Background

Barnacles of the genus Octolasmis Gray, 1825 are commonly called pedunculate barnacles or stalked barnacles. They belong to subclass Cirripedia of class Crustacea. Octolasmids are highly modified crustaceans and distributed worldwide in tropical and temperate seas (Jeffries et al., 1995). Their habitats differ from those of acorn barnacles and common goose-neck barnacles. Pedunculate barnacles of the genus Octolasmis are frequently found in shallow waters attached to the exoskeleton of the decapod Crustacea, including crabs. Only few species of octolasmids are found in depth greater than 1000 meters (Foster, 1987).

When the octolasmids inhabit branchial chambers of the crabs, they occupy space on the gills surface normally available for gaseous exchange and can severely impair host respiration (Hudson and Lester, 1994). It has been reported by Gannon and Wheatly (1992) that physiological stress is imposed on Callinectes sapidus Rathbun, 1896 (a portunid crab) by large infestation of the branchial chambers by Octolasmis mülleri (Coker, 1902). The efficiency of the respiratory process of the host may also be impaired by the accumulation of debris due to octolasmids infestation (Walker, 1974).

A survey of literature shows that only four papers have been published so far on stalked barnacles from Pakistan. First paper was published by Hashmi and Zaidi (1965) who reported stalked barnacle infestation on the gills of Scylla sp. (then identified as S. serrata - see Keenan et al. (1998) for revision of the genus) from Karachi waters. Hashmi and Zaidi (1965) identified stalked barnacles as Lepas sp. instead of Octolasmis cor (Moazzam and Rizvi, 1978; Mushtaq and Mustaquim, 2009). Two more papers were published by Moazzam and Rizvi (1978; 1982) on the systematic of the pedunculate barnacles from the Pakistan coast. They described a total of twelve species: seven species of the genus Octolasmis, two species of Lepas and one species each of Conchoderma, Poecilasma and Trilasmis. Fourth paper has been published recently by Mushtaq and Mustaquim (2009) on the occurrence and distribution of Octolasmis on the gills of mud crab Scylla cf. tranquebarica (Fabricius, 1798) from Karachi. The occurrence and distribution of octolasmids on Portunus pelagicus and P. sanguinolentus have never been studied in detail from Pakistan.

1 Materials and Methods

For the study of octolasmid infestation on the crabs, a total of 2725 specimens of the two species of Portunid crabs namely, Portunus pelagicus and P. sanguinolentus, were examined. The dorsal and ventral surfaces of all crabs were examined for octolasmids with number of each species recorded. The carapace of each crab was removed and the branchial chambers and gills were visually inspected for the presence of octolasmids. Sites of barnacle attachment were recorded, with respect to gill chamber (left or right), gill number 1 to 8 (anterior to posterior); gill surface (hypobranchial or inner surface which is concave and epibranchial or outer surface which is convex), and region on the gills (proximal, medial, and distal). Settlement was also recorded on the epipodites of the three pairs of maxillipeds (hypobranchial gill rake, epibranchial gill rake, and scaphognathite) and the inner wall of the branchial chambers. Octolasmis species were identified on the basis of morphological features such as overall shape, capitular shape and capitular plate morphology as described by Daniel (1956) and Moazzam and Rizvi (1978; 1982) and Jefferies et al. (2005). Length and width of the peduncle and capitulum were taken under stereomicroscope with the help of an ocular micrometer. Student’s t-test and Chi-square were used to compare mean values and observed and expected distribution (Zar, 1996).

2 Results

2.1 Distribution of Octolasmid in Portunus pelagicus

Out of 2725 crabs examined, 1668 were P. pelagicus (789 male, 879 female including 74 berried female). The size of the male and female crabs ranged from 23-140 mm short carapace width (mean = 82.15 mm ± 3.62 S.D) and 26-148 mm short carapace width (mean = 83.77 mm ± 3.07 S.D), respectively. Number of infested P. pelagicus was found to be 48 (2.9 % of the total P. pelagicus examined). The short carapace width of infested crabs varied from 70-140 mm (70-120 mm for non-berried female, 84-107 mm for berried female and 77-140 mm for male).

Out of 188 octolasmids found in the gill chambers of 48 infested crabs, 182 were attached on the surface of the gills while 6 octolasmids (all O. lowei) were found attached to the wall of the gill chambers and epipodites (gill cleaners). Right gill chambers harboured more octolasmids (114 out of 188 or 60.6%) than the left gill chamber (74 out of 188 or 39.4%). The average number of octolasmids found in the right and left branchial chambers was 2.38 ± 3.1 S.D and 1.54 ± 2.0 S.D, respectively, which is not significantly different (t = 1.48; α = 0.05).

