SPATIAL AND SEASONAL DISTRIBUTIONS OF CALLINECTES DANAE (DECAPODA, PORTUNIDAE) IN UBATUBA BAY, SÃO PAULO, BRAZIL

JOURNAL OF CRUSTACEAN BIOLOGY, 21(2): 414 425, 2001 SPATIAL AND SEASONAL DISTRIBUTIONS OF CALLINECTES DANAE (DECAPODA, PORTUNIDAE) IN UBATUBA BAY, SÃO PAULO, BRAZIL M. M. Chacur and M. L. Negreiros-Fransozo (MMC, MLNF) NEBECC Group of Studies on Crustacean Biology, Ecology and Culture, Departamento de Zoologia, Instituto de Biociências, UNESP caixa postal 510 CEP 18618-000 Botucatu (SP) Brasil (e-mail: mlnf@ibb.unesp.br) ABSTRACT The spatial and seasonal distributions of Callinectes danae Smith, 1869, in Ubatuba Bay, São Paulo, Brazil, were investigated as a part of a broad study on the general biology of portunids along the northern coast of São Paulo State, Brazil. Swimming crabs were collected during one year, from September 1995 to August 1996, along eight transects determined according to local physiographic features. Three replicate trawls were performed monthly at each transect. Depth, salinity, dissolved oxygen, temperature, organic matter content, and texture of the sediment were measured. Callinectes danae individuals were concentrated in shallow water close to the discharge of estuaries where the bottom is composed of fine and very fine sand. The species was more abundant in the warmer months. During the study period, C. danae exhibited continuous reproduction with a peak of reproductive intensity in June. Within this area, some sites are particularly favorable for C. danae establishment due to a combination of factors and prevailing local conditions. Distributional patterns in swimming crabs seem to be a result of habitat preferences combined with intra- and interspecific interactions among individuals (Buchanan and Stoner, 1988). Marine organisms settling in areas with favorable environmental conditions will develop more efficient morphological, physiological, and behavioral defense adaptations against predation (Pinheiro et al., 1996). Regions characterized by marked transitions in the magnitude of ecological factors generally represent the zoogeographical boundaries of animals (Vernberg and Vernberg, 1970). In this sense, environmental factors should be continuously monitored in order to evaluate the occurrence of crab species or other marine organisms in a given area (Negreiros-Fransozo et al., 1991; Negreiros- Fransozo and Fransozo, 1995). According to Ryer et al. (1990), further investigation on the spatial and temporal aspects of interhabitat movements would increase our understanding of blue crab population dynamics and their interactions within estuarine communities. Blue crab species have been extensively reported in the literature due to their abundance and fishery importance along the Brazilian coast. Pita et al. (1985) found that C. danae is the most abundant portunid species captured in the bay-estuary complex of Santos (SP), and Fransozo et al. (1992) showed that it is the fifth most abundant brachyuran species from the soft-sediment bottoms of Fortaleza Bay, Ubatuba (SP). Several papers report that juveniles of Callinectes species inhabit estuaries (e.g., Van Engel, 1958; Tagatz, 1968; Taissoun, 1969, 1973; Paul, 1982; De Vries et al., 1983; Pita et al., 1985; Hines et al., 1987; Buchanan and Stoner, 1988; Moreira et al., 1988; and Prager, 1996). Nevertheless, Norse (1978) stated that C. sapidus is reproductively conservative. This species stores energy in low salinity ecosystems, but spawning and larval release takes place in the open sea. Reproductive periodicity has been studied in several brachyuran species by means of examining monthly samples throughout the year. Breeding patterns have been classified according to the length of the reproductive period. In this sense, continuous breeding is synonymous of year-round reproduction, while restricted breeding is usually correlated with favorable environmental conditions occurring during certain months (Sastry, 1983). Callinectes danae Smith, 1869, is a Western Atlantic species, being recorded in Bermuda, Florida, Gulf of Mexico, Antilles, Colombia, Venezuela, and Brazil, from Paraiba to Rio Grande do Sul (Melo, 1996). This species occurs from muddy estuaries in 414

