A comparative study of the methods used to evaluate the activity of Teredinidae molluscs

J. Exp. Mar. Biol. EcoL, 150 (1991) 107-115 © 1991 Elsevier Science Publishers B.V. 0022-0981/91/$03.50

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JEMBE 01616

A comparative study of the methods used to evaluate the activity of Teredinidae molluscs

Andrea de Oliveira Ribeiro Junqueira, Elianne Pessoa Omena and Sergio Henrique Goncalves da Silva

Universidade Federal do Pa'o de Janeiro, Instituto de Biologia, Departamento de Biologia Marinha, llha do Fundao, Pa'o de Janeiro, Brazil

(Received 23 July 1990; revision received 5 March 1991; accepted 15 March 1991)

Abstract: Different methodologies are usually employed to evaluate Teredinidae wood-boring activity. Many authors using panels made of solid wood, estimated density by counting Teredinidae punctures on the wood surface or using x-ray techniques. However this technique does not allow the identification of species. A second approach, employing a collecting device made of sheets of wood, can be more effective for quantita- tive and qualitative analyses. The present paper compares density, species composition and diversity when using both solid and sheet panels. In addition different methods of estimating density were analysed. The results show that the evaluation of Teredinidae activity can change according to the methodology employed.

Key words: Collecting device; Methodology; Rio de Janeiro; Shipworm; Teredinidae; Wood borer

INTRODUCTION

Studies concerning the activity of wood-boring molluscs, especially ofthe Teredinidae, are important because of the extensive damage caused by these organisms to ships and wooden structures in the sea. This damage is usually followed not only by costly restoration but also by the interruption of business (Fernandes & Costa, 1967).

The distribution of Teredinidae along the coast of Brazil has been reported by many authors, including Mailer (1984). Silva (1985), Mailer & Lana (1986, 1987), Tiago (1989) and Silva et al. (1989).

Density values recorded in llha Grande Bay, Rio de Janeiro, were among the highest found in the literature (Silva, 1985). A great number of wooden structures are usually employed in marinas, wharves, fishing and pleasure crafts, and shipyards in this region. Therefore, it is necessary to determine local species composition and its seasonal variation in order to design new means of effective control.

While extensive literature concerning wood-boring activity exists, especially for tem- perate zones (Clapp & Kenk, 1963), little attention has been given to methodological

Correspondence address: A. O. R. Junqueira, Departamento de Biologia Marinha, Instituto de Biologia, Universidade Federal do Rio de Janeiro, CCS Bloco A, Ilha do Fundao, CEP, 22210, Rio de Janeiro, R J, Brazil.

108 A.O.R. JUNQUEIRA ET AL.

problems. Accurate methods are required to detect the presence of boring organisms and to establish their population densities. Because of difficulties associated with underwater inspections, wood panels are immersed in the sea and later withdrawn for microscopic examination.

A great number of authors, using panels made of solid wood, estimate population density by counting Teredinidae punctures on the wood surface (Scheltema & Truitt, 1954; Hurley, 1959; N air, 1962, 1965, 1966; Walden et al., 1967; Tsunoda & Nishimoto, 1972; or by using more sophisticated methods like x-rays (Crisp et al., 1953; Lane, 1955; Quayle, 1956; Trussel et al., 1956; Southwell & Bultmann, 1971; Norman, 1976; Rayner, 1979; GaUager et al., 1981; Mc Koy, 1981; Hoagland, 1982). Although the use of x-rays represents the best ,nethod of estimating population density, it does not allow the identification of the species. To overcome this objective, some authors remove individuals from the panels for identification. However, in this case, it is necessary to carve the wood, a process which may hurt the organisms and make analysis quite difficult.

Turner (1947) suggested the use of a collecting device made of sheets of wood. Manyak (1982) described a panel made of sheets of oak veneer pressed between two pieces of Plexiglas, which is suitable for measuring boring rates and observing boring movements. Silva (1985) made some alterations to this panel allowing for more efficient quantitative and qualitative analyses. In spite of some advantages, few studies use panels made of sheets of wood. Although both have been used independently, no comprehensive study exists which compares both methods, especially in respect to the following questions: (i) Are larval recruitment and development equal in solid and sheet panels7 (ii)Are species composition and diversity equal in solid and sheet panels? (iii) Do the two different methods of estimating density (carving and x-rays) show similar results?

