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Salt-flocculated organic matherial as a food source in estuarine food webs

University of British Columbia

Large amounts of particulate material were found to flocculate from water collected from local, organic rich streams upon addition of salt water. This material was found to compose approximately 50% humic substances and to have a C:N ratio of about 50:1. Feeding studies using floe having various degrees of bacterial colonisation showed that bacterial abundance was an important determinant of the palatability of this material to the copepod grazer, Tigriopus californicus. Palatability of flocculant particles increased linearly with increasing bacterial abundances in the range of 0-10⁶ cells • mL⁻¹, while increases in bacterial abundances above this concentration resulted in lower than expected grazing rates. Further inoculations with single strains of bacteria isolated from the floe showed that this increased palatability occurred with only certain components of the floe fauna. Ingestion of floe colonised by a "normal" bacterial fauna was found to be beneficial for the survival of Cl and adult stages of Tigriopus and was found to sustain egg production of inseminated females. The presence of floe did not, however, result in the improved survival of the earlier naupliar stages of Tigriopus. Mass spectrometric analyses suggest that significant amounts of carbon are assimilated from floe made from water collected during the winter months. As floe is ingested at very low rates in the absence of colonising microbes, benefit from the ingestion of floe is postulated to result from the conversion of floe carbon into microbial biomass and the subsequent assimilation of those microbes by the copepod grazer. The fact that few differences exist between the IR-spectra of floe food and the faecal material derived from copepods fed a floe diet suggests that little change is undergone by the bulk of the organic matrix during ingestion and passage through the copepod gut. Ingestion of floe may therefore work to protect the flocculant material from subsequent microbial degradation by compacting the material into pellets which will be rapidly delivered to the sediments as a result of high sinking rates. Feeding studies with a variety of species collected from local coastal waters suggest that a wide spectrum of organisms may ingest flocculant material when that material is present in their environs. As flocculant material is primarily produced in the winter, a time when estuarine primary productivity is low, floe is postulated to play an important role in sustaining these organisms through periods of low food availability.

Text

2010-08-25

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http://hdl.handle.net/2429/27750

Oceanography

University of British Columbia

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