Figure 1 shows that gill number 6 harboured most of the octolasmids (22.5%) followed by gill number 3 (19.2%) and 7 (15.9%). The least number of octolasmids was found on gill number 2 (2.8%) followed by gill number 8 (12.1%). Gill number 1 was not infested al all. The proximal and medial parts of the gills together harboured 87.92 % octolasmids (43.96 % on each part) and the remaining 12.08 % were found attached on the distal part of the gills. The distribution of 182 octolasmids (168 O. lowei, 11 O. cor, 2 O. angulata and 1 O. tridens) on the gill number 1 to 8 (anterior to posterior) is given in Table 1.

The hypobranchial or inner (concave) surface of the gills (Figure 2A) harboured 94.5% (172 out of 182) octolasmids while remaining 5.5% (10 out of 182) were found on the epibranchial or outer (convex) surface of the gills (Figure 2B). The octolasmids found on the epibranchial surface were all O. lowei.

2.2 Distribution of Octolasmid in Portunus sanguinolentus

The number of P. sanguinolentus examined was 1057 (635 male, 442 female including 128 berried female). The size of the male and female crabs ranged from 24-122 mm short carapace width (mean = 80.3 mm ± 7.4 S.D) and 28-130 mm short carapace width (mean = 76.9 mm ± 6.42 S.D), respectively. Number of infested P. sanguinolentus was 114 (10.8% of the total P. sanguinolentus examined). Out of which 69 (60.53%) were male and 45 (39.47%) were female including 10 berried female. The short carapace width of infested crabs varied from 67-130 mm (67-117 mm for berried female, 68-122 mm for male and 70-130 mm for non- berried female). Total number of octolasmids hosted by these 114 P. sanguinolentus was 5168.

Out of 5168 octolasmids, three were found attached either on fifth walking leg or on carapace. These three octolasmids belong to species O. warwickii. Hence no specimen of O. warwickii was found inside the gill chamber. Those octolasmids which were found inside the gill chambers number 5165. Out of these, 4867 were found attached on the surface of the gills while 298 octolasmids (160 O. lowei, 136 O. tridens and 2 O. angulata) were found attached to the wall of the gill chambers and epipodites (gill cleaner). Right gill chambers harboured more octolasmids (2694 out of 5165 or 52.2%) than the left gill chamber (2471 out of 5165 or 47.8%). The average number of octolasmids found in the right and left gill chambers was 17.74 ± 37.22 S.D and 16.26 ± 38.85 S.D respectively, which is not different significantly (t = 0.265, α = 0.05).

The distribution of 4867 octolasmids (4268 O. lowei, 487 O. tridens, 100 O. angulata and 12 O. cor) on the gill number 1 to 8 (anterior to posterior) is given in the Table 2.

Figure 3 shows that gill number 6 harboured most of the octolasmids (20.44%) followed by gill number 4 (20.40%) and gill number 5 (19.62%). These three gills together harboured 60.46% of the total (i.e. 4867) octolasmids found attached on the gill. Gill number 1 was least infested (0.12%) followed by gill number 2 (2.1%). The medial part of the gills harboured most of the octolasmids (49.6%). Distal part of the gills harboured only 11.8% octolasmids.

The hypobranchial or inner (concave) surface of the gills harboured 94.8% (4615 out of 4867) octolasmids (Figure 4A) while remaining 5.2% (252 out of 4867) were found on the epibranchial or outer (convex) surface of the gills (Figure 4B). The octolasmids found on the epibranchial surface were O. lowei (236), O. tridens (15) and O. cor (1).

3 Discussion

Results of present investigation demonstrate that the spatial distribution of octolasmids on the inside and outside surfaces of the gills of Portunus pelagicus and P. sanguinolentus is distinct and it replicates the findings of Jefferies et al. (1982), Gaddes and Sumpton (2004) and Kumaravel et al. (2009). In their study on the distribution and diversity of Octolasmis species in the sea adjacent to Singapore, Jefferies et al. (1982) found that more barnacles were attached on the inner side than on the outer side of the gills of P. pelagicus and P. sanguinolentus. Gaddes and Sumpton (2004) who studied epizoites of P. pelagicus from the Moreton Bay region, eastern Australia, reported that octolasmids were significantly more abundant on the inner (hypobranchial) side of the gills than the outer (epibranchial) side. In their study on the distribution of Octolasmis on the gills of five species of edible crabs, including P. pelagicus and P. sanguinolentus, from Tamil Nadu, India. Kumaravel et al. (2009) found most of the octolasmids on the hypobranchial surface of the gills.

