/Month

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Gambierdiscus toxicus

nd

nd

P

P

nd

nd

nd

nd

nd

nd

P

nd

Ostreopsis sp.

nd

nd

P

P

P

nd

nd

P

nd

Nd

P

nd

Prorocentrum sp.

nd

P

P

P

P

nd

nd

P

nd

nd

P

nd

Amphidinium sp.

P

nd

P

P

P

nd

nd

P

nd

P

P

nd

nd : not detected;   P : Present

 

Table 5  Density of benthic dinoflagellates associated with macroalgae

 (number g -1 of macroalga) in the Albion lagoon during 1998.

 

Species/Month

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Gambierdiscus toxicus

nd

nd

5

nd

1

nd

nd

nd

3

15

nd

3

Ostreopsis sp.

nd

nd

3

15

13

1

2

nd

4

5

2

3

Prorocentrum sp.

nd

nd

3

12

nd

nd

2

2

nd

nd

nd

nd

Amphidinium sp.

nd

nd

10

6

2

nd

nd

nd

nd

3

nd

nd

Coolia sp.

nd

nd

4

6

nd

1

25

4

nd

5

1

5

 

DISCUSSION

 

The present study provides the information on the physico-chemical and biological status of the Albion lagoon. 

 

Water quality

 

The distribution pattern of temperature showed higher values during summer months with the peak in February 1998 and lower values during September 1997 in all the stations. In general, the temperature distribution showed a single prominent peak during summer months in the lagoon (Figure 3).

 

The salinity data (Figure 3) show that the water in the public beach is least subjected to fluctuations.  Though the salinity values fluctuated considerably in the river mouth and near the slipway, the two distinct peaks of values observed during 1998 are indicative of bimodal oscillation of salinity in the lagoon near these stations.  The rain and freshwater from the River Belle Eau and agricultural activities would be the probable causes for such variations.  Though the pH of the water showed irregular trend (Figure 3), station- 1 always had higher pH values than the stations influenced by land drainage.  The higher COD values in the river mouth than in the other 2 stations might be due to the high organic content carried by the river water to the lagoon.

 

The dissolved oxygen concentrations showed 3 peaks during 1998 in all the stations. Though dissolved oxygen concentration has an inverse relationship with salinity in Vellar estuary (Vijayalakshimi and Venugopalan 1973; Thangaraj et al. 1979), no such trend could be seen in the present study. The dissolved oxygen level was lower at the stations during the summer months.  The low levels of oxygen recorded can be attributed to the increase in water temperature during the summer season.

 

In the tropical environment, freshwater discharge forms the major source of nutrient supply to the nearshore waters (Chandran and Ramamoorthi 1984).  The nature and extent of freshwater discharge is chiefly controlled by the regime of precipitation during the rainy season and to some extent by the runoff from the irrigation channels.   The normal values of nitrate-nitrogen and phosphate in certain lagoons of Mauritius range from 0.1 to 0.2 mg l-1 and from 0.02 to 0.04 mg l-1 respectively (MCFMRD, 1996).  The higher concentrations of nitrate-nitrogen and phosphate observed in the present study in the south of the lagoon (stations 2 and 3) during most of the months might be due to the discharge from the nearby animal breeding sheds and agricultural activities, besides the rain. Generally the variations in phosphate concentration could be attributed to their utilisation by phytoplankton (Krishnamurthy 1970; Santhakumari 1970) and cessation of freshwater flow. The variations may also be caused by various processes like adsorption and desorption of phosphate and buffering action of sediment under varying environmental conditions (Pomeroy et al. 1965).  Further studies on the productivity of the water would throw more light on the seasonal variations of the nutrients in the Albion lagoon.  

 

Current pattern

 

The current showed a general north - southwesterly flow pattern towards the main pass irrespective of changes in tides.  It was noted that during most of the time, the speed of the wind varied from 10 to 20 kmh-1.  In June, the prevailing wind showed a south-easterly direction whereas during the summer and transition months wind from the west was recorded on some days (wind recording - Meteorological Services 1991, 1992, 1999).  The wind appeared not to influence the current pattern and, in general, the water got into the lagoon over the reef top and drained out through passes.

