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We monitor larval abundance using automated plankton pumps that allow us to sample the water column at specified intervals for predetermined periods of time. Larvae are fixed in a 10% formalin solution within the pump and then are collected for sorting and identification.

 

Due to their small size and fragility, it has been very difficult for investigators to manipulate individual planktonic organisms or invertebrate larvae in situ. To overcome these challenges I developed the plankton tethering unit (PTU). PTUs allow us to deploy and recovered individual planktonic organisms in the field. Using PTUs we can place plankton in different habitats or during different time periods and measure the relative risk of planktivory. Currently we are using PTUs to assess seasonal variation in planktivory risk and to link predation risk to life history strategy in tunicates. For further information on PTUs, see: Bullard SG, Hay ME (2002) Plankton tethering to assess spatial and temporal patterns of planktivory over a coral reef and seagrass bed. Mar Ecol Prog Ser 225: 17-28.

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Recent work by Ph.D. candidate, John Hamilton, has produced a two-stage coupled model. This model couples hydrodynamic data with a bottom map of larval source populations within seagrass beds to predict the transport and subsequent settlement of larvae near Avery Point in Long Island Sound. This model incorporates both time and space scales relevant to the planktonic larvae in question. View life history information for the following ascidian larval species: Botrylloides, Botryllus, Didemnum, and Diplosoma.

From model prediction over time, ELVIS machines are put at appropriate locations with settlement plates exposed at 4 tidal periods to measure settlement (see predictions vs. measurements below).

View a video clip of LIS tidal cycle model in Shockwave format.

Location of local, reproductively active communities

One of four survey sites is a seagrass bed within the channel between Pine Island and Bushy Point near Avery Point.  Below is a video still of the seagrass bed at this location.

Faster flow in the shallow water on the inland side of the channel in comparison to the lower flow in the deeper water of Long Island Sound leads to the asymmetric pattern seen in the following images of larval transport during 4 tidal periods. These 4 tidal states are the 4 time periods during which the ELVIS machines are programmed to sample.

Predicted settlement estimates versus measured settlement

Information from local tidal cycles and predicted larval motion led to the formation of the following model image of settlement patterns for colonial tunicates:

 

Actual settlement patterns from field experiments utilizing our ELVIS machines are graphed below. Three colonial species (Botrylloides, Diplosoma, and Didemnum) follow the model pattern seen above. The fourth species, Ascidiella, is a solitary tunicate used as a control.


 

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Current work by Stephan Bullard includes a recent crab larvae key (see details below) as well as a work in progress for identification of tunicate and bryozoan larvae and juveniles of Long Island Sound (see photos above).

Larvae of Anomuran and Brachyuran Crabs of North Carolina: A Guide to the Described Larval Stages of Anomuran (Families: Porcellanidae, Albuneidae, and Hippidae) and Brachyuran Crabs of North Carolina, USA (Crustaceana Monographs, 1) by Stephan G. Bullard

A compilation of available descriptions of zoeal (45 species) and megalopal (34 species) stages of anomuran (families: Porcellanidae, Albuneidae, and Hippidae (and brachyuran crabs off the Atlantic coast of NC. Because many of the species have their northernmost or southernmost ranges of their distribution off North Carolina, the information is applicable to a significant portion of the east coast of North America. Line drawings are included. Identification keys, when possible, are based on external features visible with a dissecting microscope.

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