Oceanological and Hydrobiological Studies International Journal of Oceanography and Hydrobiology Volume 41, Issue 4 ISSN 1730-413X eISSN 1897- 3191
(77–80) 2012
DOI: 10.2478/s13545-012-0041-z Short communication
Reproductive Biology of the Mediterranean Green Crab Carcinus aestuarii Nardo, 1847 (Crustacea, Brachyura, Portunidae) in Homa Lagoon, Aegean Sea, Turkey Murat Özbek1, Cengiz Koçak1,*, Deniz Acarlı2 1Ege
University, Faculty of Fisheries, TR 35100, BornovaIzmir, Turkey 2Onsekiz Mart University, Gökçeada School of Applied Sciences, Department of Fisheries Technology, TR-17760 Gökçeada-Çanakkale, Turkey Key words: Reproductive biology, Carcinus aestuarii, Homa Lagoon, Aegean Sea, Mediterranean Sea Abstract
The Mediterranean green crab Carcinus aestuarii Nardo, 1847 (Crustacea, Brachyura, Portunidae) is a common inhabitant of the shallow waters of Homa Lagoon in Izmir Bay, Turkey, in the eastern Mediterranean. Monthly samples were collected in Homa Lagoon from June 2006 to May 2007 using trammel nets, fyke nets, beach seines and fence traps. In total, 608 males and 559 females of C. aestuarii were collected. The highest sex ratio (8186% females) was recorded between October and December, and in August (58% females). Ovigerous females were obtained only from November to February with the highest ratio of ovigerous females (55%) observed in January 2007. The maturation curve presenting the carapace width showed that 50% of female crabs with the carapace width of 26.84 ±1.58 mm (r= 0.72) were physiologically mature. Regression analyses indicated that the number of eggs was positively correlated with carapace width and wet weight (P < 0.05, in both cases). *
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Received: Accepted:
November 22, 2011 June 13, 2012
INTRODUCTION Carcinus aestuarii belongs to the family Portunidae and has an extensive distribution around the Mediterranean Sea to a depth of 26 m (Abello et al. 1988). Until the end of the 20th century, this species was only known to live in estuarine and lagoonal waters of the Mediterranean and Black Seas (Mori et al. 1990, Behrens Yamada and Hauck 2001), but there have also been some recent records from Japan (Sakai 1986, Furota et al. 1999). In the last two centuries, specimens of Carcinus aestuarii have been accidentally introduced into several regions outside their native range as a result of maritime commerce and ballast transport: to the Canaries (Almaça 1961), and Tokyo Bay, Japan (Sakai 1986, Ikeda 1989, Chen et al. 2004). Carcinus aestuarii plays an important role in lagoon ecosystems as a component of the diet of fish such as eels and bass, and fish that migrate to lagoons along the Mediterranean coast in search of food (trophic migration) (Mori et al. 1990). Mori et al. (1990) have provided information on the reproductive biology of C. aestuarii in Italy in the Lagoon of San Teodoro on the island of Sardinia in the Western Mediterranean. Carcinus aestuarii is preyed upon by sea bream (Sparus aurata Linnaeus, 1758) in pools of Homa Lagoon. However, there is no information on the reproductive biology of this species in Turkish seas of the eastern Mediterranean. The purpose of the present study was to investigate the reproduction of C. aestuari in Homa Lagoon, Izmir Bay. We document here the reproductive biology of C. aestuari with the aim of providing basic commercial exploitation guidelines that would ensure the lowest possible impact on the ecosystem.
78 | Murat Özbek, Cengiz Koçak, Deniz Acarlı
MATERIALS AND METHODS Monthly sampling was conducted from June 2006 to May 2007 in Homa Lagoon, Izmir Bay, in the Turkish Aegean Sea (38º27’ N - 26º55’ E) (Fig. 1). Specimens were collected by means of fyke nets, trammel nets, beach seines and fence traps. The specimens were fixed in 4% formalin solution.
Crabs were divided into CW size classes, with 2.0 mm intervals, and the frequency of juvenile and adult crabs was noted. For the physiological maturity analysis, the logistic equation was used at each size class: 𝑦=
1
1 + 𝑒 −𝑟(𝐿𝐶−𝐿𝐶50)
as proposed by Castiglioni & Negreiros-Fransozo (2006). The adult (ovigerous female) relative frequency (%) and the result of the logistic equation at each size class were obtained and graphed. The logistic equation variables were LC50 and r, where LC50 indicated CW in which 50% of the crabs reached the sexual maturity and “r” determined the curve inclination. The adjustment was assessed by the minimum square method. RESULTS Fig. 1. Map of Izmir Bay, Turkey, showing the study area.
