Victor S. Kennedy

LESSONS LEARNED FROM EFFORTS TO RESTORE OYSTER POPULATIONS IN MARYLAND AND VIRGINIA, 1990 TO 2007

ABSTRACT A century-long decline of the fishery for the Eastern oyster Crassostrea virginica (Gmelin, 1791) in Maryland and Virginia stimulated numerous efforts by federal, state, and nongovernmental agencies to restore oyster populations, with limited success. To learn from recent efforts, we analyzed records of restoration and monitoring activities undertaken between 1990 and 2007 by 12 such agencies. Of the 1,037 oyster bars (reefs, beds, or grounds) for which we obtained data, 43% experienced both restoration and monitoring, with the remaining experiencing either restoration or monitoring only. Restoration activities involved adding substrate (shell), transplanting hatchery or wild seed (juvenile oysters), bar cleaning, and bagless dredging. Of these, substrate addition and transplanting seed were common actions, with bar cleaning and bagless dredging relatively uncommon. Limited monitoring efforts, a lack of replicated postrestoration sampling, and the effects of harvest on some restored bars hinders evaluations of the effectiveness of restoration activities. Future restoration activities should have clearly articulated objectives and be coordinated among agencies and across bars, which should also be off limits to fishing. To evaluate restoration efforts, experimental designs should include replication, quantitative sampling, and robust sample sizes, supplemented by pre- and postrestoration monitoring.

The invasive dark falsemussel Mytilopsis leucophaeata (Bivalvia: Dreissenidae): a literature review

This paper reviews literature from the Americas and Europe on the dark falsemussel Mytilopsis leucophaeata (Conrad in J Acad Nat Sci Phila 6(2):256–268, 1831), including data collected in its native habitat in the Americas that appear as incidental information in published reports. Mytilopsis leucophaeata is a poorly studied dreissenid bivalve that is native to mainly oligohaline–mesohaline regions of estuaries in North America. In its native habitat, it usually occurs in very low numbers and has rarely been mentioned in field survey reports. However, occasionally in its native habitat and often in habitats where it has been introduced (as in Europe and Brazil), it may undergo population irruptions for no clear reason. This review describes habitat characteristics, environmental tolerances, and biological and ecological attributes of the species. The assembled information reveals the species to be euryhaline and eurythermal, with an unexplained ability to persist in its native estuaries even though it is relatively short-lived and usually uncommon.

Scanning Electron Microscopic Aids for Identification of Larval and Post-Larval Bivalves

ABSTRACT The identification of bivalve larvae and early postlarvae in plankton and benthic samples has long been a challenge, hampering both basic and applied research efforts in marine, estuarine, and freshwater environments. The usefulness of published optical micrographs of the early life-history stages of bivalves is limited because of the great morphological similarity of the imaged articulated shells, particularly at the early (straight-hinge) developmental stages. While a number of techniques have been refined in recent years and show promise for use in routine identifications of larval and post-larval bivalves (e.g., single-step nested multiplex polymerase chain reaction; in situ hybridization protocols through color coding with taxon-specific, dye-labeled DNA probes; coupled fluorescence in situ hybridization and cell sorting; and image analysis techniques using species-specific shell birefringence patterns under polarized light), no adequate comprehensive reference source exists that accurately depicts the morphology and morphometry of the shells of larval and post-larval stages of target bivalve species in a consistent format to assist in identification of such stages. To this end, scanning electron micrograph (SEM) sequences are presented of the disarticulated shell valves of laboratory-reared larval and post-larval stages of 56 species of bivalve molluscs from a wide spectrum of marine, estuarine, and freshwater habitats. Emphasis is placed on the usefulness of the morphology and morphometrics of consistently-oriented, disarticulated shell valves and associated hinge structures in discriminating the early life-history stages of these various bivalve species. Although the scanning electron micrograph sequences presented accurately depict the gross morphologies/ morphometrics and hinge structures of the disarticulated shell valves of the larvae and/or postlarvae of the 56 species of bivalves, it is important to emphasize that a scanning electron microscope is not necessary to observe even fine hinge structures associated with the early ontogenetic stages of these species. Such structures are readily visible using a wide range of optical compound microscopes equipped with high-intensity reflected light sources, although the disarticulated shell valves must be viewed in several planes of focus to discern the often subtle details seen clearly in the scanning electron micrographs. These morphological characters provide researchers with invaluable aids for the routine identification of the early life-history stages of these species isolated from plankton and benthic samples.

Optical Imaging and Molecular Sequencing of a Preserved Collection of Bivalve Larvae

ABSTRACT From the 1980s through 1995, scientists at numerous marine, coastal, estuarine, and freshwater laboratories spawned bivalves to provide larvae for use in identifying species based on larval hinge structures and gross shell morphometry. These larvae were preserved in 95% ethanol and stored in sample vials, many of which dried out over the years. Advantage was taken of 50 of 56 species from this collection (and two additional species that were not in the collection for a total of 52 species) to explore the use of optical techniques (polarized light and a full-wave compensation plate) to highlight birefringence patterns of larval shells to discriminate individual species. Representative images of various developmental stages of 77% (40/52) of the larval bivalve species in the collection were successfully imaged. Similarities across birefringence patterns were observed at the taxonomic ordinal and familial level. Molecular polymerase chain reaction techniques were used in an effort to sequence many of the dried-out specimens and they successfully identified 19% (10/52) of the larval bivalve species with matches in GenBank. Here it has been demonstrated that optical techniques are efficient for imaging dried-out larval bivalve shells for classification purposes and we present successful sequences of 10 species of bivalve larvae from the preserved collection.

Identification of Eastern Oyster Crassostrea virginica Larvae Using Polarized Light Microscopy in a Mesohaline Region of Chesapeake Bay

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

Technological Constraints During the First 40 Years of Eastern Oyster Crassostrea virginica Aquaculture

This article focuses on early efforts to culture eastern oyster larvae to settlement. Initial experiments were performed in 1878 and 1879 by Brooks, the first researcher to produce fertilized eggs. The subsequent challenge was to rear the microscopic larvae to settlement by feeding them and changing their culture water without losing them. Researchers like Ryder struggled with these problems, devising a number of filters and water circulation schemes, none of which were practical. Ryder eventually abandoned laboratory work and invented extensive and imaginative, but commercially unsuccessful, field trials to cultivate larvae in ponds and sluiceways. Subsequently, the Nelsons in New Jersey in the early 1900s tried similar experiments, ultimately focusing on understanding larval biology in nature and on predicting when naturally spawned larvae would settle so that settlement surfaces could be provided expeditiously. A breakthrough came in 1920 when Wells used a centrifuge to separate oyster larvae from old culture water, transferring the concentrated larval mass to new culture water. Wells then developed a system of culture vessels that enabled millions of competent larvae to be reared to settlement. Subsequently, researchers were able to study issues that enhanced the industrial culture of larvae of many bivalves, not just oysters.