José A. Cuesta

GLYPTOGRAPSIDAE, A NEW BRACHYURAN FAMILY FROM CENTRAL AMERICA: LARVAL AND ADULT MORPHOLOGY, AND A MOLECULAR PHYLOGENY OF THE GRAPSOIDEA

Abstract During an ongoing systematic revision of the Decapoda Grapsoidea (here defined as including the families Gecarcinidae, Grapsidae s. str., Plagusiidae, Sesarmidae, and Varunidae; see Schubart et al., 2000a), it became evident that adult and larval morphology of two Central American genera, Glyptograpsus and Platychirograpsus, differs greatly from that of all other genera within this superfamily. Several important morphological characters are shared by these two genera and represent synapomorphies when compared to the other grapsoids. Both of these genera lack a pleurobranch on the sixth thoracic segment. Adult males of Glyptograpsus and Platychirograpsus are all strikingly heterochelous with the major chela being conspicuously flattened anteriorly and showing a subproximal articulation with the carpus. The distal portion of the male gonopod is uncinate, with a narrowed, elongate terminus. The anteriormost portion of the sternum consists of a narrow, fused sternite terminated in a distinctly flanged tip inserted between the mouth appendages. The male abdomen exhibits immobility in the joints between segments 3 to 5 and very limited mobility in the joint between segments 1 and 2. Zoeae of the two genera show a 1,2 setation pattern on the maxillar endopod. A molecular phylogeny of the Grapsoidea, based on 16S mtDNA and including type genera of the five recognized families, confirms that the species of Glyptograpsus and Platychirograpsus together form a well-defined monophyletic unit that is distinct from all other taxa within the Grapsoidea. We therefore describe a new family, the Glyptograpsidae, to accommodate these two genera of crabs.

Spatial and temporal variation of the nekton and hyperbenthos from a temperate european estuary with regulated freshwater inflow

The aquatic macrofauna of the Guadalquivir estuary were sampled (1 mm mesh persiana net) at 5 sampling sites located along the entire (except the tidal freshwater region) estuarine gradient of salinity (outer 50 km). A total of 134 fish and macroinvertebrate species was collected but only 62 were considered common or regularly present in the estuary. Univariate measures of the community structure showed statistically significant differences among sampling sites: species richness, abundance, and biomass decreased in the upstream direction, being positively correlated with the salinity. Temporal differences of these three variables were also statistically significant. While a clear seasonal pattern (minimum densities in winter and maximum in spring-summer) was observed for abundance and biomass, no such pattern existed for the number of species. Mysids was the most dominant group throughout the estuary (96% to 99% of abundance; 49% to 85% of biomass), although fish biomass was also important at the outer estuary (36% to 38%). Multivariate analyses indicated highly significant spatial variation in the macrofaunal communities observed along the salinity gradient. These analyses suggest that the underlying structure was a continuum with more or less overlapping distributions of the species dependent on their ability to tolerate different physicochemical conditions. There were also significant temporal (intermonthly + interannual) variation of the estuarine community; the relative multivariate dispersion indicated that monthly variation was more considerable (relative multivariate dispersion >1) at the outer part of the estuary during the wet year (last 20 km) and was higher in the inner stations during the dry year (32 to 50 km from the river mouth). Since a clear negative exponential relationship was observed between the freshwater input (from a dam located 110 km upstream) and water salinity at all sampling stations, it is concluded that the human freshwater management is probably affecting the studied estuarine communities. While the higher seasonal (long-term) stability of the salinity gradient, due to the human control of the freshwater input, may facilitate the recruitment of marine species juveniles during the meteorologically unstable early-spring, the additional (short-term) salinity fluctuations during the warm period may negatively affect species that complete their lifecycle within the estuary.

Molecular phylogeny of the crab genus Brachynotus (Brachyura: Varunidae) based on the 16S rRNA gene

The crab genus Brachynotus de Haan, 1833 is restricted to the intertidal and shallow subtidal of the Mediterranean and northeastern Atlantic. It is presently recognized to consist of four species, of which three (B. foresti, B. gemmellari and B. sexdentatus) are endemic to the Mediterranean. The fourth species, B. atlanticus, is found along the Atlantic coasts of northern Africa and southern Europe, but also extends into the western Mediterranean. This high level of endemism suggests that speciation within Brachynotus is strongly correlated with the geography and geology of the Mediterranean Sea. A molecular phylogeny based on the mitochondrial large subunit (16S) rRNA gene indicates that the four species of Brachynotus form a monophyletic group within Atlantic Varunidae. The DNA sequence data also show that the genus Brachynotus can be subdivided into two species groups, one comprising B. atlanticus and B. foresti, and the other one B. gemmellari and B. sexdentatus. While B. atlanticus and B. foresti are clearly genetically distinct, B. gemmellari and B. sexdentatus are identical in the studied region of the 16S rRNA gene, suggesting a recent separation or continuing gene flow.

An illustrated key to species of Palaemon and Palaemonetes (Crustacea: Decapoda: Caridea) from European waters, including the alien species Palaemon macrodactylus

A detailed illustrated key to the identi¢cation of the European species of the genera Palaemon and Palaemonetes is provided.This key has been elaborated taking into account recent changes in the species composition of both genera for European waters, such as the invalidity of Palaemon garciacidi, which is a synonym of P. longirostris, and the presence of an introduced species, Palaemon macrodactylus that has been recently recorded at diierent localities along the Atlantic coast. The key is based on external morphological characters to facilitate its use by non-specialists. Data on the coloration, habitat and distribution of all species are also given.

