Zooplankton Feeding Ecology: Grazing by Marine Copepods and Cladocerans upon Phytoplankton and Cyanobacteria from Kingston Harbour, Jamaica

Abstract

Grazing by the copepods Tcworci /irrhiirutu and Acurlicr IiNjehorgii and the marine cladoceran Peiiilin uriro.~rri.~ on natural phytoplankton and cyanobacteria assemblages from Kingston Harbour. Jamaica, was examined in summer 1992. Food assemblages were often dominated by an unidentified filamentous cyanobacterium. with abundances of up to 1.16 x lo4 filaments.ml I. Other abundant phytoplankters included microflagellates and diatoms of the genus Nir:schiri. Mean clearance rates for the entire food assemblage ranged from 0.10 to 2.41 ml 'animal -I . h-', although most mean clearance rates were between 0.5 and I .5 ml . animal-' h-I. Patterns of selection of different food items by various grazers on different dates were variable and inconsistent. Microscopic measurements revealed that cyanobacterial filament lengths were shorter in grazed than initial aliquots during a cyanobacterium bloom in August. This suggests that grazers reduced lengths of many filaments by biting otl'portions, in addition to consuming entire filaments. Such 'filament clipping' of cyanobacteria filaments has been recorded previously in freshwater studies and suggests that grazers impact a larger portion of the phytoplankton assemblage than is accounted for by ingestion and clearance rates based only upon removal of filaments. Grazers exhibited no adverse effects from consuming cyanobacteria. Cyanohacterkd are often considered to be toxic or of poor food quality for planktonic grazers. but due to the high abundance and dominance of filamentous cyanobacteria in Kingston Harbour. if these cyanobacteria were ungrazed. there would at times be little alternative phytoplankton food for copepods and cladocerans. Our results suggest that the trophic role of tilamentous cyanobacteria in pelagic food webs of the tropical ocean should be further investigated and possibly reconsidered.

Can tropical freshwater zooplankton graze efficiently on cyanobacteria?

“…This behavior is also shown in this study for P. hessei feeding on natural particles as well as on chlorophytes (C. impressulum) or on filamentous cyanobacteria (A. solitaria, A. flos-aquae, and C. raciborskii). This confirms that calanoid copepods are able to cut the filaments of filamentous cyanobacteria, shortening them to an edible size for other zooplankton species, such as small cladocerans, as shown in other studies on freshwater (Burns & Xu, 1990a, b;Bouvy et al, 2001) and coastal marine water (Turner et al, 1998). As emphasized by these last authors, this phenomenon can have considerable ecological consequences that are generally underestimated, with a larger portion of the phytoplankton assemblage being affected by the grazers than is accounted for by ingestion and clearance rates, based only on the removal of filaments.…”

“…This copepod could, therefore, play an important role in the control of algal blooms, by direct consumption and/or the fragmentation of the largest filaments. Calanoid copepods can detect, capture, and handle large particles (such as large diatoms or cyanobacteria) before ingesting or rejecting them (Paffenhofer et al, 1982;Turner et al, 1998). During ''handling'', they damage or break particles with their mouth parts (''sloppy feeding'').…”

Ecological constraints on planktonic nitrogen fixation in saline estuaries. II. Grazing controls on cyanobacterial population dynamics

“…5b,c). Shortterm grazing studies reported here and elsewhere have demonstrated the sensitivity of colony size in filamentous cyanobacteria (Schaffner et al 1994, Turner et al 1998 and estuarine diatoms (Deason 1980) to zooplankton grazing.…”

Effects of fish farming on plankton structure in a Brazilian tropical reservoir

“…The relationships between the zooplankton and Cyanobacteria depend on the species considered and on their several sizes and physiological states (Lampert, 1987); some zooplankton species may consume Cyanobacteria and become resistant to cyanotoxins (James & Forsyth, 1990;Turner et al, 1998;Panosso et al, 2003). Thus, we suggest studies about the body size of zooplankton organisms and their consumption rates in relation to the phytoplankton community in this environment, mainly regarding the ingestion of Cyanobacteria and the influence of this relationship for the dominance of this group, in addition to research focusing on predation by the fish community.…”