Geographical variation in the genetic diversity and composition of the endangered queen conch Strombus gigas (Mesogastropoda: Strombidae) from Yucatán, México

In Mexico and elsewhere in the Caribbean, the queen conch Strombus gigas is an endangered species. Understanding the genetic connectivity of their populations will support management strategies for long-term conservation of the species. Genetic diversity and population differentiation was assessed from samples collected at Banco Chinchorro and Isla Cozumel in the Mexican Caribbean and at Arrecife Alacranes in the Gulf of Mexico. Samples were obtained from the commercial capture at Banco Chinchorro (n = 50) and Isla Cozumel (n = 40) on March 2004. On November 2004, a non-invasive method for the Arrecife Alacranes sampling was applied, taking the hemolymph of live animals (n = 65) and releasing them to the wild. The mitochondrial DNA variation at two genes (COI and Cyt-b) was analyzed. Genetic diversity at the three locations ranged between 0.55-0.65 in COI and 0.87-0.94 in Cyt-b, showing no bottleneck evidences. A non-significant fixation index (F(ST) = 0.019, p = 0.161) and a Maximum Parsimony Network tree that did not show particular clades associated with any of the geographical locations, suggested a lack of statistically significant genetic differentiation among populations. Nevertheless, the cline patterns observed in both genetic diversity and haplotypic frequencies from Banco Chinchorro through Arrecife Alacranes, and the larger genetic distance between these locations from those between Isla Cozumel, Banco Chinchorro and Arrecife Alacranes, suggest the possibility of a pattern of isolation-by distance. The role of the main current systems over the potential genetic differences in S. gigas populations along the Mexican Caribbean, and the conservation management of S. gigas at these locations as discrete units is discussed.     

Predation by xanthid crabs on early post-settlement gastropods: the role of prey size, prey density, and habitat complexity

Small predators in marine benthic communities create a hazardous environment for newly settled invertebrates, especially for the smallest individuals. To explore the effects of predation on a newly settled gastropod, queen conch (Strombus gigas Linnaeus), by a xanthid crab (Micropanope sp.), prey size, prey density, and habitat complexity were manipulated in five laboratory experiments. All crabs >3.1 mm CW killed all conch <2 mm SL when individual crabs (<14 mm carapace width (CW)) were offered individual conch that were 2–35 days old after metamorphosis (1.2–8.8 mm shell length (SL)). Only 10% of the crabs >5.0 mm CW, however, killed conch that were >5.0 mm SL, suggesting that conch may reach a size refuge from xanthid crabs at 5 mm SL. Furthermore, when given a choice, crabs (4.8 mm CW) preferred smaller conch (2.0 mm SL) to larger (3.7 mm SL), suggesting that 1 week of additional growth in shell length is advantageous to survivorship. Proportional mortality decreased as conch density increased when crabs were offered conch at seven different densities (two to 96 individuals). Crabs proved to be effective predators regardless of the amount of seagrass structure provided in a microcosm experiment, and could consume two conch in 10 s. The high densities of xanthid crabs that occur in the wild, their effectiveness as predators, and their large appetites point to the important role that small predators may potentially play in structuring the population dynamics of their small prey immediately after settlement.     

Modern benthic foraminifera on Banco Chinchorro,Quintana Roo,Mexico

Benthic foraminiferal assemblages may be used as environmental indicators on Banco Chinchorro, an isolated carbonate platform off the eastern coast of the Yucatan Peninsula. Seventy-seven species from 44 genera were identified in 14 surface sediment samples, which were collected along an E–W windward-to-leeward transect across the platform. A total of 15,493 foraminiferal tests (max. 1,200 tests per sample) were investigated and served as the basis of this study. As many taxa range throughout several platform zones, assemblages are better environmental indicators as compared to individual species. Four foraminiferal assemblages were identified using statistical methods including (1) a Homotrema assemblage, which occurs at the windward platform margin, (2) an Archaias-Homotrema assemblage which is found on the leeward margin and on platform interior coral patch reefs, (3) a Quinqueloculininae-Archaias-Rosalina assemblage of the western platform, and (4) an Archaias-Quinqueloculininae assemblage characteristic of the eastern platform interior. Environmental factors which influence variation in foraminiferal distribution and diversity on Banco Chinchorro include exposure to waves and currents and substrate (plant and algal growth). Sediment transport does not play a major role in Banco Chinchorro based on the observation that there are only limited amounts of taxa found outside their typical habitats, and, that mean grain-size and sorting of foraminiferal tests do not exhibit clear patterns. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Distribution, abundance, density and morphometry of Strombus gigas (Mesogasteropoda: Strombidae) in Alacranes reef, Yucatán, México

