Ana I. Dittel

The estuarine character of the Gulf of Nicoya, an embayment on the Pacific coast of Central America

Hydrography and exchange processes in a tropical estuary, the Gulf of Nicoya, Costa Rica, are described from data collected in 1979 and 1980. The measurements and analyses were made in both the dry season and wet season and include temperature, salinity, and density at twenty locations in the gulf and currents (over a semi-diurnal tidal cycle) at five locations. These new results enlarge on the early study by Peterson (1958). Circulation in the lower gulf shows a marked east-west asymmetry due to the predominant runoff along its eastern shore from Rio Barranca and Tarcoles. The freshened surface water from the upper gulf combines with the runoff from these rivers and flows southward along the eastern side of the lower gulf. This flow is compensated by a northward flow of more saline water on the western side at all depths and on the eastern side along the bottom. The boundary between the southward and northward surface flow is marked by a strong salinity front in the rainy season. There is a rapid increase in tidal energy density toward the shoaling northern reaches of the lower gulf, between San Lucas Island and Puntarenas Peninsula. Enhanced mixing must accompany this increase, and direct measurements in the constriction between San Lucas and Puntaneras show that tidal mixing is dominant in transporting salt into the upper gulf against the freshwater runoff.

Seasonal changes in nutrients and dissolved oxygen in the Gulf of Nicoya, a tropical estuary on the Pacific coast of Central America

Concentrations of ammonium, nitrite, nitrate, inorganic phosphate, and dissolved oxygen were measured at 15 stations in the Gulf of Nicoya during rainy and dry seasons. Results allowed division of the gulf into three areas. The upper gulf is an area greatly affected by changes in rainfall as levels of nutrients varied by an order of magnitude seasonally. The lower gulf shows less seasonal variation and is characterized by low concentrations of nutrients and high concentrations of oxygen at the surface and high concentrations of nutrients and low concentrations of oxygen at the bottom. Nutrient-rich bottom water in the lower gulf appears to be entrained from offshore by the positive estuarine character of the gulf. This process is facilitated by the extremely narrow shelf along the Pacific coast of Costa Rica. These oceanic waters are mixed vertically in the mid-gulf region and carried into the upper gulf by estuarine circulation.

Reproductive periodicity of the tropical crab Callinectes arcuatus Ordway in Central America

Abstract The Gulf of Nicoya, an estuary on the Pacific coast of Central America, contains a large population of the portunid crab Callinectes arcuatus . Results of a 12 month survey indicated that spawning activity occurs throughout the year, but with a distinct peak during the five-month dry season (December-April). Mature females were most prevalent in the upper regions of the gulf during the rainy season and appeared to migrate to the lower gulf to spawn during the dry season. Patterns of spawning and apparent migration differed from those reported in an earlier study of C. arcuatus along the Pacific coast of Mexico.

Lunar rhythms in the egg hatching of the subtidal crustacean: Callinectes arcuatus Ordway (Decapoda: Brachyura)

Abstract Gravid female portunid crabs, Callinectes arcuatus , were held in a recirculating seawater system and the development of the eggs was observed. Based on morphological criteria, nine developmental stages were noted. The relationship between a given stage and the subsequent time to hatching was determined. Based on this, an index was devised that predicted hatching date from microscopic observation of an egg mass. This index was used to predict the date of hatching of eggs from 439 crabs collected in the Gulf of Nicoya, Central America, and the frequency of hatching was analysed in relation to the lunar and tidal cycles. Significantly more eggs hatched during periods of spring than neap tides. The adaptive significance of this rhythmicity is unclear at present.

Benthic invertebrates of a tropical estuary: Gulf of Nicoya, Costa Rica

Summary Crustaceans showed considerable differential distribution in response to a variety of features. Portunid crabs may be responding to salinity gradients, peak abundance of shrimp may be associated with detritus from rivers flowing into the Gulf and mantis shrimp may be influenced by sediment type and biotic interactions. Because of the ecologic and economic value of crustaceans these findings are significant in terms of red tides (Hargraves and Viquez 1981) and potential perturbations in the Gulf of Nicoya. Differences between shallow tropical marine ecosystems and temperate counter-parts concern chemical and physical characteristics (temperature, light, rainfall, nutrients), community structure (species diversity, population density, biomass), and biological functions (primary productivity, growth rates, resource sharing) (Johannes and Betzer 1975). Spight (1977) posed some generalizations concerning differences between tropical marine and temperate communities. These generalizations included: (1) ...

Population biology of the portunid crab Callinectes arcuatus Ordway in the Gulf of Nicoya, Costa Rica, Central America

Abstract Tropical blue crabs Callinectes arcuatus were collected by trawling in the Gulf of Nicoya on the Pacific coast of Costa Rica, Central America. The gulf population was generally dominated by females. Adult females were common in the upper, more estuarine regions of the gulf during rainy season, but appeared to migrate to the lower gulf during dry season for spawning. Biomass varied with seasonal changes in abundance, but was generally similar to biomass of C. sapidus in Chesapeake Bay. Analysis of size frequency indicated that the population is numerically dominated by adults during January and February and that juveniles are common during the remainder of the year. Extrapolation of available data suggests that female crabs reach maturity in approximately one year after hatching.

