Pacific Costa Rica Research Articles

Checklist of invertebrates and conspicuous fishes in rocky reefs and Sargassum beds in the North Pacific of Costa Rica

Introduction: The marine biodiversity is well known in some areas and for some marine ecosystems of the Pacific coast of Costa Rica. The marine sector of Área de Conservación Guanacaste, in the North Pacific of the country, is a priority area for conservation of marine and coastal biodiversity.
 Objective: Our aim was to increase the knowledge of marine biodiversity in a conservation priority site in Costa Rica and in poorly or scarcely studied marine ecosystems, such as rocky reefs and Sargassum beds, respectively.
 Methods: The study was conducted in Bahía Salinas and Golfo de Santa Elena in 2013. In January, four rocky reefs were visited; while in February three rocky reefs and one Sargassum bed were visited. We identified the macroinvertebrates and conspicuous fish species through underwater visual census methods (timed swim and band transects). The mean density of each species was estimated through band transects method.
 Results: A total of 25 invertebrates and 34 fish species were identified. We found a high number of species of invertebrates (23) and fish species (33) in rocky reefs, but few species on Sargassum beds (eight invertebrates and ten fish species). Species composition differed between marine ecosystems.
 Conclusions: Our study further evidence the limited knowledge of invertebrates and fish communities in these marine ecosystems in the North Pacific of Costa Rica. Considerably more surveys and field work are required to support management decisions that are backed by sound scientific knowledge.

Residency of bull sharks, Carcharhinus leucas (Carcharhiniformes: Carcharhinidae), at San Pedrillo Islet in Islas Murciélago, North Pacific of Costa Rica

Introduction: The bull shark, Carcharhinus leucas, is particularly vulnerable to anthropogenic actions because of its permanence in coastal ecosystems; populations depletion is registered in different places around the world. Aggregations of bull sharks have been reported in the North Pacific of Costa Rica, at Islas Murciélago, within the Guanacaste Conservation Area.
 Objective: To study the residency of bull sharks at San Pedrillo islet, Islas Murciélago.
 Methods: During the study period (June 2013 to February 2015) we used passive telemetry to tag 10 bull sharks.
 Results: All the sharks tagged were females, they were detected on 59 798 occasions by the acoustic receiver deployed in San Pedrillo. Acoustic signals from tagged sharks were received for a total period of 1 to 229 days (mean = 73.9 ± 71.3 days), with the last detections occurring on 9 January 2015. The Residency Index for each tagged shark across the entire monitoring period ranged from 0.41 to 1.00. The bull shark activity showed a significant pattern throughout the day at the receiver that specifically corresponded with the daily light cycle.
 Conclusions: This study concludes that San Pedrillo is an aggregation site (cleaning station) for bull sharks (C. leucas), possibly related to reproduction and not feeding behaviors.

Compound-specific stable carbon and hydrogen isotope analyses of late-Holocene vegetation and precipitation change at Laguna Los Mangos, Costa Rica

New compound-specific isotope analyses of a sediment core from Laguna Los Mangos in southern Pacific Costa Rica improves understanding of late-Holocene precipitation change in a region with limited paleoprecipitation records that is vulnerable to future climate change. We established paleoprecipitation and paleovegetation records from compound-specific stable hydrogen and carbon isotopic compositions of terrestrially-derived n-alkanes (δ2Halkane and δ13Calkane) to assess paleohydrologic variability and potential linkages to paleoecological change and human activity as revealed by prior analyses of the Los Mangos core. The δ2Halkane values were corrected for isotopic fractionation using pollen counts from the same core. The Los Mangos record extends to 4200 cal yr BP and small increases in δ13C values of C29, +0.6‰, and C31 alkanes, +0.3‰, (δ13CC29, 31) indicate a slight increase in C4 vegetation after initial introduction of maize agriculture to the watershed at ca. 3360 cal yr BP. This slight increase in C4 vegetation is followed by the largest positive carbon isotope excursions in the record, as compared to record averages (δ13CC29 = +3.2‰, δ13CC31 = +5.0‰). Paleohydrologic variability likely influenced vegetation and human activity at Los Mangos. Lake desiccation during the late-Terminal Classic Drought (TCD) resulted in a sedimentary hiatus in the Los Mangos record from ca. 950 to 450 cal yr BP. Positive excursions in comparison to record averages occur for both δ2HC29 and δ2HC31 proxies (δ2HC29 = +25.3 to +13.4‰ and δ2HC31 = +6.5‰) during the middle Little Ice Age (LIA) and indicate drier than average conditions, but there is no evidence of desiccation during this period. Thus, drought conditions during the LIA were apparently not as severe at Los Mangos as during the TCD, possibly because of differing forcing mechanisms for LIA climate that originated, or were more clearly expressed, in the Atlantic basin.