A population of the conch Strombus gigas was sampled in 109 transects (100 x 10 m each) for an area of 109000 m2 (eight surveys in 1998 and six in 1999) in Yucatan, Mexico; S. gigas was the most abundant conch species (97% of individuals) and ocurred at depths of 0.5-18 m. Mean density was 0.0084 individuals/m2 (Standard deviation SD=0.0138, n=1910). Maximum density (0.015 individuals/m2) was at 0.5-2 m and minimal (0.001 individuals/m2) at 16-18 m. Shell length was 120-290 mm (mena=211.6, SD=26, n=1136). Shell lip thickness, measured only in adults, was 1-28 mm (mean=8.7, SD=7.5, n=1136).     

The ammonitella: a model of formation with the aid of the embryonic shell of archaeogastropods

Recent archaeogastropoda secrete their first conch (primary shell) without producing increments of growth. This conch remains attached to the epithelium responsible for its production until completed. Only afterwards does tissue detach from the edge of the shell and the conch begins to function as a protective exoskeleton. After a potential swimming phase by the veliger larva, the organic primary shell is deformed by mechanical means through muscular tension from the inside and the outside of the conch. It then becomes mineralized by aragonitic crystallites and, thus, functional for the use of a benthic animal. The embryonic conch of ammonites (ammonitella) is devoid of increments of growth. The inner lip (dorsal side) of the aperture became flattened after the evenly rounded primary conch had been secreted. The primary organic shell was mineralized by aragonitic crystallites from within. All these features of the formation of the ammonitella can be interpreted in the light of early shell formation of recent archaeogastropods.     

Microclimate of American crocodile nests in Banco Chinchorro biosphere reserve, Mexico: Effect on incubation length, embryos survival and hatchlings sex

Crocodilians have temperature-dependent sex determination (TSD) in which incubation temperature determines sex of embryo. Global warming is expected to alter hatchling sex ratio, leading to the extinction of small populations. Regional climate influence on crocodile nest microclimate and hatchlings' characteristics is poorly known. Here, microclimate in natural nests of American crocodile (Crocodylus acutus) and its relation with incubation length, hatchling sex and nesting success was studied in Banco Chinchorro Biosphere Reserve (Mexico) from 2007 to 2010. Temperature and relative humidity in different locations within and outside the nests were registered by data loggers. Incident solar radiation above nest was calculated from hemispheric photographs. Incubation length, proportion of hatchling reaching complete development and hatchling sex were determined at hatching. Nest temperatures exhibited a cyclic daily fluctuation due to solar radiation, which is the major heat source for nests. Clutch temperature was relatively stable and its daily amplitude was negatively correlated with clutch depth and size. Rainfall was the major source of clutch temperature decrease. Clutch and metabolic temperatures increased significantly during incubation. A small sample size failed to demonstrate a statistical relationship between length of incubation and mean clutch temperature. Proportion of embryos reaching complete development depended on maximum and minimum clutch temperature, maximum daily amplitude of clutch temperature and maximum decrease in clutch temperature on a period ≤4 day. Results confirmed a Female-Male-Female TSD pattern for C. acutus, with 31 and 32.5 °C as possible pivotal temperatures. Population and hatchling sex ratios were male-biased and fate of crocodiles of Banco Chinchorro could depend on the magnitude of temperature increase in the future.     

