INTEGRATING AUTOMATED IMAGING AND A NOVEL IDENTIFICATION TECHNIQUE TO ESTIMATE MORTALITY AND IDENTIFY FACTORS THAT INFLUENCE THE VERTICAL DISTRIBUTION OF CRASSOSTREA VIRGINICA LARVAE

Understanding the population dynamics and complete life cycle of bivalves is important for effectively manage them. Most of the literature and research to date has focused on juvenile and adult bivalves, much less is known about larvae. The larval stage of the bivalve life cycle has been difficult to study due to the lack of a rapid automated approach for identifying species. However, a new technique, called ShellBi, has emerged that utilizes color patterns on the larval shell under polarized light to identify bivalve larvae. The objective of this chapter was to review the scientific basis for ShellBi and to apply it to bivalve larvae in Choptank River with the goal of distinguishing C. virginica from seven other species that spawn at the same time. A digital camera and polarized light microscope were used to capture images of the shells of bivalve larvae under standard and cross-polarized light. Images of C. virginica were distinguishable from other species based on these patterns, especially at later stages of development. These images could serve as a visual guide to identify C. virginica collected from the Choptank River and other tributaries with similar species in Chesapeake Bay

Species-specific patterns in bivalve larval supply to a coastal embayment

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2011Larval supply is an important process linking reproductive output to recruitment of benthic marine invertebrates. Few species-specific studies of bivalve larvae have been performed due to the lack of suitable methods for species identification. This thesis focused on applying a method to identify larvae from field samples from Waquoit Bay, MA using shell birefringence patterns. This method was then used to address variability in larval supply for three bivalve species on weekly, tidal, and hourly scales. Sampling weekly for six months during two years showed large variability in larval concentrations on this time scale. Abundances of most species were related to bay temperature, and species distributions among sampling sites were indicative of transport potential and population coherence. Greater growth of larvae in 2009 compared to 2007 was attributed to more wind-induced mixing and better food availability in 2009. Integrative samples over each tidal event for a 14-day period demonstrated that larvae were mostly constrained by water masses. During a period when there were sharp tidal signals in temperature and salinity, larval concentrations were higher in bay water compared to coastal waters on incoming tides. After a storm event, water mass properties were less distinct between tidal events and a semidiurnal signal in larval concentrations was no longer apparent. The timing of periods of high larval concentrations did not always coincide with periods of highest water mass flux reducing net export in some cases. On an hourly scale, the vertical distribution of larvae affected by water column stratification and strength of tidal flow. Strong currents and a fresh upper layer both prevented larvae from concentrating at the surface. There was little evidence of peaks in larval concentrations associated with a given tidal period. Species-specific data can provide new perspectives on larval transport. For the three species studied, Anomia simplex, Guekensia demissa, and Mercenaria mercenaria, different source areas, patterns for growth, and potential for export were observed. Applying species-specific identification methods to future studies of bivalve larval transport has the potential to relate larval abundance to settlement patterns, an important component of larval ecology and shellfish management.Funding for this thesis research was provided by an award to from NOAA Sea Grant to S. Gallager (grant NA06OAR417002), an award to S. Gallager and C. Mingione Thompson from the Estuarine Reserves Division, Office of Ocean and Coastal Resource Management, National Ocean Service, National Oceanic and Atmospheric Administration (grant NA07NOS42000024), the WHOI Academic Programs Office, a WHOI Coastal Ocean Institute student grant, the WHOI Biology Department, and the WHOI Ocean Life Institute

Larval responses to turbulence and temperature in a tidal inlet: Habitat selection by dispersing gastropods?

Author Posting. © Sears Foundation for Marine Research, 2010. This article is posted here by permission of Sears Foundation for Marine Research for personal use, not for redistribution. The definitive version was published in Journal of Marine Research 68 (2010): 153-188, doi:10.1357/002224010793079013.Marine larval dispersal is affected by hydrodynamic transport and larval behavior, but little is known about how behavior affects large-scale patterns of dispersal and recruitment. Intertidal habitats are characterized by strong and variable turbulence relative to shelf and pelagic waters, so larval responses to turbulence may affect both dispersal and habitat selection. This study combined observations and theoretical approaches to model gastropod larval responses to multiple physical variables in a well-mixed tidal inlet. Physical measurements and larvae were collected in July 2004 in Barnstable Harbor, Massachusetts (USA). Physical measurements were incorporated in an advection-diffusion model where larval vertical velocity is a function of turbulence dissipation rate, temperature, and the temperature gradient. Modeled larval distributions were fitted to observed concentration profiles by maximum likelihood to estimate larval behavioral velocity (swimming or sinking) as a function of environmental conditions. These quantitative behavior estimates were used to test hypotheses about behavioral differences among groups and to assess the relative impact of different cues on overall larval behavior. Larvae of five common gastropod species from different coastal habitats reacted most strongly to turbulence but had genus-specific responses to environmental cues. Larvae of a species from tidal inlets (the mud snail Nassarius obsoletus) had near-zero velocities under calmer conditions and sank in strong turbulence. In contrast, larvae from exposed beach habitats (Crepidula spp. and Anachis spp.) sank in weak turbulence and swam up in strong turbulence, with additional responses to temperature and temperature gradient. Larval responses also differed between small and large size classes and between flood and ebb tides. Behavior of mud snail larvae would contribute to retention inside the inlet and near adult habitats, whereas behavior of beach snail larvae would contribute to rapid export from muddy inlets lacking suitable adult habitats.This work was funded by the Woods Hole Oceanographic Institution (WHOI) Coastal Ocean Institute, the WHOI Rinehart Coastal Research Center, the National Science Foundation (NSF OCE- 0326734), NSF and US Office of Naval Research grants to S. Elgar and B. Raubenheimer, and the WHOI Sea Grant (National Oceanic and Atmospheric Administration, Grant No. NA16RG2273, project no. R/O-38-PD). Analyses were completed while HLF was a postdoctoral scholar at Scripps Institution of Oceanography (SIO), supported by the California Current Ecosystem Long-Term Ecological Research program (NSF OCE-0417616) and by SIO funding to P. Franks