CHACUR AND NEGREIROS-FRANSOZO: DISTRIBUTION OF CALLINECTES DANAE 415 Fig. 1. Ubatuba Bay, Brazil, with the location of sampled transects (I VIII). mangroves and algae-covered broken shell bottoms, to beaches and open ocean depths of 75 m, showing a high tolerance to a wide range of salinity conditions (Williams, 1984). In this paper we investigate the spatial and seasonal distributions of the blue crab C. danae in Ubatuba Bay (Fig. 1), and their relation to the variation of some environmental factors, namely temperature, salinity, depth, dissolved oxygen, organic matter contents, and granulometric composition of the substratum. Additionally, the reproductive period of this species is also evaluated based on the seasonal frequency of ovigerous females. MATERIALS AND METHODS Specimens of C. danae were obtained in Ubatuba Bay, SP, by trawling. A commercial fishing boat equipped with two double-rig nets was used. Mesh size used was 12 mm in the net body and 10 mm in the cod end. The continental shelf in the region of Ubatuba is 120 km wide, divided in two major areas. The inner shelf is about 50-m deep and mainly exposed to continental in-

416 JOURNAL OF CRUSTACEAN BIOLOGY, VOL. 21, NO. 2, 2001 Fig. 2. Plots of mean environmental factors on the eight transects sampled in Ubatuba Bay (box = standard error; bar = standard deviation; plots sharing at least one letter do not differ significantly, α = 0.05 and plots without letter mean that there is no difference among months). fluence, while the outer shelf depth ranges from 50 to 120 m, being directly affected by the open sea (Zembruscki, 1979). Four main rivers, Indaiá, Grande, da Lagoa and Acaraú River, flow into Ubatuba Bay. Thereby, water salinity is low at the inner area of the bay where deposition of organic matter together with domestic sewage is high. In the outer region the influence of oceanic currents prevails (Nakagaki, 1994). The hydrographic dynamics in the study region follow different seasonal patterns. During summer, warm, lowsalinity Coastal Waters (CW) occupying the 20-m surface layer join the warm, high-salinity waters of the Brazilian Current (BC). In this season, South Atlantic Central Waters (SACW) emerge, bringing cold, low-salinity, nutrient-enriched waters to the surface layer. Based on such dynamics and specific climate conditions taking place in surrounding areas, a circulation model has been proposed in which the wind and the Brazilian Current were considered controlling factors (Castro-Filho and Miranda, 1987).

CHACUR AND NEGREIROS-FRANSOZO: DISTRIBUTION OF CALLINECTES DANAE 417 Fig. 3. Plots of environmental factors sampled from September 1995 to August 1996 in Ubatuba Bay (box = standard error; bar = standard deviation; plots sharing at least one letter do not differ significantly, α = 0.05). For sampling purposes, the bay was divided into eight subareas, situated at different distances from the mouth of the bay, based on presence or absence of rock cliff or a sand beach along the boundaries, by degree of influence of fresh water inflow, by depth, organic matter content, and by grain size composition of the bottom surface sediments. Monthly trawl samples were taken throughout the year from September 1995 to August 1996 on eight transects, each one enclosing a 7,000-m 2 area; samples were replicated on three consecutive days. After each trawl, swimming crabs were sorted, placed in plastic bags, labeled and conditioned, and stored in thermal boxes with pricked ice. In the laboratory, specimens were counted to obtain numbers of individuals collected per transect. At the midpoint of each transect, three substratum samples were obtained with a van Veen grab, and three bot-

