Sistema Regional de Información
en línea para Revistas Científicas de América Latina,
el Caribe, España y Portugal

Thirteen species of Pilargidae (Annelida: Polychaeta) from the subtidal and intertidal Pacific Coast of Costa Rica are reported. A new species, Sigambra vargasi n. sp., is described and an as yet undescribed species, Sigambra sp. A, is also reported. The occurrence of Sigambra tentaculata (Treadwell), Loandalia riojai Salazar-Vallejo, Pilargis berkeleyi Monro, Ancistrosullis hamata Hartman and Ancistrosyllis jonesei Pettibone are range extensions for these species. The occurrence of Sigambra pellibaneae Hartmann-Schroder, Pirandalia tricuspis (Müller), Cubira incerta Webster, Ancistrosyllis papillosa Jones and Ancistrosyllis hartmanae Pettibone are new re cords of these species for the eastern Pacific Ocean. Synelmis cf. albini (Langerhans) is also reported. A taxonomic key to these species is included.

There are no detailed studies on the sympatric dolphin species of Golfo Dulce, Studies in other areas have indicated that the presence of sympatric dolph ins is maintained by each species using different habitats. This study describes the distribution of bottle nose (Tursiops truncatus) and pan-tropical spoiled (Stenella allenuata) dolphins in Golfo Dulce and its relation to habitat. A total of 428 boat surveys were conducted from September 1991 through December 1992. There were 529 bottlenose dolphin sightings and 200 spotted dolphins sightings. The two species were only once observed in mixed aggregations. There were differences in relative abundance and group size between both dolphin species. Bottlenose dolphins were found mostly in shallow waters, close to shore, near rivers. and along steep marine slopes. Spotted dolphins were associated with deeper waters and increased distance from shore. Despite apparent differences in habitat preferences. the two dolphin species were commonly observed in tile same areas, albeit at different times, due in part to seasonal variations in dolphin distribution and habitat preference. Most notably during the Late Wet season of 1991 bottlenose dolphins were found in the middle and spotted dolphins at both ends of the Gulf. This pattern was almost reversed during the Late Wet season of 1992. The observed seasonal variation patterns are inadequately explained by habitat-preference arguments alone.

From July 1996 to June 1997, 123 sightings of bottlenose dolphins and 17 sightings of spotted dolphins were made in Golfo Dulce. south Pacific of Costa Rica. Behavioral patterns of both bottlenose and spotted dolphins were analyzed. classifying behavior in five categories such as travelling. feeding. passive socializing. active socializing and milling. Instantaneous data recording was used, and only sightings equal or longer than 15 minutes were considered. Correspondence Analysis revealed differences in diurnal patterns between the two species while seasonal patterns showed important similarities. Diurnal differences were explained in terms of external aspects (i.e. prey) instead of internal requirements due to time proportions for each activity were similar. Coincidence of time proportion spent on feeding activities during dry season (January-April) as well as coincidence of time proportion invested on active social activities during late wet season (September-December) in the two species were explained on a survival basis.

Basic physico-chemical parameters and benthic invertebrate diversity were measured from several streams that drain into the Golfo Dulce (southern Pacific coast of Costa Rica) during 1996-1991. A total of 15 sites were visited in the Osa Peninsula, and the Esquinas and Coto-Colorado river basins, all under 100 m in altitude. Dissolved oxygen and suspended solids differed among sites. even though dissolved oxygen always showed values within a narrow range above 15% saturation, meaning that no site had oxygen deficit at the time of sampling. Suspended solids varied greatly: rivers with high values also had low values during low discharge. A cluster analysis based on the physico-chemical data yielded two groups separated mainly by the variability and maximum value of suspended solids. The benthic fauna is poor in species and is composed of insect larvae (48 species), crustaceans (seven species, of which three are freshwater species) and other three invertebrate species. The most abundant groups were Ephemeroptera and Decapoda. Total diversity was also quite variable (range 1-22 species depending on site). Diversity is best explained by substrate type and suspended solids load.

The organic contaminant load within the sediments of Golfo Dulce has so far gone unstudied. Concentrations of persistent pesticides were ascertained for comparison with future contaminant loads and for evaluation of response of biota to these compounds. Forty seven sediment cores were collected from the shores of Golfo Dulce. Costa Rica for quantification of persistent pesticide contamination, particle size distribution, and organic matter content The gulf has to date had only minimal accumulations of pesticides. The deep anoxic fine-grained organic sediments in the northern portion of the gulf have had minimal impact from humans. However, evidence of pesticide metabolites. and aromatic hydrocarbons may indicate an accumulation of some contaminants and degradation of others in this zone. The Esquinas River sediments were found to contain numerous persistent pesticides. such as a, B, y, and 6-BHC. The Coto-Colonado River sediments are coarser in texture. with low organic contents and may not retain pesticides efficiently. The pesticide load from this river may be transported great distances within the gulf. The Golfito area had link pesticide contamination, however, aromatic and diesel hydrocarbons were in great abundance in the sediments.

