Vertical distribution, sex ratio, size structure and mate encounters of Firoloida desmarestia in the southern Gulf of Mexico were analyzed during 4 seasons (in February, May, August and November). A total of 395 individuals were collected with an opening−closing net at 5 levels of the 105 m upper water column. Results indicated that the species reproduces throughout the year, with a reproductive peak in May and a low reproductive period from August to February. Length measurements indicated that females (as long as 30 mm) are larger than males (18 mm). Estimations of a 'spatial overlap' index showed a high overlap degree between sexes, suggesting that patterns in their vertical distribution are not a reproductive barrier. Sex ratio (F:M) at birth seemed to be 1:1, but during most of the year the adult sex ratio was dominated by females. We propose that larger dimensions and faster swimming speeds of females provide competitive advantages over males in searching for food and avoiding predators. Simulations of mate encounters indicated that values during the low reproductive season were low under turbulent and nonturbulent conditions (< 4.9 males d −1 female −1), but enough to fertilize a high percentage of females. During the high reproductive season, encounters were as high as 17.2 males d −1 female −1 because the high density of adult population and the influence of wind-induced turbulence. We suggest that some biological features of females (seminal receptacle and exocrine gland) compensate for the low encounter rates. A conceptual model for the population dynamics of F. desmarestia is proposed.
We report 37 species of heterobranch sea slugs from the National Park Alacranes reef, located in the Campeche Bank, at the south-eastern Gulf of Mexico, of which 18 species are reported for the first time in this reef. With this contribution, the species richness in this national park increases to up to 67. The speciesNakamigawaia felis, Petaliferasp.,Elysia flava, Elysia pratensisandBulbaeolidiasp. are reported in the Gulf of Mexico for the first time. The geographical distribution ranges forOxynoe azuropunctata, Elysia ornata, Placida kingstoni, Aphelodoris antillensisandTritonia hamnerorumare extended westward. Those forElysia flava, Pleurobranchus areolatusandFelimare ruthaeare extended both northward and westward.
The distribution and abundance of hippoid zoeal stages offshore Veracruz, southern Gulf of Mexico, and the migration routes of these larvae in the western Atlantic, were analysed. Samples were collected with a Bongo net and larval dispersal was analysed applying the HYCOM hydrodynamical model; particles (virtual larvae) originating from 35 sites were tracked for 77 days. Larvae of Albunea paretii Guérin-Méneville, 1853 were the most abundant, and dispersal simulations indicated that older larvae occurring off Veracruz might originate from Texas. However, a substantial proportion of self-recruitment (7.8%) can occur, mainly due to the seasonal changes in direction of currents over the shelf as well as the high variability in weather conditions. Results also suggest that several generations of A. paretii are needed for the species to reach Veracruz from South America. A hypothetical model regarding the migration routes of A. paretii larvae in the western Atlantic is proposed.
This study examines the sexual differences in relative growth and morphometrical traits of the land crabJohngarthia planata(Stimpson, 1860). Individuals came from Clipperton, where an expedition was conducted in April 2015. A total of 275 individuals were captured manually, sexed and measured in seven dimensions from the carapace and chelae. Measurements were fitted to a power function to analyse the degree of allometry in growth. Results indicated that males had larger body and chelae sizes than females. For both sexes growth was negatively allometric for the carapace and positively allometric for the chelae. We hypothesize that stronger bodies in males confer advantages during intraspecific combats and their enlarged chelae are associated to their sexual behaviour. For each sex, measurements of both right and left chelae showed a homochelic condition. We suggest that these symmetrical features provide stability and balance to their body when feeding, fighting or excavating their burrows.
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