The effects of oil and oil dispersants on the skeletal growth of the ...

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2 Bermuda Biological Station for Research, Ferry Reach, St. George's 1-15, Bermuda. Accepted 8 September 1984. Abstract. Specimens of the hermatypic coralĀ ...
Coral Reefs

Coral Reefs (1984) 3:191-198

9 Springer-Verlag 1984

The Effects of Oil and Oil Dispersants on the Skeletal Growth of the Hermatypic Coral Diploria strigosa Richard E. Dodge 1, Sheila C. Wyers 2, H. R. Frith z, Anthony H. Knap 2, S.R. Smith 2 and T. D. Sleeter 2 1 Nova University Oceanographic Center, 8000 N. Ocean Drive, Dania, Florida 33004-3078, USA 2 Bermuda Biological Station for Research, Ferry Reach, St. George's 1-15, Bermuda Accepted 8 September 1984

Abstract. Specimens of the hermatypic coral species

Diploria strigosa were exposed to various concentrations (1-50 ppm) ofoil or oil plus dispersant for 6-24 h periods in four laboratory and two field experiments. After dosing, corals were transplanted to, or left in, the field and recollected approximately one year later for extension (linear) growth analysis by the alizarin stain method. The experiments were designed to assess the long-term effects of brief low-level concentrations of chemically dispersed oil and oil alone on corals in a situation, for example, where an oil slick (treated and non-treated with dispersants) passes over a reef. No significant differences between extension growth parameters (Septa increase, Columella increase) and a calical shape parameter (New Endotheca Length) of treated corals versus controls were found in any of the experiments. In two summer experiments calical relief (Fossa length) was found to be depressed in corals of some of the experimental treatments.

Introduction

Coral reefs are significant ecosystems in the world's subtropical and tropical oceans and are sensitive to a wide variety of man-induced perturbations or change. There is a threat of short-term oil pollution to corals and coral reefs from oil refineries, oil production activities of offshore platforms, and spills associated with the proximity of shipping routes to many coral reef areas. Few field studies refer specifically to the effect of oil on corals, and although there is some indication of immediate coral mortality following a spill, few data are available on long-term effects. Researchers have stressed the need for more quantitative measurements of coral physiological processes to monitor changes which may not be apparent in qualitative observations after exposure to oil. Laboratory studies have begun to address the question of sub-lethal toxicity and in some cases deleterious effects have been noted in response to both chronic and short-

term exposures (Loya and Rinkevich 1980; Neff and Anderson 1981; Peters et al. 1981). Results, however, have been difficult to relate to typical oil spill conditions in the field because of the lack of quantitative chemical data on oil concentrations during dosing (Ray 1981; Knap et al. 1983). The above considerations are particularly applicable for research on effects of chemically dispersed oil. Chemical dispersants can be a highly efficient method for oil spill control; however, past experimental evidence (Lewis 1971; Elgershuizen and De Kruijk 1976; Eisler 1975), has suggested chemical disperants are toxic. Consequently, their use has tended to be restricted to offshore areas. Conclusions from such past experiments have been based on results at high concentrations, apparently unrealistic of what could happen in the natural environment (e.g., McAuliffe et al. 1981). In this study we have conducted experiments to assess the effects of chemically dispersed crude oil on the skeletal growth (extension) rate of the major reef-building coral (Diploria strigosa) of Bermuda (Dodge et al. 1982). This parameter was selected because a) it is the product of many physiological processes and consequently may be sensitive to the cumulative effects of sub-lethal toxicity, b) it is important to reef ecology in the competitive success of corals and in maintaining the physical habitat of the associated reef community, and c) it makes possible long-term measurements of change. We have also evaluated corallite shape parameters as a possible stress index.

Methods and Materials

Laboratory Specimens of the reef-building coral Diploria strigosa were collected at a patch reef site on the Bermuda North Ledge Flat reefs at depths of approximately 3-6 m. Corals of roughly uniform size (approximately 12 cm in diameter) and hemispherical shape were transported to the Bermuda Biological Station and next transferred to a running seawater system (see Knap et al. 1983).

192 Table 1. Description of laboratory and field experiments. Treatments are listed as type of dispersed or non-dispersed oil, concentration in ppm, and duration of exposure. The number in parentheses following is the number of corals within each treatment. Treatment abbreviations are: EX, Exxon dispersed oil; BP, British Petroleum dispersed oil; OIL, Light Arabian crude alone; DISP, Exxon dispersant alone Experiment A Number of treatments 9

B

C

D

Z

Y

6

5

6

4

3

Treatment deseription

Control (5) OIL 22 ppm/24 h (12) BP 43ppm/ 6 h (5) EX 46ppm/ 6h (5) BP 35ppm/24h(5) EX 39ppm/24h (5)

Control (12) EX 20ppm/24h(12) EX 21ppm/ 6h(12) BP 17ppm/24h(12) OIL 21ppm/24 h (12)

Control (12) DISPlppm/24h(12) EX 19ppm/24h(12) EX 12ppm/ 6h(12) BP 15ppm/24h(12) OIL19 ppm/24 h (12)

