Benthic community structure and ecosystem functions in above- and below-waterfall pools in Borneo

Waterfalls are geomorphic features that often partition streams into discrete zones. Our study examined aquatic communities, litter decomposition and periphyton growth rates for above- and below-waterfall pools in Ulu Temburong National Park, Brunei. We observed higher fish densities in below-waterfall pools (0.24 fish m−2 vs. 0.02 fish m−2 in above-waterfall pools) and higher shrimp abundance in above-waterfall pools (eight shrimp/pool vs. less than one shrimp/pool in below-waterfall pools). However, macroinvertebrate densities (excluding shrimp) were similar among both pool types. Ambient periphyton was higher in below-waterfall pools in 2013 (4.3 vs. 2.8 g m−2 in above-waterfall pools) and 2014 (4.8 vs. 3.4 g m−2 in above-waterfall pools), while periphyton growth rates varied from 0.05 to 0.26 g m−2 days−1 and were significantly higher in below-waterfall pools in 2014. Leaf litter decomposition rates (0.001 to 0.024 days−1) did not differ between pool types, suggesting that neither shrimp nor fish densities had consistent impacts on this ecosystem function. Regardless, this research demonstrates the varied effects of biotic and abiotic factors on community structure and ecosystem function. Our results have highlighted the importance of discontinuities, such as waterfalls, in tropical streams.</p

Tracking seasonal changes in North Sea zooplankton trophic dynamics using stable isotopes

Trophodynamics of meso-zooplankton in the North Sea (NS) were assessed at a site in the southern NS, and at a shallow and a deep site in the central NS. Offshore and neritic species from different ecological niches, including Calanus spp., Temora spp. and Sagitta spp., were collected during seven cruises over 14 months from 2007 to 2008. Bulk stable isotope (SI) analysis, phospholipid-derived fatty acid (PLFA) compositions, and δ 13CPLFA data of meso-zooplankton and particulate organic matter (POM) were used to describe changes in zooplankton relative trophic positions (RTPs) and trophodynamics. The aim of the study was to test the hypothesis that the RTPs of zooplankton in the North Sea vary spatially and seasonally, in response to hydrographic variability, with the microbial food web playing an important role at times. Zooplankton RTPs tended to be higher during winter and lower during the phytoplankton bloom in spring. RTPs were highest for predators such as Sagitta sp. and Calanus helgolandicus and lowest for small copepods such as Pseudocalanus elongatus and zoea larvae (Brachyura). δ 15NPOM-based RTPs were only moderate surrogates for animals’ ecological niches, because of the plasticity in source materials from the herbivorous and the microbial loop food web. Common (16:0) and essential (eicosapentaenoic acid, EPA and docosahexaenoic acid, DHA) structural lipids showed relatively constant abundances. This could be explained by incorporation of PLFAs with δ 13C signatures which followed seasonal changes in bulk δ 13CPOM and PLFA δ 13CPOM signatures. This study highlighted the complementarity of three biogeochemical approaches for trophodynamic studies and substantiated conceptual views of size-based food web analysis, in which small individuals of large species may be functionally equivalent to large individuals of small species. Seasonal and spatial variability was also important in altering the relative importance of the herbivorous and microbial food webs