From the Barrier Reef Ecosystems Off Belize, Central America
Total Page：16
File Type：pdf, Size：1020Kb
Hydrobiologia 278: 93- 105, 1994. T.B. Reynoldson & K.A. Coates (eds), Aquatic Oligochaete Biology V. 93 0 1994 Kluwer Academic Publishers. Printed in Belgium. Habitat preferences and species associations of shallow-water marine Tubificidae (Oligochaeta) from the barrier reef ecosystems off Belize, Central America Robert J. Diaz ’ & Christer Erseus 2 ’ Virginia Institute of Marine Science, School of Marine Science, College of William and Mary, Gloucester Point, Virginia 23062 U.S.A.: 2Department of Invertebrate Zoology, Swedish Museum of Natural History, Box 50007, S-104 05, Stockholm, Sweden Key words: aquatic Oligochaeta, Tubificidae, Caribbean fauna, animal-sediment relations, coral reefs, gutless fauna Abstract The marine tubificid oligochaete fauna of Belize is the most diverse that has been described for the Caribbean Sea, with records for over 50% of all known Caribbean species. Tubificids were sampled at 77 stations around the outer barrier of the coral reefs off the Belize mainland. A total of 1,529 individuals representing 52 species were collected. Species distribution patterns were controlled mainly by sediment type and the presence or absence of mangroves. Six species (Phallodrilus molestus, Tubt$coides bermudae, Inanidrilus leukodermatus, Heterodrilusjlexuosus, Bathydrilus formosus, Smithsonidrilus hummelincki) with diverse life history characteristics were common and had broad habitat preferences being found in various types of heterogeneous sandy sediments. Heterodrilus jlexuosus was the only common species in these samples known only in Belize. The other five common species range from Belize to Florida or Bermuda. Most other species have narrower habitat preferences and are limited to specific habitats. For example, one group of gutless species was restricted to organically enriched fine to medium sands, a group of Limnodriloidinae occurred only in mud around mangrove cays, and a group of meiofaunal species were restricted to saline groundwater. Introduction Baker, 1984; Davies, 1985; and Diaz et al., 1987) but little is known of subtropical and tropical The total species diversity of marine Tubificidae assemblages. Taxonomic studies of shallow sub- (Oligochaeta) has surpassed that of the freshwa- tropical and tropical marine tubificid oligochaetes ter Tubificidae. Compared to the freshwater spe- indicate that they are very diverse and abundant cies, however, little is known of the ecology and (Erseus, 1990 and references therein). habitat preferences of the marine species. Some The marine tubificid fauna of the Caribbean work has been done on the autecology of indi- region (Bermuda, Florida, Barbados, and Belize) vidual tubificid species from temperate areas has received the most taxonomic attention with (Brinkhurst, 1964; Hunter & Aurthur, 1978; over 100 species described. Belize appears to be Birtwell & Arthur, 1980; Diaz, 1980; Bamber & the most species rich area of the Caribbean with Spencer, 1984; ErsCus & Diaz, 1989) and on tem- about 50% of these species (Erseus, 1990). In this perate marine tubificid assemblages (Cook, 1971; paper we have taken the data on the ‘Belizean’ 94 fauna collected by ErsCus (1990) and analyzed around the outer barrier of the coral reefs off the them for ecological patterns and habitat prefer- Belize mainland. While the purpose of these col- ences. lections was primarily taxonomic, sufficient ma- terial was collected to evaluate ecological and The belize barrier reef ecosystems habitat relationships. At each station approxi- mately equal amounts of sediment were examined The barrier reef ecosystem off the Belize main- for Tubificidae. Because of taxonomic problems land is the largest continuous reef in the Carib- with immature individuals only sexually mature bean Sea. It is 10 to 32 km wide and 250 km long individuals were preserved and identified to spe- (Rtitzler & Macintyre, 1982a). Carrie Bow Cay, cies. Qualitative notes were also made on the the center of our collection area, sits on top of the physical characteristics of the site. barrier reef proper. The area to the west of Car- Numerical classification was used to classify rie Bow Cay forms a shallow Thalassia domi- species and stations into groups based on species nated lagoon, less than 5 m deep (Rtitzler & Ma- abundance and distribution patterns. The flexible cintyre, 1982a). To the east of Carrie Bow Cay the sorting algorithm was used (/I = -0.25) with the reef system rapidly grades from reef crest to inner quantitative form of the Bray-Curtis similarity co- fore reef, 2 to 12 m, to outer fore reef, 12 to 40 efficient (Boesch, 1977). Both species and station m, to outer barrier reef platform over a distance analyses were done on a reduced set of the