Trophic status based on nutrient concentration scales and primary producers community of tropical coastal lagoons influenced by groundwater discharges

Changes in the rate of primary production as an indication of trophic status of aquatic ecosystems have been one of the major indicators of their health. Despite different approaches been devised for evaluating this process, few are useful for comparison and generalization of their results. The coastal zone ecosystems of Yucatan (SE Mexico) exhibit hydrological variability closely associated with the groundwater discharges, which are the only freshwater sources in the coastal ecosystems. In order to learn about the trophic status of karstic tropical coastal lagoons, three of them (Celestun, Chelem and Dzilam) located in Yucatan (SE, Mexico) were monitored for inorganic nutrients, Chl-a, phytoplankton and macrophyte productivity. The nitrate concentrations suggest that the trophic status was influenced by fresh water springs, being meso-eutrophic in Celestun, oligotrophic in Chelem, and mesotrophic in Dzilam. In the case of ammonium ions, the three lagoons were mesotrophic, indicating that processes such as remineralization play an important role in the trophic dynamic of these shallow ecosystems. According to phosphate concentrations, Celestun and Dzilam were mesotrophic, and Chelem was oligotrophic. External inputs of phosphate and bioturbation by waterfowl may be responsible of these differences. Primary productivity at Celestun was greater than at Chelem and Dzilam lagoons and the contribution by seagrasses was significant in all three. It is found that indices based on nutrient concentration and phytoplankton biomass are useful as an indication of trophic status in groundwater influenced coastal lagoons. Moreover, estimations on the total system productivity, and the relative contribution of each primary producer, is a holistic approach useful for understanding trophic dynamic in shallow tropical coastal ecosystems.     

Approaching a functional measure of vulnerability in marine ecosystems

Ecosystem vulnerability is a major concern for management purposes, especially when directed toward conservation and sustainable exploitation. We estimate the relative vulnerability of selected marine-ecosystems in the Gulf of Mexico through simulation experiments based on trophic models. The same perturbation pattern was applied to different functional groups at different trophic levels. Perturbation consisted of increasing biomass extraction for a single group up to 98% at a constant rate over 50 years. The ratio Ascendency to Capacity of Development, A/C, was estimated as a measure of ecosystem order. The maximum negative difference respect to the initial A/C represents the gain of entropy. The slope of the relationship between entropy gained and the trophic level provides an estimate of the relative vulnerability of the ecosystem. This was applied to five ecosystems in the Gulf of Mexico: Florida coral reef; Mexican coastal lagoon, Terminos Lagoon; and three continental shelves, the northern Gulf of Mexico, USA; Yucatan and the Campeche Sound, Mexico. The pattern of vulnerability among ecosystems is related to ecosystem complexity. The coral reef exhibited a lower slope, corresponding to higher vulnerability, which is related to higher connectivity, production efficiency, and net ecosystem production. Increasingly higher slopes, corresponding to lower vulnerability, followed a gradient from the coral reef to the continental shelves to the least vulnerable system, the coastal lagoon. Middle trophic levels contribute to higher vulnerability. This interpretation is supported by the concept of energy flows within trophic networks. The relevance of these findings for management is discussed.     

Microsatellite and mitochondrial DNA analyses of the genetic structure of blacktip shark (Carcharhinus limbatus) nurseries in the northwestern Atlantic, Gulf of Mexico, and Caribbean Sea