MATERIALS AND METHODS

The research took place in Ponta de Leste, Ilha Grande Bay, (23°02'03 ' ' S, 44 ° 14'09" W) on the southern coast of Rio de Janeiro State, Brazil. This area is a protected marine system with several islands and small bays. Its waters receive a large amount of wood from inland forests. Two kinds of panels were used to collect Teredinidae. The first, one consisted of 12 pine wood sheets (Araucaria angustifolia (Bertol) O. Kuntze), 100 x 80 x 0.8 mm each, set between two pieces of ceramic plates and two pieces of wood. The assembly was held together by two brass bolts (Silva, 1985). For the second panel, a similar structure was used, but, instead of wood sheets, a solid block of wood with the same dimensions was used.

The 72 panels were placed 1 m deep and 15 cm apart, on two racks consisting of PVC pipe suspended by a floating system. During the 1-yr experiment (July 1987-June 1988), three panels of each kind were recovered every month. In the laboratory the panels were analysed in two ways. First, sheet panels were dismantled and the organisms were

TEREDINIDAE ACTIVITY: COMPARING METHODS 109

counted and identified. Second, solid panels were x-rayed and then carved with a former, withdrawing the organisms for counting and identification.

Statistical results were obtained by a two-way ANOVA, the T test proposed by Hutcheson (1970) and the Mann-Whitney test (Zar, 1984). Specific diversity was calculated using Shannon-Wiener index (Washington, 1984).

RESULTS AND DISCUSSION

COMPARING SHEET PANELS AND SOLID PANELS

The average number of individuals found in sheet panels and solid panels is shown in Table I. Teredinidae densities in both increased with time reaching a maximum value after 7 months in sheet panels and after 5 months in solid panels, decreasing after these periods. The decrease after this maximum value was probably caused by a reduced amount of available wood for larval recruitment. The highest percentages of dead animals were observed after these periods, reaching 100~ in solid panels (Fig. 1).

This apparent decrease of density was also probably due to an imperfect analysis of the panels. Many panels were damaged resulting not only in loss of wood but also in the loss of pallets of dead individuals that were not counted. In solid panels that presented higher densities, this decrease was more pronounced.

During the first 6 months of immersion the average number of individuals in solid panels was higher than in sheet panels. This difference was corroborated by two-way ANOVA (P < 0.05, data were transformed using x/~). The Mann-Whitney test was also used due to the high S D value of the three monthly samples. This test also allows comparisons between the density of sheet panels and solid panels. Significant differences were obtained only for 2, 3 and 5 months of immersion. The test showed

TABLE I

Average number of organisms, panel- ~ and respective SO values obtained li'om three methods during experiment.

Month Sheet panel Solid panel (carving method) Solid panel (x-rays method)

1 12.0 4. 8.0 23.3 4- 25.0 13.3 4- 10.9 2 28.3 __+ 5.0 51.3 4. 18.6 34.6 4. 21.9 3 53.6 4. 23.9 91.7 4- 6.40 65.3 4- 6.7 4 85.0 4- 20.2 122.3 4- 51.6 66.7 4- 2.5 5 77.7 4- 7.6 126.3 4- 25.8 74.7 4- 7.4 6 76.3 4- 19.8 92.3 4- 9.30 115.3 4- 5.9 7 96.0 __+ 17.5 57.3 4. 23.5 79.0 4. 4.6 8 58.0 4. 23.8 38.7 4- 6.40 60.3 __+ 4.5 9 62.7 4. 20.4 51.7 4. 3.20 60.3 +__ 23.2

10 53.0 4- 14.7 30.3 4- 13.3 61.0 4- 7.90 I l 46.0 __+ 20.8 21.3 4. 3.80 24.3 4- 6.00 12 48.7 4- 20.0 35.7 __+ 6.40 45.3 4. 7.70