 

Coral ecosystem and fish fauna

 

Among the 11 species of acroporiids recorded in the lagoon, Acropora. nobilis, A. robusta and A. cytherea were dominant.  The other genera were represented by a few species each.  Mass spawning of the acroporiids viz. Acropora formosa, A. nobilis, A. robusta and A. cytherea, which was observed in the lagoon at a depth of 1.0-1.5 m on 3rd november 1998 between 21h and 22h during the full-moon at spring tide, indicates that the environment is healthy for the proliferation and establishment of corals.  The results of the substrate cover estimation clearly indicate the site preference by living organisms.  The dominance of seagrass in station A where the fluctuation in salinity was very wide due to Belle Eau River discharge and in station E where the salinity fluctuated narrowly shows that the seagrass is not affected by fresh water input and forms an integral part of the biota in the whole of the lagoon.  The near total absence of the corals in station A is natural since they are stenohaline.  The dominant cover of Acropora in Station C is indicative of a favourable zone for corals in the lagoon.

 

Fishes belonging to the order Perciformes appear to be dominant in the lagoon.  Of the 3865 fish observed, the perches contributed to 97.4%.  During the present study, fishes of the family Pomacentridae were found to have wider distribution, The species Stegastes lividus, which were especially distributed in Station C (branching coral area), ranked first in abundance with 657 individuals followed by Dascyllus aruanus (532 individuals), Chromis viridis (358 individuals), and Abudefduf sparoides (195 individuals).  The other significantly distributed families of fish recorded were Scaridae, Labridae, Mullidae and Acanthuridae.  While Tetraodontiformes were represented by 2 families, namely, Tetraodontidae and Balistidae, the other orders, Siluriformes, Beryciformes and Scorpaeniformes, were represented by one family each. The occurrence of 87 species of fishes in an area of about 12000 m2 indicates the species richness of the Albion lagoon

 

Coliform indicators

 

Presence of FC in the water of a locality indicates the existence of other disease causing pathogenic bacteria (Elliot and Colwell 1985).  In the present study, the density of both TC and FC bacterial populations was observed in the following order: station 2 > station 3 > station 1.  However, no consistency in the seasonal variation of bacterial population was noticed during both years.  In station 2, where the fresh water influence is substantial, the higher bacterial count denotes the land source faecal contamination drained mainly from animal rearing sheds located in the region (Basant Rai et al. in press).  Besides, the lower saline water that existed through most part of the year in station 2 would have triggered the build up of the bacterial density as high saline water increases the die-off rates of the coliforms (EPA, 1993; NCDEHNR, 1994).

 

An FC count of more than 200 CFU/100ml indicates a higher risk of infection in case of direct contact with water.  Since, the values of indicator bacteria in Station 1 show that their load is below the limit of Guidelines for Coastal Water Quality, 1999 (200CFU/100ml) , the public beach at Albion is safe for recreational and other water sports.  This conclusion has also support from the current pattern in the lagoon that flows from north to southwest.  Hence, the faecal contaminated water draining into the lagoon through the Belle Eau River does not reach the public beach in the north. Though in station 3 the FC values do not exceed the limits specified for in the guidelines during most part of the year, higher values during November 1997 and May 1998 are indicative of faecal contamination

 

Dinoflagellates

 

Fish toxicity especially ciguatera toxins produced by certain benthic dinoflagellates influences the economic and nutritional aspects of tropical coral island nations (Glaziou and Legrand 1994).  The ciguatoxins arise from less oxidised precursors called gambiertoxins which are produced by the benthic dinoflagellate, Gambierdiscus toxicus (Lewis and Holmes 1993; Holmes et al. 1994). The present study shows that the population density of G. toxicus in the Albion lagoon varies from 0-15 cells g-1 of macroalga (Table 5). 

 

The distribution pattern of G. toxicus in the ciguatera endemic areas varies considerably (Yasumoto et al. 1984).  While in French Polynesia, the population of G. toxicus varied from 0 to 54,000 cells g-1 of macroalga, the values ranged from 0 to 780 in New Caledonia; however, Guam and Okinawa had 9.8 and 0.05 cells of G. toxicus g-1 of macroalga respectively.  A comparison of the density of G. toxicus in the Albion lagoon in the present study with other ciguatera endemic regions in the Pacific (Yasumoto et al. 1984) may indicate that Mauritius is a ‘moderately toxic area’.  However, this has to be confirmed by more studies on the toxicity of the strain of G. toxicus distributed in the Mauritian waters as differences in toxicity levels of G. toxicus between the clones isolated from various geographical regions have been reported (Bomber et al. 1989).  Further, in the Caribbean, G. toxicus from lower latitudes had higher toxicity indicating that latitudes may have an influence on their toxicity level (Bomber et al. 1989) besides the genetic origin (Durant-Clement 1986).  