Lipid profiling suggests species specificity and minimal seasonal variation in Pacific Green and Hawksbill Turtle plasma.

In this study, we applied multiple reaction monitoring (MRM)-profiling to explore the relative ion intensity of lipid classes in plasma samples from sea turtles in order to profile lipids relevant to sea turtle physiology and investigate how dynamic ocean environments affect these profiles. We collected plasma samples from foraging green (Chelonia mydas, n = 28) and hawksbill (Eretmochelys imbricata, n = 16) turtles live captured in North Pacific Costa Rica in 2017. From these samples, we identified 623 MRMs belonging to 10 lipid classes (sphingomyelin, phosphatidylcholine, free fatty acid, cholesteryl ester, phosphatidylserine, phosphatidylinositol, phosphatidylglycerol, phosphatidylethanolamine, ceramide, and triacylglyceride) and one metabolite group (acyl-carnitine) present in sea turtle plasma. The relative ion intensities of most lipids (80%) were consistent between species, across seasons, and were not correlated to body size or estimated sex. Of the differences we observed, the most pronounced was the differences in relative ion intensity between species. We identified 123 lipids that had species-specific relative ion intensities. While some of this variability is likely due to green and hawksbill turtles consuming different food items, we found indications of a phylogenetic component as well. Of these, we identified 47 lipids that varied by season, most belonging to the structural phospholipid classes. Overall, more lipids (n = 39) had higher relative ion intensity in the upwelling (colder) season compared to the non-upwelling season (n = 8). Further, we found more variability in hawksbill turtles than green turtles. Here, we provide the framework in which to apply future lipid profiling in the assessment of health, physiology, and behavior in endangered sea turtles.

Environmental monitoring and risk assessment in a tropical Costa Rican catchment under the influence of melon and watermelon crop pesticides

A monitoring network was established in streams within a catchment near the Costa Rican Pacific coast (2008–2011) to estimate the impact of pesticides in surface water (84 samples) and sediments (84 samples) in areas under the influence of melon and watermelon production. A total of 66 (water) and 47 (sediment) pesticides were analyzed, and an environmental risk assessment (ERA) was performed for four taxa (algae, Daphnia magna, fish and Chironomus riparius). One fungicide and seven insecticides were detected in water and/or sediment; the fungicide azoxystrobin (water) and the insecticide cypermethrin (sediments) were the most frequently detected pesticides. The insecticides endosulfan (5.76 μg/L) and cypermethrin (301 μg/kg) presented the highest concentrations in water and sediment, respectively. The ERA revealed acute risk in half of the sampling points of the melon-influenced area and in every sampling point from the watermelon-influenced area. Safety levels were exceeded within and around the crop fields, suggesting that agrochemical contamination was distributed along the catchment, with potential influence of nearby crops. Acute risk was caused by the insecticides chlorpyrifos, cypermethrin and endosulfan to D. magna, fish and C. riparius; the latter was the organism with the overall highest/continuous risk. High chronic risk was determined in all but one sampling point, and revealed a higher number of pesticides of concern. Cypermethrin was the only pesticide to pose chronic risk for all benchmark organisms. The results provide new information on the risk that tropical crops pose to aquatic ecosystems, and highlight the importance of including the analysis of sediment concentrations and chronic exposure in ERA.

