J. Mar. Biol. Ass. U.K. 12000), 80,941^942 Printed in the United Kingdom SHORT COMMUNICATIONS
Spatial dispersion and density of the Paranemonia vouliagmeniensis population in Vouliagmeni Lagoon
Chariton-Charles Chintiroglou*, Chrysanthi Antoniadou and Panagiotis Damianidis Aristotle University of Thessaloniki, School of Biology, Department of Zoology, Box 134 GR-54006 Thessaloniki 1Macedonia), Greece. *E-mail: [email protected]
A number of biological parameters relevant to the population dynamics of Paranemonia vouliagmeniensis are discussed.The abiotic factors of the lagoon's waters are stable throughout the year. Paranemonia vouliagmeniensis populations follow di¡erent patterns of distribution 1aggregated or random) in relation to human in£uence, and can thus become a reliable bioindicator for the lagoon.
The northern coast of the lagoon has a typical, natural hard and conductivity around 25 mS cm71. Therefore any change in the bottom and on the southern coast, an arti¢cial sand^gravel structure and function of the lagoon's assemblages should be attrib- Chintiroglou et al. 11996). This study of the spatial dispersion of uted to the e¡ects of biotic interactions rather than abiotic factors. Paranemonia vouliagmeniensis was carried out at three sampling Anemones were observed on all types of substrate. The sites, which were selected according to intensity of use by anemone population found on hard substrates were not a¡ected by bathers; samples were collected from a depth of 1 m. The ¢rst, the bathers'activities. However, those that grow on the algae thalli 1site A) is situated at the north-east side of the lagoon, where the and in shallow waters 1about 1m deep) were in£uenced 1a) by the number of bathers is limited. The shallow water area 1down to bathers' activities; and 1b) by the `diving gardeners', employed to 1m) of the sublittoral zone is no wider than 3 m. The second, cut the algae down to improve the underwater scenery. Figure 1A 1site B) is situated on the southern coast of the lagoon, where shows the relative variation in frequency of the anemones found on bathers are numerous. In contrast, the third, 1site C), which also algae thalli at greater depths 43 m. The number of individuals had a high presence of algae, is lightly used by bathers. The 1ind 5 l71)oftheP.vouliagmeniensis population varied signi¢cantly shallow water area 1down to 1 m) of the sublittoral zone was in time 1Kruskal^Wallis test H10.4; P0.02), with the greatest broader than 7 m. Additional algae samples were collected, in population numbers in winter and spring. Most of the anemones nylon bags from deeper parts of the lagoon 13^5 m). found on the algae thalli were small 1Chintiroglou et al.,1996).All Samples were collected by SCUBA diving during 15 young individuals must be released from the parent anemones consecutive months. More than 30 dives were carried out in all between October and May, and start to settle on algal thalli the di¡erent habitats of the lagoon. A 50Â50 cm metal frame during the winter and spring months. was the minimum sampling surface used to estimate the spatial Table 1 shows that P.vouliagmeniensis populations follow dispersion and density of P.vouliagmeniensis populations 1Castric- di¡erent patterns of distribution at the three sampling sites. At Fey, 1984). Numbers of individuals enclosed in that frame were site B, where human in£uence is more intense, an aggregated recorded at ten randomly chosen spots, at each of the three distribution was observed 1w2 22.48^48.61; P=0.05) throughout sampling sites. Sampling was carried out in all four seasons of the the year. However, the distribution of the anemones at sites year 122/06/97, 11/10/97, 14/03/98 and 17/05/98). The collected A and C appeared to be random 1w2 13.9^ 17.01; P0.05) in anemones' population was made up of a total of 120 frames. Addi- autumn and spring and aggregated 1w2 22.48^83.42; P=0.05) tional £ora samples, collected from a depth 43 m, contained 5 l in winter and summer. The distribution at site A in the winter of algae and were preserved in 10% formalin. Twelve samples season is random 1w2 18.35; P=0.05). were collected in total 112 bagsÂ5 l), three each season, and the The two-way ANOVA showed that there was no signi¢cant number of anemones was recorded and their relative abundance di¡erence from site to site in density 1ind m72)1F1.3, P0.27) 1ind 5 l71) calculated. In addition, extra anemone samples were 1Figure 1B). However, density di¡ered signi¢cantly between collected every two months in order to examine the percentage seasons 1F10.6, P0.0001), due to low values from 42.4 Æ20.6 to of young individuals. 