Caimona Suarez and Conde Distribution and abundance of Callinecles spp and Arenaeus aibraiius 



21 



abundance for Callincctea species are similar to another 

 Caribbean locality (Buchanan and Sloner. 1988): Laguna 

 Joyuda (Puerto Rico). All the Callinectcs spp. recorded in 

 this coastal estuarine lagoon were also present in the es- 

 tuarine station of Ensenada de La Vela. Callinectcs danae 

 was the dominant species in both sites, whereas C e.v- 

 asperatus and C. larvatus were present in low numbers. 

 Callinecles maracaiboensis was very scarce at Ensenada 

 de La Vela, but it was not reported at all in Lagiina Joyu- 

 da (Buchanan and Stoner, 1988), although Buchanan and 

 Stoner cautioned that specimens of this species might 

 have been misclassified and listed as C. bocoiirti. On the 

 other hand, the high abundance of A. cribrarius at the ma- 

 rine front of Ensenada de La Vela differed from that of 

 other studies in the Caribbean and Gulf of Mexico, where 

 this species has been reported in low numbers. For in- 

 stance, in the SW Gulf of Mexico A. cribrarius was less 

 than 1% of the total portunid community (Garcia-Montes 

 et al., 1988). In Laguna de Terminos (Mexico), a polyha- 

 line coastal lagoon, four species of Callinecles were found 

 in a population sui-\ey conducted during a whole year, but 

 no individuals of Arenaeus were reported (Roman-Contre- 

 ras. 1986). In the same lagoon, Sanchez and Raz-Guzman 

 (1997) caught a single individual of A. cribrarius out of 

 986 specimens collected over a 17-year span. The differ- 

 ences probably are probably due to the polyhaline con- 

 ditions at these settings, thus restricting the viability of 

 A. cribrarius. However, in temperate sandy beaches, this 

 species can be very common. On Bogue Banks, in North 

 Carolina, Arenoeus cribrarius ranked as the most impor- 

 tant brachyuran in a high-wave-energy sandy beach ( Leb- 

 er, 1982). In the surf zone at Folly Beach, South Carolina, 

 A. cribrarius was one of the dominant brachyuran crabs 

 during the summer and also a key predator of benthic or- 

 ganisms (DeLancey, 1989). A. cribrarius is considered to be 

 well-adapted to marine and slightly hypersaline salinity 

 regimes and to habitats with heavy surf and sand scouring 

 in shallow coastal waters (Fischer, 1978; Williams, 1984). 

 This fact was evident in our study, in which A. cribrarius 

 was abundant and clearly constrained to a narrow strip in 

 the surf zone. 



Our results suggest the importance of salinity as an ex- 

 eluding axis in the distribution of some species of swim- 

 ming crabs in the surf and estuarine pond of Ensenada de 

 La Vela. In our study, A. ciibrarius was present in salini- 

 ties from SOVcc to 43" i. thus exceeding the upper limits of 

 tolerance commonly reported for this species. The restrict- 

 ed distribution of this species is probably a consequence of 

 its stenohalinity (27.5-36.5"( i (Gunter, 1950; Norse, 1978; 

 Williams, 1984; Pinheiro, 1991; Avila and Branco, 1996), 

 although very occasionally it may show up in estuaries 

 (Williams, 1965) and can tolerate experimental salinities 

 down to 17.25'w (Norse, 1978). This range indicates that A. 

 cribrarius prefers marine or near-marine environments, 

 thus explaining its absence in station 3 (estuarine). In 

 spite of being considered to be well adapted to heavy surf 

 in shallow coastal waters (Fischer, 1978; Williams, 1984), 

 A. cribrarius appeared to be abundant in all three fore- 

 shore stations, independent of water movement, and was 

 most abundant in the more protected stations 1 and 2. Be- 



cause the salinity did not show any major differences be- 

 tween foreshore and offshore habitats, other factors are 

 at stake in determining the zonation obsei-ved for the oth- 

 er species. One of the main elements to consider is sub- 

 strate composition (Norse and Fox-Norse, 1979; Pinheiro 

 et al, 1997). Pinheiro et al. (1997) stated that distribu- 

 tional patterns of portunids in Fortaleza Bay (Brazil) are 

 driven mainly by the granulometric composition of the 

 sediments. Substrates at the foreshore and estuarine pond 

 differed from offshore bottoms: at the foreshore the sedi- 

 ment was mainly sand; at the estuarine station a muddy 

 bottom prevailed. At the offshore stations, silt was the 

 main substrate. Hence, this difference could influence the 

 distribution of swimming crabs in Ensenada de La Vela. 



Callinecles danae was found in both biotopes at the fore- 

 shore but was more abundant at the estuarine site. In the 

 marine stations of the surf zone, C. danae appeared more 

 frequently in the most protected areas. The appearance and 

 persistence of this species in both environments probably 

 stems from its euryhalinity. In several Caribbean locations, 

 C. danae has been obsei-ved dwelling in polyhaline environ- 

 ments (Taissoun, 1969; Norse, 1978; Buchanan and Stoner, 

 1988). Based on this evidence, it is not surprising to find 

 C. danae in the entire range of salinities in Ensenada de 

 La Vela, although it is important to underline that at the 

 estuarine station it appeared when salinity was below the 

 minimum (ll%o) reported by Norse (1978). Also, several of 

 the portunid species in the surf zone in Ensenada de La 

 Vela were found in higher salinities than those reported by 

 Norse ( 1978) in several localities in Jamaica, except C. ma- 

 racaiboensis and C. larvatus. The absence of C. ornatus at 

 the foreshore stations may be due to reasons other than the 

 sampling method, because the same method was used by 

 Carmona-Suarez and Conde (1996), where specimens of C 

 ornatus were frequently captured at different sites in the 

 State of Falcon, Venezuela, including Ensenada de La Vela. 



Total abundance of all swimming crabs both at the surf 

 zone and at the estuarine station fluctuated widely and 

 randomly through the year. This pattern also emerged 

 when only the temporal abundance variations of the domi- 

 nant species, A. cribr-arius and C. danae, were examined. 

 No significant correlations were found between abundances 

 of these two species and rainfall, dissolved oxygen, water 

 temperature, or salinity fluctuations. However, the inverse 

 correlation of dissolved oxygen and abundance reached al- 

 most significant levels for both species at the marine fore- 

 shore and indeed was significant for the total abundance 

 of crabs in the surf Additionally, there was a positive cor- 

 relation between rainfall and total abundance of crabs in 

 the estuarine zone, possibly due to the increment of organ- 

 ic material washed into this environment from adjacent 

 terrestrial areas. Although bibliogi-aphic evidence supports 

 the adaptation of portunids to low levels of dissolved oxy- 

 gen in their environment (DeFur et al., 1990; Rantin et al., 

 1996; Manguni, 1997), and the relation between respira- 

 tion rates and salinity in two Callinecles species (Rosas et 

 al., 1989), nothing supports the idea that the increase of 

 swimming crab densities is due to the decrease in dissolved 

 oxygen. It might be possible that augmenting food resourc- 

 es would increase populations of fishes and invertebrates 



