Álvaro Morales-Ramírez

Trophic planktonic dynamics in a tropical estuary, Gulf of Nicoya, Pacific coast of Costa Rica during El Niño 1997 event

Durante las epocas seca y lluviosa de 1997 se analizo la dinamica trofica del plancton en el Golfo de Nicoya, costa Pacifica de Costa Rica. En dos profundidades de penetracion de luz se determinaron la temperatura del agua, salinidad y oxigeno disuelto. En cada profundidad se cuantificaron los nutrientes inorganicos, biomasa fitoplanctonica total y nanofitoplanctonica, recolectandose muestras para analisis taxonomicos fitoplanctonicos. Se realizaron arrastres oblicuos para estimar abundancias, composicion y peso seco del zooplancton. La estimacion indirecta de la tasa de herbivoria se realizo utilizando el presupuesto de pigmentos. El estudio coincidio con la ocurrencia de un evento El Nino reflejado en cambios de las caracteristicas fisico-quimicas del agua en la zona de Punta Morales. La concentracion de algunos nutrientes mostro una correlacion con la salinidad y se encontraron diferencias significativas entre las epocas transicion y lluviosa en las biomasas fitoplanctonicas. Se identifico un total de 43 taxa fitoplanctonicos, donde flagelados, diatomeas centricas y pennadas representaron el 90% de la abundancia. Los copepodos fueron el grupo zooplanctonico mas abundante y Acartia lilljeborgii, Pseudodiaptomus sp. y Paracalanus parvus, los herbivoros dominantes; los valores del peso seco de herbivoros vario entre 0,6 y 50 mg m-3. La tasa de herbivoria mostro un promedio de 0,67 ± 0,83 d-1. Se encontro un comportamiento estacional con cambios en las concentraciones de nutrientes, disponibilidad del fitoplancton e incremento de las temperaturas, donde la predacion y presion de herbivoria ocasionaron cambios en la estructura de las poblaciones planctonicas en la zona interna del Golfo de Nicoya

New species of Monstrilloida (Crustacea: Copepoda) from the Eastern Tropical Pacific

Monstrilloid copepods were collected from the oceanic island Isla del Coco in the Eastern Tropical Pacific; two undescribed species were found, one of Cymbasoma and one of Monstrillopsis. The first species, represented by females only, is distinguished by the structure of its fifth legs, the antennular armature and the position of the ovigerous spines. The new Monstrillopsis, represented by male specimens, is distinguished by its genital lappets and details of the antennule armature. The isolation of this island, 532 km from the mainland, and the limited dispersal means of monstrilloids suggest potential endemism of these species. A recent record of Cymbasoma tumorifrons from the Mexican Pacific was found to represent a new species of Cymbasoma. It can be distinguished from C. tumorifrons, probably a Mediterranean form, by its body shape and antennular armature. These findings double the number of monstrilloid species known from the Eastern Tropical Pacific.

Report on some monstrilloids (Crustacea: Copepoda) from a reef area off the Caribbean coast of Costa Rica, Central America with description of two new species

Monstrilloid copepods were collected during zooplankton surveys in the reef area of the Cahuita National Park, Caribbean coast of Costa Rica, Central America. These specimens represent three species, two of them undescribed. A male resembling the supposedly cosmopolitan Monstrilla grandis Giesbrecht, 1891 was recorded. Differences among populations from distinct geographic areas suggest that this species represents a complex. Some South American records are likely to be conspecific with the type material. Monstrillopsis cahuitae sp. nov. is related to congeners with an elongate, distally bilobed male genital apparatus, but can be distinguished by having six caudal setae. Cymbasoma alvaroi sp. nov. differs from its congeners by a combination of characters, including a rounded frontal process, the position of the oral papilla, the ornamentation of the cephalic area, and the length and shape of the fifth leg inner lobe. These are the first records of the monstrilloid fauna of the Costa Rican Caribbean. http://www.zoobank.org/urn:lsid:zoobank.org:pub:6F3574B3-0541-4BAE-A3AC-AC79FEEE4D75