Abstract We investigated the genetic structure of blacktip shark (Carcharhinus limbatus) continental nurseries in the northwestern Atlantic Ocean, Gulf of Mexico, and Caribbean Sea using mitochondrial DNA control region sequences and eight nuclear microsatellite loci scored in neonate and young-of-the-year sharks. Significant structure was detected with both markers among nine nurseries (mitochondrial PhiST = 0.350, P < 0.001; nuclear PhiST = 0.007, P < 0.001) and sharks from the northwestern Atlantic, eastern Gulf of Mexico, western Gulf of Mexico, northern Yucatan, and Belize possessed significantly different mitochondrial DNA haplotype frequencies. Microsatellite differentiation was limited to comparisons involving northern Yucatan and Belize sharks with nuclear genetic homogeneity throughout the eastern Gulf of Mexico, western Gulf of Mexico, and northwestern Atlantic. Differences in the magnitude of maternal vs. biparental genetic differentiation support female philopatry to northwestern Atlantic, Gulf of Mexico, and Caribbean Sea natal nursery regions with higher levels of male-mediated gene flow. Philopatry has produced multiple reproductive stocks of this commercially important shark species throughout the range of this study.     

Taxonomy and biogeography of the fiddler crabs (Ocypodidae: Genus Uca) of the Atlantic and Gulf coasts of eastern North America

Fifteen species of fiddler crabs are reported for eastern North America between Massachusetts and Quintana Roo, Mexico. Thirteen occur in the United States and 11 in Mexico, with eight in common to the two countries. Of 13 species in the Gulf of Mexico, five are endemic and a sixth is restricted largely to the peninsulas of Florida and Yucatan. The status of U. rapax in the northern Gulf remains to be resolved. Range limits of most species approximate one or the other of two sets of intersecting thermal and geological boundaries that subdivide the Gulf of Mexico along north-south and east-west axes. Species belonging to subgenus Minuca tend to replace one another at the thermally-controlled Carolinian-Caribbean marine biotic boundary across the Florida peninsula and northern Gulf. However, only U. minax of all the North American fiddler crabs exhibits the classical disjunct Carolinian distribution, and this appears basically to reflect the discontinuous distribution of temperate salt marshes that are the habitat of the species. Distributions of species belonging to subgenus Celuca adhere for the most part to the subdivision of the Gulf into western terrigenous and eastern carbonate sedimentary provinces. The northern transition occurs in the vicinity of Apalachee Bay and the southern at Laguna de Terminos. A third distributional pattern is shown by U. subcylindrica , a specialized endemic species of the hypersaline Laguna Madre system of the western Gulf. The level of endemism in the fiddler crabs is relatively high in comparison with that of other marine groups within the Gulf of Mexico. This may be a consequence of the adaptations of fiddler crabs as specialized deposit feeders to regional differences in climatic and edaphic characteristics of a marginally marine upper shore habitat. The distributional patterns of the endemics could prove useful in reconstructing palaeoecological events of evolutionary significance within the Gulf of Mexico.     

Trophic plasticity in the Atlantic sharpnose shark (Rhizoprionodon terraenovae) from the north central Gulf of Mexico

Quantifying the trophic role of sharks in coastal ecosystems is crucial for the construction of accurate ecosystem models. This is particularly important for wide-ranging species like the Atlantic sharpnose shark (Rhizoprionodon terraenovae), ubiquitous across the northern Gulf of Mexico. We used gut content and stable isotope analyses to determine if differences in abundance of Atlantic sharpnose sharks in the waters around Mobile Bay, Alabama translated into differences in dietary sources or trophic position among sharks sampled east and west relative to the mouth of the bay. Gut content analysis suggested that Atlantic sharpnose sharks eat primarily teleost fishes (%IRI?>?90% across size classes), and both stomach content and stable isotope analyses highlighted an ontogenetic shift in diet. Nitrogen stable isotope data from liver and muscle tissues indicated regional shifts in trophic position for Atlantic sharpnose sharks. The mixing model SIAR (stable isotope analysis in R) v.4.0.2 was used to suggest possible contributions from likely prey items for Atlantic sharpnose sharks sampled east and west of Mobile Bay. Portunid crabs and shrimp made higher contributions to the diet of Atlantic sharpnose sharks in the western region, compared to higher and more variable contributions from fish like croaker (Micropogonias undulatus) and hardhead catfish (Arius felis) in the eastern region. Our results suggest trophic plasticity in Atlantic sharpnose sharks, findings that emphasize the importance of examining regional variation in trophic position when constructing coastal foodweb models.     

