BULLETIN OF MARINE SCIENCE, 67(1): 137–146, 2000
THE POLYCHAETE CRYPTOFAUNA FROM COZUMEL ISLAND, MEXICAN CARIBBEAN
Víctor Ochoa-Rivera, Alejandro Granados-Barba and Vivianne Solís-Weiss
ABSTRACT The polychaete cryptofauna collected in dead coral substrates in the shelf of Cozumel Island, Mexican Caribbean is analyzed here. Samples were taken with SCUBA diving on transects perpendicular to the coastline (depths 2 to 22 m). Nineteen families, 36 genera and 42 species were found. The Eunicidae dominate in density and species richness with a mean density of 315 ind m−2 (seven species), followed by the Syllidae with 94 ind m−2 (five species) and the Amphinomidae with 73 ind m−2 (three species). Eunice cariboea, a characteristic species of coral reef areas in the Gulf of Mexico (representing here 36% of the total collected, and Syllis (Typosyllis) ortizi are the dominant species in Cozumel. There is some effect related to depth and anthropogenic influence, on the density and species richness because the lowest values were found in the shallower sampling zones (approximately 332 ind m−2 and 20 species, versus 931 ind m−2 and 32 species, in the deeper zones) and the populations’ composition at each site is quite different. Compared with other areas sampled in the extensive Mexican coral reef environments in the Gulf of Mexico, in Cozumel the densities of polychaetes and species richness are high.
Cozumel Island is one of the main tourist attractions in the Mexican Caribbean, as one of the most popular cruise destinations in the western Caribbean. The development of the island is completely based on activities related to sea resorts, mainly SCUBA diving, due to the presence of important coral reefs zones. In fact, extensive coralline areas are found along the Atlantic coast of Mexico, but the most important areas are distributed in the Mexican Caribbean; they constitute the northern end of the Belize Barrier reef, consid- ered the second most important reef formation worldwide, famous for its extension, biodiversity and beauty. The reef potential for human use is high but its low resistance to man-made activities and impacts, especially pollution, make it a delicate matter to con- sider in its exploitation. Corals are especially propitiate for the development of microhabitats with a varied assortment of organisms which can live in them or on their surface: the cryptofauna (Peyrot- Clausade, 1974, 1979; Hutchings and Weate, 1977). The cryptofauna is primarily com- posed of polychaetes and crustaceans, which constitute the dominant groups (Kohn and Lloyd, 1973; Ibarzábal, 1993). The polychaetes from these habitats account for up to two thirds of this cryptic macrofauna in coral reefs (Grassle, 1973), and are a source of food for fish and some predatory gastropods (Vivien and Peyrot-Clausade, 1974). They also interact significantly with the corals themselves, using large quantities of the mucus ex- creted by them, recycling the detritus and organic matter trapped among the corals and influencing in general bioerosion, epiflora development and reef fossilization processes (Ebbs, 1966; Taylor, 1976; Hutchings, 1983; Perry, 1998). In spite of the increasingly recognized importance of the polychaetes in all habitats of the marine environment, and in this case as part of the fauna associated to the coralline systems, the studies on cryptofauna in the eastern littorals of Mexico are rare: one study
137 138 BULLETIN OF MARINE SCIENCE, VOL. 67, NO. 1, 2000
Figure 1. Study area. Location of sample stations at Cozumel Island. by Kornicker et al. (1959) in Yucatán, and the unpublished theses of Horta-Puga (1982), Sánchez-Wall (1992) and Carrera-Parra (1993) in Veracruz. Our studies on the polychaetes’ cryptofauna on blocks of dead corals have previously been carried out in the main coral reef areas of the southwestern Gulf of Mexico: Cayo Arcas, Cayo Arenas, Triangulos Oeste and Alacran reef, where they represent about 50– 60% of the total collected (Ochoa-Rivera, 1996). However, in Cozumel Island, up to now the cryptofauna was virtually unknown. Dead coral blocks were used for this study since they are known to harbor a diversified and abundant cryptofauna, especially polychaetes, that are very different and much richer in species than the borers in living corals. Also, the comparison with other such studies is easier since they are based on dead coral cryptofauna too (Hutchings, 1981; Hutchings and Murray, 1982; Kiene and Hutchings, 1992; Ibarzábal, 1993).