418 JOURNAL OF CRUSTACEAN BIOLOGY, VOL. 21, NO. 2, 2001 Table 1. Results of the tendency analysis to classify the granulometric composition of sediments (phi Φ) in the sampled sites in Ubatuba Bay during the study period (Sept. 1995 Aug. 1996). Transects Months I II III IV V VI VII VIII September 3.37 2.85 2.92 1.090 1.09 2.24 2.99 3.92 October 3.39 3.17 2.32 1.58 0.99 1.61 3.36 4.10 November 3.00 3.34 2.40 1.82 1.17 2.77 3.25 3.73 December 3.36 3.43 2.95 2.10 1.91 2.16 3.78 3.37 January 3.22 3.45 2.45 2.13 1.65 3.51 3.27 3.83 February 3.36 3.35 2.70 1.70 2.01 3.00 3.04 3.51 March 3.39 3.44 3.19 2.04 1.04 3.40 3.26 3.73 April 2.94 3.35 3.33 2.14 0.68 3.45 3.44 3.76 May 3.35 3.47 4.58 1.53 1.05 4.36 3.42 4.13 June 3.15 3.40 2.51 1.57 1.18 3.05 2.86 4.55 July 3.03 3.49 3.29 1.46 1.37 3.88 3.38 4.61 August 3.90 3.43 4.20 1.68 1.23 3.96 3.33 4.70 Central sediment tendency 3.32 3.33 2.90 1.82 1.26 2.87 3.33 3.85 Category Very fine Very fine Fine Medium Medium Fine Very fine Very fine sand sand sand sand sand sand sand sand tom-water samples were collected with a Nansen bottle. Depth was measured in each sampling station using a graduated rope that was attached to the Van Veen grab. In the laboratory, about 200 g of sediment were dried at 70 C during 72 h, split into aliquots, and submitted to the organic-matter and grain-size analyses. Components were characterized according to the Wentworth (1922) scale to determine substratum composition. The phi Φ (mean diameter) value was used according to Suguio (1973) to calculate the central tendency. Organic-matter contents (%) were obtained by ashweighting: 3 aliquots of 10 g each per subarea per month were placed in porcelain crucibles and submitted for a period of 3 h at 500 C, and the samples were then weighed again. The water samples were collected from the bottom using a Nansen bottle, which allowed recording simultaneously water temperature, salinity, and the amount of dissolved oxygen. The temperature ( C) was measured with a thermometer attached to the bottle and salinity ( ) using an optical refractometer. The amount of dissolved oxygen (mg/l) was calculated by the Winkler method proposed by Golterman and Clymo (1969), and modified by the addition of azide. More details about the laboratory procedures and statistical analyses to verify seasonal variation of environmental factors can be found in Mantelatto and Fransozo (1999a). Callinectes danae individuals were separated by transect and collection month. Sex determination of all individuals was carried out by examining the abdominal morphology. The adherence of the abdomen to the thoracic sternites was checked to identify juvenile individuals (Taissoun, 1973) and assess morphologic maturity of crabs. In the case of females, the presence of eggs on the pleopods was also verified. Crabs were separated into four categories: adult males, adult non-ovigerous females, ovigerous females, and juveniles, for which the absolute frequency was calculated based on the total number of individuals recorded in each transect in a given month. An analysis of multinomial proportions (Goodman, 1965) was used to compare monthly frequencies of ovigerous and non-ovigerous females during the study period. Spatial and seasonal variability of environmental factors were assessed between the eight transects and all sampled months. An analysis of variance (ANOVA) was performed, and Tukey s multiple comparison tests were carried out to analyze for statistical differences between means at the 5% significance level (Ostle, 1973). Relationships between the biological and the environmental variables were evaluated by means of partial and multiple correlation analyses (Sokal and Rohlf, 1995; Zar, 1996). RESULTS Temperature and salinity did not vary significantly (P > 0.05) among transects. The temperature mean values varied from 22.5 C in transect I to 24.9 C in transect VIII, and the salinity mean values varied from 32.5 in transect VIII to 33.7 in transect I (Fig. 2A, B). Mean values of dissolved oxygen concentration (F 7,88 = 2.61; P < 0.05) varied from 4.61 mg/ml to 5.5 mg/ml, respectively, from transect III to V. Transects V and VIII Table 2. Results of the partial correlation coefficients of the association between C. danae abundance and analyzed environmental factors in Ubatuba Bay during the study period (Sept. 1995 Aug. 1996). Temperature Salinity Dissolved oxygen Organic matter Depth Coefficient 0.2035 0.1057 0.0277 0.2640 0.4601 Probability P = 0.026 P = 0.907 P = 0.758 P = 0.004 P = 0.000005

CHACUR AND NEGREIROS-FRANSOZO: DISTRIBUTION OF CALLINECTES DANAE 419 Fig. 4. Histograms (± SD) of mean percentage granulometric composition along transects I VIII. (bar = standard deviation; G, gravel; VCS, very coarse sand; CS, coarse sand; MS, medium sand; FS, fine sand; VFS, very fine sand, and S+C, silt + clay).