Decapod crustaceans associated with macroinvertebrates in Pacific Costa Rica

Decapod crustaceans are a diverse group that exploits various types of habitats in Costa Rica, where they represent 8.1% of the marine diversity of the country. This group includes families containing species with strictly symbiotic behavior, e.g., the Palaemonidae and Pinnotheridae. Despite the high diversity of decapods and the importance of symbionts in marine ecosystems, very little research has been done regarding symbiosis in Costa Rica and the Central American region. The objective of the present study is to present a check list of the species of decapods that are associated with macroinvertebrates in Pacific Costa Rica. The research was carried out using different sources, including a literature review, the Crustaceans Collection of the Zoology Museum of the University of Costa Rica, and field surveys between 1970 and 2019 along the Pacific coast of Costa Rica, and Isla del Coco, 500 km offshore. One-hundred associations are reported, of 74 species of symbiotic decapods with six host phyla. Seventy-four associated with Cnidaria, 15 with Echinodermata, four each with Annelida and Mollusca, two with Chordata, and one with Porifera. In total, there were 14 new reports of decapods occurring on Isla del Coco and four new reports of decapods for Costa Rica: Pseudocoutierea elegans, Raytheres clavapedatus, Tuleariocaris holthuisi, and Calyptraeotheres pepeluisi. These results highlight the need to conduct more detailed studies to determine the real diversity and ecological importance of the associations between marine organisms.

The effect of coral reef degradation on the trophic structure of reef fishes from Bahía Culebra, North Pacific coast of Costa Rica

Fishes play numerous key ecological roles that are critical for maintaining the structure and function of coral reefs. Natural and anthropogenic disturbances can produce structural changes in coral reef habitats, which consequently may affect the trophic structure and dynamics of reef fish assemblages. Therefore, changes in the coral cover of coral reefs, caused by disturbance events can impact the abundance of reef fishes. This study determined the effect of habitat degradation on the trophic structure of coral reef fishes from Bahia Culebra, a bay located in the north Pacific of Costa Rica. We examined whether spatial and temporal changes in live coral cover (LCC) and substrate type between two periods (1995–1996 and 2014–2016) influenced the trophic structure of coral reef fishes. While planktivorous fishes maintained similar abundances between periods, omnivorous fishes (mainly facultative corallivores) were less abundant in sites with low LCC. There was a decline in abundance of mesopredators (e.g. sharks, groupers, snappers), probably because of both shelter loss and overfishing. Macroalgae feeders, herbivores-detritivores and invertivores showed high abundance in disturbed coral reefs, which could be related to predator decline or to increased algal resource abundance. Despite high abundance of herbivorous fishes, high macroalgae coverage persisted during the 2014–2016 period. The results from this study suggest that degradation of coral reef habitats from Bahia Culebra have affected the trophic structure of reef fish assemblages, and potentially the functioning of this coastal ecosystem.

Crecimiento demográfico y degradación de los recursos: El caso del agua en las comunidades Ojo de Agua y Crun Shurin, de los territorios indígenas Boruca y Térraba del Pacífico de Costa Rica (2000-2019)

En el presente artículo se investiga la gestión social del recurso hídrico en las comunidades indígenas Ojo de Agua y Crun Shurin, del Pacífico de Costa Rica, con la intención de identificar a los actores sociales e institucionales involucrados, así como las relaciones entre ellos. Específicamente, se exploran los retos en materia de acceso al agua manifestados por personas indígenas de ambas comunidades, así como el papel de las instituciones estatales en la búsqueda de soluciones a dichas problemáticas. Se hizo uso de entrevistas grupales, estadísticas sobre el crecimiento demográfico en los dos territorios y se evaluó, mediante análisis de laboratorio, la calidad del agua que consumen diariamente, para señalar posibles fuentes de contaminación.

Reef environments of Murciélago Islands and Santa Elena peninsula, Guanacaste conservation area, Costa Rican pacific

The ecology of the marine environments of the Murciélago Islands and the Santa Elena Peninsula have been studied little despite their high biodiversity. This area is influenced by a coastal upwelling. In 2014, 2016 and 2018, the region was visited to assess the composition and diversity of its reef environments. Bottom coverage, macroinvertebrate diversity and abundance, and reef fish biomass were quantified. The substrate was dominated by turf and crustose calcareous algae. Live coral coverage has decreased compared to previous reports for the area. Sea urchins were the macroinvertebrates with the highest densities, while species of commercial interest presented low densities, this may suggest some degree of fishing pressure. 84 reef fish species were identified, making the islands area with the greatest diversity of reef fish in the North Pacific of Costa Rica. Coral biotopes in this region are key to the conservation of connectivity between reef areas due to their high diversity.

