Competition with macroalgae and benthic cyanobacterial mats limits phytoplankton abundance in experimental microcosms

Abstract

Competition for nutrients among estuarine phytoplankton and algal mats (a combination of floating and attached green macroalgae and attached cyanobacterial mats) was studied using replicate expenmental microcosms. At high nutnent loading (nitrate-N = 77 F M d -l ) , the growth of phytoplankton was reduced by a factor of 10 in the presence of the algal mats. Without the algal mats the phytoplankton was very abundant (> 5 X 106 cells rill-l) and dominated by small flagellates, while in the presence of the algal mats the phytoplankton assemblage was sparse and diatoms, flagellates, and unicellular blue-greens were common. The competition hierarchy was cyanobacterial mats >> attached green macroalgae > floating green macroalgae > phytoplankton. When nutrient supply rate was low (nitrate-N = 1.2 pM d-l), the presence of the algal mats shifted the phytoplankton from flagellates to blue-green algae, but did not affect total biomass of the phytoplankton. We conclude that the attached forms of macroalgae as well as the cyanobacterial mats were better competitors for high levels of nutrients than the phytoplankton. This resource competition may explain the negative correlation found in field studes between phytoplankton and macroalgae growing in shallow nutrient-enriched estuaries.

Biogeochemical modelling of Ria Formosa (South Portugal)

“…This contradicts results obtained by other authors in shallow coastal lagoons and bays, where macrolgae production dominates over phytoplankton (Sfriso et al, 1992;Valiela et al, 1992;McGlathery et al, 2001). The lower phytoplankton production has been attributed to nutrient competition between macroalgae and phytoplankton (Fong et al, 1993;ThyboChristensen & Blackburn, 1993;McGlathery et al, 1997) and to water residence times shorter than phytoplankton doubling time (Valiela et al, 1997). This contradiction may be tentatively explained by:…”

Benthic-Pelagic Links: Responses of Benthos to Water-Column Nutrient Enrichment

“…Chlorates, suggesting a high rate of ac-rophyll increased with depth in the control and i of phosphorus that might otherwise all 3 enriched treatments, and there was no depth x nutrient interaction. Also, the phytoplankton response and maximum P loading rate were moderate relative to other enrichment studies (Hall et al 1970, Nilsson et al 1991, Fong et al 1993, Havens et al 1996, and the reduction in light was not likely to overcome nutrient limitation in a 2-m-deep environment.…”

World’s Largest Macroalgal Blooms Altered Phytoplankton Biomass in Summer in the Yellow Sea: Satellite Observations

“…In addition, the release of nutrients due to decomposition of macroalgae might also stimulate the growth of phytoplankton [13]. For the world's largest MABs in the Yellow Sea [5,8], it is difficult to assess the interactions between macroalgae and phytoplankton in such a large region through in situ observations [11][12][13]; to date, there has been no such report for the Yellow Sea, possibly due to difficulties in assessing long-term alternations in phytoplankton in the presence of macroalgae.…”

“…The growth of macroalgae might reduce phytoplankton biomass through nutrient competition [11,12]: macroalgae in the growing and expanding stage consumed nutrients in water column and reduced nutrient availability to phytoplankton. In addition, the release of nutrients due to decomposition of macroalgae might also stimulate the growth of phytoplankton [13].…”