Copepod grazing and their impact on phytoplankton standing stock and production in a tropical coastal water during the different seasons

详细信息    查看全文

• 作者：L. Jagadeesan ; R. Jyothibabu ; N. Arunpandi…
• 关键词：Copepods ; Phytoplankton biomass ; Chlorophyll a ; Ingestion ; Tropical waters ; Grazing pressure
• 刊名：Environmental Monitoring and Assessment
• 出版年：2017
• 出版时间：March 2017
• 年：2017
• 卷：189
• 期：3
• 全文大小：
• 刊物类别：Earth and Environmental Science
• 刊物主题：Monitoring/Environmental Analysis; Environmental Management; Ecotoxicology; Atmospheric Protection/Air Quality Control/Air Pollution; Ecology;
• 出版者：Springer International Publishing
• ISSN：1573-2959
• 卷排序：189

文摘

The grazing rate of copepods on the total and size-fractionated phytoplankton biomass in a coastal environment (off Kochi, southwest coast of India) were measured during pre-monsoon (PRM), peak southwest monsoon (PKSWM), late southwest monsoon (LSWM) and post-southwest monsoon (PSWM). The phytoplankton standing stock (chlorophyll a-Chl. a) and growth rate (GR) were less during the PRM (Chl. a 0.58 mg m−3; GR 0.23 ± 0.02) and PSWM (Chl. a 0.89 mg m−3; GR 0.30 ± 0.05) compared to PKSWM (Chl. a 6.67 mg m−3; GR 0.43 ± 0.02) and LSWM (Chl. a 4.09 mg m−3; GR 0.40 ± 0.04). The microplankton contribution to the total Chl. a was significant during the PKSWM (41.83%) and LSWM (45.72%). Copepod density was lesser during the PRM (1354 No m−3) and PSWM (1606 No m−3) than during PKSWM and LSWM (4571 and 3432 No m−3, respectively). Seasonal changes in phytoplankton biomass, phytoplankton size structure, and copepod community were closely related to the hydrographical transformations in the study domain. Dominant calanoid copepods in the study region ingested 8.4 to 14.2% of their daily ration from phytoplankton during the PRM and PSWM, which increased to >50% during the PKSWM and LSWM. The cyclopoid Oithona similis was abundant during the PKSWM, ingesting only 21% of their daily ration from phytoplankton. Temporal variation in the phytoplankton biomass and copepod species composition caused differences in community level top-down control. The copepod community ingestion on phytoplankton was high during the LSWM (18,583 μg C m−3d−1), followed by PKSWM (9050 μg C m−3d−1), PSWM (1813 μg C m−3d−1), and PRM (946 μg C m−3d−1). During the low Chl. a period (PRM and PSWM), dominant calanoid copepods showed a positive selectivity for the micro- and nano-phytoplankton size fractions, whereas during the high Chl. a period (PKSWM and LSWM), they showed a positive selection for nano-phytoplankton fractions. Irrespective of the seasons, dominant calanoid copepods showed a negative selection of pico-phytoplankton fraction. The cyclopoid O. similis and Poecilostomatoid Corycaeus danae showed a positive selection of nano- and pico-phytoplankton fractions rather than micro-fraction. The grazing pressure of copepod community ingestion on micro-fraction was less (0.56% of the phytoplankton biomass and 1.06% of the phytoplankton production) during the PKSWM. This study provides, for the first time, clear findings on the seasonal variation in the top-down control of phytoplankton by copepods in a tropical coastal water ecosystem and discusses its implications on phytoplankton blooming, plankton food web, and biogeochemistry.