420 JOURNAL OF CRUSTACEAN BIOLOGY, VOL. 21, NO. 2, 2001 Fig. 5. Callinectes danae: Histograms of frequency (%) of occurrence of each category of sex/age of crabs in each transect (I VIII) in Ubatuba Bay. differ from transect III (Fig. 2C). Depth (F 7,88 = 302.83; P < 0.05) varied among sites, with transects V, VI, and VII contrasting with transects II and III (Fig. 2D). With respect to organic-matter content, significant differences were also detected (F 7,88 = 19.09; P < 0.05). Smallest mean percentage values of organic matter content were found in transects I, II, VII, and VIII, the values ranging from 5.3% to 6.9% (Fig. 2E). In the seasonal analyses, temperature varied significantly (F 11,84 = 57.34; P < 0.05), with lowest mean values found in winter (July and August) and highest mean values in summer (February) (Fig. 3A). Significant differences were also found in salinity (F 11,84 = 68.88; P < 0.05), with mean values ranging from 29.6 in November to 35.3 in January (Fig. 3B), and oxygen (F 11,84 = 4.70; P < 0.05), with mean values varying from 4.28 mg/l in June to 5.9 mg/l in March (Fig. 3C). Depth and organic matter did not show significant statistical variation (Fig. 3D, E). The granulometric composition of the sediment in the eight transects (Fig. 4) ranged from gravel to silt + clay. During the study period, small variation was observed in the texture of the sediment. Central-tendency analyses to classify the granulometric composition of sediments in the sampled sites along the study period are listed in Table 1. In transects I, II, VII, and VIII, there was a predominance of very fine sand, while fine sand prevailed in transects III and VI and medium sand in transects IV and V. The adjusted multiple correlation between the abundance of C. danae and the group of environmental variables (temperature, salinity, oxygen, organic matter, and depth) was significant (0.5382; P < 0.0001) (Table 2). Therefore, there appears to be a relationship between such factors and the number of individuals. Partial correlation analyses showed that crab abundance is positively correlated with temperature and negatively correlated with depth and organic matter contents (P < 0.05). There was no significant relationship of crab abundance with salinity or oxygen concentration (P > 0.05). A total of 2,406 crabs was sampled: 668 adult males, 956 adult non-ovigerous females, 227 ovigerous females, and 555 juveniles. The frequency distributions of each group within the eight sampled transects indicated that the largest catches occurred on transects

CHACUR AND NEGREIROS-FRANSOZO: DISTRIBUTION OF CALLINECTES DANAE 421 Fig. 6. Callinectes danae: Histograms of frequency (%) of occurrence of each category of sex/age of crabs in each sampled month (Sept. 1995 Aug. 1996) in Ubatuba Bay.