Effects of egg mass and local climate on morphology of East Pacific leatherback turtle Dermochelys coriacea hatchlings in Costa Rica

Global climate patterns are shifting due to anthropogenic causes, putting pressure on many species that are unable to adapt to such rapid changes. Sea turtle clutches, for example, normally develop between 26 and 33°C, but tolerate higher temperatures at the end of development. High temperatures, protracted rainfall, and droughts have been linked to fewer hatchlings. Likewise, climatic conditions can affect the size of sea turtle hatchlings, which could affect their probability of survival. We analyzed the effects of a biotic factor (egg mass) and environmental factors (precipitation and incubation temperature) on East Pacific leatherback turtle Dermochelys coriacea hatchling sizes in Costa Rica. Hatchling size (mass, straight carapace length, straight carapace width, and head width) was affected by both biotic and environmental factors. While egg mass was the strongest predictor for hatchling mass, temperature was the strongest for carapace length and head width. Carapace width was most strongly predicted by precipitation. Hatchling carapace length and width decreased with increases in temperature and increased with higher levels of precipitation. Hatchling mass also decreased with increasing temperature, although the relationship was not statistically significant. Head width decreased with greater precipitation during development. These findings suggest that increases in temperature and decreases in precipitation may not only decrease the number of hatchlings produced, but may also produce smaller leatherback hatchlings in Pacific Costa Rica, which may impair hatchling survival in the first hours after emergence.

Four new deep-water flabelligerid species from Pacific Costa Rica (Annelida, Sedentaria, Flabelligeridae).

The discovery of four undescribed flabelligerid species from deep-water in Pacific Costa Rica resulted in the restriction of Diplocirrus Haase, 1915. As currently understood, Diplocirrus and Pherusa Oken, 1807 are separated after their morphological pattern. The species belonging in Diplocirrus have two types of branchiae, poorly developed cephalic cages and multiarticulate neurochaetae, whereas Pherusa species have branchiae of one type, well-developed cephalic cages and completely anchylosed neurochaetae. Benthic sampling and processing usually damage cephalic cages and if chaetae are completely broken, one could regard specimens without them, when they actually have it, but lost after sieving. Sampling using Alvin deep-sea submarine at methane seeps off Costa Rica resulted in some well-preserved specimens, and some of them fall between these two genera because they have well developed cephalic cages, and multiarticulate neurochaetae. Saphobranchia Chamberlin, 1919, with Stylarioides longisetosa von Marenzeller, 1890, as type species, is herein reinstated for some species previously included in Diplocirrus, restricted. The transferred species, including three ones newly described herein, have branchiae of a single type, long cephalic cage and body chaetae, and neurochaetae basally anchylosed and medially and distally articulated; some species currently included in Diplocirrus described from Arctic or deep water sediments are transferred into it. A key to identify all species in Saphobranchia, and another key to identify species in the restricted Diplocirrus are also included. The three new Saphobranchia species are S. canela n. sp., S. ilys n. sp. and S. omorpha n. sp. The fourth species belongs in Lamispina Salazar-Vallejo, 2014, and it is herein described as L. polycerata n. sp. after the presence of some long papillae along anterior margin of chaetiger 1.

Sustainability Performance through Technology Adoption: A Case Study of Land Leveling in a Paddy Field