STUDY A REA
Cozumel is an oval shaped island, the largest in the Mexican Caribbean with a surface area of 489 km2. It is located off the northeastern coast of Quintana Roo State, 23 km east of the town of Playa del Carmen (the mainland) and approximately 230 km SW from Cuba. Coral reefs are present along the coastline especially in the southwestern region. The island has a calcareous shelf about 350–400 m wide, with a gentle slope and a sudden drop at its end, from approximately 30 to 490 m depth, towards the Cozumel Channel that separates it from the mainland. The sediments are com- posed primarily of shell fragments, spicules and calcareous algae. The climate is warm and humid with abundant rains in summer and under the influence of hurricanes during the summer. Their strength and periodicity are the fundamental factors affecting climate. Erosion generated either by anthropogenic or natural processes is evident in this area. OCHOA-RIVERA ET AL.: POLYCHAETE CRYPTOFAUNA FROM COZUMEL ISLAND 139
METHODS
The two sampling areas are located in the western populated area of Cozumel: in front of the ‘Acuario’ restaurant, an area under human influence, and alongside ‘Caletita’ beach, a relatively unaltered region (Fig. 1). Sampling was conducted in five stations along two transects perpendicu- lar to the coastline, at depths of 2 to 22 m; five to eight Porites spp. and Acropora spp. blocks of dead coral (size mean 15 × 8 × 3 cm) were manually sampled at all stations, with snorkeling in the shallower zones, and by SCUBA diving in the deeper ones. The coralline material was measured to obtain the total surface collected, and placed in fresh water for 10 h in order to induce the organisms to leave the coral cavities under the osmotic shock caused by fresh water. Recovery of the organ- isms was 90% with this method. The remaining organisms were extracted by fragmenting the blocks. All the specimens were fixed in 10% formaline and later transferred to 70% alcohol. The relative importance of the species present was determined with the simple dominance Index, the diversity index from Shannon-Weaver and the evenness index from Pielou. The specimens are deposited in the polychaete collection of the Instituto de Ciencias del Mar y Limnología, U.N.A.M. (CP-ICML- UNAM), Mexico.
RESULTS AND DISCUSSION
The 42 species of polychaetes collected in this study and listed in Table 1 belong to 36 genera and 19 families. In terms of biological diversity and species richness, these results stand out in comparison to other coralline cryptofauna sampled in the Gulf of Mexico where, in the four localities sampled, the number of families varied from seven to 14, the number of genera from 11 to 26 and the number of species from 14 to 38, except in Alacran reef where 48 species were recorded (Ochoa-Rivera, 1996). In this study, the dominant family was the family Eunicidae with a mean density of 315 ind m−2 which corresponds to 46% of the total collected, followed by the Syllidae with 94 ind m−2 (14% of the total collected) and the Amphinomidae with a mean density of 73 ind m−2 (11% of the total collected). The family with the highest species richness was the Eunicidae with seven species, followed by Syllidae and Nereididae with five species each (Table 1). From the total number of species collected, 18 are common to all other areas surveyed in the Gulf of Mexico and 23 are only recorded from Cozumel (Table 1). A range exten- sion in the distribution of four species (Lepidasthenia varius Treadwell, 1917, Thalenessa sp. A Wolf, 1984, Paramphinome sp. B Gathof, 1984, Magelona sp. C Uebelacker and Jones, 1984) is recorded for the greater Caribbean since they were previously recorded only in the northern region of the Gulf of Mexico and the shores of Florida (Table 1). The remaining 20 species are commonly found in the greater Caribbean. The dominant species is Eunice cariboea Grube, 1856 with a total density of 1219 ind m−2 and a mean density of 244 ind m−2 that corresponds to 36% of the total collected. It is followed by Syllis (Typosyllis) ortizi San Martin, 1992, with a total density of 342 ind m− 2 and a mean density of 68 ind m−2 (10%) and Paramphinome sp. B Gathof, 1984 with a total density of 262 ind m−2 and mean density of 52 ind m−2 (8%); Polyophtalmus pictus (Dujardin, 1839) and Lysidice ninetta Audouin and Milne Edwards, 1833 follow with similar values in species densities (206 ind m−2 and 194 ind m−2 in total density and 41 ind m−2 and 39 ind m−2 in mean density respectively) (Table 1). When applying the Simple Dominance Index, the same trend is seen, with E. cariboea as the clear dominant (35.8) followed far behind by S. (T.) ortizi (8.1), P. pictus (6.7) and 140 BULLETIN OF MARINE SCIENCE, VOL. 67, NO. 1, 2000
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L. ninetta (4.7). All other values are around 2 or below, including Paramphinome sp. B, which in terms of total and mean density had scored third (Table 1). The highest densities and species richness were found in the families Eunicidae and Syllidae; these results are similar to those found by previous authors in different areas (Horta-Puga 1982; Kohn and Lloyd, 1973; Reichelt, 1979; Yamanishi and Kubo, 1982 and Abbiati et al., 1991). In the last four studies, the dominance of the eunicids and syllids is attributed to their physiological and anatomical characteristics. In the case of the eunicids, where several habitats have been sampled, it was found that they are often associated to hard substrates and shallow waters, and that they can be characterized as boring organ- isms, which either dig galleries in the skeletons of corals, with mucus covered walls, or live attached to interstices in rocks, sponges or corals (Hutchings, 1981; Fauchald, 1992). The eunicids then can be considered an important part of the boring cryptofauna in the reef. Recently, eunicids (Lysidice and Nematonereis) have been found boring inside of Posidonia oceanica seagrass scales (remains of leaf bases still connected to the rhizome) (Guidetti et al., 1997). Some morphostructural characteristics, such as their jaw apparatus, are used to con-
