Flow effects on benthic grazing on phytoplankton by a Caribbean reef

Abstract

We present measurements of flows and fluxes of phytoplankton to Conch Reef, Florida, a Caribbean reef dominated by sponges and soft corals, located in 15 m of water offshore of Key Largo. Vertical profiles of chlorophyll a, a proxy for phytoplankton biomass, showed a near-bed depletion, indicating the existence of concentration boundary layers. Along with simultaneous measurements of velocity profiles, near-bed turbulence, and temperature stratification, these profiles were used to compute a, the mass transfer velocity of phytoplankton to the bed (i.e., the flux to the bed normalized by near-bed concentration). The a value ranged from 240 to +130 m d 21 , with a significant linear positive relationship with shear velocity. The median value of a 5 48 6 20 m d 21 is larger than would be expected, given the observed population of filter-feeding sponges. Nonetheless, these large values of a are consistent with values found recently for another coral reef as well as for a soft bottom estuarine community. Taken as a whole, these measurements indicate that reefs with large roughness and/or energetic currents should be able to support higher biomasses of benthic organisms than would low relief reefs or reefs in sluggish waters.

Multifaceted impacts of the stony coral Porites astreoides on picoplankton abundance and community composition

“…Although many corals, including P. astreoides , have obligate symbiotic relationships with Symbiodinium spp., heterotrophic feeding on phytoplankton (Yahel et al ) and zooplankton (Sebens et al ; Wijgerde et al ) are thought to be important supplementary energy sources. Depletion of picoplankton and Synechococcus , from grazing or other processes, have been previously seen in assemblages of coral, sponge and other reef organisms (Ribes et al ; Genin et al ; Monismith et al ). To our knowledge, this is the first report of putative coral grazing on other picoplankton taxa.…”

Trait-mediated ecosystem impacts: how morphology and size affect pumping rates of the Caribbean giant barrel sponge

“…In shallow-water systems, and where they occur in dense assemblages, benthic suspension feeders may control phytoplankton biomass, thereby clarifying the water and increasing light availability to ecologically important benthic autotrophs (Cloern 1982, Officer et al 1982. On coral reefs, benthic suspension feeders can deplete phytoplankton concentrations in overlying waters and represent an important pathway for the retention of allochthonous carbon and nutrients in coral reef ecosystems (Yahel et al 1998, Monismith et al 2010.…”

“…It is likely that ambient currents of habitats where X. muta typically occur are of sufficient strength to provide individuals a continuous supply of unfiltered seawater (e.g. Monismith et al 2010). However, it remains to be seen if morphological differences reflect spatial variability of the flow regime across coral reefs.…”

Tidal variability of nutrients in a coastal coral reef system influenced by groundwater

“…This similarity indicates that the composition of nutrients in the water column was closely related with biological processes during both tidal periods, but the biological effect appeared to be less evident during the spring tide as inferred from the less significant correlations. The net release of nutrients during the neap tide with a very Redfield-like ratio suggests that the net nutrient fluxes in this system were likely to be dominated by the uptake and remineralization of plankton/oceanic organic particles by benthic filter feeders as observed in other reefs (e.g., Ayukai, 1995;Ribes et al, 2005;Southwell et al, 2008;Genin et al, 2009;Monismith et al, 2010). The net uptake of nitrate and phosphate was mainly done by reef primary producers.…”