Control (5) OIL12 ppm/6 h (5) BP 6ppm/6h(5) EX 27ppm/6h(5)

Control (20) BP 21 ppm/6h(20) EX 20 ppm/6 h (20)

1

2"

2"

5b

10 b

16

15

15

15 Cemented

15 Cemented

1/26/82

6/16/82

9/30-10/1/81 10/7-8/81 11/12/81

2/6-11/82 3/3-4/82 4/5,13/82

7/1-2/82 7/14-15/82 8/12/82

9/24-28/81 10/5-6/81 -

5/13,19-27/82 6/22,24/82

11/1/82

4/7/83

8/20/83

9/23/82

6/19/83

397

390-395

384

364

393

Control (10) EX 2ppm/24h(4) EX 5ppm/24h(4) EX 17ppm/24h(5) BP 2ppm/24h(5) BP 17ppm/24h(5) OIL 1 ppm/24 h (5) OIL 4 ppm/24 h (5) OIL 18 ppm/24 h (5)

Number of 1 tanks/ treatment Number of Varies, approx measure- 15 ments/ coral/ parameter Original 7/27-29/81 collection date Stain date 8/5-6/81 Dosing date 8/12-13/81 Transplant 9/11,14/81 date Recollection 8/20,27/82 date Number 379-386 of days staining to recollection

9/14--25/81

9/6/81

4/27-29/82

a One tank off each treatment received slightly more light (see Dodge et al, 1984) b Number of underwater chambers used

Corals were randomly assigned experimental aquaria at densities less than 15/tank. After an acclimation period of approximately one week, specimens were stained with alizarin red S (Lamberts 1978) at a concentration of 10 mg/1 typically for 24 h in static aerated conditions. The corals were allowed to recover from possible effects of staining (Dodge et al. 1984) for at least one week. For one experiment (exp. C) low water temperatures necessitated specimens to be exposed to alizarin (10 mg/1) under static aerated conditions for an 8 h period on each of seven sequential days. Treatments consisted of Arabian Light crude oil only or combinations of Arabian Light with the dispersants Corexit 9527 (Exxon) (1:20 dispersant to oil) or 1100WD (British Petroleum) (1:10). Arabian Light is assumed to be a representative moderately toxic crude oil. Caution, however, should be used when comparing relative toxicity of various oils especially within the context of experimental design, with regard to water soluble fraction or water accomodated fraction, and with respect to static or flow-through bioassay systems. Combinations of dispersant and oil were made according to the manufacturer's specifications and were initially physically mixed in separate chambers followed by introduction at appropriate flow rates into aquaria of the flow-through system. A flow-through system was employed in preference to a static system which can exaggerate the effects of pollution (Cohen et al. 1977; Eisler 1975). Concentrations were selected within the range of 1-50 ppm. The limited data from chemically dispersed slicks show the highest concentrations of dispersed oil can range from 1-20-40 ppm within a depth of 10 m (McAuliffe et al. 1981; Knap et al. 1983). Exposure times were from

6-24 h to be consistent with a major isolated spill passing over a coral reef. To maintain a relatively constant dose, the water accommodated fraction (WAF) ofoil (or oil content of water) was measured every 30 rain in each experimental tank by use of hexane extracts measured on a Perkin-Elmer 650-20 s fluoresence spectrometer (excitation 310 nm/slit 10 nm, emission 360 nm/slit 2.5 nm). Fluorescence readings were converted to "ppm oil" by reference to a standard concentration curve which was prepared by the quantitative addition of Arabian Light crude to hexane and then serial dilution by weight. Neither of the dispersants imparted any additional fluorescence at the concentrations analyzed. Concentrations were adjusted regularly and maintained as close to a proposed level as possible. The treatment concentration was taken as the average of hourly weighted means over the duration of the exposure (Sleeter et al., in preparation). After dosing corals were maintained in the laboratory flow-through seawater system for approximately one month. They were next cemented (Hudson 1979) back to a reef similar to the collection site and tagged. After approximately 1 year, colonies were recollected for growth measurement. Table 1 provides a detailed description of each experiment.

Field Experimental chambers constructed of plexiglass (41 cm cube) were designed to temporarily isolate Diploriastrigosa colonies in the field at 34 m depth for treatment applications. In the first field experiment (Z) selected corals were removed from their natural substrate and cemented nearby on flatter surfaces (one coral per chamber) to facilitate chamber

193

Fig. 1. Underwater view of plexiglass chamber used to stain and dose corals with oil or dispersed oil in field experiments Z and Y

sealing. In the second field experiment (Y) specimens (two per chamber) were cemented to concrete slabs which allowed a fighter chamber seal for maintaining stain and/or oil concentrations. Initially, colonies were stained for 6-8 h periods over 1-3 days using a concentration of approximately 10 mg/1 alizarin. Mixing within chambers was maintained by divers who operated a stirring propellor (Fig. I). Between staining events, chambers were removed. After final staining, specimens were left to recover for approximately one-two weeks. Corals were next exposed to pre-weathered (nC-7 and lower removed) dispersed oil mixtures for 6 h. Water samples were taken at approximately hourly intervals by divers, extracted on site, and transported by fast launch to Bermuda Biological Station for concentration analyses. Results were reported back to the field site for adjustment of concentration within the chambers. Mixing was accomplished by diveroperated chamber propellors (Fig. 1). After dosing, chambers were removed and corals were visually monitored for one year and recollected for growth analysis. Details of each field experiment are presented in Table 1.

