Functional response of Fucus vesiculosus communities to tributyltin ...

Hydrobiologia 188/189: 277-283, 1989. M. Munawar, G. Dixon, C. I. Mayfield, T. Reynoldson and M. H. Sadar (eds) Environmental Bioassay Techniques and their Application. © 1989 Kluwer Academic Publishers. Printed in Belgium.

277

Functional response of Fucus vesiculosus communities to tributyltin measured in an in situ continuous flow-through system C. Lindblad, U. Kautsky, C. Andr6, N. Kautsky & M. Tedengren Department of Zoology and Asko Laboratory, University of Stockholm, S-106 91 Stockholm, Sweden

Key words: macroalgae, disturbance, primary production, community metabolism, hazard assessment

Abstract

The effects of antifouling paint leachate containing tributyltin on community metabolism and nutrient dynamics were measured in situ on natural communities dominated by Fucus vesiculosus. The measurements were made in two areas with different salinities and at various TBT concentrations up to about 5 Mg 1- '. A portable continuous flow-through system was used in which the communities were incubated for a week. Continual measurements of oxygen, temperature, light and flow rate of water were made. A Perturbation Index (PI) and an Absolute Disturbance Index (ADI) were used to describe the changes due to treatment relative to the control, and to obtain a total picture of disturbance using all measured parameters. Photosynthesis was particularly strongly affected and changes were obvious in oxygen production and nutrient uptake at TBT levels as low as 0.6 #g 1-. Introduction The study of natural or induced changes in functional responses of ecosystems or communities under naturally fluctuating environmental conditions is an important component of bioassay studies. Well controlled laboratory tests offer many advantages (e.g. constant light, temperature, salinity, the use of cultured organisms), but meaningful extrapolation of such results to real complex field situations is almost impossible (Cairns, 1983). Field observations yield important information about local changes in the ecosystem, but for an understanding of the mechanisms, long time-series and reference sites are needed. Well designed enclosures to study the functional processes at the ecosystem level (e.g. primary production, community respiration, nutrient cycling) offer a convenient bridge between laboratory tests and field observations.

In the Baltic sea the salinity increases from about 0.5%0 in the northern Bothnian Bay to around 9%0 in the southern Baltic Proper (Kullenberg, 1981). The northern limit of the Fucus community is in the Bothnian Bay where salinity falls below 2.8%0 (Kautsky, 1988). On shallow hard substrata Fucus vesiculosus is the dominant biotic element. With some 30 species of macrofauna and epiflora it is the richest algal community in the Baltic Sea and an important foraging and nursery area for fish. Fucus is sensitive to changes in the environment, for example increased sedimentation (Rannberg et al., 1985) and decreased light penetration in the water (Kautsky et al., 1986). Paper mill wastes have resulted in large areas devoid of Fucus around the effluent outlets (Lindvall, 1984). Fucus can also be more sensitive to disturbance in areas with low salinity as shown for other Baltic species (Tedengren et al., 1988).

278 Tributyltin (TBT) is commonly used as a biocide in antifouling paint. Its concentrations in coastal areas range from 200). Water samples for determination of NH 4 -N and PO4 -P were taken from the waste discharge every six hours during the two days before treatment and during the first and third days after treatment. The analyses were carried out in the laboratory using standard colorimetric methods (Carlberg, 1972). To minimize disturbance, stones with intact Fucus plants were placed into jars. The entire epifaunal (e.g. Idotea baltica, Gammarus spp., Hydrobia spp., Theodoxus fluviatilis, Mytilus edulis), and - algal (e.g. Dictyosiphon foeniculaceus, Elachista fucicola, Ectocarpus siliculosus, Ceramium tenuicorne) communities were included. The biomass of epiphytic algae was between 10 and 20%, and of animals about 10% of the total biomass. After the communities were placed in the jars, the parameters were measured over 36 hours to obtain undisturbed values before treatment. The treatment started in five of the jars when the incoming water was led through PVC pipes of two different lengths (23 cm and 70 cm) painted on the inside with the antifouling paint 'Interracing'

279 (International Paint Company) containing Tributyltin (TBT) as the active agent. Assuming leaching rates of 22.5 pg TBT cm - 2 day- ' (Laughlin et al., 1984), we calculated TBT concentrations to be 1.6 g 1- ' and 5 plg 1- , in the two treatments. After three days, water samples were taken, immediately frozen and sent for later TBT-analyses to Harbor Branch Oceanographic Institution USA. Three jars where left untreated and served as controls during the seven-day experiment.