Similar distribution of octolasmids on the gills of other portunid crabs, such as Callinectes sapidus, C. danae, Scylla serrata, S. tranquebarica and Charybdis feriatus has also been reported by several authors (Humes, 1941; Hashmi and Zaidi, 1964; Walker, 1974; Voris et al., 1994; 2000; Santos and Bueno, 2002; Yan et al., 2004; Mushtaq and Mustaquim, 2009). Even on the inner side of the gills, the octolasmids tend to concentrate on the proximal and medial parts of the gills rather than distal one. This finding of the present study is also in consistent with earlier studies (Jefferies et al., 1982; Gaddes and Sumpton, 2004; Mushtaq and Mustaquim, 2009). This distribution of barnacles on the gills correlates well to the flow of water through the branchial chamber.

In crabs, most of the water enters through the Milne Edwards openings at the bases of the chelipedes while some water may also enter through pores situated in between walking legs. After entering into the branchial chamber, water moves posteriorly into the lower (hypobranchial) part of the branchial chamber, then dorsally between the gill lamellae and finally anteriorly in the upper (epibranchial) part of the branchial chamber from where it is expelled out of the chamber through exhalent aperture. The distribution of barnacles appears to be non-random on the gills and is controlled mainly by the ventilatory flow through branchial chamber.

Walker (2001) studied distribution of Octolasmis angulata within the branchial chambers of Charybdis callianasa (Herbst, 1789), a portunid crab from Moreton Bay, Queensland, Australia. He found that O. angulata was principally attached to the cuticle of the anterior chamber wall in the epibranchial space, although attachment to the gills did occur. This contrasts with the present study, and earlier studies mentioned above, in which the gills are the principal sites of attachment rather than the wall of the epibranchial chamber. On the basis of his result, Walker (2001) predicted that C. callianasa frequently buries itself into soft bottom in nature. Because in this buried position the respiration current is likely to be reversed with water entering through the epibranchial space and leaving through the openings at the bases of chela and legs.

The right and left branchial chambers of a crab may host different number of octolasmids and in some cases only one branchial chamber is infested. Voris et al. (1994), who studied patterns of distribution of Octolasmis angulata and O. cor on the mangrove crab Scylla serrata, considered the branchial chamber as the “host unit” and not individual crab (which has two branchial chambers) in analyzing barnacle abundance and distribution as a function of density. According to them, when a cyprid larva enters into a branchial chamber, it can only explore site of attachment in that particular chamber only. It cannot monitor the conditions of the other branchial chamber of the same crab for its settlement. They however, mentioned that the two branchial chambers of a crab are not wholly independent as they have several factors in common, such as size of the crab, moult stage, general health condition and habitats visited. However, in the literature the common practice is to consider individual crab as “host unit” while analyzing abundance and distribution of epizoites and this was the case in the present study. The right and left branchial chambers of infested P. pelagicus and P. sanguinolentus were found to harbour different number of octolasmids during present study. However, the mean barnacle abundance in the two branchial chambers of P. pelagicus and P. sanguinolentus was not found significantly different. This is consistent with findings of Jefferies et al. (1992) who reported that octolasmids distribution between the left and right chamber of mangrove crab Scylla serrata was not significantly different from 50:50 (binomial test, p<0.01).

The majority of the octolasmids was found attached on gill number 6 in P. pelagicus and P. sanguinolentus in the present study which supports the finding of Gaddes and Sumpton (2004) who reported the highest octolasmids settlement (27.6%) on the gill number 6 of P. pelagicus from Australia. However in mangrove crab Scylla serrata from Thailand, Voris et al. (1994) found gill number 4 as the most heavily infested by octolasmids while Mushtaq and Mustaquim (2009) reported gill number 7 in Scylla cf. tranquebarica from Pakistan which had the highest number of octolasmids on it. Size of the crab was found positively correlated with the number of octolasmids in the present study, although the relationship was not found strongly correlated. Similar observations have been reported earlier by Jefferies et al. (1992) for Scylla serrata from Thailand, Santos and Bueno (2002) for Callinectes danae from Brazil, Mantelatto et al. (2003) for ten species of brachyuran crabs from Brazil, Yan et al. (2004) for Charybdis feriatus from China, Kumaravel et al. (2009) for five species of crabs including P. pelagicus and P. sanguinolentus from India and Mushtaq and Mustaquim (2009) for Scylla cf. tranquebarica from Pakistan.

Authors’ contributions

JM designed and conducted the experiments. SR collected the samples and did the work on it. All authors read and approved the final manuscript.

Acknowledgments

Thanks are due to Pakistan Science Foundation for providing the financial support for this study. The present study was carried out within the Research Project No. PSF/Res/S - KU/ Bio (342).