At a laboratory, the carapace width (CW) and carapace length (CL) of each ovigerous female were measured using digital calipers (with an accuracy of 0.01 mm). The egg mass of each ovigerous female was detached from the pleopods and weighed using a digital balance with an accuracy of 0.001 g. After that, the wet weight (WW) (not blotted with filter paper) of each ovigerous female without eggs was recorded using a digital balance with an accuracy of 0.01 g (only undamaged specimens were included). The eggs were counted under a dissecting microscope with a manual counter. A sub-sample of five eggs was taken in each case and measured using a micrometric scale. The embryonic developmental stages were determined according to Boolootian et al. (1959) and adapted for C. aestuarii as follows: • Initial stage (1): egg is completely filled with yolk; no sign of cleavage or cellular differentiation, and no embryo pigmentation visible, • Middle stage (2): eggs with slight embryo eye pigmentation, and • Final stage (3): yolk is restricted to a reduced patch; the embryo is fully differentiated, with clear segmentation of limbs and eye pigmentation. Copyright© of Institute of Oceanography, University of Gdansk, Poland www.oandhs.org
During the study period from June 2006 to May 2007 (and an additional sampling in January 2008), 608 males and 559 females of C. aestuarii specimens were caught. The highest sex ratio was recorded from October to December (81-86% females), and in August (58% females) (Table 1). 449 females were non-ovigerous (80.3%) and 110 females were ovigerous (19.7%). From January to July and from August to September the number of females decreased with a percentage ranging from 20.0% to 0.6%. Ovigerous females were obtained only between November and February and the highest ratio of ovigerous females was observed in January 2007 (55.0%) (Fig. 2). Table 1 Monthly distribution of males, females and the sex ratio values (females/males + females). Number of Number of Males Females June 2006 37 8 July 110 13 August 47 65 September 20 18 October 24 150 November 30 124 December 22 136 January 2007 10 9 February 63 5 March 55 14 April 70 9 May 120 8 Total 608 559 Months
Sex ratio [f/(f+m)] 0.18 0.11 0.58 0.47 0.86 0.81 0.86 0.47 0.07 0.20 0.11 0.06 0.48
Reproductive Biology of the Mediterranean Green Crab in Homa Lagoon, Aegean Sea, Turkey| 79
Fig. 2. Carcinus aestuarii in Homa Lagoon, Turkey. Monthly distribution of the ratio of ovigerous females to total females.
Individual fecundity and size of the 110 females analyzed varied from 6,000 to 126,969 eggs (42,201 ±8 eggs) and CWs of ovigerous female crabs ranged from 16.84 to 39.28 mm (27.903 ±4.29 mm), respectively. The wet weight of the egg brood (WE) varied from 0.21 to 4.68 g (1.49 ±0.82 g), corresponding to 5.7-28.8% (18.5 ±4.1%) of the total wet weight of a female. A adjustment of the maturation curve showed that CW in which 50% of the females were physiologically mature is 26.84 ±1.58 mm (r = 0.72) (Fig. 3). Regression analyses indicated that the number of eggs (EN) is positively correlated with CW and WW (P < 0.05, in both cases). Scatterplots revealed an exponential relationship between EN and CW (Fig. 4), while the relationships between EW and WW (Fig. 5) and between EN and EW (Fig. 6) came close to straight lines.
Fig. 4. Carcinus aestuarii in Homa Lagoon, Turkey. Relationship between the number of eggs (EN) and carapace width (CW).
Fig. 5. Carcinus aestuarii in Homa Lagoon, Turkey. Relationship between the weight of eggs (EW) and wet weight (WW).
Fig. 6. Carcinus aestuarii in Homa Lagoon, Turkey. Relationship between the number of eggs (EN) and egg weight (EW).
DISCUSSION
Fig. 3. Carcinus aestuarii in Homa Lagoon, Turkey. Mean minimum size at the onset of sexual maturity (size of ovigerous females).