Marine Biodiversity of Eastern Tropical Pacific Coral Reefs

The eastern tropical Pacific (ETP) is an isolated oceanic region exposed to extreme oceanographic conditions, including low salinity, low pH, high temperatures during El Nino, and low temperatures during La Nina and seasonal upwelling. The coral reefs in this region have a relatively limited suite of species compared to other coral reef areas of the world, but much like more diverse reefs the species present interact in complex ways. Here we synthezise the knowledge of taxonomic groups of reef organisms from prokaryotes to vertebrates, including algae, sponges, cnidarians, annelids and other worms, molluscs, crustaceans, echinoderms and fishes. We also present summaries on the biodiversity of associated functional groups and habitats, including (a) reef zooplankton and cryptic fauna, and (b) soft benthic environments, rhodolith beds and mesophotic environments. Several factors that structure the biodiversity of ETP coral reefs are explored, including biological, physical and chemical controls. ETP coral reefs are relatively simple systems that can be used as models for studying biodiversity and interactions among species. We conclude this review by highlighting pressing research needs, from very basic inventories to more sophisticated studies of cryptic assemblages, and to investigations on the impacts of natural and anthropogenic effects on ETP coral reef biodiversity.

Morphological variability and distribution of the exotic Asian Mesocyclops thermocyclopoides (Copepoda: Cyclopoida): in the Neotropical region

From a series of biological samples collected from different freshwater environments in Costa Rica, Central America, the exotic Asian cyclopoid Mesocyclops thermocyclopoides Harada, 1931 was identified. We analyzed the mor- phology and appendage ornamentation of different Neotropical populations of this species, including specimens from Honduras, southeastern Mexico, and Costa Rica. We also examined Asian specimens from Taiwan, Indonesia, Vietnam, and Thailand, and performed a comparison of the Neotropical and Asian populations including a Principal Component Analysis (PCA). The Neotropical and Asian specimens show subtle morphological variations in the antennules, anten- nae, mandibles, swimming legs 1-4, and fifth legs. Some characters in the Neotropical group appear to diverge from the Asian pattern and the PCA indicated that intercontinental populations of M. thermocyclopoides are far from being homo- geneous. These intra-specific differences are described to expand the known morphological range of this species and to provide the first comparative analysis of an exotic copepod in the Americas. Our analysis suggests that the geographic isolation of the American populations and the subtle morphological divergences with respect to the Asian patterns could be related to speciation processes in the Neotropical region, but also intra-Asian differences are reported. In the Neotropical region this species appears to be restricted to southeastern Mexico, Central America, and one Caribbean island; its potential as biological control of mosquito might enhance its spread in the region.

Fixed-nitrogen loss associated with sinking zooplankton carcasses in a coastal oxygen minimum zone (Golfo Dulce, Costa Rica)

Oxygen minimum zones (OMZs) in the ocean are of key importance for pelagic fixed-nitrogen loss (N-loss) through microbial denitrification and anaerobic ammonium oxidation (anammox). Recent studies document that zooplankton is surprisingly abundant in and around OMZs and that the microbial community associated with carcasses of a large copepod species mediates denitrification. Here, we investigate the complex N-cycling associated with sinking zooplankton carcasses exposed to the steep O2 gradient in a coastal OMZ (Golfo Dulce, Costa Rica). 15N-stable-isotope enrichment experiments revealed that the carcasses of abundant copepods and ostracods provide anoxic microbial hotspots in the pelagic zone by hosting intense anaerobic N-cycle activities even in the presence of ambient O2. Carcass-associated anaerobic N-cycling was clearly dominated by dissimilatory nitrate reduction to ammonium (DNRA) at up to 30.8 nmol NH4+ individual-1 d-1, followed by denitrification (up to 10.8 nmol N2-N individual-1 d-1), anammox (up to 1.6 nmol N2-N individual-1 d-1), and N2O production (up to 1.2 nmol N2O-N individual-1 d-1). In contrast, anaerobic N-cycling mediated by free-living bacteria proceeded mainly through anammox and denitrification in the anoxic bottom water, which underpins the distinctive microbial metabolism associated with zooplankton carcasses. Pelagic N-loss is potentially enhanced by zooplankton carcasses both directly through N2 and N2O production, and indirectly through NH4+ production that may fuel free-living anammox bacteria. We estimate that in the hypoxic water layer of Golfo Dulce, carcass-associated N2 and N2O production enhance N-loss as much as 1.4-fold at a relative carcass abundance of 36%. In the anoxic bottom water, however, N-loss is likely enhanced only marginally due to high ambient rates and low zooplankton abundance. Thus, zooplankton carcasses may enhance N-loss mainly at the hypoxic boundaries of OMZs which are usually more extensive in open-ocean than in coastal settings. Notably, these contributions by zooplankton carcasses to pelagic N-loss remain undetected by conventional, incubation-based rate measurements.