Growth and sex maturation of a population of Saccostrea palmula (Mollusca: Bivalvia), Costa Rica

Growth and sexual maturity in Saccostrea palmula were studied between May 1998 and May 1999, in Morales estuary, Punta Morales, Puntarenas, Costa Rica (n = 540 individuals according to sample size equation). The weight-length relationship for the population was Pt = 2.13 x 10(-2) Lt1.6602 and von Bertalanffy growth function was Lt = 68.2 (l- e -0.1577 t). The mean sex ratio was 1.00 male: 0.92 females with sexually mature individuals found throughout the year. Spawning activity was highest between November and January. The mean condition index (IC = PCF/PV x 100) for the population was 121.53 +/- 2.24 and the mean meat yield was 10.32 +/- 1.64%.     

Length frequency and morphometric analysis of the non-indigenous red-rimmed melania (<Emphasis Type="Italic">Melanoides tuberculata</Emphasis>) populations in Slovakia

The red-rimmed melania Melanoides tuberculata (O. F. Müller) has been used in the aquarist trade and biocontrol programs, leading to its emergence outside its native range. Two populations of the red-rimmed melania occur in Slovakia. We investigated the morphometric features of mentioned populations and made a comparison. These two populations differ significantly in investigated features. Mean shell length of red-rimmed melania individuals from the Opatovce nad Nitrou was 14.7 mm, while the mean shell length of specimens from Pie??any was 24.4 mm (p?<?10^?6). Mean shell width, aperture length, and aperture width for specimens from the Opatovce nad Nitrou was 4.4 mm, 4.1 mm, and 2.3 mm, respectively. Mean shell width, aperture length, and aperture width of Pie??any specimens was 7.5 mm (p?<?10^?6), 7.1 mm (p?<?10^?6), and 3.8 mm (p?<?10^?6), respectively. The maximum shell length of specimens from the Opatovce nad Nitrou site was 22–23 mm, while shell length of specimens from Pie??any reached 32–33 mm. Regression analysis of the shell length and shell width, aperture length and aperture width, indicate equivalent relationship of the shell patterns for the two populations. Population structure analysis provided first inside of their population status, identifying a proliferating population at the Opatovce nad Nitrou site, while only adult individuals were observed at the site in Pie??any. The red-rimmed malania is a good candidate for possible biological invasions in thermal waters of temperate zone.     

Shell growth and chamber formation of aquarium-reared Nautilus pompilius (Mollusca, Cephalopoda) by X-ray analysis

Observations on the growth rate of aquarium maintained Nautilus pompilius in different developmental stages, i.e. juveniles (shell length about 8.75 cm), late juveniles (approximately 10 cm), and early adolescent (approximately 13.5 cm), indicate that this species is fully grown at an age of 7.3-8 years. The age calculations are based on two different computations: (1) the measurement of the increase of the shell length per day and (2) the formation of new septa in time intervals of 150+/-5 days, as demonstrated by X-ray analyses. After N. pompilius hatches, its shell grows about 139 mm to reach full growth and approximately 28 septa are formed. With an increase of the shell length of 0.052 mm per day, it takes about 2,673 days (7.3 years) to reach maturity. Provided that the process of chamber formation follows an exponential function, these computations result in approximately 2,925 days (8 years) to reach full maturity. Supposing that N. pompilius may live for several years after onset of maturity like Nautilus belauensis, the total life span for this species may exceed 11-12 years.     

The Micro/Nanostructure Characteristics and the Mechanical Properties of Hemifusus tuba Conch Shell

<正> The mollusk shell mobilizes calcium from environment for skeletal mineralization.This occurs through synthesizing solidsin solution in the presence of organic molecules of specific interior regions of the conch shell.The ultrastructure and microhardnessof the Hemifusus tuba conch shell living in the Huang/Bo sea area are investigated in the paper.It is shown that thecomposition and microstructure of the mollusk shell vary in different positions.The prodissoconch shell consists only of aragonitewith the crossed-lamellar microstructure.While the spiral shell and the body shell of the Hemifusus tuba conch shell arecomposed of one calcite layer and several aragonite layers.The calcite layer consists of cylindrical grains,but the aragonitelayers are crossed-lamellar ultrastructure at three size scales.The minimum structure size (the third-order lamella) is at about20 nm - 80 nm.The margin of shell aperture is only composed of calcite with cylindrical grains.This natural optimization of theshell microstructure is intimately due to the growth of the Organic matrix.At different positions the microhardness of molluscshell is different due to different crystal structures and crystal arrangements.The growth process of shells allows a constantrenewal of the material,thus enabling their functional adaptation to external environments.     

