The movement patterns of mangrove fish during tidal cycles are virtually unknown, yet needed to understand fish habitat use. The intertidal migration of the four-eyed fish Anableps anableps L. (Anablepidae, Cyprinodontiformes), a surface-swimming species, was observed along 2 large mangrove-lined creeks in North Brazil. The number, direction and size of the fish crossing fixed line transects were recorded at 5 min intervals using visual surveys during daylight at spring, mid-and neap tide cycles. Migration took place in a surge and was predictably structured and directly related to water level, current speed and direction, and recurred independent of creek and tide. The fish rode the early flood tide upstream towards the creek heads. After the ebb current peak, they returned in a surge along the same pathways. The intertidal distances travelled ranged from 0.7 to > 2 km per tide. Fish density maxima occurred at early flood and late ebb tide, with more fish swimming alone during flood tide and largest group sizes during ebb tides. At neap high tides, fish aggregated in fewer accessible creek heads. When spring tides inundated wider creek areas and made additional creek heads available, maximum fish dispersal occurred. Small fish underwent migrations at shallower water depths than larger fish, thereby optimizing foraging and refuge time. Creek heads were prime feeding grounds, and intertidal creeks were the pathways connecting trophic flows of A. anableps, highlighting that in the management of mangrove ecosystems, complete drainage systems deserve protection. Striking similarities in tidal migrations of resident salt marsh species suggest that equal evolutionary pressures resulted in universal migratory strategies of estuarine resident taxa.
Highlights ► We test why juvenile flatfish use biogenic habitats. ► Flume tank results show that young flatfish can use tube worm reefs as shelter. ► Stomach content of plaice show that juveniles use biogenic habitats to feed. ► Tube worm structures of Lanice conchilega serve as shelter and feeding ground.
In order to determine the concentration and distribution of the phytoplankton biomass in waters of the islands of Old Providence and Santa Catalina, Colombian Caribbean a survey with 47 superficial samples, 12 in the whole water column, was carried out in 2005. Physicochemical parameters varied through the year; temperature fluctuated between 25 and 30 °C, salinity between 28 and 39, and pH between 8.30 and 9.65. Chlorophyll a and phaeopigment a concentrations were low, a characteristic of oligotrophic oceanic areas; chlorophyll a presented an average of 0.198±0.017 μg/L and 0.693±0.149 μg/L for dry and rainy seasons, while the phaeopigment a had a value below 0.01 μg/L in both seasons. It was found that the phytoplanktonic community is young and with an elevated renovation rate.
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