Nitrogen isotopes in otoliths reconstruct ancient trophic position

The ratio of ¹⁵N/¹⁴N (δ¹⁵N) from consumer and prey tissue is commonly used in ecological studies to determine trophic level, food web structure, and mean trophic level in aquatic ecosystems. There is a predictable positive relationship between the δ¹⁵N values in tissue and trophic level, caused by the bioaccumulation of ¹⁵N in tissues of consumers with each step up the food chain. Reconstructing trophic structure or food chain length over time may provide resource managers with insights about ecosystem biodiversity and resilience. Yet, in many marine systems the absence of baseline information before anthropogenic disturbances makes comparative studies addressing ecosystem responses extremely difficult. Here we attempt to retrospectively reconstruct trophic position in four species of fish from the upper Gulf of California, Mexico before perturbations such as overfishing or the damming of the Colorado River. We first validated if otolith δ¹⁵N approximates the δ¹⁵N observed in fish tissue. We then used the δ¹⁵N encapsulated in ancient fish otoliths that are between 1,000 and 5,500 years old to define the food web structure. Our results suggested that δ¹⁵N in otoliths has slightly more positive δ¹⁵N than soft tissue. The δ¹⁵N values from ancient otoliths appropriately defined the fishes’ relative trophic position. We found significant differences in δ¹⁵N between functional groups, apex predator versus intermediate predators. Juveniles and adult fishes displayed trophic separation between functional groups. Our findings advocate the application of δ¹⁵N analysis of prehistoric otoliths for establishing pre-disturbance ecological benchmarks.     

线虫作为土壤健康指示生物的方法及应用

简述了线虫作为土壤健康指示生物的优势,归纳了常用指数和分析方法,对成熟指数及基于营养类群的一些指数和分析方法进行了详细介绍.与其他指数相比,成熟指数更能敏感地反映土壤环境的受胁迫程度,基于营养类群的指数和分析方法可以在生态系统功能水平上更好地揭示土壤环境的健康状态.概述了以上指数和方法在农业、森林、草原及其他生态系统中的应用研究.结合目前存在的一些问题,提出以下建议:加强对土壤线虫生活史和食性等特性的认识;进一步完善现有指数,将多种指数和分析方法结合使用;加强土壤线虫在多种生态系统及大尺度地域空间内的应用.     

Feeding biology of the flatfish Citharichthys spilopterus (Bothidae) in a tropical estuary of Mexico

The flatfish Citharichthys spilopterus Günther 1862 is the most common bothid in the coastal lagoons of the Gulf of Mexico. The objective of the present study was to describe the trophic biology of this species in the tropical coastal lagoon of Tampamachoco, Mexico. For the diet analysis, we used multivariate discriminant analysis and trophic niche breadth. The morphological analysis showed that the features of the bucco-pharyngeal cavity, the large stomach and the short intestine of this flatfish relate to a carnivorous habit. The overall diet showed that this species is a third-order consumer, feeding mainly on fish (52%, mainly gobies) and crustaceans (36%, mostly decapods). Diet and trophic niche breadth showed no significant differences between sexes (P > 0.1). By contrast, there were significant ontogenetic differences in the diet and trophic niche breadth, where larger C. spilopterus were almost entirely piscivorous and showed the narrowest trophic niche. As the flatfish grew in size there was a trend toward the consumption of larger prey. The importance of copepods and peracarids correlated inversely with flatfish size (P < 0.001), but fish prey correlated directly to flatfish size (P < 0.001). Likewise, there was an inverse significant correlation between niche trophic breadth and flatfish size (P < 0.005). There were also significant seasonal differences in the diet (P < 0.02), related to the availability and vulnerability of prey in the lagoon during the dry and rainy seasons. However, the trophic niche showed no significant differences between seasons. Finally, we discuss the advantages of discriminant analysis applied to evaluate differences among diets of fish groups when compared with other bivariate and multivariate techniques.     