The effects of predation by the mummichog, Fundulus heteroclitus (L.), on the abundance and distribution of the salt marsh snail, Melampus bidentatus (Say)

Enclosure and exclosure experiments were conducted in Canary Creek marsh to examine how predation by a killifish, Fundulus heteroclitus (L.), affects the abundance and size distribution of the salt marsh snail, Melampus bidentatus (Say). Enclosures (7.6 × 19.7 m) were stocked with Fundulus heteroclitus at densities of one-half normal, normal, twice normal, and four times normal density. Fish exclusion pens were also built. In both years of study, the mean density of snails increased significantly in pens where fish were excluded or their density reduced. During the same period in each year, the density of snails in pens containing higher than normal fish density fell by ≈50%.

Fish density also affected the size distribution of snails within pens. In both years, mean shell length of snails in the pen with the highest density of fish was significantly greater, and mean shell length of snails within fish exclusion pens was significantly lower than in all other treatments. Gape size limitation of F. heteroclitus causes selective predation on small snails and apparently is responsible for the difference in mean shell length among treatments.

Density and size distribution measurements of the natural Melampus bidentatus population in Canary Creek marsh were also taken. Larger snails were found to occur in the low marsh zone, whereas smaller snails occurred in the high marsh zone. Since the high marsh area is flooded less often than the low marsh, and the grass types found in the high marsh zone are known to afford protection from fish predation, the distribution of snails in the marsh is consistent with the idea that fish predation is an important factor influencing the distribution of snails in Canary Creek marsh.     

Annual reproductive cycle and growth of the pen shell Atrina maura (Pterioidea: Pinnidae) on sand-bottom culture in the Ensenada Pabellones lagoon system,Gulf of California,Mexico

Abstract

The reproductive cycle and growth of the pen shell, Atrina maura, which was cultured in the Ensenada Pabellones lagoon system, Gulf of California, from March 2008 to March 2009, is described in this article. Histological techniques and the condition index were used to determine its reproductive condition. The sex ratio was 0.57 females:1.72 males within the population studied. There were no differences (χ², p < 0.05) in shell length (SL) between males and females. The mean length of the sampled specimens ranged between 50.99 ± 4.86 mm and 218.16 ± 8.87 mm. The histological results confirmed that A. maura is a gonochoristic organism that presents synchronic development of the gonads. The maturity and spawning phases were observed throughout the study period, with the exception of March and May 2008. The frequency of the gonad development stages obtained per month suggests that this species reproduced two times annually, with one important reproductive period from June to September, a minor reproductive period from November to February, and two resting periods as follows: July to August and January to February 2009.     

Growth patterns of Mytilopsis leucophaeata,an invasive biofouling bivalve in Europe

Abstract

For the first time, growth of Mytilopsis leucophaeata, an important European fouling species, was investigated. By means of growth cages, individual shell growth of three cohorts, with, respectively, initial shell lengths of ≤5 mm, 10 mm and 15 mm, was monitored in the harbour of Antwerp, Belgium, during 2003 – 2004. M. leucophaeata followed an oscillatory growth pattern with a single summer growing period per year (May to August). Growth decreased during wintertime, but never ceased completely. M. leucophaeata has an average growth rate of <3 – 6 mm year^?1. Temperature was found to be the main environmental factor affecting growth. The von Bertalanffy growth function was used to model growth of individuals ≤5 mm, resulting in L_∞ = 16.7 mm and K = 0.56. Based on a combination of growth of all three cohorts, the hypothetical growth of an average individual mussel could be modelled over a 5-year period, resulting in a maximum length >19 mm with a growth rate of 0.41. Its longevity (more than 5 years) and the positive effect of higher water temperatures on growth, combined with its high resistance to chlorination, provides M. leucophaeata with a high potential for severe and long-lasting biofouling     