422 JOURNAL OF CRUSTACEAN BIOLOGY, VOL. 21, NO. 2, 2001 with higher levels of dissolved oxygen and with increased median diameter of sediment grains (Fig. 8C, F). The species was more abundant in shallow areas (3.5 m) and in sediments with low organic-matter content (5.5%) (Fig. 8D, E). Fig. 7. Callinectes danae: Bar graph of ovigerous females present in Ubatuba Bay in each sampled month (Sept. 1995 Aug. 1996) (bars sharing at least one letter do not differ significantly, α = 0.05). VI, VII, and VIII, with 16.33%, 11.39%, and 67.50% of all individuals, respectively, totaling 95.22% of all crabs (Fig. 5). With reference to demographic categories, the profile is similar to that obtained in the distribution of individuals in transects. Highest catches of crabs were obtained in February (21.4%) and March (22.5%), with a smaller peak in June (Fig. 6A). Adult males, adult non-ovigerous females, and juveniles were also more abundant in February and March (Fig. 6B, C, D, E). Ovigerous females were more abundant in February and June (Fig. 6F). Non-ovigerous females outnumbered ovigerous females throughout the study period. The frequency of occurrence of ovigerous females showed statistical differences (P < 0.05) along the sampled months (Fig. 7). Although ovigerous females occurred throughout the year, the proportion of ovigerous females was always lower than that of adult non-ovigerous females. For C. danae, there was no evidence that some differences found have any correlation with environmental factors, including temperature. Thus, we suggest that other factors such as interspecific competition or food availability could be investigated to clarify the pattern observed. Largest catches of C. danae occurred in high temperatures (30.5 C) (Fig. 8A). The occurrence of this species along the salinity gradient (31.0 ) shows a slight variation, indicating its tolerance to different salinity conditions (Fig. 8B). Crab abundance increases DISCUSSION Compared to other measured variables, temperature seems to be the most important factor affecting temporal abundance of this species. Thermal variation may partially influence crab density, because capture rates were higher during summer than winter. Buchanan and Stoner (1988) also verified this fact for a C. danae population inhabiting an estuarine lagoon on the east coast of Puerto Rico. Callinectes danae is an euryhaline species (Shumway, 1983) which releases its larvae in the sea. Juveniles then migrate to the estuaries where they develop and grow. Mansur (1997), who studied the distribution of C. danae in the Acaraú river (Ubatuba Bay), found that almost 100% of the individuals collected in low salinity waters were juveniles. In the present study, 73% of all juveniles were found in the Grande River mouth, thus supporting that such individuals are mainly concentrated in estuarine grounds. In benthic communities, spatial heterogeneity accounts for most variability in the relative abundance of a given species (Buchanan and Stoner, 1988; Watson et al., 1990). Depth, transect location (mainly regarding its distance to estuarine waters), and sediment texture are probably the main factors ruling spatial distribution of C. danae in Ubatuba Bay. Due to the heterogeneity of sampling sites used in this study, it is not possible to examine separately the relationship between a single environmental factor and the occurrence of C. danae. A certain combination of the analyzed factors would probably render favorable conditions for the establishment of a single population in a specific area. The species studied herein is mainly distributed in shallow bottoms composed by very fine sandy sediments. High water temperature, low salinity, and low organic-matter content of sediments are also favorable conditions. According to Sastry (1983), several environmental factors such as temperature, photoperiod, food availability, and social conditions can influence the reproduction of a species. Continuous reproduction can be

CHACUR AND NEGREIROS-FRANSOZO: DISTRIBUTION OF CALLINECTES DANAE 423 Fig. 8. Callinectes danae: Distribution of the mean number of individuals within sex/age classes per trawl with varying environmental factors (temperature, salinity, dissolved oxygen, depth, organic matter, grain average diameter). found in some tropical and subtropical portunid species such as Callinectes arcuatus Ordway, 1863; Ovalipes punctatus (De Haan, 1833); Portunus pelagicus (Linnaeus, 1758); and Callinectes ornatus Ordway, 1863, studied by De Vries et al. (1983); Du Preez and Mclachlan (1984); Batoy et al. (1987); and Mantelatto and Fransozo (1999b), respectively. A continuous reproductive pattern was found for C. danae in this study, with yearround occurrence of ovigerous females. This outcome supports previous results of Pita et al. (1985), Medeiros and Oshiro (1992), and Costa and Negreiros-Fransozo (1998).

424 JOURNAL OF CRUSTACEAN BIOLOGY, VOL. 21, NO. 2, 2001 Capture rates of C. danae increase considerably during summer and autumn. Moreira et al. (1988) found in the bay-estuary complex of Santos-São Vicente maximum capture peaks of C. danae in the summer months. Probably, the swimming crabs move towards shallow waters during the entrance of cold waters from SACW in the summer months which could increase the capture rate in such areas. The relationship between the abundance of C. danae and the variation of certain environmental factors is probably due to the fact that the climatic conditions and the local ecological parameters oscillate within the tolerance limits of the species, favoring the continuity of physiological processes. The complete life cycle of C. danae takes place within Ubatuba Bay and its surrounding estuaries. ACKNOWLEDGEMENTS We are thankful to the Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) for providing financial support (# 96/3333 3; 94/4878 8). 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