origi- of less than a kilometer (Burke, 1982). Further nal data. Species with only one or two collection eastward, about 22 km, is a large platform reef occurrences were dropped from the analysis. To (Glovers Reef) that protects the Carrie Bow Cay evaluate the strength of the species and station area from open ocean waves. This protection is groups nodal analysis was conducted (Lambert & a principle factor that has allowed the develop- Williams, 1962). Nodal analysis is a post classi- ment of highly diverse communities in the Carrie fication analysis that compares how well species Bow Cay area (Burke, 1982). station groups are formed. The tide around Carrie Bow Cay has a mean Constancy and fidelity statistics (Lambert & range of 15 cm and is mixed semidiurnal (Kjerfve Williams, 1962) were used to estimate the strength et al., 1982). Channels to the north and south of of the species-station groups. Constancy is a Carrie Bow Cay are the main exchange routes measure of species occurrence and can be ex- between the reef system and ocean. While tidal pressed as currents are weak the almost constant wind-wave action supports the movement of materials on c, = a,dOO%/(ninj) ) and off the reef. The complex physical structures of the reef system interacting with the water cur- where aij is the total number of occurrences of rents and protection from ocean waves have led species in species group i and site group j, and IZ~ to an extremely high diversity of habitats. This and nj are total number of species and stations in physical diversity of habitats is further enhanced the respective groups being compared. Expressed by the organisms occupying and building the reefs. as a percentage, 100% constancy means every Details of the physical and biological aspects of species group occurred at least once at every sta- the Belize barrier reef ecosystems can be found in tion in the site group being considered. Fifty per- (Rtitzler & Macintyre, 1982b). cent constancy is when any combination of spe- cies occurrences is half the total possible number of species x station occurrences. Materials and methods Fidelity measures the average frequency of oc- currence of species in a group relative to the rest ErsCus (1990), with the assistance of others, col- of the collection. It estimates the preference or lected marine tubificid oligochaetes at 85 stations avoidance of species for a particular site group 95 and can be expressed as Fauna1 composition A total of 1,529 individuals representing 52 tubi- ficid species in 15 genera were collected (Table 1). using the same terms as constancy. The summa- About half of the genera (7 of 15) were repre- tion terms go across all site groups (j = l,...,J) for sented by one or two species, accounting for about a particular species group (i). When fidelity is 2O”i, of the total species. The four most speciose equal to 1 the species group (i) has no preference genera, accounting for about half (27 of 52) of the for the site group (‘j), less than 1 indicates avoid- species, were Heterodrilus, Phallodrilus, Olavius, ance, and greater than 1 preference. Programs and Limnodriloides. The remaining four genera COMPAH and NODAL of the Virginia Institute (Inanidrilus, Bathydrilus, Thalassodrilides, and of Marine Science, College of William and Mary Smithsonidrilus) represented about 30 % (16 of 52) werr: used for these analyses. of the species. Of the 52 species in the collection 21 (40%) occurred at only one or two stations and were Results considered rare. A third of the species (17) oc- curred at three to six different stations and were Of the 90 stations collected by Erseus (1990) we considered uncommon. Of the remaining species, used 72. Eight of the stations dropped were col- 14 occurred at eight or more stations and were lected at different times or with different methods. common. Three species (Heterodrilus JEexuosus The other ten stations were dropped because of Erseus, 1990, Phallodrilus molestus Erseus, 1988, their low information content, as explained below. Inanidrilus leukodermatus (Giere, 1979)) were very The physical descriptions of the retained stations common, occurring at 30 or more stations. These are given in Erseus (1990). The location of each three species also accounted for 42% of the total sampling area is in Fig 1. individuals collected (Table 1). Their average Tobacco Range 1 Fig. 1. Location of sampling areas on the barrier reef ecosystems off the coast of Belize. 96 Table 1. Marine Tubificidae collected at 77 stations located throughout the outer barrier of the coral reef ecosystems offthe coast of Belize. Station Number of occurrences individuals Subfamily Rhyacodrilina Heronidrilus gravidus Ers6us, 1990 5 8 Heterodrilus flexuosus Erseus, 1990 37 158 Heterodrilus rams Ers6us, 1990 2 5 Heterodrilus paucifascis Milligan, 1987 9 97 Heterodrilus