Ann. Limnol. - Int. J. Lim.
Volume 53, 2017
|Page(s)||293 - 307|
|Published online||28 August 2017|
Depth distribution of zooplankton in relation to limnological gradients under different stratification and interannual regimes in a deep, tropical crater lake
Department of Fisheries and Water Resources, School of Natural Resources, University of Energy and Natural Resources (UENR),
P.O. Box 214,
2 Department of Theoretical and Applied Biology, Kwame Nkrumah University of Science and Technology (KNUST), Kumasi, Ghana
3 Biology Department and Large Lakes Observatory, University of Minnesota-Duluth, 2205 East Fifth Street, Duluth, MN 55812, USA
* Corresponding author: email@example.com
Accepted: 24 July 2017
Zooplankton vertical distribution was studied in Lake Bosumtwi to understand how spatial and temporal variations in the water column affected diurnal and nocturnal patterns. Biweekly samples were collected for 24 consecutive months at the deepest point from 2005 to 2006. Water column properties shaping habitat suitability, namely temperature, light intensity, dissolved oxygen and phytoplankton biomass, varied markedly with depth but less with season. Most zooplankton stayed in the epilimnion continuously and their distribution was unaltered by lake stratification, mixing and restratification. Species dwelt permanently in the epilimnion without any necessity to migrate. Reduced water column variability and resultant weak selective pressures suppressed greater dispersion of species. Chaoborus ceratopogones (Theobald) was the main invertebrate predator and performed upward and downward movements on a diel cycle. Competing prey species overlapped extensively in spatial and temporal degree of habitat use. Chaoborus, however, segregated in deep water during the day, thereby minimizing prey vulnerability and promoting coexistence among predators and prey. During night-time residence, prey species may be exposed to increased predation risk from Chaoborus but gains in reproductive potential in warm, food-rich surface waters may offset losses to mortality. Our results suggest that high degree of habitat constancy and consequently weak selective pressures contributed to the lowered behavioural responses of zooplankton. The persistently skewed distribution of zooplankton is adaptive to predation and competition and promotes species coexistence. This behaviour will optimize growth and reproductive benefits over the cost of descent to suboptimal conditions in deep water.
Key words: Lake Bosumtwi / Mesocyclops bosumtwii / vertical distribution / tropical / water column parameters
© EDP Sciences, 2017
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