Concordant Biogeographic Patterns among Multiple Taxonomic Groups in the Mexican Freshwater Biota

In this paper we analyse the degree of concordance in species richness and taxonomic distinctness (diversity) patterns among different freshwater taxonomic groups in order to test three long held patterns described in Mexican freshwater biogeography: 1. The aquatic biota of Mexico includes two distinct faunas, a rich Neotropical component in the south and a south-eastern region and a less rich Nearctic component towards central and northern latitudes of the country. 2. A hotspot of species richness and diversity has been recorded in the Usumacinta, including the Yucatan Peninsula. 3. The presence of two distinct biotas in Mexico, an eastern one distributed along the Gulf of Mexico slope, and a western one associated to the Pacific versant. We use species richness and taxonomic distinctness to explore patterns of diversity and how these patterns change between zoogeographical regions. This paper points out a clear separation between Neotropical and Nearctic drainage basins but also between eastern (Gulf of Mexico) and western (Pacific) drainage basins. Present data gives additional empirical support from freshwater biota for three long held beliefs regarding distributional patterns of the Mexican biota. The neotropical basins of Mexico are generally host to a richest and more diversified fauna, that includes more families, genera and species, compared to the less rich and less diverse fauna in the nearctic basins.     

Serpulids (Polychaeta: Serpulidae) from the Northwestern Caribbean: Hydroides and Serpula

From the study of more than 450 specimens of Hydroides and Serpula, 12 species from the Grand Caribbean Region were identified and characterized. Eight species were collected along the shores of the Yucatan Peninsula and five were found in other localities in the Gulf of Mexico, seven others are from Cuba and comments on type specimens of five species are also included. One morphometric analysis made on Hydroides mucronatus Rioja and Hydroides cf. mucronatus, indicated several differences among them. Comments on all species are also included.     

Biomass diversity and stability of food webs in aquatic ecosystems

The diversity–stability hypothesis in ecology asserts that biodiversity begets stability of ecological systems. This hypothesis has been supported by field studies on primary producers in grasslands, in which the interaction between species is mostly competition. As to ecosystems with multitrophic predatory interaction, however, no definite consensus has been arrived at for the relation between trophic diversity and ecosystem stability. The stability index suitable to ecosystems with predatory interaction is given by MacArthurs idea of stability and its formulation by Rutledge et al. More suitable indices of stability (relative conditional entropy) are proposed in this study for the comparison of different ecosystems, and the validity of the diversity–stability hypothesis for food webs (networks of predation) with many trophic compartments in natural aquatic ecosystems is examined. Results reveal that an increase in the biomass diversity of trophic compartments causes an increase in the whole systemic stability of food webs in aquatic ecosystems. Hence, evidence of the whole systemic validity of the diversity–stability hypothesis for natural aquatic ecosystems with ubiquitous multitrophic predatory interaction was obtained for the first time.     

Stable isotopes differentiate bottlenose dolphins off west-central Florida

Distinguishing discrete population units among continuously distributed coastal small cetaceans is challenging and crucial to conservation. We evaluated the utility of stable isotopes in assessing group membership in bottlenose dolphins (Tursiops truncatus) off west-central Florida by analyzing carbon, nitrogen, and sulfur isotope values (δ¹³C, δ¹⁵N, and δ³⁴S) of tooth collagen from stranded dolphins. Individuals derived from three putative general population units: Sarasota Bay (SB), nearshore Gulf of Mexico (GULF), and offshore waters (OFF). Animals of known history (SB) served to ground truth the approach against animals of unknown history from the Gulf of Mexico (GULF, OFF). Dolphin groups differed significantly for each isotope. Average δ¹³C values from SB dolphins (−10.6‰) utilizing sea grass ecosystems differed from those of GULF (−11.9‰) and OFF (−11.9‰). Average δ¹⁵N values of GULF (12.7‰) and OFF (13.2‰) were higher than those of SB dolphins (11.9‰), consistent with differences in prey trophic levels. δ³⁴S values showed definitive differences among SB (7.1‰), GULF (11.3‰), and OFF (16.5‰) dolphins. This is the first application of isotopes to population assignment of bottlenose dolphins in the Gulf of Mexico and results suggest that isotopes may provide a powerful tool in the conservation of small cetaceans.     