Energy is required in all agricultural activities. Diagramming material flows needed by crop production systems supports the proper analysis of energy flows interactions within a system’s boundaries. The latter complemented with an economic analysis gives a clear view of how beneficial a new practice within a crop cycle is—in this case, the variable slope (VS) land leveling (LL) operation. VS is a global navigation satellite system (GNSS, with real time kinematics—RTK—accuracy) LL technique used to create a smooth continuous surface with a constant slope, by cutting and filling topsoil layers only in those points presenting “anomalies” of micro-relief which make the movement of water difficult. This operation is important for paddy production since: (i) it enables to crop during dry seasons by harnessing the water of rivers and wells, and (ii) improves the production during rainy seasons, by allowing the farmer to manage the drainage timely and homogeneously. The present study aims to analyze, from the energy perspective, the effects of the VS leveling implementation in a paddy field (located in the Costa Rican Pacific), throughout input (labor, gas oil, etc.) and output (yield and price) data of five consecutive years (2011–2015). A material flow diagram was created representing two scenarios: before and after leveling the land. The materials were converted into energy (MJ ha−1) data, used for the estimation of EROI (energy return on investment), EP (energy productivity) and EB (energy balance) indices, while looking for a clearer understanding of the LL impact on the use of energy within the agroecosystem. Moreover, in order to complement the energy perspective, an economic point of view was considered as well through a profitability analysis where the total gain obtained over the years with LL was compared with that obtained without LL. Results showed that the increase in energy consumed by incorporating VS leveling is compensated by the gradual increase of energy embodied in yield, increasing energy balance (EB) from 26,192 MJ ha−1 up to 91,166 MJ ha−1. Similarly, EROI and EP were duplicated with LL. Economic total gain after incorporating the VS increased from less than 500 USD ha−1 up to 1800 USD ha−1 in the third year after leveling. Yield is more affected under adverse weather conditions with irregular water supply, either limited or excessive; and effects are less pronounced when the yield limiting factor is associated with biotic stress unrelated to irrigation and drainage facts. An environmental positive impact should also be noted, since VS allowed the production benefits of having highly-efficient irrigation and drainage systems, while avoiding major damage to topsoil layers.

Conservation status of fish and marine invertebrate of rocky reefs and sandy substrates in two unprotected bays of the Papagayo Gulf, Costa Rica

Introduction: North Pacific Costa Rica is generally considered rich in marine habitats and species. However, some areas are subject to fishing pressures that could degrade ecosystems. The Gulf of Papagayo comprises protected and unprotected areas with various degrees of impact. Objectives: Our aim was to evaluate the conservation status of fish and invertebrate communities in rocky reefs and sandy areas in two unprotected bays of the Gulf of Papagayo. Methods: The study was conducted at Cabuyal and Zapotillal Bays, south of Santa Rosa National Park. From December 2017 to April 2018, a total of thirty-five transects were done parallel to the coast at 3-10 m depth. We identified fish and invertebrate species and estimated biomass by trophic group in fish, and density in invertebrates. Results: We found a high number of species of fish (81) and invertebrates (70) in rocky reefs, which indicates a biodiverse ecosystem, but few species of fish in sandy areas. Species composition differed between the two bays. Density of juvenile fishes was high in Zapotillal Bay, suggesting that the area could be important for recruitment and breeding. Fish biomass was higher in sandy areas than in rocky reefs and all trophic groups had lower biomass than in other unprotected areas of the region. On average, reef fish biomass was 1.57 ± 0.67 (s.e.) t ha-1, similar to previous reports for Costa Rican North Pacific. By trophic group, piscivorous and planktivorous had the highest biomass in sandy areas and piscivorous and carnivorous in rocky reefs. Mean coral cover was low with 4.09 % ± 2.51 (s.e.), similar to previously reported for the region. Conclusions: Cabuyal and Zapotillal Bays in the Gulf of Papagayo are biodiverse in fish and invertebrates. However, the area may be impacted by local fisheries and other human activities, affecting fish and invertebrate populations, and coral formations. Our study fills some gaps in knowledge of marine biodiversity in the Gulf of Papagayo that can contribute to the conservation of marine life in North Pacific Costa Rica.

Unearthing 20th-century treasures: new records of deep-sea crustaceans from the Costa Rican Pacific

Abstract We report on 13 species collected during the 1973 expedition onboard the MY “Velero IV”: seven Euphausiidae (krill), two Benthesicymidae shrimp, two Sergestidae shrimp, one Acanthephyridae shrimp, and one Portunidae crab. Four species are new records for Costa Rica: Bentheogennema burkenroadi, Gennadas scutatus, Neosergestes consobrinus, and Phorcosergia filicta.

