Trophic interactions within the plantonic food web in mangrove channels of Twin Cays, Belize, Central America

Abstract

The tidal channels of mangrove islands such as Twin Cays, Belize support a productive and diverse microplankton assemblage. In turn, this microplankton community supports large populations of copepods that form dense aggregations in the prop-root environment along the margins of these channels. The growth rate of the phytoplankton community and the grazing rate of the heterotrophic microzooplankton community were measured using the seawater dilution method. In separate experiments, the grazing rate of the swarm-forming copepod Dioithona oculata on natural microplankton assemblages was measured. Chlorophyll concentrations in the natural plankton assemblages used in these experiments ranged from 1-to-1 1 pg Chl a L-'. Dinoflagellate populations typically ranged from 17-to-50 cells ml-', with heterotrophic dinoflagellates generally exceeding autotrophic forms in abundance. Ciliates were the second most abundant form of heterotrophic microzooplankton with populations ranging from 1 -15 cells ml-' . Results of the dilution experiments indicate that, during the study period, microzooplankton grazed between ca. 60-90% of potential phytoplankton production and phytoplankton growth exceeded microzooplankton grazing in all experiments. Grazing studies with D. oculata indicated that copepod ingestion rates were highest on ciliates and autotrophic dinoflagellates and that copepod populations are capable of grazing about 10% of the protozoan population each day.

Two-way bioinvasion: tracking the neritic non-native cyclopoid copepods Dioithona oculata and Oithona davisae (Oithonidae) in the Eastern Mediterranean Sea

“…In our study, D. oculata presented the highest abundance in October, when low chlorophyll a and pico-and nano-eukaryote values were recorded. These results suggest that D. oculata might feed on other food sources, such as larger protozooplankton, to maintain its large population, as was observed by Buskey et al (2004) when phytoplankton availability is limited.…”

“…Santhosh et al (2018) observed that in laboratory conditions, D. oculata feeds on microalgae but can also consume ciliates and similar protozoans. Buskey et al (2004) observed that D. oculata prefers feeding on large cells, showing higher clearance rates when fed on ciliates and autotrophic dinoflagellates compared to heterotrophic dinoflagellates. In our study, D. oculata presented the highest abundance in October, when low chlorophyll a and pico-and nano-eukaryote values were recorded.…”