Thierry Brulé

Effects of temperature, algal food, feeding rate and density on the larval growth of the milk conch (Strombus costatus) in Mexico

Abstract Effects of temperature, algal food, feeding rate and larval density on the development and shell growth stage of conch veligers, Strombus costatus , were studied over a period of 30 days in laboratory cultures. Experiments were conducted at 24°C, 28°C, 32°C and 28 ± 2°C. After hatching, the veligers developed to metamorphosis within 26 days at 28°C, 28 days at 28 ± 2°C and 35 days at 24°C. Rearing was not successful at 32°C. Conch larvae were fed with the algae Isochrysis aff. galbana (Tahiti), Tetraselmis chuii and Isochrysis/Tetraselmis mix. The best rate of growth per day was 39.69 μm in Isochrysis/Tetraselmis mixed food. Experiments were conducted at 500, 1000, 2000, 3000, 4000, 5000 and 6000 Isochrysis aff. galbana cells larva −1 day −1 . The veligers showed an optimal growth at 3000 cells larva −1 day −1 . The conch veligers were reared at five larval densities: 100, 200, 300, 400, and 500 larvae/l, and showed an optimal growth at 100 larvae/l, while poorest growth was observed at 500 larvae/l.

Observations on ingestion and digestion of unicellular algae by Strombus gigas larvae (Mollusca, Gastropoda) using epifluorescence microscopy

Abstract Epifluorescence microscopy was used to observe the ingestion and digestion of unicellular algae in gastropod larvae. Larvae started feeding 8 h after hatching. Three kinds of diet were tested during the period of this study: Isochrysis aff. galbana, Tetraselmis chuii and Isochrysis-Tetraselmis mixture. All the experiments were conducted at 29°C. It was shown that ingestion was faster with Tetraselmis than with Isochrysis. Within 10 min 43% of the larvae had ingested Tetraselmis and no larvae had ingested any Isochrysis. Within 30 min, 60% of the larvae had ingested Tetraselmis while only 25% had ingested Isochrysis. Using a scale based on the quality of fluorescence, it was possible to determine the time interval to digest a diet, which is shorter with Tetraselmis than with Isochrysis. After 8 h the digestion index reached 45% for larvae fed with Tetraselmis while it was only 28% for larvae fed with Isochrysis. Using a quantitative scale based on measurements of the fluorescent surface in each larva, it was demonstrated that the amount of diet ingested is higher with Tetraselmis than with Isochrysis. These results indicate that Tetraselmis chuii forms an adequate diet for young veligers of Strombus gigas.

Ingestion and digestion of eight algae by Strombus gigas larvae (Mollusca, Gastropoda) studied by epifluorescence microscopy

Abstract Epifluorescence microscopy was used to observe the ingestion and digestion processes of eight algae diets in 18-day-old Strombus gigas larvae. The eight diets used were: Isochrysis aff. galbana, Tetraselmis chuii, Tetraselmis suecica, Dunaliella tertiolecta, Chlamydomonas coccoides, Thalassiosira fluviatilis, Chlorella sp. and Chaetoceros sp. Observations were made at 0.5, 1, 2, 3, 4, 5, 6, 7, 8 and 24 h after feeding. Ingestion index was faster with T. chuii, Chaetoceros sp. and Chlorella sp. than with I. aff. galbana, D. tertiolecta, C. coccoides, T. fluviatilis and T. suecica . Digestion began at the second hour, being faster with Chaetoceros sp. and Chlorella sp. and slower with D. tertiolecta and T. fluviatilis . Values of ingestion and digestion indices were specific for each alga. This research was performed to provide helpful information in selecting the best diet for each larval stage, according to culture conditions.

Occurrence of Apicomplexa-like structures in the digestive gland of Strombus gigas throughout the Caribbean.

The queen conch, Strombus gigas, is a marine resource of ecological and economical importance in the Caribbean region. Given its importance in this region, and the critical status of most populations, the reproductive biology of this species has been studied to support management decisions. It was from these studies that a generalized sporozoan infection was detected. This study describes the geographic distribution of a coccidian (Apicomplexa) parasite infecting the digestive gland of S. gigas throughout the Caribbean. The parasite was present in every location sampled. Based on histological analysis, the parasites from all locations are similar and appear to complete their life cycle within the digestive gland. The highest occurrence of the parasites was registered in samples from Puerto Rico (54 parasites per field) and Martinique (45 parasites per field). The lowest incidence was registered on the Mexican coast of Yucatan peninsula, at Alacranes and Chinchorro with 17 parasites per field. Data showed significant differences among sites (Kruskal Wallis H=106.957; p ≤ 0.05). The abundance of parasites found in the digestive ducts and in the faeces suggests the liberation of parasites to the environment. A gradual decrease in abundance was found from East to West of the Caribbean sea.