To get a clear picture of the total effect of the treatments the PI values for individual parameters were plotted in a multidimensional space, where the origin represents an undisturbed community and each PI one dimension. The absolute distance from the origin divided by the number of parameters used (n) summarizes the total effect of all measured parameters (PI(X)), for example PI (R), PI (GP/R). We call this the Absolute Disturbance Index (ADI) (Lindblad et al., 1988) which has the following formula: ADI = X

Indices Ecosystem functional changes were measured by different indices based on basal processes such as gross primary production (GP), respiration (R), biomass (B), oxygen content (O), phosphorus (P) or nitrogen (N) excretion. The GP/R ratio is a measure of the amount of self-maintenance of a community and Giddings and Eddlemon (1978) used this as an indicator of stress in the ecosystem; a change in the ratio indicates disturbance. Another index, the Perturbation Index (PI) gives a measure of the disturbance (Lindblad et al., 1986, 1988). Each measurement value after disturbance is divided by the mean of values before perturbation and then divided by the corresponding measurement of the controls. Thus PI also normalizes differences in biomass and physiological status in the tested communities. The formula for PI is:

(PI(X,)-

1)2

Results The analyses of the TBT in water samples are shown in Table 1. The calculated concentrations did not correspond exactly with the analyzed TBT concentrations. Evidently, TBT was taken up by the biota and particles. The leaching rates were probably slower than the theoretical values, particularly at low salinities. Net community production (NP) before treatment was in the range of 10-30 mg 02 g- ' · day ' in the two study areas. NP decreased strongly after treatment in both areas; at the low salinity it decreased to below zero (Fig. la, 2a). The diurnal range in respiration rate (R) was 10-30 mg 02 g- ' day- ' before treatment at both salinities. Respiration of all communities increased slightly after treatment and no differences

V-Ti

PI(X)= -

-

n,

Table 1. Results from TBT analysis at different salinities and theoretical concentrations

T b

TBT conc. (pg I1')

Cinb

T = treated jars before (i) and after (j) treatment, C = control jars time before (i), after (j) treatment, n = number of measurements before (b) and after (a) treatment, X = oxygen or any other parameter used.

Tube length

Salinity 6.3%o Salinity 26.5%0 Theoretical conc. n.a. = not analyzed.

23 cm

70 cm

Background conc. in the water

n.a. 0.6 1.6

2.8 4.7 5.0

0.1 0.3 -

280

A

20 I?

I- 1

NP(b)

nS 0

nm

i

h

i NP(a)

A

I

3o

iNPia R (b)

I~uR R (a) (b)

o N to 0

B

0

-40

-40

IIII[ -

50

) = GP(a)

I~~~~~~=P& 0

4

-

GP/R(a)

D

2

0

0

D

I

0

N To 0

C

1, 1

Pl

=PI(NP) - PI(GP)

2

_;l

nI I

II

I

OCP (b)

GP (a)

P(NP) =nPIGP)

m PR)

1

I 0

E

M ADI(GP.R)

L

0 2.8

g TBT 1-1

controls

Fig. 1. Metabolism measurements for each jar with Fucus communities in low salinity (6%). Three replicates treated with 2.8 jig TBT 1-' and three controls. A. Net production (NP) and respiration (R) before (b) and after (a) treatment. B. Gross production (GP) before (b) and after (a) treatment. C. GP/R ratios before (b) and after (a) treatment. D. Perturbation Index for PI (NP), PI (GP), PI (R), PI (GP/R). E. Absolute Disturbance Index(ADI) calculated from PI (GP) and PI (R).

were visible between the different salinities (Fig. la, 2a). Gross production (GP) was 20-40 mg 02 g- 1· day- at both sites before treatment. After treatment the strongest effects were found at the low salinity where GP fell to a mean value of 8.6 mg 02 g- I day- '. At the high salinity GP was reduced to about 18 mg 02 g- day- at

ADI(GP.R)

_

0

N

4.7l1-T 0.6,.g1 TBT

Mm

2 I

controls

Fig. 2. Metabolism measurements for each jar with Fucus communities in high salinity (26.5%o). Two replicates treated with 4.7 jig TBT 1- and two replicates treated with 0.6 #g TBT I- ' and three controls. A-E are explained in Fig. 1.

4.7 ug 1- TBT while the low concentration of TBT (0.6 tg I- ) gave a mean value of 32 mg 02 g- (Fig. lb, 2b). The decrease in GP shows that the decrease in NP is not only an effect of increased respiration. The GP/R ratios ranged between 1.3 and 10. The ratio was generally higher at the high salinity (mean 2.8) than at the low (mean 1.9) before treatment. After treatment the GP/R mean value decreased to 1.3 at the high salinity and 0.3 at the low salinity (Fig. c, 2c). When calculating the

281 1 I

-1 o

tCOLG -2 9 t_

z

-4

-6( I

Dayl I

Day2 I

Day3 I Day4

I Day5

I

Day6 I

Fig. 3. P04-P and NH4-N excretion or uptake. Means calculated on samples taken from three treated Fucus communities and three controls in low salinity (6%).