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Mori et al. (1990) found that ovigerous females of C. aestuarii in the Lagoon of San Teodoro, Italy, were present from late November to early May with a maximum in February. Similarly, Veillet (1945) and Démeusy (1958) reported that ovigerous females in the Lagoon of Thau and in Séte were present from November to March. Our observations showed sharp declines in the density of female C. aestuarii in the Lagoon of Homa in February and May (see Table
80 | Murat Özbek, Cengiz Koçak, Deniz Acarlı
1), and ovigerous females were caught only from November to February with a peak in January 2007. Our results suggest that the reproductive behavior observed in the study area is similar to that described for other localities in Italy. Although Amanieu et al. (1978) and Crivelli (1981) reported two spawning periods for C. aestuarii along the Mediterranean coast, Mori et al. (1990) reported a single brood per year, and this was also observed in the present study. The size in which the sexual maturity is reached and how it is determined are important aspects of the biological cycle of decapods, and can be determined through the study of reproductive biology, and morphometric techniques can indicate allometric changes in the size related to external morphological maturity (Castiglioni & Negreiros-Fransozo 2006). The size at sexual maturity is a basic parameter, which allows us to define the mechanism governing the balance of the parental stock and which can notably contribute to studies of environmental effects on the population biology (Mori et al. 1990). The available data on the size at puberty of C. aestuarii females from the middle and western parts of the Mediterranean are related to the smallest ovigerous females. Veillet (1945) remarked that female C. aestuarii in the Lagoon of Thau reaches puberty at CWs of almost 21 mm. Similarly, Démeusy (1958) observed sexual maturity to occur at mean CW size of 25 mm (CW ranging from 20 to 29 mm; MORI et al. 1990). Crivelli (1982) observed puberty at CW of 28 mm in the Lagoon of Tampan, while Mori et al. (1990) observed CW of 29.1 mm at puberty in the Lagoon of S. Teodoro, in Sardinia. In this study, we found that female C. aestuarii reaches puberty at CW of 26.84 mm in Homa Lagoon, which is similar to the observations by other authors (Démeusy 1958, Crivelli 1982, Mori et al. 1990). The fact that most of the ovigerous females are caught with fish barriers during their migration from the Lagoon into the sea could explain the decreases in the populations of this species (Mori et al. 1990). In that case, the minimum legal size limit for C. aestuarii could be set as the size when females are mature at CW of 27 mm plus one growth increment of ca. 7 mm, i.e. CW 34 mm (Mori et al. 1990). REFERENCES Abelló, P., Valladares F. J., Castellón, A., 1988, Analysis of the structure of decapod crustacean assemblages off the Catalan coast (North-West Mediterranean), Marine Biology, 98: 39–49 Almaça, C., 1961, Variabilidade de alguns caracteres usados na Copyright© of Institute of Oceanography, University of Gdansk, Poland www.oandhs.org
taxonomia do Gen. Carcinus Leach, Revista da Faculdade de Ciéncias de Lisboa, 7: 137–153 Behrens Yamada, S., Hauck, L., 2001, Field identifi cation of the European green crab species Carcinus maenas and Carcinus aestuarii, Journal of Shellfish Research, 20 (3): 905-912. Boolootian, R.A., Farmanfarmaian, A., Turcker J., 1959, Reproductive cycles of five west coast crabs, Physiological Zoology, 4: 213–220 Castiglioni, D., Negreiros-Fransozo, M.L., 2006, Physiologic sexual maturity of the fiddler crab Uca rapax (Smith, 1870) (Crustacea, Ocypodidae) from two mangroves of Ubatuba, Brazil, Brazilian Archives of Biology and Technology, 49 (2):239–248 Chen, R.B., Watanabe, S., Yokota, M., 2004, Feeding habits of an exotic species, the Mediterranean green crab Carcinus aestuarii, in Tokyo Bay, Fisheries Science, 70: 430–435 Crivelli, A.J., 1982, Biology of three Malacostraca (Decapoda) in a Mediterranean Lagoon with particular emphasis on the effect of rapid environmental changes on the activity (Catchability) of the species, Estuarine Coast Shelf Science, 15: 591–604 Démeusy, N., 1958, Réchèrches sur la mue de puberté du Decapode Brachyoure Carcinus maenas Linné, Archives De Zoologie Experimentale et Generale, 95: 258–490 Furota, T., Watanabe, S., Watanabe, T., Akiyama, S., Kinoshita, K., 1999, Life history of the Mediterranean green crab, Carcinus aestuarii Nardo, in Tokyo Bay. Japan. Crustacean Research, 28: 5-15 Ikeda, H., 1989, Notes on Carcinus mediterraneus Czerniavsky found in Tokyo Bay, Natural History Report of Kanagawa, 10: 83–85 Mori, M., Mancon, R., Fanciulli, G., 1990, Notes on the reproductive biology of Carcinus aestuarii Nardo (Crustacea, Decapoda) from the lagoon of San Teodoro (Island of Sardinia, Italy), Rivista di Idrobiologia, 29: 763–774 Sakai, T., 1986, Rare species and their genus of crabs in Japan, Researches on Crustacea, 15: 1–4 Veillet, A., 1945, Recherches sur le parasitisme des crabes et des galathées par les rizocéphales et les épicarides. Annales de l'Institut Océanographie Paris, 22:193–341