Nutritional potentialities of Chlamydomonas coccoides and Thalassiosira fluviatilis, as measured by their ingestion and digestion rates by the Queen Conch larvae (Strombus gigas)

Abstract Epifluorescence microscopy and ingestion and digestion indices were used to study the nutritional potentialities of two algae cells, Chlamydomonas coccoides and Thalassiosira fluviatilis , as a function of their ingestibility and digestibility by the Queen conch ( Strombus gigas ) larvae. The ingestibility and digestibility of both algae, which have been seldom used in conch hatcheries, were evaluated at four larval ages: 1, 10, 18 and 30 days after hatching. Veligers were reared at 100 larvae 1 −1 and the temperature was kept at 28 ± 1 °C. Ingestion and digestion rates were observed continuously for 8 h in 1920 larvae. The ingestion rate for those larvae fed T. fluviatilis were lower than the ingestion rate for those fed C. coccoides . It was also observed that larvae digested C. coccoides better than T. fluviatilis . Ingestion and digestion kinetics, as well as stomach filling of S. gigas larvae showed that the feeding behaviour of young larvae and those close to metamorphosis differed considerably. The ingestion and digestion levels indicate that C. coccoides is a food source recommended for S. gigas larvae.

From Shelf to Shelf: Assessing Historical and Contemporary Genetic Differentiation and Connectivity across the Gulf of Mexico in Gag, Mycteroperca microlepis

Describing patterns of connectivity among populations of species with widespread distributions is particularly important in understanding the ecology and evolution of marine species. In this study, we examined patterns of population differentiation, migration, and historical population dynamics using microsatellite and mitochondrial loci to test whether populations of the epinephelid fish, Gag, Mycteroperca microlepis, an important fishery species, are genetically connected across the Gulf of Mexico and if so, whether that connectivity is attributable to either contemporary or historical processes. Populations of Gag on the Campeche Bank and the West Florida Shelf show significant, but low magnitude, differentiation. Time since divergence/expansion estimates associated with historical population dynamics indicate that any population or spatial expansions indicated by population genetics would have likely occurred in the late Pleistocene. Using coalescent-based approaches, we find that the best model for explaining observed spatial patterns of contemporary genetic variation is one of asymmetric gene flow, with movement from Campeche Bank to the West Florida Shelf. Both estimated migration rates and ecological data support the hypothesis that Gag populations throughout the Gulf of Mexico are connected via present day larval dispersal. Demonstrating this greatly expanded scale of connectivity for Gag highlights the influence of “ghost” populations (sensu Beerli) on genetic patterns and presents a critical consideration for both fisheries management and conservation of this and other species with similar genetic patterns.

REPRODUCTIVE STRATEGIES OF THE EASTERN OYSTER CRASSOSTREA VIRGINICA (GMELIN 1791) IN TROPICAL LAGOONS OF THE MEXICAN GULF OF MEXICO

ABSTRACT The oyster fishery is 1 of the most important coastal fisheries in Mexico. Management is based on a minimum legal size of 80 mm and several seasonal bans that vary along the coast of the Gulf of Mexico. We describe the gonad development cycle of Crassostrea virginica (Gmelin 1791) along the Mexican coast of the Gulf of Mexico for 5 lagoons for the years 2000 and 2004, between latitudes 21°41′16.75″ N and 18°23′51.08″ N. Significant differences in duration and intensity were observed among reproductive stages associated with different environmental conditions. Gametogenesis and mature stages correlated positively with temperature and total chlorophyll, respectively. Spawning correlated negatively with salinity in both years. Maturity correlated positively with total chlorophyll levels. The reproductive stages varied from seasonal, a few months, to continuous throughout the year. Recovery, expressed as the number of organisms in postspawning and resting stages, was fast for populations that presented constant gametogenesis and spawning, with less than 50% of the population in postspawning and resting stages. Environmental fluctuations in total chlorophyll are the regulating factors for gametogenic activity, rather than latitudinal temperature variations. This makes monitoring environmental conditions in the lagoons or gonad development a necessity to predict reproduction and recruitment for proper management of the oyster resource.

Effects of photoperiod on development, growth and survival of larvae of the fighting conch Strombus pugilis in the laboratory

Abstract Fighting conch, Strombus pugilis , larvae were reared from hatching to settlement under three photoperiods, with light phases of 0 light (0 L), 12 light (12 L) and 24 light (24 L) per day to test their effect on development, growth and survival. Proboscis appeared at 21 days in different percentages for three photoperiods: 30% for larvae under 0 L, 50% for larvae under 12 L and 54% for larvae under 24 L. For the three photoperiods the veligers were competent for metamorphosis between 27 to 31 days. Under 0 L conditions frequency of metamorphosis was lower. The settlement period was similar in 24 L and 12 L conditions, but the duration was significantly longer below 0 L conditions. Continuous light had a negative effect on survival, while continuous darkness was advantageous. The percentage of survival at settlement was significantly lower under 24 L (13%) and 12 L (22%) conditions, while 0 L was 44%. Larval growth averaged 22.56, 23.36 and 29.60 μm dia. −1 below 0 L, 12 L and 24 L conditions, respectively. The siphonal length at settlement was longer for larvae under 24 L than that below 0 L and 12 L conditions.