Gradients of coastal fish farm effluents and their effect on coral reef microbes

Coastal milkfish (Chanos chanos) farming may be a source of organic matter enrichment for coral reefs in Bolinao, Republic of the Philippines. Interactions among microbial communities associated with the water column, corals and milkfish feces can provide insight into the ecosystem's response to enrichment. Samples were collected at sites along a transect that extended from suspended milkfish pens into the coral reef. Water was characterized by steep gradients in the concentrations of dissolved organic carbon (70-160 microM), total dissolved nitrogen (7-40 microM), chlorophyll a (0.25-10 microg l(-1)), particulate matter (106-832 microg l(-1)), bacteria (5 x 10(5)-1 x 10(6) cells ml(-1)) and viruses (1-7 x 10(7) ml(-1)) that correlated with distance from the fish cages. Particle-attached bacteria, which were observed by scanning laser confocal microscopy, increased across the gradient from < 0.1% to 5.6% of total bacteria at the fish pens. Analyses of 16S rRNA genes by denaturing gradient gel electrophoresis and environmental clone libraries revealed distinct microbial communities for each sample type. Coral libraries had the greatest number of phyla represented (range: 6-8) while fish feces contained the lowest number (3). Coral libraries also had the greatest number of 'novel' sequences (defined as < 93% similar to any sequence in the NCBI nt database; 29% compared with 3% and 5% in the feces and seawater libraries respectively). Despite the differences in microbial community composition, some 16S rRNA sequences co-occurred across sample types including Acinetobacter sp. and Ralstonia sp. Such patterns raise the question of whether bacteria might be transported from the fish pens to corals or if microenvironments at the fish pens and on the corals select for the same phylotypes. Understanding the underlying mechanisms of effluent-coral interactions will help predict the ability of coral reef ecosystems to resist and rebound from organic matter enrichment.     

Effects of dietary vitamin K on survival, growth, and tissue concentrations of phylloquinone (PK) and menaquinone-4 (MK-4) for juvenile abalone, Haliotis discus hannai Ino

The experiment was conducted to investigate the effects of dietary vitamin K on survival, growth and tissue vitamin K concentrations of abalone, Haliotis discus hannai. Eight purified diets were formulated to provide a series of graded levels of menadione sodium bisulfite (MSB) (0-320 mgkg(-1) diet). The brown alga, Laminaria japonica, was used as a control diet. Abalone juveniles of similar size (mean weight 1.18+/-0.04 g; mean shell length 18.65+/-0.18 mm) were distributed in a flow-through system using a completely randomized design with nine treatments and three replicate groups per treatment. Animals were hand-fed the appropriate diets once daily at 17:00 for a 120-day period. Survival and carcass composition were not significantly affected by the dietary treatments (P>0.05). Significantly lower growth rate was found in abalone fed diet supplemented with antibiotic (suphaguanidine) than in those fed the other diets, but no significant difference in growth rate related to dietary level of MSB was observed. The concentrations of menaquinone-4 (MK-4) in muscle and viscera increased with increasing dietary MSB up to 10 mgkg(-1). No phylloquinone (PK) was detected in tissues except that the abalone fed the control diet, Laminaria japonica, produced a relatively high level of PK. It seemed to be that the 10-mg MSBkg(-1) diet is sufficient to that allowing the maintenance of 'steady-state' tissue concentration in juvenile abalone. Dietary MSB was converted to MK-4 in abalone. Either MK-4 or PK deposited in the body is derived from food.     