In the Western Indian Ocean region, ciguatera is associated with the massive proliferation of dinoflagellates like G. toxicus and P. lima triggered mainly by natural disturbances on the offshore banks and the transmission of phycotoxins to the coral reef food chain (Quod et al. 1995).  In the Albion lagoon, the dinoflagellates such as G. toxicus , Ostreopsis sp, Prorocentrum sp, Amphidinium sp. and Coolia sp. are occurring.  Hence, the environmental aspects of fish toxicity should not be overlooked as various human activities and natural disturbances in the coral reef ecosystem can lead to blooming of dinoflagellates.

 

CONCLUSION

 

The following conclusions can be drawn from the present study carried out in the Albion lagoon:

 

The seasonal distribution of temperature shows a prominent peak during summer months.

 

Variations of salinity of water in most part of the lagoon follow a bimodal oscillation and are influenced by the discharge from Belle Eau River and rain.

 

The nutrient levels of the water are mainly governed by the land-based activities.

 

The current flow in the lagoon is always from the  north to south-west.

 

Among the corals, acroporiids establish good substrate cover in the lagoon where salinity fluctuations are negligible.

 

The lagoon supports a rich fish species diversity mostly belonging to the order perciformes.

 

The sanitary quality of the water in the public beach at Albion indicates that the beach is safe for recreational purposes.

Occurrence and density of the dinoflagellate Gambierdiscus toxicus indicate that the island may be a ‘moderately ciguateric area’.  However, this conclusion needs further validation.

 

REFERENCES

 

APHA.  1995. Standard methods for the examination of water and wastewater. 19th edition, American Public Health Association, Washington, D.C.

 

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BOMBER JW, TINDALL DR and MILLER DM.  1989. Genetic variability in toxic potencies among seventeen clones of  Gambierdiscus toxicus (Dinophyceae) Journal of Phycology. 25:617-635.

 

CHANDRAN R and RAMAMOORTHI K.  1984.  Hydrobiologial studies in  the gradient zone of the Vellar estuary : II Nutrients. Mahasagar-Bulletin of the National Institute of Oceanography, 17:133-140.

 

DURANT-CLEMENT M.  1986. A study of toxin production by  Gambierdiscus toxicus in culture. Toxicon, 24:1153-1157.

 

ELLIOT EL and COLWELL RR  1985.  Indicator organisms for estuarine and marine waters, FEMS Microbiology Reviews, Vol. 32, pp. 61-79.

 

ENGLISH S, WILKINSON C and BAKER V.  1997. Survey manual for tropical marine resources. 2nd edition. Australian Institute of Marine Science, Townsville.pp 390.

 

EPA see under Environmental Protection Agency.

 

ENVIRONMENTAL PROTECTION AGENCY.  1993. Guidance specifying management measures for sources of nonpoint pollution in coaster waters.  Office of water, Washington, DC. 840-B-92-002. January 1993.

 

GLAZIOU P and LEGRAND AM.  1994. Review article – The epidemiology of ciguatera fish poisoning. Toxicon 32:863-873.

 

GOVERNMENT OF MAURITIUS.  1999. Guidelines for Coastal Water Quality  1999.  General Notice No. 620 of 1999 on 30 April 1999, Government of Mauritius.

 

HOLMES MJ, LEWIS RJ, SELLIN M and STREET R.  1994. The origin of ciguatera in Platypus Bay. Memoirs of Queensland Museum, 34:497-504.

 

JEHANGEER MI.  1978. The state of aquatic pollution in Mauritius. In Sixth FAO/SIDA Workshop on aquatic pollution in relation to protection of living resources : Scientific and administrative basis for management measures. Nairobi and Mombassa, Kenya, 12 June- 22 July 1978.

 

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LEWIS RJ and HOLMES MJ.  1993. Origin and transfer of toxins involved in ciguatera. Comparative Biochemistry and Physiology 106C:615-628.