Marine biogeographic boundaries and human introduction along the European coast revealed by phylogeography of the prawn Palaemon elegans

A phylogeographic analysis is carried out for the widely distributed European littoral prawn Palaemon elegans in order to test for potential genetic differentiation and geographic structure. Mitochondrial sequences were obtained from 283 specimens from the northeastern Atlantic, the Baltic, Mediterranean, Black and Caspian Seas. Our study revealed a surprisingly complex population structure. Three main haplogroups can be separated: one from the Atlantic (Type I) and two from the Mediterranean (Types II and III). While the Mediterranean types occur in sympatry, a clear phylogeographic break was observed along the Almería-Oran Front separating Type I and giving evidence for a genetic isolation of Atlantic and Mediterranean populations. Type III represents the most distinct haplogroup with high levels of nucleotide divergence, indicating the occurrence of a cryptic species with a Messinian origin. The colonization of the southeastern Baltic Sea is most likely due to human introduction.

Assessment of the interaction between the white shrimp, Palaemon longirostris, and the exotic oriental shrimp, Palaemon macrodactylus, in a European estuary (SW Spain)

Results of field surveys, stomach content analysis, and laboratory measurements of oxygen consumption at different salinities in the exotic shrimp Palaemon macrodactylus and its native counterpart P. longirostris from the Guadalquivir estuary (SW Spain) were used to assess interaction between both species. After its first record in this estuary in 1998, P. macrodactylus has shown a gradual increase in density and its estuarine population has been clearly dominated by juveniles. Feeding habits of both shrimps indicated a strong trophic overlap between them, with mysids as main prey. Their salinity-related and spatial distribution patterns show that maximal inter-specific overlap between the two populations occurs in the inner, less saline part of the estuary. Specific oxygen consumption rates under different salinities and water oxygen concentrations suggest a more efficient metabolism and a higher tolerance to hypoxic conditions in brackish waters by P. macrodactylus than by P. longirostris. Such inter-specific physiological differences could have made it possible for the exotic P. macrodactylus to invade an estuarine stretch that, prior to its arrival, was infra-utilized by native species.

Effects of the river discharge management on the nursery function of the Guadalquivir river estuary (SW Spain)

Within the Guadalquivir estuary, young recruits of marine species seem to respond to changes in freshwater flow by moving with the mass of estuarine water that is most “suitable” for them. The control of the river flow, from a dam 110 km upstream from the river mouth, has an immediate effect on the estuarine salinity gradient, displacing it either seaward or upstream. Consequently, there is a reduction or enlargement of the estuarine area that is used as nursery grounds. The analysis of the temporal estuarine recruitment and spatial distribution of young stages of marine species, during six annual cycles, provides evidence that the estuarine zone used as nursery grounds is mainly that part situated seaward from an isohaline value of 5. The relationship between the position of that isohaline (D5) and the freshwater discharges from the dam was also examined during high and low tides. It was found that a high percentage of the isohaline position variation (75% and 73% at high and low tides, respectively) can be explained by the freshwater volume discharged from the dam during the previous week. These preliminary results suggest that an accurate model of the relationship between these two variables may be a useful tool for future management strategies of freshwater discharges to the estuary.

The first zoeal stage of two species of Grapsidae (Decapoda, Brachyura) and a key to such larvae from the Brazilian coast

First zoeal stages of the grapsinid Goniopsis cruentata (Latreille, 1803) and the sesarminid Aratus pisonii (H. Milne Edwards, 1837), are described and illustrated. Grapsinae zoeae can be distinguished from the other grapsid larvae by the absence of lateral spines on the carapace and the reduction of the antennal exopod to a small seta. A key to the first zoeal stage of the Brazilian coast Grapsidae is provided.

Morphological and molecular differentiation between three allopatric populations of the littoral crab Pachygrapsus transversus (Gibbes, 1850) (Brachyura: Grapsidae)

The littoral grapsid crab species Pachygrapsus transversus (Gibbes, 1850) has a wide distribution ranging from the eastern Pacific to the eastern Atlantic and Mediterranean. The American continent and the Atlantic Ocean are believed to act as barriers for dispersal of planktotrophic larvae. The crab populations studied, from the eastern Pacific (Panama), the western Atlantic (Caribbean), and the eastern Atlantic (Spain) were, therefore, assumed to be genetically isolated. Remarkable differences in DNA sequence of the 16S mt-DNA gene as well as in larval and adult morphometry and coloration were found between these populations. A closer genetic similarity between the amphi-Atlantic populations in comparison to the Pacific animals, suggests the occurrence of occasional gene flow across the Atlantic Ocean.

First zoeal stages of Grapsus adscensionis (Osbeck) and Planes minutus (Linnaeus) (Brachyura: Grapsidae) described from laboratory hatched material, with notes on larval characters of the Grapsinae

The first zoeal stage of Grapsus adscensionis and Planes minutus is described and illustrated. Comparisons are made with known larvae of congeneric species and previous descriptions of Planes minutus. Larval features of the Grapsinae are evaluated taking into account all previous larval descriptions from this subfamily. The presence of minute knob-like or hooked projections on the carapace of the zoea I, which in subsequent zoeal stages develop into lateral carapace spines is proposed as a typical larval feature for subfamily Grapsinae.