Anthropometric study of male external genitalia of 320 healthy Nigerian adults

Five basic measurements of the male external genitalia were studied in 320 healthy male medical students belonging to the various parts of Nigeria (West Africa). Their ages range from 17 to 23 years. The measurements were as follows: average length of the penis (81.6 +/- 0.94 mm); circumference of the penis (88.3 +/- 0.02 mm); circumference of the scrotum (212.6 +/- 2.48 mm); length of right testis (46.8 +/- 0.54 mm); width of right testis (32.4 +/- 0.37 mm); length of left testis (46.0 +/- 0.53 mm); and width of left testis (31.4 +/- 0.36 mm). The size of the genitalia increases with the increase in age in younger year groups. The adult stages of genitalia development are reached at the age of 21 years in 89.0% of the individuals. The growth of the genitalia is continued with the increasing height and weight, but this growth slows down after attaining a definite height and weight.     

Population structure and growth of the Japanese littleneck clam <Emphasis Type="Italic">Ruditapes philippinarum</Emphasis> in Amursky Bay,Sea of Japan

This paper deals with the size, age, and sex structure of population and growth of the Japanese littleneck clam Ruditapes philippinarum in Amursky Bay (Peter the Great Bay, Sea of Japan). One-year-olds and individuals with a shell length less than 19.8 mm were not found in the population under study. The population consisted mostly of 3-4-year-old clams (72.4%) with a shell length of 35–45 mm (67.8%). The maximum recorded age of R. philippinarum was 7 years, and maximum shell length was 52.7 mm. The male to female ratio was approximately 2: 1. Hermaphroditism (2.1%) and parasitic castration (1.4%) were observed. Linear growth rates of clams were found to increase until the age of three years old (11.6 ± 0.6 mm/year). Mollusks reach a commercial size of over 35 mm in shell length in the fourth year of life. The parameters of the von Bertalanffy equation describing group linear growth were L _∞ = 56.6 mm, k = 0.302 year^?1, and t ₀ = 0.468 year. The relationship between the shell length and the wet body weight is described by the equation W = 0.000253L^2.954.     

Size-related and seasonal patterns of egg collar production in Polinices pulchellus (Gastropoda: Naticidae) Risso 1826

Polinices pulchellus held in the laboratory produced egg collars all year round. Egg collar production was greatest during July and August and only occurred in females >8-10 mm shell length. The largest individuals (14-16 mm shell length) had the highest fecundity and ceased egg-laying in late September, whilst 8-14 mm individuals laid egg collars until November. Small females (4-6 mm) grew rapidly during the warmer, summer months (April to August), became sexually mature and began laying egg collars in mid-September. Both the range of egg collar wet weights and the maximum wet weight of an individual egg collar increased with female size class. Temperature strongly affected the length of time between the laying of egg collars and the hatching of larvae (9-10 days at 19-20 °C and 14-15 days at 13-14 °C). A close relationship was also found between egg collar wet weight and the number of veliger larvae released.     

Relative growth and reproductive cycle of the date mussel Lithophaga lithophaga (Linnaeus, 1758) sampled from the Bizerte Bay (Northern Tunisia)

Relative growth and the reproductive cycle of the date mussel Lithophaga lithophaga were studied from September 2002 to October 2003 in the Bizerte Bay (Northern Tunisia). Relationships between shell length and shell width, shell height as well as volume-related variables (shell dry weight, soft tissues dry weight and total wet weight) showed negative allometries in both sexes except for shell width in males (isometry) and shell height in both sexes (positive allometry). The sex ratio was unbalanced, within the length range of 6–48 mm, 49.43 % of the animals were males, 24.39 % females and 26.17 % sexually undifferentiated; within the length range of 49–92 mm, the respective values were 41.19, 52.7 and 6.1 %. Histological investigations as well as analyses of the condition index and the gonadosomatic index (CI and GSI) revealed the presence of a single reproductive cycle per year. Spawning occurred at the end of August and early September and was associated with a decrease in seawater temperature and salinity. A resting phase occurred in winter, coinciding with the lowest water temperatures. Histological examinations of the gonads of a total of 130 specimens revealed only two cases of hermaphroditism. The present study constitutes a useful baseline for a sustainable management of local wild stocks of L. lithophaga.