52.8 Æ18.1ind m72, in spring. Thus, the population density of Morisita's index was used to estimate the spatial dispersion of P.vouliagmeniensis di¡ered between summer and spring 1Fisher the three P.vouliagmeniensis populations. Chi square was calculated PLSD value 0.1 and Sche¡ F- test values 4.2), winter and spring in order to determine the signi¢cance of deviation from random 1Fisher PLSD value 0.1) and autumn and spring 1Fisher PLSD spatial dispersion 1Elliott, 1973; Bakus, 1990). All data were value 0.1). The highest density values were observed in summer converted to base 10 logarithms, after standardization to m2.All and autumn, with minor di¡erences between sites. The highest tests, such as the data normality test or one- and two-wayANOVA, density at site C 1137 Æ63 ind m72) occurred in summer, while at were carried out according to Bakus 11990) and were aimed at site B 1148 Æ48 ind m72) in autumn. ¢nding the di¡erences in P.vouliagmeniensis densities 1mean The mean density of the anemones at the three sites, annually, number ind m72).The Fisher PLSD test was also used in order to was: site A, 68.1 Æ33.9 ind m72;siteB,87.8Æ50.8 ind m72; and examine partial di¡erentiations. The non-parametric Kruskal^ site C, 84.8 Æ50.2 ind m72. The mean density of the anemones Wallis test 1Siegel, 1956) was employed to compare the relative in the four seasons was: summer: 94þ59.9 ind m72; autumn: abundance of the anemones found in the algae samples. 99.9 Æ47.6 ind m72; winter: 76 Æ32.1ind m72; and spring: The abiotic factors of the lagoon's waters varied within a very 46.8 Æ18.5 ind m72. These values show that the highest densities small range throughout the year.Temperature never dropped below at all sites appeared in summer and autumn, and the lowest in 188C 118^288C), salinity varied slightly around17psu, pH around 7 spring, while winter values are without a precise trend.
Journal of the Marine Biological Association of the United Kingdom 2000) 942 SHORT COMMUNICATIONS
Table 1. Statistical parameters concerning the populations spatial dispersion. Bold text indicates a random distribution.
Site A Site B Site C
Summer Autumn Winter Spring Summer Autumn Winter Spring Summer Autumn Winter Spring 1997 1997 1998 1998 1997 1997 1998 1998 1997 1997 1998 1998
Mean 20.1 19.7 15.1 13.2 16.2 37 21.4 10.6 34.2 18.2 21.1 11.3 SD 13.6 6 5.5 4.5 9.4 12 8.6 5.1 15.8 5.9 8.6 4.3 Variance 186.3 35.6 30.8 20.4 87.5 143.8 73.8 26.5 248.4 34.4 74.5 1.4 Morisita's index 1.42 1.08 1.12 1.11 1.3 1.09 1.14 1.21 1.91 1.09 1.15 1.13 w2 values 83.42* 16.24 18.85* 13.9 48.61*34.97* 31* 22.48* 65.36* 17.01 31.79* 14.5
*, rejections of the random hypothesis. 11991) and Sala et al. 11996), who found that the bathing activity in a coastal region directly in£uences the structure of the benthic assemblages. The di¡erent distributions at sites A and C in the winter season is also signi¢cant. At site A, where the extent of the upper sublittoral zone is small, the anemones' density reaches the higher `tolerance' limit in a shorter period of time, possibly prompting the anemones to migrate to more suitable settlement sites sooner. In other words, the migration is completed before the end of the winter season, resulting in a random 1Morisita's index1.12), low density, distribution. At site C in contrast, where the size of the respective area is larger than site A, the population density increases at slower rate. As a result, the popu- lation density fails to reach the `tolerance' limit soon enough for the migration to start, therefore, the