Epibenthic amphipod abundance and predation efficiency of the pink shrimp Farfantepenaeus duorarum (Burkenroad, 1939) in habitats with different physical complexity in a tropical estuarine system

Amphipod abundance and biomass were determined in soft-bottom substrates (S BS), monospecific Thalassia testudinum patches and T. testudinum with attac hed macroalgae (SAV) from Terminos Lagoon. Amphipods were absent in SBS, an d their density and biomass were higher in SAV (3351 individuals m(-2), 171 8 mg AFDW m(-2)) than in T. testudinum (1220 ind m(-2), 625 mg AFDW m(-2)). Although macroalgae and seagrasses are recognised as an alternative refuge against predation for amphipods, the high abundance of amphipods in SAV su ggests that macroalgae represent a habitat that provides greater food avail ability. Pink shrimp Farfantepenaeus duorarum (Burkenroad, 1939) consumptio n rate (Mo) of epibenthic amphipods was experimentally evaluated. Mo intens ifies as prey density increases and varied from 0.39 to 2.39 mg AFDW h(-1) Predation efficiency of F. duorarum on epibenthic amphipods was also evalua ted in four artificial habitats with different physical complexity: soft-bo ttom substrates (SBS), small woody debris (SWD), seagrasses with densities of 300 and 1200 shoots m(-2) (S300 and S1200, respectively), macroalgae (MA ), and at two prey densities (962 and 2406 ind m(-2)). Amphipod consumption rate by F. duorarum varied from 1.20 to 2.07 ind h(-1) in S1200 and MA, re spectively. Habitat complexity had a significant effect on consumption rate , but prey density did not. Habitat physical complexity and predation effic iency maintained an inverse and a non-linear relationship. Presumably, the decrease in predation efficiency in association with the habitat complexity is due to the differential refuge value of these habitats. However, predat ion efficiency may also be influenced by either the microhabitat use by amp hipods, the shrimp's dependence on seagrasses, or by differences in habitat value caused by the diel behavioural distribution pattern of amphipods and shrimp. Both field and experimental results highlight the importance of ev aluating the relative value of tropical estuarine habitats through the stud y of the relationship between habitat physical complexity and predator-prey interactions. They also emphasise that inherent biological and ethological factors of the predator and prey involved, coupled to spatial and temporal variations in the habitat, should also be considered. (C) 2000 Elsevier Sc ience B.V. All rights reserved.