Structural variations of phytoplankton in the coastal seas of Yucatan,Mexico

A study was done of the relationship between hydrographic variables and the composition, abundance, community structure and biomass spectrums of coastal phytoplankton at scales greater than 100 km on the Yucatan Peninsula (SE Gulf of Mexico). This was done during the season of greatest environmental instability in the region, the northwind season (late fall to winter). Samples were collected at stations in the west (Campeche), north (Yucatan), and east (Quintana Roo) zones of the Peninsula. Measurements were taken of temperature, salinity, dissolved oxygen, dissolved inorganic nutrients (ammonia, nitrite, nitrate and phosphate) and chlorophyll a, and samples were taken for phytoplankton analysis. The hydrographic results showed the Campeche zone as having the lowest salinity (<35 psu) values, as well as the highest inorganic nutrient and chlorophyll a values, all of which are related to continental water contributions. The Yucatan zone had the lowest temperatures and the lowest inorganic nutrient values, indicating influence from the Yucatan Current and the Gulf of Mexico. A total of 159 phytoplankton species were identified, dominated by diatoms (>80%) and dinoflagellates. Phytoplankton exhibited greater concentration, richness, equitability and diversity in Campeche, while the lowest community structure values were had in the Quintana Roo zone. The ordination analysis demonstrated that the dominant genera were the diatoms Chaetoceros, Pseudonitzschia and Thalassionema. The biomass spectrums exhibited the lowest slope in environments of higher heterogeneity, with Campeche being the most disturbed and heterogeneous zone and Quintana Roo that with the least heterogeneity.     

Echinoids (Echinodermata: Echinoidea) from the Gulf of Mexico

The echinoid fauna of the Gulf of Mexico collected during three research cruises (20-1260 m depth) was surveyed from samples were taken at 43 stations. A total of 190 individuals were identified (eight orders, 11 families, 15 genera and 18 species). Six species are new records for the Gulf of Mexico: Stylocidaris lineata, Phormosoma placenta placenta, Plesiodiadema antillarum, Plethotaenia spatangoides, Brissopsis atlantica and Hypselaster limicolus. This adds to the little information available on the echinoid fauna of Tamaulipas, Veracruz, Tabasco, Campeche and Yucatan states in Mexico.     

Hermit crabs (Anomura: Paguroidea) distribution patterns in the Colombian Caribbean Sea

Hermit crabs represent the marine life in the Colombian Caribbean, and are important for the dynamic equilibrium maintenance in ecosystems, the ecological interactions and their impact on food web stability. Generally, in order to come up with some conservation strategies, strong bio-geographical information is needed for poll cies definition. With this aim, this study analyzed the distribution patterns of hermit crabs in the Colombian Caribbean Sea. through classification and spatial ordination multivariate analyses, using historical records from years 1916 to 2006. Besides, the world distribution of Colombian species and their geographic affinity in the Caribbean and Western Atlantic were identified. The results show deep differences between coastal and continental slope faunas, and latitudinal differences in the assemblages, with the identification of three groups: Northeast. Center and Southwest. The differences in faunal composition that support these three groups were determined. Based on maps of the Colombian marine ecosystems, it was found that the main factors affecting the distribution of hermit crabs were the Caribaná slope (depth), water-mass temperature, Guajira sea-grass beds, and particular conditions of "Coralline Archipelagos" and "Darién" eco-regions. Colombian hermit crab fauna is more related to the North Atlantic and the Antilles, than to the South Atlantic and the Gulf of Mexico. Additionally, geographical sub-provinces in which Colombia is included, these were found as transition zones among Northern and Austral subprovinces of the Greater Caribbean.     