 

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Annex 1  Species composition of fish in Albion Lagoon

No.

Family name

Genus name

Species small name

No of observed fish at each site

(2 000 m 2 )

total 12 000 m 2

A

B

C

D

E

F

Total

1

Muraenidae

Siderea

Grisea

 

 

 

 

2

 

2

2

Plotosidae

Plotosus

lineatus

20

22

 

 

 

 

42

3

Belonidae

Tylosurus

crocodilus

 

 

 

 

1

 

1

4

Holocentridae

Myripristis

Berndti

6

4

 

 

 

 

10

5

Holocentridae

Sargocentron

diadema

 

 

 

 

 

1

1

6

Scorpaenidae

Dendrochirus

Zebra

2

 

 

 

 

 

2

7

Scorpaenidae

Pterois

volitans

 

3

 

 

 

 

3

8

Scorpaenidae

Scorpaenopsis

diabolus

 

 

 

1

 

 

1

9

Scorpaenidae

Taenianotus

triacanthus

 

 

 

 

 

1

1

10

Serranidae

Epinephelus

Merra

 

1

1

1

 

1

4

11

Serranidae

Epinephelus

hexagonatus

 

3

6

1

1

2

13

12

Serranidae

Epinephelus

macrospilos

 

1

 

1

 

 

2

13

Serranidae

Epinephelus

spilotoceps

 

4

6

2

5

1

18

14

Serranidae

Grammistes

sexlineatus

 

1

 

 

 

 

1

15

Apogonidae

Apogon

sp. (juv.)

 

48

 

 

 

 

48

16

Apogonidae

Cheilodipterus

macrodon

 

2

1

 

 

1

4

17

Carangidae

Caranx

sp.

1

 

 

 

1

 

2

18

Gerreidae

Gerres

oyena

 

 

 

 

2

 

2

19

Lethrinidae

Gnathodentex

aureolineatus

 

 

1

 

 

 

1

20

Lethrinidae

Lethrinus

harak

2

4

1

 

16

 

23

21

Lethrinidae

Monotaxis

grandoculis

 

2

 

 

 

 

2

22

Mullidae

Mulloidichthys

flavolineatus

23

38

 

 

38

5

104

23

Mullidae

Parupeneus

barberinus

 

 

 

 

1

 

1

24

Mullidae

Parupeneus

bifasciatus

 

18

 

1

 

 

19

25

Mullidae

Parupeneus

ciliatus

 

 

3

 

1

16

20

26

Mullidae

Parupeneus

cyclostomus

 

65

 

 

 

 

65

27

Mullidae

Parupeneus

macronema

4

 

2

8

1

8

23

28

Mullidae

Parupeneus

pleurostigma

 

19

 

 

 

 

19

29

Chaetodontidae

Chaetodon

auriga

 

13

 

 

 

2

15

30

Chaetodontidae

Chaetodon

blackburni

 

1

 

 

 

 

1

31

Chaetodontidae

Chaetodon

kleini

 

2

 

 

 

 

2

32

Chaetodontidae

Chaetodon

madagaskariensis

 

4

 

 

 

 

4

33

Chaetodontidae

Chaetodon

melannotus

 

1

 

 

 

 

1

34

Chaetodontidae

Chaetodon

trifascialis

 

3

 

 

 

 

3

35

Chaetodontidae

Chaetodon

trifasciatus

 

17

1

 

 

1

19

36

Chaetodontidae

Chaetodon

vagabundus

2

24

 

1

 

2

29

37

Pomacentridae

Abudefduf

sexfasciatus

 

 

1

 

 

 

1

38

Pomacentridae

Abudefduf

sparoides

 

195

 

 

 

 

195

39

Pomacentridae

Chromis

viridis

22

 

336

 

 

 

358

40

Pomacentridae

Chrysiptera

annulata

 

 

 

2

 

 

2

41

Pomacentridae

Chrysiptera

unimaculata

 

4

 

42

 

1

47

42

Pomacentridae

Dascyllus

aruanus

50

 

183

 

 

299

532

43

Pomacentridae

Dascyllus

trimaculatus

1

3

 

 

 

 

4

44

Pomacentridae

Plectroglyphidodon

dickii

 

5

 

 

 

 

5

45

Pomacentridae

Plectroglyphidodon

johnstonianus

 