New species and new records of Phragmatopoma (Polychaeta: Sabellariidae) from Tropical America

The genus Phragmatopoma included, until now, only four valid species with distributions in Eastern Pacific and Western Atlantic. Since most taxonomic studies of Phragmatopoma include poor and uninformative descriptions, the aim of this work was to expand previous descriptions of the sabellariids of Phragmatopoma genus from Tropical America. Sabellariids from two Mexican collections, the Reference Collection of El Colegio de la Frontera Sur, Chetumal, and Laboratorio de Sistemática de Invertebrados Marinos (LABSIM), Universidad del Mar, Puerto Ángel, were revised. Six hundred sixty-six specimens were revised, and eight species were identified. Three new species are proposed: Phragmatopoma balbinae n. sp., from southern Mexican Pacific, P. carlosi n. sp., from northern Mexican Pacific and P. villalobosi n. sp., from Pacific of Costa Rica. Another morphospecies, Phragmatopoma sp., from Pacific of Costa Rica is characterized; however, it is only one specimen. Two species, Phragmatopoma digitata and P. peruensis, previously buried in the synonyms of P. virgini (type locality: Straits of Magellan, Chile), are considered as valid species. Also, new records of P. californica and P. caudata were made in Baja California and Veracruz, respectively. Additionally, the use of standard terminology for the description of opercular paleae and chaetae is proposed.

A 3600-year record of drought in southern Pacific Costa Rica

AbstractWe analyzed the δ2H composition ofn-alkanes isolated from Laguna Zoncho, a small lake in southern Pacific Costa Rica, to reconstruct paleohydrology. Using a core that spans the past 3600 years, we found evidence of dry periods, most notably during the Terminal Classic Drought (TCD; ~1200 cal yr BP) and the Little Ice Age (~400 cal yr BP). Previous work at Laguna Zoncho, using bulk sedimentary δ13C and geochemical analysis, found that agriculture began to decline during the TCD. Our δ2H records confirm the occurrence of arid conditions coincident with the TCD at Laguna Zoncho and show that, despite receiving more than 3000 mm of precipitation per year, this region is susceptible to multidecadal droughts.

Fire history across the Little Ice Age in southern Pacific Costa Rica

We present two high-resolution records of Late Holocene (Meghalayan) fire history from lakes in the lowlands of southern Pacific Costa Rica and compare them with evidence of pre-Columbian agriculture in the same cores and with records of regional paleoclimate. Macroscopic charcoal influx at Laguna Danta and Laguna Carse shows several major and minor peaks for approximately the last ~ 800 years, but does not show the decline at the time of the Little Ice Age and Spanish contact evident in other charcoal records from the region. Stable carbon isotope values in sediments indicate that agricultural activity at Laguna Danta declined following the onset of the Little Ice Age, but the association between fire and indigenous agriculture at the study sites is not strong. Instead, drought appears to be a primary driver of fire in the lowlands of southern Pacific Costa Rica. Some peaks in macroscopic charcoal at Laguna Danta coincide with shifts in the mean latitudinal position of the Intertropical Convergence Zone in the Caribbean as reconstructed from the Cariaco Ti record. We also identify a decrease in the stable nitrogen isotope values of lake sediments associated with increased fire activity, a pattern also documented in temperate ecosystems. We interpret our charcoal records to indicate both human use of fire in agricultural settings and wildfires in intact forests driven by regional changes in climate.

Field Spectroradiometry for African Oil Palm Plantations in the Pacific of Costa Rica

This study allowed the leaf-scale spectral characterization of African oil palm by conducting field work with a portable spectroradio meter in plantations of the Central and South Pacific of Costa Rica. Spectral signatures of healthy, diseased and nutrient-deficient oil palms were collected. A geodatabase was designed and implemented for geographical, spectral and phytosanitary records. Determination of spectral signatures allows developing spectral libraries of different types of vegetation, soils and water. It also improves the classification of satellite images for thematic cartography and provides the calculation of multiple indices, among others. Healthy vegetation presents low reflectivity in the visible, although there is a peak in the green wavelength due to the presence of chlorophyll. The spectral behavior of diseased vegetation shows a reflectivity curve with a decrease in the infrared and an increase in the red and blue wavelengths. Reflectivity also depends on the water content of the plant.