References

Coker R.E., 1902, Notes on a species of barnacles (Dichelaspis) parasitic on the gills of edible crabs, Bull. U.S. Fish Comm., 21: 401-412

Daniel A., 1956, The Cirripedia of the Madras Coast, Bull. Madras Govt. Museum, VI (2), 1-40, Plates: 1-X

Foster B.A., 1987, Barnacle ecology and adaptation, pp.113-133, In: A.J. Southward(ed.): Crustacean Issues 5, Barnacle Biology, A. A. Balkema, Rotterdam

Gaddes S.W., and Sumpton W.D., 2004, Distribution of barnacle epizoites of the crab Portunus pelagicus in the Moreton Bay region, eastern Australia, Mar. Freshwater Res., 55: 241–248

https://doi.org/10.1071/MF02136

Gannon A.T., and Wheatly M.G., 1992, Physiological effect of an ectocommensal gill barnacle, Octolasmis mulleri, on gas exchange in the blue crab Callinectes sapidus, J. Crust. Biol., 12: 11-18

https://doi.org/10.2307/1548714

Hashmi S.S., and Zaidi S.S., 1965, Incidence of Lepas infestation on the gills ofScylla serrata (Forskal) in Karachi waters, Agric. Pak., 16: 177-129

Hudson D.A., and Lester R.J.G., 1994, Parasites and symbionts of wild mud crabs Scylla serrata (Forskak) of potential significance in aquaculture, Aquaculture, 120: 183-199

https://doi.org/10.1016/0044-8486(94)90077-9

Humes A.G., 1941, Notes on Octolasmis mülleri (Coker), a barnacle commensal oncrabs, Trans. Amer. Microsco. Soc., 24(3): 215-222

Jefferies W.B., Voris H.K., and Yang C.M., 1982, Diversity and distribution of the pedunculate barnacle Octolasmis in the seas adjacent to Singapore, J. Crust. Biol., 2: 562-569

https://doi.org/10.2307/1548096

Jefferies W.B., Voris H.K., and Poovachiranon S., 1992, Age of the mangrove crab Scylla serrataat colonization by stalked barnacled barnacles of the genus Octolasmis, Biol. Bull., 182: 182-194

Jefferies W.B., Voris H.K., Poovachiranon S., and Heil L.C., 1995, The life cycle stages of the Lepadomorph barnacle, Octolasmis cor, and methods for their laboratory culture, Phuket Mar. Biol. Cen. Res. Bull., 60: 29-35

Kumaravel K., Ravichandran S., and Rameshkumar G., 2009, Distribution of Barnacles Octolasmis on the gill region of some edible crabs, Acad. J. Entomol., 2: 39-39

Moazzam M., and Rizvi S.H.N., 1978, Pedunculate Cirrripedes from Pakistan, Pakistan J. Zool., 10: 175-190

Moazzam M., and Rizvi S.H.N., 1982, Addition to the pedunculate Cirrripedefauna of Pakistan Coast, Pakistan J. Zool., 14: 234-237

Mushtaq S., and Mustaquim J., 2009, The occurrence and distribution of stalked barnacles of the genus Octolasmis on the gills of mud crab or mangrove crab, Genus Scylla, Crustaceana, 82: 53-61

https://doi.org/10.1163/156854008X363696

Santos C., and Bueno S.L.S., 2002, Infestation by Octolasmis lowei (Cirripedia:Poecilasmatidae) in Callinectes danae and Callinectes ornatus (Decapoda:Portunidae) from São Sebastião, Brazil, Journal of Crustacean Biology, 22(2): 241-248

https://doi.org/10.1163/20021975-99990231

https://doi.org/10.1651/0278-0372(2002)022[0241:IBOLCP]2.0.CO;2

Voris H.K., Jeffries W.B., and Poovachiranon S., 1994, Pattern of distribution of two barnacle species on the mangrove crab Scylla serrata, Biol. Bull., 187: 346-354

https://doi.org/10.2307/1542291

Voris H.K., Jeffries W.B., and Poovachiranon S., 2000, Size and location of stalkedbarnacles of the genus Octolasmis on the mangrove crab Scylla serrata, Journal of Crustacean Biology, 20(3): 483-494

https://doi.org/10.1651/0278-0372(2000)020[0483:SALROS]2.0.CO;2

https://doi.org/10.1163/20021975-99990064

Walker G., 1974, The occurrence, distrubtion and attachement of the pedunculatebarnacle Octolasmis mulleri (Coker) on the gills of crabs, particularly the blue crab, Callinectes sapidus Rathbun, Biol. Bull., 147: 678-689

https://doi.org/10.2307/1540750

Yan Y., Huang L., and Miao S., 2004, Occurrence of the epizoic barnacle Octolasmisangulata on the crab Charybdis feriatus from Daya Bay, China, J.Mar. Biol.Assoc.UK., 84: 619-620

https://doi.org/10.1017/S0025315404009646h

Zar J.H., 1996, Biostatistical analysis, 3^rd edition, Prentice-Hall, Upper Saddle River, NewJersey, pp.790