Diversity of the free-living marine and freshwater Copepoda (Crustacea) in Costa Rica: a review.

Abstract The studies on marine copepods of Costa Rica started in the 1990’s and focused on the largest coastal-estuarine systems in the country, particularly along the Pacific coast. Diversity is widely variable among these systems: 40 species have been recorded in the Culebra Bay influenced by upwelling, northern Pacific coast, only 12 in the Gulf of Nicoya estuarine system, and 38 in Golfo Dulce, an anoxic basin in the southern Pacific coast of the country. Freshwater environments of Costa Rica are known to harbor a moderate diversity of continental copepods (25 species), which includes 6 calanoids, 17 cyclopoids and only two harpacticoids. Of the +100 freshwater species recorded in Central America, six are known only from Costa Rica, and one appears to be endemic to this country. The freshwater copepod fauna of Costa Rica is clearly the best known in Central America. Overall, six of the 10 orders of Copepoda are reported from Costa Rica. A previous summary by 2001 of the free-living copepod diversity in the country included 80 marine species (67 pelagic, 13 benthic). By 2009, the number of marine species increased to 209: 164 from the Pacific (49% of the copepod fauna from the Eastern Tropical Pacific) and 45 from the Caribbean coast (8% of species known from the Caribbean Basin). Both the Caribbean and Pacific species lists are growing. Additional collections of copepods at Cocos Island, an oceanic island 530 km away of the Pacific coast, have revealed many new records, including five new marine species from Costa Rica. Currently, the known diversity of marine copepods of Costa Rica is still in development and represents up to 52.6% of the total marine microcrustaceans recorded in the country. Future sampling and taxonomic efforts in the marine habitats should emphasize oceanic environments including deep waters but also littoral communities. Several Costa Rican records of freshwater copepods are likely to represent undescribed species. Also, the biogeographic relevance of the inland copepod fauna of Costa Rica requires more detailed surveys.

Chaetognaths or Arrow Worms

The knowledge of chaetognaths in the two Costa Rican coasts is both scarce and asymmetrical. Less than 20% of the number of potential species (115) have been effectively recorded from this country. The Pacific side has been sur- veyed much more intensely than the Caribbean coast. This is attributed to the large zooplankton surveys in the Eastern Tropical Pacific (ETP) that included sampling sites in Costa Rican waters. These expeditions yielded relevant data to the current knowledge of the ETP region chaetognath fauna, including Costa Rica. Up to 19 species have been effectively recorded in the Costa Rican Pacific waters, about 50% of the known species richness in the ETP. Conversely, only nine species have been reported for the Caribbean waters of Costa Rica, a figure far from the 25 species known to be distributed in the Caribbean Basin. The relevance of developing zoo- plankton surveys that include a close analysis of the chaetognath fauna is empha- sized in terms of the trophic relevance of these predators in the pelagic realm.

A new species of Pontella (Calanoida, Pontellidae) from an oceanic island of the eastern tropical Pacific

Abstract During a survey of the epipelagic zooplankton of the Isla del Coco, an oceanic island off the coast of Costa Rica, eastern tropical Pacific, female and male specimens of a pontellid calanoid copepod belonging to the genus Pontella were collected. It was recognized as an undescribed species belonging to the Pontella fera species-group. It is most closely related to P. tenuiremis Giesbrecht, 1889 and P. fera Dana, 1849. The new species, P. cocoensis, can be distinguished from these and other congeners by having a unique combination of characters including: 1) the female genital double-somite has a longer lateral process than that illustrated by Giesbrecht (1893) for P. tenuiremis, 2) the lateral genital process bears two subdistal rounded protuberances; 3) the right margin of the genital double-somite is swollen and lacks a process; 4) the presence of modified, arrow-shaped setae on several segments of the female antennule; 5) a short, telescoped female anal somite; and 6) a thumb-like process with a rounded protuberance on the medial surface of the first exopodal segment of the male leg 5. The mouthparts, with sparsely spinulate setae on both the maxilla and maxilliped, and bicuspidate teeth on the mandibular edge, suggest that this new species is omnivorous. This is the first species of Pontella described from Costa Rican waters.