110 A.O.R. JUNQUEIRA ET AL.

H o R ' r A L . I r v

100 I

I |"~.t 5 ' ~" 0 !1 ,,o°|

.~: , r._.,

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0 ......... r .......... i . . . . . . . . . . . . . . . . . . . ~i M

I. :.--'. 3 4 5

°,,

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Fig. 1. Percentages of dead animals of Teredinidae in sheet (dashed bar) and solid panels (solid bar) during experiments.

a high variability between samples, which makes it difficult to estimate Teredinidae densities correctly. This is probably caused by the small number of samples (three from each kind of panel) analysed monthly.

COMPARING X-RAYS AND CARVING METHOD

Panels analysed by the carving method in the first months showed higher densities than when using the x-ray method (Table I). These results were confmned by the two-way ANOVA (p < 0.05). Therefore, during 5 months of im_mersion, Teredinidae densities were better sampled by the carving method. The x-ray method could not detect many young individuals which did not have a distinct shell, calcified tube or pallets (Fig. 2). After 5 months, when the panels were in shards, the x-ray method represented the best methodology for panel examination. This technique did not lose pallets of dead specimens.

SPECIES COMPOSITION AND DIVERSITY

The total number of individuals of each species obtained from each of the two methods is shown on Table II.

During the experiment, 11 Teredinidae species were observed, of which five were abundant, i.e., Lyrodus floridanus (Bartsch), Teredo furcifera Von Martens, Bankia carinata (Gray), B. gouldi (Bartsch) and Nototeredo knoxi (Bartsch). Bankia campanellata Moll et Roch, B. destructa Clench et Turner, Teredo bartschi Clapp, T. navalis Linnaeus, Bankiafimbriatula Moll et Roch and Lyrodus massa (Lamy, 1923) were present in small number.

Considering all the organisms (alive and dead) the dominant species was L. floridanus,

TEREDINIDAE ACTIVITY: COMPARING METHODS 111

Fig. 2. Radiography showing Teredinidae density after 3 months of immersion.

showing values between 67 and 84~ of the number of specimens during 12 months. When only living organisms are considered, N. knoxi becomes dominant after 8 months in solid panels and after 9 months in sheet panels (Table III). Silva (1985) suggested that the L. floridanus replacement could be due to N. knoxgs high capacity of surviving in destroyed wood. Turner & Johnson ( 1971) reported that N. knoxi gets sufficient food from the plankton, differing from other species that are predominantly xylophages. This could explain how this species can survive using a little amount of wood supply.

Most species occur in both kinds of panels, thus the species composition was similar in solid and sheet panels. The more conspicuous species were present in both panels (L.floridanus, 7".furcifera and B. carinata). Some rare species were present in low numbers in only one kind of panel.

In most months the species number in solid panels was higher than in sheet panels.

112 A. O. R. JUNQUEIRA ET AL.

TABLE II

Total number of individual species found in 3-monthly sheet and solid panels during experiment.

Month L. floridanus T. furcifera B. carinata B. gouldi N. knoxi Others

1 Sheet 6 I 2 0 0 1 Solid 27 2 2 0 0 1

2 Sheet 34 25 14 2 0 ! Solid 75 15 9 0 1 l

3 Sheet 101 29 16 1 3 1 Solid 158 49 20 3 5 0

4 Sheet 160 46 13 3 10 1 Solid 203 50 9 8 5 2

5 Sheet 111 33 5 2 13 0 Solid 276 34 7 5 11 3

6 Sheet 118 24 12 1 20 0 Solid 205 30 8 3 9 1

7 Sheet 173 67 4 8 27 0 Solid 1 ! 0 25 16 3 6 3

8 Sheet 110 30 8 1 8 0 Solid 75 12 9 1 11 1

9 Sheet 128 36 5 2 14 0 Solid 63 7 7 1 10 2

10 Sheet 91 19 11 2 24 1 Solid 56 11 6 2 6 0

11 Sheet 93 17 4 1 14 0 Solid 52 15 1 0 2 1

12 Sheet 75 41 8 1 7 4 Solid 86 11 2 2 1 1

The maximum number of species occurred in sheet panels (nine species), while in solid panels a maximum of eight species were found.