Fig. 2. Cross-section sketch of Diploriastrigosacorallite giving names of various skeletal structures (left). The alizarin stain trace is indicated by the heavy dashedline. The locations of the various measurement parameters (right)are presented: Septa increase, Columella increase, Old Fossa length, New Fossa length, New Endotheca Length. Scale: the width of the endotheca is approximately 1 cm

Growth Measurement Procedure Specimens were sectioned using a diamond bit masonary saw to obtain a medial slab several cm in thickness. Coral tissue adhering to the growth surface was partially sprayed away with water. Slabs were dried and embedded under partial vacuum in clear casting polyester resin. These were then sectioned medially and each cut face was polished to a transparent surface (of the resin) suitable for low power microscopy (Dodge 1982). Measurements (Fig. 2) were made under a microscope on individual corallites (typically eight or more) over the slab growth surface which were accurately cross-sectioned and stained. Stain lines were well revealed in the septa and columella, but not in the endotheca base dissepiment. This was because septa (and columella) are secreted relatively continuously; whereas, the endotheca base, once initially formed, is probably calcified only slightly. The parameters of upward growth (extension) measured were: increase in septa length and increase in columella length. The parameters of corallite shape measured were the length of the old and new fossa and the length of the new (present at collection) endotheca. The determination of Septa increase was facilitated because septa are well-defined skeletal structures of simple geometry in cross-section allowing a precise distance between the original stained septa top and the final growth surface to be measured, The determination of Columella increase was less precise. In cross-section the original stained eolumella top

could be located because the strain line was clear and the anastomosing of septa usually provided a unique top point. At the collection growth surface, however, incomplete formation often made identification of a precise top point difficult. For measurement the columella top was assigned as midway between the last two anastomosing septa. The actual top was therefore consistently and slightly underestimated.

Results

Upward Growth-Laboratory S e p t a i n c r e a s e d a t a o f e x p e r i m e n t s A a n d B (Figs. 3, 4) were subjected separately to one-way ANOVA (analysis o f v a r i a n c e ) w i t h o n e level o f n e s t i n g ( S o k a l a n d R o h l f 1981) w h i c h c o m p a r e d effects ( g r o w t h d i f f e r e n c e s ) between treatments and subordinately growth differences b e t w e e n c o r a l s w i t h i n t r e a t m e n t s as w e l l as d i f f e r e n c e s between measurements within corals. A mixed model A N O V A (fixed effects f o r t r e a t m e n t s , r a n d o m effects f o r

194

EXR A

I.l.:

o,.e IO

I/d

tt

~1.0

-"XP C

~1.2. 0

I

z I

I i

I

I

t tilt

,~ 0 z

I

I

E6. E "4.,

O9

TR. ppm

C

C)IL I 24

EX 2

13P O;L 2 4 24 24

EX 5 24

OIL 18 24

EX 17 ?.4

BP 17

h 24 24 Fig.3. Mean Septa increase (lower) and New Fossa/Old Fossa (upper) of corals within treatments (TR) of experiment A showing concentrations (ppm) and hours (h) of exposure. OIL refers to oil only, EX to Exxon dispersed oil, BP to British Petroleum dispersed oil as discussed in the text. Error bar = + 1 SD

EXP. B

~1.2, (r

ttI

~6. E E

I

tt

I

I

I

I

tt[ tt

I

C

ppm

I

EX 21 6

h

I

21 24

!

BP 17 24

EIX 20 24

EXP D

0

t

tttt

~l.0, 0 Z

I

OIIL

Fig. 5. Mean Septa increase (lower) and New Fossa/Old Fossa (upper) of corals within treatments (TR) of experiment C showing concentrations (ppm) and hours (h) of exposure. Otherwise same as Fig. 3 caption

~1.2 84

I

E d4.

I

I

I

I

I

]t ] t I ]

~ - 2 . 84

O~

O~

TR. P EX OIL BP EX pprn 43 46 22 35 39 6 6 24 24 24 h Fig. 4. Mean Septa increase (lower) and New Fossa/Old Fossa (upper) of corals within treatments (TR) of experiment B showing concentrations (ppm) and hours (h) of exposure. Otherwise same as Fig. 3 caption

Table 2 Source

,,

TR.

la.; -io

3 Z

Degrees of freedom

Sums of squares

a, Experiment A. Parameter: Septa one level of nesting Treatments 8 140.736 Corals 39 624.664 Within 992 139.800 1,039

Mean squares

F ratio

P

increase: One-way ANOVA with 17.592 16.017 0.141

0.953 113.654

NS