MEPS 293:177-190 (2005)  -  doi:10.3354/meps293177

ABSTRACT: In this paper, we present results of a 4 year investigation of the dynamics of patches of fiddler crab larvae (Uca spp.) in southern Delaware Bay and the nearby coastal ocean. The study addressed 4 research questions: (1) What are the processes that result in the genesis and transport of patches; (2) How large are patches; (3) What is the density of larvae within a typical patch; and (4) How long do patches remain integral? The investigation included characterization of the 2-dimensional distribution of larvae as determined by high-frequency plankton sampling and determination of trajectories of patches using satellite technology. We also conducted numerical model simulations of the early stages of patch formation and compared model outcomes to real world observations. Results of earlier investigations have shown that fiddler crab larvae are released near the time of high tide during nocturnal spring tidal periods. Our results indicate that newly hatched fiddler crab larvae are exported from small tidal rivers in a single, long continuous patch. These patches probably result from synchronized spawning of a large number of females. Along-stream dimensions of the patches at our sampling site were at least 8 to 9 km, and maximum densities of larvae were as high as 3 × 10⁴ m^–3. Only part of each patch exited the river during the first ebb tide following hatching. Numerical simulations showed that the remaining portion exited the river during subsequent ebb tides following hatching. Patches observed in Delaware Bay were no longer constrained by the river banks and consequently spread out in response to dissipative physical processes; maximum densities were ~10³ m^–3. Numerical simulations demonstrated a similar change in shape of patches as they entered the bay. Trajectories of bay patches were strongly influenced by tidal circulation, which resulted in transport of larvae back and forth along the shore of the bay at tidal frequency. Patches of Uca larvae were also observed on the inner shelf near the mouth of the bay. Shelf patches consisted mainly of advanced-stage zoea larvae, with maximum densities up to several hundred m^–3. Megalopae were also observed in patch-like aggregations, both in open bay water and in the river; densities were on the order of 10² m^–3.

KEY WORDS: Uca larvae · Zoeae · Megalopae · Patches · Models