Energy flow and network analysis of Terminos Lagoon, SW Gulf of Mexico

The food web in Terminos Lagoon, south-western Gulf of Mexico was dominated by the detrital pathway, with benthic invertebrates playing a significant role in transferring energy from detritus to higher trophic levels. The fish yield per unit of net primary production was only 0.04%. Fractional trophic levels ranged from 1.0 to 3.31, with fish occupying the highest trophic levels. Using network analysis, the system network was mapped into a linear food chain and five discrete trophic levels were found with a mean trophic transfer efficiency of 7%. Analysis of mixed trophic impacts showed that fish had very little impact on the other compartments, due to their relatively low biomass and consumption, with exception of the Engraulidae. Detritus and lower trophic levels had significant positive impacts on other groups in the system, suggesting 'bottom-up' control of the food web. A high detritivory: herbivory ratio (4.6: 1) indicated that most of the primary production was recycled through the detritus-based food web. A Finn cycling index of 7% and average path length of 10 were obtained.     

Carrion cycling in food webs: comparisons among terrestrial and marine ecosystems

In light of current global changes to ecosystem function (e.g. climate change, trophic downgrading, and invasive species), there has been a recent surge of interest in exploring differences in nutrient cycling among ecosystem types. In particular, a growing awareness has emerged concerning the importance of scavenging in food web dynamics, although no studies have focused specifically on exploring differences in carrion consumption between aquatic and terrestrial ecosystems. In this forum we synthesize the scavenging literature to elucidate differences in scavenging dynamics between terrestrial and marine ecosystems, and identify areas where future research is needed to more clearly understand the role of carrion consumption in maintaining ecosystem function within each of these environments. Although scavenging plays a similar functional role in terrestrial and aquatic food webs, here we suggest that several fundamental differences exist in scavenging dynamics among these ecosystem types due to the unique selection pressures imposed by the physical properties of water and air. In particular, the movement of carcasses in marine ecosystems (e.g. wave action, upwelling, and sinking) diffuses biological activity associated with scavenging and decomposition across large, three‐dimensional spatial scales, creating a unique spatial disconnect between the processes of production, scavenging, and decomposition, which in contrast are tightly linked in terrestrial ecosystems. Moreover, the limited role of bacteria and temporal stability of environmental conditions on the sea floor appears to have facilitated the evolution of a much more diverse community of macrofauna that relies on carrion for a higher portion of its nutrient consumption than is present in terrestrial ecosystems. Our observations are further discussed as they pertain to the potential impacts of climate change and trophic downgrading (i.e. removal of apex consumers from ecosystems) on scavenging dynamics within marine and terrestrial ecosystems.     

Construction and evaluation of a robust trophic network model for the northern Gulf of Mexico ecosystem

A critical issue in understanding trophic connectivity in ecological systems is the lack in quality and quantity of information about feeding habits. In this work, we present a method for integrating a diversity of feeding habits data from published studies to evaluate the impact on indices that describe characteristics of individual taxa and their connectivity. We focus our study on feeding habits of the fishes of the northern Gulf of Mexico and seek to understand the importance of the forage fish Gulf Menhaden (Brevoortia patronus) in predator diets. We created a database of diet studies from the northern Gulf of Mexico that included six diet metrics: frequency of occurrence, wet weight, dry weight, number, volume, index of relative importance, and index of caloric importance. We then used this information to construct a set of traditional networks (all prey and predators were from a single taxonomic level and trophic connections were parameterized with a single diet metric). We also constructed a “robust” network where all taxa were identified to the lowest taxonomic level and trophic connections were parameterized using a resampling approach that included all available information. Linear regression and resampling methods were used to convert data reported in other diet metrics into the frequency of occurrence diet metric. For both traditional and robust networks, we used network indices to describe topological properties. With the robust network, we conducted removal simulations where the forage fish species Gulf Menhaden, and associated Clupeidae representatives, were removed from the network and the feeding effort of the predators was reallocated among their other prey items. We found that network and node-specific indices were sensitive to the choice of taxonomy and diet metric level. In the robust network, predator species with the greatest number of identified prey had the lowest precision in their connections and prey from the Arthropoda phyla had the lowest precision for connections. From the removal and reallocation simulations, we found that Actinopterygii and Arthropoda were the most impacted prey taxa with 1.2% to 4.3% increase in predation and approximately 23 taxa would receive 50% of the reallocated predation. Overall, the resampling methods we present provide a potential means for combining disparate diet data and enables a comprehensive understanding of trophic interactions within an ecosystem.     