Behavioral and Neuroendocrine Correlates of Sex Change in the Gilthead Seabream (Sparus aurata)

Sequential hermaphroditism is the most radical form of environmental sex determination observed in fish: functional adult males or females retain their ability to change sex even as adults. Among the factors that affect sex change in these species, the least understood is the social environment. Here, I studied the influences of social context on sex change in the Gilthead Seabream, Sparus aurata, by using the individual‟s dominance rank as an indicator of social status. To understand the role that the brain might play in sex change, I also studied the two main neuroendocrine factors that serve as the sexually differentiated axes of neural plasticity in most teleost species: AVT and GnRH. To do this, I first developed a set of tools designed to address the challenges associated with observing the behavior of aquacultured species. Using these tools, I provide the first in-depth study of seabream captive behavior, including the results of size-matched and sex-matched paired encounters. I found that females are more aggressive than males, but this difference is influenced by gonadal developmental status. I also showed that small but young males are more aggressive than bigger but older females. I cloned the AVT mRNA in seabream, and validated a quantitative assay to measure total brain AVT levels together with GnRH-1, GnRH-2, and GnRH-3 levels. I found that AVT and GnRH-3 levels rise during the onset of the hypothesized sex-change window, and drop to pre-quiescent levels until spawning, when all of these factors seem to increase their expression levels again. I also show for the first time, that GnRH-2 and dominance rank are strongly correlated in seabream during the spawning season but not during quiescence. GnRH-1 was strongly correlated to rank during quiescence but not during spawning. Finally, neither dominance rank nor size were a good predictor of the outcome of sex change, which seems to contradict what has been documented in sequential hermaphrodite reef fishes. I provide a model that accounts for this apparent contradiction and conclude that the Gilthead seabream remains true to the size-advantage hypothesis of sex allocation theory, if size and dominance are seen as proximate, rather than ultimate, factors

Desarrollo del cultivo integral de la coquina Donax trunculus (Linnaeus, 1758). Ciclo reproductivo, cultivo en criadero y en el medio natural

Donax trunculus (Linnaeus, 1758), denominada comúnmente coquina y cadelucha en Galicia, es una especie de molusco bivalvo de distribución atlántico – mediterránea, cuyos bancos naturales en la actualidad se encuentran en regresión. Se trata de una especie con un elevado interés comercial y supone un recurso económico importante para el sector marisquero de Galicia. El desarrollo del cultivo en criadero de la coquina, como estrategia para la obtención de semilla, con fines de repoblación para aumentar la producción, supone un claro beneficio para el sector. La población de D. trunculus estudiada, presenta un ciclo anual de reproducción con un corto período de reposo y un amplio período de madurez y puesta que va del mes de marzo en adelante, finalizando hacia el mes de julio. Macroscópicamente, a partir del estadío de gametogénesis avanzada o período en el que la gónada aparece ocupada en su mayor parte por tejido folicular, se pueden definir los sexos de la coquina, presentando las hembras la gónada de color violeta y los machos, de color blanco. La marcada estacionalidad a lo largo de la evolución del ciclo gametogénico, determina cambios en la composición bioquímica mayoritaria de los individuos. Los carbohidratos mantienen una relación inversa con el ciclo gametogénico, disminuyen conforme este avanza. A medida que los carbohidratos disminuyen, los lípidos aumentan, mientras que las proteínas mantienen un patrón de evolución estable y no relacionado con el ciclo. El conocimiento de los diferentes estadíos embrionarios y tiempos de transformación, constituye una parte importante en el proceso de optimización del cultivo de este bivalvo. El estudio de la variación en composición bioquímica durante el desarrollo larvario de la coquina así como la determinación de los requerimientos nutricionales y movimiento de reservas energéticas durante esta etapa, contribuyen a la optimización y establecimiento de un protocolo de cultivo en criadero de D. trunculus. Con la optimización y estandarización de cada una de las fases de cultivo en criadero y en el medio natural de la especie, se puede afirmar que existe la posibilidad de obtener semilla de D. trunculus en criadero para su posterior siembra en bancos naturales hasta llegar a su talla comercial