Mangrove habitats as nurseries to juvenile shrimps (Penalidae) in Guimaras, Philippines.

Penaeids were sampled from seven coastal habitats in Guimaras, Philippines over a one-yr period using a variety of gears (including pocket seine, barrier net and box trap). A total of 8993 shrimps belonging to 5 genera and 13 species were collected from an island mangrove; tidal flat; riverine mangrove mudbank, mangrove forest, and midriver; and deep offshore waters near the island and the river mouth. Among the 8 offshore species, Metapenaeopsis palmensis, Parapenaeopsis cornuta and Trachypenaeus longipes were confined to this habitat. Juveniles of the dominant intertidal species Metapenaeus anchestus and M. ensis were restricted to the high-salinity island and the brackishwater river, respectively but adults were present in the adjacent offshore waters, indicating different salinity tolerance. Juvenile M. ensis, M. elegans, Penaeus merguiensis, and P. indicus may be classified as estuarine, and juvenile M. anchestus, P. latisulcatus and P. semisulcatus as marine. Juveniles of M. moyebi, M. philippinensis and P. monodon were found in both the island and river. Peaks of juvenile recruitment to the mangrove habitats in May and Nov coincided with moderate salinity (approximately 20 ppt) and high water temperatures (30-31 deg C). Evidence for a strong nursery function of the riverine mangrove, compared to the island mangrove, includes greater abundance, smaller juvenile sizes, lack of modal size progression, and absence of maturing females in the dominant riverine species M. ensis and P. merguiensis. Among 7 penaeids found in the riverine sites, only P. monodon and P. merguiensis entered the mangrove forest in substantial numbers, suggesting a dependence on mangrove vegetation. Activity patterns of juvenile M. anchestus, M. philippinensis, P. monodon and P. merguiensis exhibited a strong diel periodicity--burying during the day, and emergence at right to swim, feed, and attach to shelters. Burying was greater among Metapenaeus than Penaeus juveniles. Shelter used was observed only in P. monodon and P. merguiensis, consistent with field observations that these species use mangrove vegetation. Regulation of fish predation on shrimps was evaluated in terms of habitat structures and sediment. Snapper Lutjanus argentimaculatus predation on the shelter-using P. merguiensis and P. monodon was significantly greater on bare sediment than among mangrove pneumatophores and leaf bracts, and decreased with increasing density of pneumatophores. Predation on the burying M. ensis by snapper was also higher or a pebble substrate than on sand. In contrast, structures and sediment size had no effect on shrimp predation by the sea bass Lates calcarife.