Allyn B. Powell¹, Donald E. Hoss¹, MAŁGORZATa Konieczna² and Leonard Ejsymont^2
1Center  for Coastal Fisheries and Habitat Research, 101 Pivers Island Road, Beaufort, North Carolina 28516, USA
²Sea Fisheries Institute, Plankton Sorting and Identification Center, K. Królewicza 4, 71-550 Szczecin, Poland

Key words: Florida Bay ichthyoplankton, changes in ichthyoplankton composition.

Abstract.
This paper summarizes two cooperative research studies between the Plankton Sorting and Identification Center (PSIC) and the Beaufort Laboratory in Florida Bay. Florida Bay is a shallow lagoon located for the most part in Everglades National Park, Florida, USA. The bay is compartmentalized into partially submerged carbonate mud banks, basins, and numerous mangrove islands. During the last two decades, significant changes have occurred in the bay with respect to ichthyofauna composition, seagrass abundance, salinity regimes, algal blooms, and water clarity. Ten larval collecting trips were made between March 1984 and September 1985. Twenty stations were sampled in Florida Bay and adjacent waters with a 61 cm bongo sampler fitted with 333 mm mesh nets. Only 11 stations occurred in Florida Bay and were located primarily along the Florida Keys and western Florida Bay. Four recreational important species were targeted - spotted seatrout (Cynoscion nebulosus, Family Sciaenidae), gray snapper (Lutjanus griseus, Family Lutjanidae), red drum (Sciaenops ocellatus, Family Sciaenidae), and snook (Centropomus undecimalis, Family Centropomidae). Spotted seatrout was the only target species whose larvae were commonly collected. We collected one red drum larvae, no snook larvae, and 15 potential gray snappers, but because of taxonomic problems, we could not identify the larval snappers to species. Spotted seatrout spend their entire life in Florida Bay and spawn mainly in the western Florida Bay. Based on larval collections, which were comprised mainly of preflexion stage larvae, spawning is minimal in late fall and the winter months, peaks during mid-to-late spring and continues during the summer at moderate levels, then declines in winter. One of the most striking patterns observed was the dominance and ubiquitous distribution of gobiid larvae. They ranked first in abundance at 13-, 16-, and 18- out of 20 stations in 1984-1985 during spring, summer and fall, respectively. They were dominant in diverse habitats. In 1994-1995 we conducted a comparative study (1984-1985 vs. 1994-1995) to examine changes in icthyoplankton composition that might have occurred in response to environmental changes in the bay between 1984-1985 and 1994-1995. We sampled ichthyoplankton using the same techniques at six of the same stations visited in 1984-1985. We used the non-parametric Kruskal-Wallis test to compare densities between the two sampling periods. Zooplanktivorus engraulids made up a larger part of the ichthyoplankton in 1994-95, and their densities are underestimated as numerous unidentified clupeiforms were most likely engraulids. The most notable change in engraulid densities was observed in western Florida Bay where seagrass die-off was most pronounced. Dramatic changes in densities of juvenile engraulids, mainly bay anchovy (Anchoa mitchelli), between 1984-85 and 1994-95 in Florida Bay occurred in concordance with the larval occurrences (Thayer et al. 1999). Relative to the other commonly collected taxa, there were no significant differences in densities between the two time periods for larval gobiids, callionymids or clinids.