struct their galleries, a fact that is corroborated by the presence of CaCO3 (aragonite, the main component of corals) impregnated in their jaws (Fauchald, 1992). In the Eunicidae, the mandibular plate is used for grazing in genera like Eunice and Lysidice, and it is large in the genus Palola, in particular P. siciliensis Grube, 1840, collected in our study area. Syllids are small, highly motile polychaetes common in shallow waters and hard sub- strates and well represented in cryptic habitats, where they can constitute the most abun- dant and diverse fauna (Blake et al., 1995). They are found in sponges, hydroids, ascid- ians or interstitially in sands and mud; some species build mucous tubes attached to hy- droids (Ben-Eliahu, 1977). In this family, no jaw structures are found that could help in gallery boring, but they do take advantage of the existing cracks and crevices to hide in; this is why they are commonly considered as part of the opportunistic cryptofauna. The amphinomids have been considered opportunists and important biodestructive or- ganisms in coral reefs as large predators of live coral and associated fauna (Kohn and Lloyd, 1973). The most common species are Eurythoe complanata Pallas, 1766 and Hermodice carunculata Pallas, 1766. Mardsen (1962) observed the feeding habits of H. carunculata in Barbados, in the field as well as in the laboratory, finding that this species browses over short distances, mainly on the coral genus Porites, very early in the morning and occasionally in the evening. These results are similar to what we observed in the reef areas studied in the Gulf of Mexico, where the eunicids and syllids are dominant among the polychaetes. Eunice cariboea is a very common and frequent species in this type of habitat in the Gulf of Mexico and reported as common in the Caribbean, whereas the dominant syllid collected in Cozumel, S. (T.) ortizi, is common only in the Caribbean, and is replaced in the Gulf of Mexico by S. (T.) alosae San Martin 1992 (Ochoa Rivera, 1996). The densities of polychaetes recorded in this habitat were high: a mean of 996 ind m−2 per sampling station in the area under anthropogenic influence (Acuario), higher than the 489 ind m−2 per sampling station in the unaltered area of Caletita (Table 2). Looking at the composition of the polychaete fauna in both sampling localities, we found that it was quite different: 10 species were common to both (they represent 24% of the total), 16 (38% of the total) were only found in Caletita, and 16 only in Acuario (Table 1). Of the species common to both areas, we can see that the densities are seldom similar (except for 144 BULLETIN OF MARINE SCIENCE, VOL. 67, NO. 1, 2000
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P. pictus). In the Acuario station we found that the density of E. cariboea was five times higher than in the Caletita stations, while densities almost doubled for the species H. spongicola, S. (T.) ortizi and C. mirabilis. In contrast, for the species Paramphinome sp. B, the density was approximately four times higher in Caletita than in Acuario, and the densities of the species G. abranchiata, L. ninetta and P. siciliensis were twice as high. Regarding depth, there were lower densities and diversities in the shallower zones: we found a mean of 332 ind m−2 (with 20 species) versus 931 ind m−2 (with 32 species) in the deeper sampling zones. Diversity values do not show striking differences between both sites, but the lowest values are found in Acuario station, especially in the deep station where density was highest (Table 2). This together with the differences observed between H' and H'max values at that station seems to indicate some disturbance or impact on the populations under study. More comprehensive studies are under way to confirm all these results.
CONCLUSIONS
Dead coral substrates in Cozumel Island have high values of density and species rich- ness for polychaetes, the eunicids and syllids being dominant and the most common families representing this cryptofauna in reef areas around Mexico. The dominant species in all cases is E. cariboea that represented 36% of the total collected. The taxonomic composi- tion and densities in the two areas sampled is not similar, the differences being mostly attributed to anthropogenic activities. This is the first formal study about cryptic polycha- etes in Cozumel Island; however, to corroborate these results, it is necessary to perform more comprehensive studies of the cryptofauna of polychaetes from this island.
ACKNOWLEDGMENTS
Thanks are due to the C.F.E. (Comisión Federal de Electricidad) and ICML-UNAM for financ- ing this study. M. Á. Molina Ruiz, L. D. Ortiz Lozano and M. Ángel García are deeply acknowl- edged for their field collaboration.
LITERATURE CITED
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ADDRESS: Laboratorio de Ecología Costera, Instituto de Ciencias del Mar y Limnología, Apartado Postal 70-305, México, D.F., 04510, Mexico. CORRESPONDING A UTHOR: (V.S.-W) Laboratorio de Ecología Costera, Instituto de Ciencias del Mar y Limnología, Apartado Postal 70-305, México, D.F., 04510, Mexico.