Abstract
Tropical reef ecosystems are generally considered to be sinks of marine zooplankton, mainly due to the predation by scleractinian corals and other planktivores. The present study aims to evaluate the zooplankton community of a coastal reef in two specific environments: the reef edge and open-water channels between patch reefs. Sampling was carried out at two patch reefs that border the Tamandaré coastal lagoon system (Pernambuco State, Brazil). Two passive stationary nets (64 μm mesh size) were used: the Reef Edge Net (REN) and the Channel Midwater Neuston Net (CMNN). Sampling was performed simultaneously at both reefs during eight nocturnal sampling campaigns, always at new moon ebb tides. Zooplankton was classified by “origin” (estuarine, reef, neritic and neritic/estuarine). During all campaigns and at both sites, a significant buildup of zooplankton at the reefs was observed. Reef edges showed significantly higher abundance (77,579 ± 73,985 ind. m−3) and biomass (48.9 ± 45.5 mg C m−3) of zooplankton compared to open-water channels (9982 ± 11,427 ind. m−3 and 11.4 ± 21.9 mg C m−3, respectively). A total of 65 taxonomic groups were identified. Copepods were the most abundant group with a contribution of 69% for total zooplankton abundance, followed by foraminiferans, gastropod veligers, appendicularians, cirripedians nauplii, and polychaete larvae. Copepods from neritic/estuarine environments dominated the reef edges in both relative abundance and relative biomass (91% and 88%, respectively). The unexpectedly high abundance of copepods and other holoplankton at the reef edges, when compared to Indo-Pacific and Caribbean reefs, is probably due to very low cover of corals and other zooplanktivorous sessile animals (< 0.2%) on these coastal reefs, which leads to a very low predation mortality for zooplankters. Also, we propose that the reduced water column above the reef top leads to a buildup of very high densities in these environments.
Highlights
Reef-associated zooplankton plays an important role as a link in food webs between primary producers and higher trophic levels [1,2,3,4,5]
The demersal zooplankton comprises larval and adult stages of organisms living in reef caves at daytime and migrating towards the water column after sunset to feed on detritus and plankton
The present study is the first to reveal the existence of specific micro- and mesozooplankton communities exported from the reef tops of a shallow tropical reef
Summary
Reef-associated zooplankton plays an important role as a link in food webs between primary producers and higher trophic levels [1,2,3,4,5]. The demersal zooplankton comprises larval and adult stages of organisms living in reef caves at daytime and migrating towards the water column after sunset to feed on detritus and plankton. This “emergent” strategy has probably evolved to avoid visual diurnal planktivorous organisms as well as nocturnal benthic predators [7, 9]. Some holoplanktonic species form swarms near the reef bottom during the day and disperse at night [1, 17] This behavior occurs to facilitate mating and for protection during the mating periods [17, 18]
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