It was noticed that the number of individuals in each species stabilized in solid panels earlier than in sheet panels. This was probably caused by overpopulation of the panel, which reduced the available wood for new recruitment. It also explains why some species, such as L. floridanus and 7". furcifera, were initially more abundant in solid panels. N. knoxi first colonized solid panels but reached a high density in sheet panels after 4 months of immersion.

The values of diversity (using Shannon-Wiener index) from the two kinds of panels is presented on Table IV. In addition, the T test proposed by Hutcheson (1970) also was applied to compare diversity between sheet and solid panels. We verified that the diversity of solid panels was different from sheet panels in the 2-, 5-, 6- and 12-month panels. Usually diversity in solid panels was lower than that in sheet panels. These values were more related to the different levels of dominance of L. floridanus than to species number in both panels. In solid panels the high degree of dominance of L. floridanus inhibited the recruitment of other species. Although differences in species number betwcen the two kinds of panels occurred in some months, dominance values of L. floridanus are almost the same in both of them determining similar diversity values.

TEREDINIDAE ACTIVITY: COMPARING METHODS 113

TABLE III

Dominance values of L. floridanus and N. knox/obtained from total number of individuals (T) and from number of living individuals (L) found in sheet and solid panels.

Month L. floridanus N. knox/

T L T L

1 Sheet 46.2 46.2 0 0 Solid 81.8 81.8 0 0

2 Sheet 42.4 42.4 0 0 Solid 71.4 71.4 0.9 0

3 Sheet 66.9 67.3 2.0 2.0 Solid 59.4 67.1 1.9 1.8

4 Sheet 68.7 73.3 4.3 5.1 Solid 71.7 73.4 1.8 2.0

5 Sheet 67.3 65.0 7.9 10.5 Solid 81.4 81.5 3.2 5.6

6 Sheet 65.2 59.0 11.0 24.0 Solid 79.2 50.0 3.5 4.0

7 Sheet 61.3 39.7 9.6 33.0 Solid 67.5 62.5 3.7 12.5

8 Sheet 69.6 38.9 5.1 33.3 Solid 68.8 27.3 10.1 63.6

9 Sheet 69.2 34.6 7.6 34.6 Solid 70.0 16.6 11.1 50.0

10 Sheet 60.3 33.3 15.9 66.0 Solid 65.9 33.3 7.0 66.6

! 1 Sheet 67.4 14.2 11.0 14.2 Solid 82.6 0 3.6 0

12 Sheet 51.8 50.0 5.1 25.0 Solid 81.4 0 1.1 0

TABLE IV

Diversity values (Shannon-Wiener index) obtained from three sheet and three solid panels during experiment.

Month Sheet Solid

l 0.51 0.29 2 0.55 0.40 3 0.42 0.41 4 0.41 0.38 5 0.41 O.3O 6 0.43 0.32 7 0.45 0.47 8 0.39 0.44 9 0.40 0.45

10 0.50 0.44 11 0.39 0.28 12 0.54 0.30

! 14 A.O.R. JUNQUEIRA ET AL.

Data from this study answer the questions proposed in the introduction. The Teredinidae recruitment is not the same in both experimental test panels. Considering the first 6 months, a correction factor of 1.6 for sheet panels density can be applied to obtain the value for solid panels density. Sheet panels underestimated Teredinidae density in spite of making it easy to quantify and to identify the species.

The variability of samples is another important problem, pointing out the necessity of a preliminary study to determine the correct sample size in order to evaluate Teredinidae density.

While examining solid panels we noticed that x-rays did not detect young organisms. On the other hand, this technique was efficient for evaluating organisms in the damage panels.

Differences in species composition between solid and sheet panels were not found. The different diversity values observed were related to the different dominance values of L. floridanus in each kind of panel.

Finally these results show that the methodology of evaluation must be considered before comparing the activity of Teredinidae between two areas.

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