Richness and endemism of helminth parasites of freshwater fishes in Mexico

Distribution records of 152 adult helminth taxa parasites of freshwater fishes in Mexico were analysed to determine areas of high richness and endemism. Distribution maps were prepared for each taxon and overlaid onto a map of Mexico divided into 1 × 1 degree grid-cells. Richness was determined by counting recorded helminth species in each grid-cell. A corrected weighted endemism index was calculated for each grid-cell, and the relationship between richness and endemicity was analysed with an Olmstead–Tukey corner test of association. Five areas of high richness and endemism were identified: (1) Los Tuxtlas and the Papaloapan river basin, on the Gulf of Mexico; (2) the Grijalva-Usumacinta basin near the Gulf of Mexico coastal plain; (3) the Yucatan Peninsula; (4) the Sierra de Manantlán Biosphere Reserve in western Mexico; and (5) the Pátzcuaro lake, in central Mexico. The distribution of richness and endemism of helminth parasites of freshwater fishes in Mexico is congruent with distributional patterns described for other freshwater taxa in Mexico. Patterns of richness and/or endemism in the studied areas can be explained by the ichthyological composition of their bodies of water. The present study establishes an objective way of analysing the relationship between richness and endemicity, and suggests that helminths can make valuable contributions to regionalization of geographical areas and for identification of rich and biologically complex areas with potential for conservation of aquatic systems.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 435–444.     

Genetic differences within and between species of deep-sea crabs (chaceon) from the North Atlantic Ocean

The deep-sea red crab Chaceon quinquedens is a commercially important crustacean on the Atlantic continental shelf and slope of North America. To assess genetic subdivision in C. quinquedens, we examined the nucleotide sequence of the mitochondrial 16S rDNA gene and the internal transcribed spacers (ITS) of the nuclear ribosomal repeat in samples from southern New England and the Gulf of Mexico. We compared those data to sequences from two congeners, a sympatric species from the Florida coast, C. fenneri, and an allopatric eastern Atlantic species, C. affinis. The 16S rDNA data consisted of 379 aligned nucleotides obtained from 37 individuals. The greatest genetic difference among geographical groups or nominal species was between C. quinquedens from southern New England and C. quinquedens from the Gulf of Mexico. Haplotypes from these two groups had a minimum of 10 differences. All 11 C. fenneri samples matched the most common haplotype found in C. quinquedens from the Gulf of Mexico, and this haplotype was not detected in C. quinquedens from southern New England. The three haplotypes of C. affinis were unique to that recognized species, but those haplotypes differed only slightly from those of C. fenneri and C. quinquedens from the Gulf of Mexico. Based on 16S rDNA and ITS data, genetic differences between C. quinquedens from southern New England and the Gulf of Mexico are large enough to conclude that these are different fishery stocks. Our results also indicate that the designation of morphological species within the commercially important genus Chaceon is not congruent with evolutionary history. The genetic similarity of C. affinis from the eastern Atlantic and C. quinquedens from the Gulf of Mexico suggests these trans-Atlantic taxa share a more recent common history than the two populations of "C. quinquedens" that we examined.