Migration between the Hudson and New York Bight

I begin this section by documenting differential transport between the Hudson River Estuary and NewYork Bight. Then, I present evidence that these transport patterns are maintained behaviorally. I discuss how larvae are (1) retained in the upper estuary, (2) exchanged between the estuary and shelf, and (3) transported on the continental shelf. Lastly, I suggest that larval migrations to the continental shelf are as reliable as migrations that are completed within the estuary.

larval migrations

Fivelarvalmigrationpatternswere documentedfor eighteen taxa: (1) larval retention in the Hudson River estuary by five taxa of invertebrates and two taxa of fishes, (2) retention in the estuarine plume by one taxon of crab, (3) larval migration from the estuary beyond the estuarine plume by three taxa of crabs, (4) larval migration from New York Bight into the estuary by one taxon of fish, and (5) larval retention on the shelf by one taxon of crab and five taxa of fishes (Fig. 12.2). Lastly, the larvae ofthe one taxon of crab and five taxa of fishes that live on the continental shelf largely remained there throughout development. A substantial body of work suggests that the same species-specific larval migration patterns occur along the Atlantic coast of the United States (Epifanio and Garvine, 2001).

Figure 12.2. Larval migration patterns documented for the Hudson River Estuary and New York Bight. 1) Estuarine retention: eggs or larvae of two gastropods (periwinkle Littorina littorea, slipper shell Crepidula fornicata), one barnacle (Balanus improvisus), two mud crabs (Rhithropanopeus harrisii, Dyspanopeus sayi), spider crabs (Libinia spp.) and two fishes (bay anchovy Anchoa mitchilli, naked goby Gobiosoma bosc) were released in the estuary and larvae primarily remained there through development. 2) Estuarine-shelf migration: larvae of three crab taxa (lady crab Ovalipes ocellatus, fiddler crabs Uca spp., blue crab Callinectes sapidus) were released in the estuary, emigrated to the shelf and returned to the estuary as postlarvae. 3) Shelf-estuarine migration: bluefish (Pomatomus saltatrix) spawned on the shelf, larvae immigrated to the estuary and returned to the shelf as juveniles. 4) Shelf retention: larvae of rock crabs Cancer spp. and eggs of five fish taxa (Gulf Stream flounder Citharichthys arctifrons, fourspot flounder Hippoglossina oblonga, smallmouth flounder Etropus microstomus, Atlantic butterfish Peprilus triacanthus, searobins Prionotus spp.) were released on the shelf, and larvae mostly remained there through development.

Figure 12.2. Larval migration patterns documented for the Hudson River Estuary and New York Bight. 1) Estuarine retention: eggs or larvae of two gastropods (periwinkle Littorina littorea, slipper shell Crepidula fornicata), one barnacle (Balanus improvisus), two mud crabs (Rhithropanopeus harrisii, Dyspanopeus sayi), spider crabs (Libinia spp.) and two fishes (bay anchovy Anchoa mitchilli, naked goby Gobiosoma bosc) were released in the estuary and larvae primarily remained there through development. 2) Estuarine-shelf migration: larvae of three crab taxa (lady crab Ovalipes ocellatus, fiddler crabs Uca spp., blue crab Callinectes sapidus) were released in the estuary, emigrated to the shelf and returned to the estuary as postlarvae. 3) Shelf-estuarine migration: bluefish (Pomatomus saltatrix) spawned on the shelf, larvae immigrated to the estuary and returned to the shelf as juveniles. 4) Shelf retention: larvae of rock crabs Cancer spp. and eggs of five fish taxa (Gulf Stream flounder Citharichthys arctifrons, fourspot flounder Hippoglossina oblonga, smallmouth flounder Etropus microstomus, Atlantic butterfish Peprilus triacanthus, searobins Prionotus spp.) were released on the shelf, and larvae mostly remained there through development.

An initial picture of differential larval migration emerged over the last quarter century by piecing together results of previous studies, which typically focused on only one species, larval habitat, or development stage. One of the strengths of the present study is that alllarval stages of the dominant species of crabs and fishes were surveyed across the full range of larval habitats to definitively document inshore-offshore shifts in larval assemblages and stages of development. This comprehensive approach has yielded a more complete picture of the range of larval transport patterns than the simpler classification of retention and export (Strathmann, 1982). Itis nowclear that the dichotomy ofretention and export really represents a continuum of larval migration by crab species, ranging from short migrations within different regions of the estuary to longer migrations between the lower estuary and different regions of the continental shelf (Fig. 12.3). This results in horizontal zonation of species in the plankton between the upper estuary and the edge of the continental shelf. Larval migration by fishes also results in a predictable spatial gradient with larvae either largely remaining in the estuary, remaining on the shelf or migrating from the shelf to the estuary. Thus, larvae ofsome species remain near parents either in the estuary or on the continental shelf, while others migrate between these environments. How was this differential transport accomplished?

behavioral regulation of larval migrations

Behavior must have beenimportant because larvae migrated in opposite directions at the same time, i.e., different species move in opposite directions

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