11

2

 

 

 

13

46

Pomacentridae

Pomacentrus

caeruleus

 

16

 

 

 

 

16

47

Pomacentridae

Stegastes

fasciolatus

 

 

 

7

 

32

39

48

Pomacentridae

Stegastes

limbatus

 

 

5

 

 

 

5

49

Pomacentridae

Stegastes

lividus

 

 

574

 

 

83

657

50

Pomacentridae

Stegastes

nigricans

 

 

5

 

 

106

111

51

Pomacentridae

Stegastes

pelicieri

 

8

 

 

 

 

8

52

Pomacentridae

Stegastes

Sexfasciatus

 

 

 

 

 

6

6

53

Pomacentridae

Stegastes

sp.

 

2

4

 

 

 

6

54

Labridae

Anampses

caeruleopunctatus

 

9

 

 

 

 

9

55

Labridae

Cheilinus

trilobatus

 

7

3

4

 

3

17

56

Labridae

Cheilio

inermis

8

2

1

 

 

 

11

57

Labridae

Coris

aygula

 

5

 

 

 

 

5

 

Labridae

Coris

Aygula (juv.)

 

10

 

 

 

 

10

58

Labridae

Gomphosus

caeruleus

 

 

1

 

 

2

3

59

Labridae

Halichoeres

hortulanus

 

7

 

 

 

 

7

60

Labridae

Halichoeres

Hortulanus (juv.)

 

8

 

 

 

 

8

60

Labridae

Halichoeres

marginatus

 

41

 

1

 

 

42

61

Labridae

Halichoeres

nebulosus

3

 

 

46

 

3

52

62

Labridae

Halichoeres

scapularis

10

40

21

17

 

10

98

 

Labridae

Halichoeres

Scapularis (juv.)

11

 

 

 

 

 

11

63

Labridae

Labroides

dimidiatus

 

28

2

 

 

 

30

64

Labridae

Nvaculichthys

taeniurus

 

 

 

1

 

 

1

65

Labridae

Stethojulis

bandanensis

3

8

6

15

18

 

50

 

Labridae

Stethojulis

Bandanensis (juv.)

 

 

 

77

 

7

84

66

Labridae

Thalassoma

genvittatum

 

19

 

 

 

2

21

67

Labridae

Thalassoma

hardwickii

 

 

10

25

 

7

42

68

Labridae

Thalassoma

sp. (juv.)

 

42

 

 

 

 

42

69

Scaridae

Leptoscarus

vaigiensis

8

69

 

4

8

 

89

 

Scaridae

Leptoscarus

Vaigiensis (juv.)

102

 

 

 

64

69

235

70

Scaridae

Scarus

ghobban

 

 

8

 

 

 

8

71

Scaridae

Scarus

sordidus

 

123

39

4

 

16

182

72

Scaridae

Scarus

sp.

 

4

 

 

 

 

4

73

Blenniidae

Ecsenius

sp.

 

8

 

 

 

 

8

74

Gobiidae

Istigobius

decoratus

5

 

 

 

13

1

19

75

Gobiidae

 

 sp.

7

 

 

 

 

 

7

76

Siganidae

Siganus

sutor

 

28

 

 

 

1

29

77

Zanclidae

Zanclus

cornutus

1

13

5

 

 

5

24

78

Acanthuridae

Acanthurus

triostegus

 

41

13

12

 

7

73

79

Acanthuridae

Ctenochaetus

binotatus

3

88

 

 

 

 

91

80

Acanthuridae

Ctenochaetus

strianus

 

1

 

 

 

 

1

81

Balistidae

Rhinecanthus

aculeatus

 

3

1

 

 

9

13

82

Monacanthidae

Oxymonacanthus

longirostris

 

 

 

 

 

2

2

83

Monacanthidae

Rhinecanthus

aculeatus

 

 

 

2

 

 

2

84

Tetraodontidae

Arothron

nigropunctatus

 

 

1

 

 

 

1

85

Tetraodontidae

Canthigaster

bennetti

 

3

 

 

 

 

3

86

Tetraodontidae

Canthigaster

valentini

3

7

 

 

 

 

10

87

Tetraodontidae

Ostracion

meleagris

3

5

 

 

 

 

8

 

 Total

 

 

300

1163

1243

275

172

712

3865