distribution is aggregated 1Morisita's index1.15) and the density is high. Nevertheless, in spring the distribution at site C appears to be random 1Morisita's index1.14), which means that the migration there is completed by late winter or early spring, when lower density is observed. Figure 1. Seasonal variation of the mean abundance of Paranemonia vouliagmeniensis living on algae in deeper water 1A) and at the three We would like to express our gratitude to the Ministry of sampling sites in shallow water 1B). S, summer, A, autumn, W, Development, General Secretariat for Research and Technology winter, Sp, spring. Bars indicate ÆSE. for ¢nancing this research programme and also the Managerial Board of the lagoon, the Municipality of Vouliagmeni and every- The reproductive and migratory behaviour of the species one who has supported us in our endeavour to accomplish this task. seem to be the most important of the biotic factors, but human impact is also of great importance, Chintiroglou et al. 11996). REFERENCES Thus at site B, where human activities were more intense, conta- gious distribution was prominent throughout the year, in high Bakus, J.G., 1990. Quantitative ecologyand marine biology . or low densities. This is an entirely di¡erent pattern of disper- Rotterdam: A.A. Balkema. sion to that observed in the other two sites 1A and C). This Castric-Fey, C., 1984. Revue des me¨ thodes actuelles d'e¨ tudes des substrats durs infralittoraux. Oceanis, 10, 207^237. pattern may be attributed to the activities of the bathers, espe- Chintiroglou, C., 1996. Observations on a population of the sea cially during the spring, summer and autumn seasons, as well as anemone Anemonia viridis 1ForskÔl, 1775) in the north Aegean to the high population density during summer. sea. Oebalia, 22, 71^82. Anemone dispersion at sites A and C, which appear to be Chintiroglou, C.C., Valkouma, T. & Culley, M., 1996. Biological random during autumn and spring, is the result of migration and studies in Athens Lake Vouliagmeni. I. The allometry of density of the population. Low densities in spring occur as recruits feeding and body size in a population of the sea anemone migrate to deeper sites in the lagoon.This process begins in winter Paranemonia vouliagmeniensis Doumenc et al. 1987 1Actiniaria: and is completed by spring and may explain the high abundance of Anthozoa). Journal of the Marine Biological Association of the anemones on algae at the deeper sites during these two seasons United Kingdom, 76, 603^616. 1see Figure 1A). There are two migration seasons in the life of Elliott, M.J., 1973. Some methods for the statistical analysis of P.vouliagmeniensis. One during which juveniles migrate to deeper samples of benthic invertebrates. Freshwater Biological Association, Special Publication, 25, 148 pp. waters to ¢nd better feeding conditions and to avoid any spatial Pax, F., 1936. Anthozoa. In Tierwelt der Nord- und Ostsee vol. 30 intraspeci¢c competition. The second and reverse migration 1ed. Grimpe and Wagler), pp. 81^317. pattern concerns the larger/mature individuals leaving the algae Povey, A. & Keough, M.J., 1991. E¡ects of trampling on plant on which they settled, Chintiroglou et al. 11996). High densities are and animal populations on rocky shores. Oikos, 61, 355^368. consequently observed at sites A and C in the summer where the Sala, E., Garrabou, J. & Zabala, M., 1996. E¡ects of diver distribution of anemones is aggregated. The distribution at site A frequentation of Mediterranean sublittoral populations of the in summer is aggregated, even though the anemones'density does bryozoan Petapora fascialis. Marine Biology, 126, 451^459. not di¡er from that at sites with random distribution 1e.g. site C in Siegel, S., 1956. Nonparametric statistics for the behavioral sciences. autumn).This implies that the activities of the bathers play a role Tokyo: McGraw^Hill, Kogakusha Ltd. in distribution, which agrees with the results of Povey & Keough Submitted 14 June 1999. Accepted 6 April 2000.
Journal of the Marine Biological Association of the United Kingdom 2000)