Population status of the American crocodile, Crocodylus acutus (Reptilia: Crocodilidae) and the caiman, Caiman crocodilus (Reptilia: Alligatoridae), in the Central Caribbean of Costa Rica

American crocodile (Crocodylus acutus)(Reptilia:Crocodilidae) and caiman (Caiman crocodilus)(Reptilia:Alligatoridae) population status, in the Costarican Central Caribbean. Two species of crocodilians have been described in Costa Rica, american crocodile (Crocodylus acutus: Cuvier 1807), and caiman (Caiman crocodilus: Linnaeus 1758). In Costa Rica, data has been generated on both species, but populations in the Pacific have received more attention from researchers; due to the fact that the Pacific slope has a greater development, which brings greater social pressure on the attention of the incidents generated by the encounter between humans and crocodiles. This study, performed during 2017, was done in an area of approximately 400 km2, characterized by having a wide and dense network of water courses, which includes the Matina, Pacuare, Reventazón and Parismina rivers. In these rivers, an average of 25 kilometers were traveled from the coastline up stream to the interior of the territory, including the Tortuguero canals, and other water bodies that connect these rivers, as well as in the most important lagoons and secondary channels. Three repetitions were made per segment. A population of 1084 caimans and 503 crocodiles is estimated; for a relative abundance of 8.64 and 2.80 ind/Km respectively. Speaking of caimans, up to 12% of individuals of reproductive age were observed, while for crocodiles that number was only 2%. The presence of both species in the different places studied, turned out to be significantly different for crocodiles and for caimans (Kruskal-Wallis, p≤0,000). Likewise, the size distribution is similar for crocodiles reported in all environments (Kruskal-Wallis, p≤0.15), while for caimans it indicates that there is a different distribution for sizes, according to the environment in which they are found (Kruskal -Wallis, p≤0,000), with a bias against of the Pacuare and Matina rivers. It was possible to estimate a sex ratio of 1.25 and 0.83 males to females, in crocodiles and caimans respectively, with 9 and 11 captures in that same order, in individuals of recruits, juvenile and subadult sizes. The Matina River and the Jalova Lagoon are the two main sites for the observation of crocodiles, their abundances are lower than those reported for the Pacific of Costa Rica, in whereas caimans, with a more homogeneous distribution throughout the sampling area, have a relative abundance considerably more than that reported in Honduras (2.2 ind/km), but lower than the 12.5 reported forLa Rambla de Sarapiquí, in the Northern Zone of Costa Rica.

Stable isotope analysis of vegetation history and land use change at Laguna Santa Elena in southern Pacific Costa Rica

Laguna Santa Elena (8.9290° N, 82.9257° W, 1055 m a.s.l.) is a small lake in the Diquis archaeological sub-region of southern Pacific Costa Rica. Previous analyses of pollen and charcoal in a sediment core from Santa Elena revealed a nearly 2,000 year history of vegetation change, maize cultivation and site occupation that is consistent with the archaeological record from the lake basin and surrounding area. Here we present the results of new loss-on-ignition, geochemical and bulk stable carbon (δ13C) and nitrogen (δ15N) isotope analyses of the Santa Elena sediments that supplement and refine the previous reconstruction. Like many lakes in Central America and the Caribbean, Laguna Santa Elena was a magnet for humans throughout its history. As a result, the lake experienced vegetation modification by humans and maize cultivation at varying intensities over a long duration. The Santa Elena sediments provide a record of palaeoenvironmental change during times of major culture change and increasing cultural complexity in the Diquis region, which occurred during intervals of broader changes driven by external forcing mechanisms, including the Terminal Classic Drought (TCD), the Little Ice Age (LIA) and the Spanish Conquest. Our high resolution lake sediment study from Santa Elena reveals details of these events at the local scale that are unobtainable by other means, including the timing of the initial intensification of maize cultivation at ca. 1,570 cal bp (ad 380) and two intervals of population decline coinciding with the TCD at ca. 1,085 cal bp (ad 865) and near the start of the LIA at ca. 683 cal bp (ad 1267).