Perturbation Index of NP, GP, R and GP/R there are clear differences between treated communities and the controls. For the controls, PI was around 1 which means that these parameters did not change during the experiment. The PI (R) increased after TBT treatment at both sites while PI (NP), PI (GP) and PI (GP/R) decreased. The largest changes were visible at the low salinity. The higher concentration of TBT (4.8 pgl - l) used in the high salinity tests showed stronger effects than the low dose (0.6 pg 1- ). Communities at the low salinity, however, were still most affected (Fig. d, 2d). The Absolute Disturbance Index calculated on PI (GP) and PI (R) gave a disturbance mean value of 0.61 for communities in low salinity treated with 2.8 pg TBT 1-'. At the high salinity, 4.7 pg TBT 1- ' gave an ADI mean value of 0.46 and the low concentration of 0.6 pg TBT - ' gave a mean value of 0.40. The controls in both study areas gave mean values of 0.12 (Fig. le, 2e). Although the nutrient data were variable and sampling rather spaced out in time, there was a tendency towards decreased nutrient uptake and increased release in all TBT treatments.

Ammonium (NH 4 -N) and phosphorus (PO4-P) showed diurnal fluctuations with uptake during the day and release at night. Control communities at the low salinity had a PO4-P uptake in the afternoon (15.00 h), of up to 4 tg g- ' DW h- ' and release values of 5-10 pg g - ' DW h - ' during the night. TBT-treated communities had a release of 10-20 pg g- h - ' during the whole diurnal cycle. The NH 4 -N uptake ranged from 0-10 pg g- before treatment. After treatment no uptake was measured while the release was between 10 and 50 pg g- ' h- (Fig. 3).

Discussion In general our results show that the Fucus-based ecosystem is very sensitive to TBT and the flowthrough method used was adequate for measuring the functional response to these disturbances. Bioassay studies at the community and ecosystem levels are more relevant for predicting the impact of disturbance on the environment if the communities used in the study include several species with interactions at different trophic levels. Also

282 important for adequate results in all bioassay studies is the choice of ecologically relevant communities (Cairns & Niederlehner, 1987; Giesy & Odum, 1980; Underwood & Peterson, 1988). We have used the Fucus vesiculosus community, the dominating biomass on littoral hard bottoms along the Swedish east coast. It is difficult to establish experimental protocols for ecosystem monitoring purposes. The use of flow-through systems such as ours largely reduces errors due to oxygen saturation during experiments. Temperature, light and nutrients follow the natural variations. Another advantage is that we are able to use communities taken from the field directly for measurements. This avoids disturbance arising from storage of organisms or possible artifacts due to the use of laboratory cultivated species. Our small enclosure system allows adequate replication and makes it possible to obtain statistically valid results on the effects of disturbance. When measuring several community parameters at different experimental sites with different treatments, problems arise due to differences in basal metabolism between individual samples, and changes in light or temperature making direct comparisons difficult. The use of indices such as the Perturbation Index (PI) and the Absolute Disturbance Index (ADI) make such comparisons possible because they eliminate non-treatment effects. Even metabolic differences due to size are normalized which makes long term comparison possible without destructive weighing after each measurement. Tributyltin was shown to change all measured parameters of the Fucus community at both low and high salinities. Respiration and production were strongly affected, in addition to decreases in nutrient uptake. A difference in sensitivity at the two salinities was observed. The same reduction in functional response was evident for the 2.8 #g TBT 1- ' treatment in the low salinity Baltic Sea as for the 4.7ug TBT 1- treatment in the high salinity North Sea. This difference in sensitivity is probably due to the fact that organisms living in low salinity close to their distribution limit are less resistant to toxicants (Tedengren etal., 1988).

At the high salinity site, there was only a small difference between the effects at the low and high TBT doses. This probably means that even a dose of 0.6 #g 1- is significant and effects would be visible at even lower concentrations. The apical parts of all the treated Fucus vesiculosus plants changed colour to red-brown compared to the green-brown control algae. This has also been observed by Schonbeck & Norton (1980). This is probably due to the photo oxidation of the polyphenols and to destroyed cell membranes. Laboratory investigations with microalgae exposed to tin compounds have shown that primary production was inhibited and growth was reduced at 0.1 Mg TBT and TBTO 1- (Beaumont & Newman, 1986; Wong etal., 1982). Experiments with the Gastropod Nucella lapillus exposed to TBT concentrations of 0.01-0.02 g 1-' for 4 months showed a high degree of imposex, the introduction of male sex in the female (Bryan et al., 1986). It is evident that TBT is active at very low concentrations for consumers as well as for primary producers. Our investigations show such drastic changes in functional response of the Fucus communities that TBT additions would probably result in a decline of the Fucus community, followed by a change in the ecosystem to favor opportunistic species.

Acknowlegements We are thankful to Dr. Klaus Koop and Dr. Arno Rosemarin for giving valuable comments on the manuscript. We also thank three anonymous referees for their comments and suggestions.

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