Biology of the Vent Crab Bythograea thermydron: A Brief Review

Abstract This paper provides a review of relevant literature concerning the vent crab Bythograea thermydron. This body of work describes a crab species that shares fundamental biological characteristics with typical shallow-water brachyuran crabs, yet possesses a suite of highly evolved traits specific for life at hydrothermal vents. Bythograea thermydron is one of only six known species of Bythograea and is very abundant at vent sites along the East Pacific Rise. Because of the large amount of scientific work at this location, almost everything known about bythograeid vent crabs is based on studies of this single species. This review specifically deals with biogeography, systematics, and evolution; morphology, physiology and special adaptations; ovarian development; mating, brooding, and hatching; and larval biology and dispersal. The various sections emphasize comparisons with shallow-water crabs and highlight characteristics such as: (1) the unique eye structure in the adult stage, which is adapted for sensing the exceptionally dim light that is generated by the vents themselves; (2) the extreme tolerance of adults and juveniles to conditions of low oxygen and high sulfides; (3) the exceptional eurythermal character of juvenile and adult physiology; and (4) the seasonality of ovarian development and subsequent reproductive activity. Discussion of larval biology presents various scenarios of larval dispersal and recruitment back to the vent sites.

ABUNDANCE OF INVASIVE AND NATIVE CRAB LARVAE IN THE MOUTH OF DELAWARE BAY: HEMIGRAPSUS SANGUINEUS AND UCA PUGNAX

ABSTRACT We compare larval distributions of the invasive Asian shore crab Hemigrapsus sanguineus and the native fiddler crab Ucapugnax. Our study was conducted in the coastal ocean adjacent to Delaware Bay on the east coast of the United States. Subtidal circulation in the study area is dominated by the Delaware Coastal Current, which is formed by the estuarine plume that extends southward out of the bay and along the inner continental shelf. The offshore edge of the current is marked by a strong density front and by convergent circulation along the frontal boundary. Surface plankton tows were taken at fine-scale intervals along saw-tooth transects traversing the front on 3 consecutive days in early August. Coincident physical measurements delivered hydrographic data throughout the investigation. Results provided a synoptic view of larval distribution near the bay mouth and showed patchy occurrence of the 2 species within the sampling area. Approximately 8.7 × 105 U. pugnax larvae were collected during the study, compared with 2.5 × 104 H. sanguineus. Analysis of spatial distribution with respect to the coastal current showed a marked difference between early- and late-stage larvae for each species. Zoea stage I larvae were most common in the main stream of the coastal current. In contrast, the distribution of advanced stages was skewed toward the frontal region. Larvae entrained in the frontal circulation are likely retained near Delaware Bay, whereas those in the main stream of the coastal current may undergo long-distance transport along the continental shelf.

Transport and retention of the mitten crab ( Eriocheir sinensis ) in a Mid-Atlantic estuary: Predictions from a larval transport model

Invasive species cause extensive ecological damage in freshwater and marine habitats and are a threat to biodiversity in aquatic ecosystems world-wide. One such species, the Chinese mitten crab, Eriocheir sinensis, has invasive populations in northern Europe and San Francisco Bay, and there are confirmed reports of breeding female crabs in both the Chesapeake and Delaware Bays. Despite their threat to these ecosystems, there are still large gaps in the current understanding of this species’ larval biology that are critical to predicting the potential for large populations to establish in East Coast bays and estuaries. We addressed these issues by using a physical circulation model of Delaware Bay and the adjacent coastal ocean coupled to a modified particle advection scheme. We used this model to examine the effects of different physical mechanisms and larval behavior on transport, retention, and settlement of larvae in the bay. The circulation model produced flow fields using observed winds and river discharge for 2006 as well as systematic variations of river discharge and wind direction. Since little is known regarding mitten crab larval behavior, the larval component was purposefully general and incorporated a suite of behaviors such as tidal, diel, and ontogenetic vertical migration; however, results of this study showed that vertical migration affects the magnitude, but not locations of larval settlement. Simulations revealed that changes in the time and location of spawning can result in large variations in retention and settlement of larvae in Delaware Bay and the coastal ocean, due to seasonal variations of the physical flow field. Overall results of our study showed that the estuarine and coastal circulation typically found along the Middle Atlantic coast of the United States can result in significant retention of new and established E. sinensis populations in large estuaries as well as transport of larvae to new coastal locations.

DISTRIBUTION, ABUNDANCE, AND SEXUAL COMPOSITION OF STOMATOPODS IN THE GULF OF NICOYA, COSTA RICA

ABSTRACT Stomatopod Crustacea were collected by trawling in the Gulf of Nicoya on the Pacific Coast of Costa Rica. Abundances, size-frequency distributions, and sexual composition were measured at 12 stations. Eight stations in the upper, more estuarine regions of the Gulf were sampled monthly, while the 4 stations in the lower Gulf were sampled approximately weekly. Four species of Squilla were identified: S. parva Bigelow, S. aculeata Bigelow, S. mantoidea Bigelow, and S. panamensis Bigelow. However, only S. parva and S. aculeata were abundant at the stations sampled. Distribution and abundance differed between the two common species. Squilla parva was restricted to the lower Gulf, whereas S. aculeata was found both in the upper and lower Gulf. In contrast to S. parva, S. aculeata was significantly more abundant in the upper Gulf than in the lower Gulf. In both species the population was dominated by females. Nevertheless, the relative abundance of males of S. aculeata varied with location in the Gulf. Size distribution of both species varied significantly among months. Although the population was dominated by larger individuals, juveniles were frequent during most of the year.