A first checklist of the genera of aquatic insects from Costa Rica is presented. The material has been collected since 1990 throughout the entire country and is deposited at the Museo de Zoología, Universidad de Costa Rica. The collection includes only the aquatic stages from each order and contains a total of 278 genera from 92 families in 11 orders.

The influence of pig farm sewage on waler quality and diatoms was studied in two tropical streams over a five-month period. Sewage water inflows led to increased concentrations of soluble reactive phosphorus. ammo­nium, nitrite and to oxygen deficits. Due to self-purification, a decrease of ammonium coupled with an increase in nitrate occurred downstream. In total, 127 species of diatoms were recorded. Thirteen species restricted to tropical regions were found particularly at the spring-site. Correlation between dominant species and hydro-chemical pa­rameters were calculated: Nitzshiq fonticola occurred especially at unpolluted sites, Gomphonema parvulum, Navicula subminuscula and Nitzschia palea were more abundant at sewage-polluted sites and Cocconeis placentula seemed to be tolerant to pollution. A cluster-analysis showed that diatom assemblages at the spring-site were different from all other sites. Light and water current were discussed as factors influencing the spring-site assemblages.

A survey of the benthic macroalgae and physical data was monthly performed in Rio Savegre from its headwaters to its lowplain course. The macroalgae were observed with a viewing box at 20 cm intervals following a fixed rope across the stream and microscopical observations were made at laboratory. The species composition of benthic macroalgae found in Rio Savegre is characteristic for unpolluted. clear. carbonate poor streams. From the source to the mouth a change from species adapted to cold. fast flowing streams to species adjusted to higher temperatures. lower current velocity and periodic desiccation was observed. There was a replacement of the multilayered. well structured macroalgal community in the upper part of the river by surface films formed by microalgae in the lower part. In addition a high-light community consisting of Spirogyro sp., Nostoc verrucosum and Tetraspora sp. could be distinguished from the dim-light species Prosiola mexicana and Hildenbrandia sp.

Effects of pig farm sewage water in two tropical streams were studied for a five month period consider­ing physical chemical and biological parameters. The method of Lange-Bertalot and the method of Steinberg & Schiefele, both based on benthic diatoms, were applied for the biological water assessment. Results were compared to indices calculated from the physical chemical variables (oxygen, nitrate, nitrite, ammonia and phosphate). Ac­cording to both methods the percentages of the diatom species groups reflected the increase: and subsequent de­crease of pollution. However, in both methods, species groups did often not fit the criteria of the classification schemes for calculation of water quality. The sources of these problems were discussed in this paper. More infor­mation on the ecological requirements of diatoms in tropical areas is needed to design procedures for water quality assessment for tropical streams.

Thee Gandoca-Manzanillo region is part of the Limón Basin, located in southeastern Costa Rica. The de­positional environment of Testiary sedimentary rocks shows a progressive shallowing through geologic lime, from deep marine (Miocene-Pliocene) to deltaic-fuvial and coral reef environments (Quaternary). Thee most dramatic geologic effect of the Limón-I991 earthquake was coseismic uplift of the shoreline, which ranged from 0.3 to 0.6 m in the Gandoca- Manzanillo region. This event caused liquefaction of thick deposits of young, fine-grained fluvial sediments in the region, and produced a tsunami affecting the vicinity of Manzanillo and Punta Uva, but the heaviest damage was reported in northwesterm Panamá. The effects of the tsunami may have been diminished in Costa Rica because of the presence of fringing reefs, and the fact that this part of the coast had been coseismically uplifted by the time tsunamis arrived at the coast. Two platform levels were dated using radiocarbon method on coral sam­ples. The platform level at 1.5·2.0 m had radiocarbon ages of 5 220±5O years B.P. and 4 540±50 years B.P., and the 8.0-10.0 m terrace level was dated at 27 14S±290 years B.P yielding a 1.8 mm/year long-term coseismic uplift rate. Variations in the heights of individual platforms reflect a very irregular coseismic uplift behavior, and proba­bly also an irregular earthquake time recurrence period. However, similarities between the 1991 and 1822 events suggest 150 to 200 year as the earthquake recurrence time.