The contribution of epiphyton to the primary production of tropical floodplain wetlands

Abstract

Tropical floodplains are one of the most productive ecosystems on earth. Studies on floodplain productivity have primarily focused on trees and macrophytes, rather than algae, due to their greater biomass. However, epiphyton—algae and bacteria attached to the submerged portion of aquatic macrophytes—is a major source of energy in many tropical floodplains. Epiphyton productivity rates are unknown for most tropical floodplain wetlands, and spatial variability is not well understood. In this study, we measured primary productivity of epiphyton in Kakadu National Park in northern Australia. We estimated the relative contribution of epiphyton to aquatic production (epiphyton, + phytoplankton + macrophytes). We sampled sites dominated by different macrophyte structural types: vertical emerging grasses, horizontal emerging grasses, submerged macrophytes, and macrophytes with floating leaves. Epiphyton productivity was highly influenced by the structural type of the macrophyte. Highest potential productivity per weight was measured from epiphyton growing on macrophytes with floating leaves and horizontal grasses (1.52 ± 0.53 and 1.82 ± 0.61 mgC/dw g epiphyton/h, respectively) and lowest in submerged macrophytes and vertical grasses (0.57 ± 0.26 and 0.66 ± 0.47 mgC/dw g epiphyton/h, respectively). When considering the areal biomass of the macrophyte and the amount of epiphyton attached, epiphyton on horizontal grasses and submerged macrophytes had productivity values approximately ten times higher (45–219 mgC/m2/d) compared to those on vertical grasses and macrophytes with floating leaves (2–18 mgC/m2/d). Epiphyton contributed between 2 to 13 percent to the aquatic production of these tropical floodplain wetlands.

Estuarine crocodiles in a tropical coastal floodplain obtain nutrition from terrestrial prey

“…We also included direct field observations of feeding behavior and gut contents. Our study sites are within three rivers in Northern Australia ( Fig 1 ) which maintain intact hydrology and have large and highly productive seasonal floodplains [ 22 , 23 ]. The main goals of the study were: first, to identify the sources of nutrition of the estuarine crocodile population in Kakadu National Park, Northern Australia, and second, to investigate how introduced and abundant terrestrial prey may have affected the ecological role of this iconic predator in the region.…”

Sea catfishes (Ariidae) feeding on freshwater floodplains of northern Australia

“…Thus, our second hypothesis that ariid catfishes spawn on the floodplain has little support. Although it does not appear that floodplains of the Mitchell and Flinders rivers were used for spawning, high rates of primary and secondary floodplain production (Pettit et al 2011;Adame et al 2017) may enhance juvenile development and support postpartum adult growth. Many fish had visible mesenteric fat deposits indicative of energy storage and good condition (Brown and Murphy 2004).…”

“…When river floodplains are located close to the river terminus, there is increased potential for inundation to expand the links between terrestrial, riverine and marine ecosystems. For example, when inundated, the vast terminal floodplains of northern Australia are contiguous with, and grade into, the receiving marine environment (Ward et al 2011), creating the opportunity for marine, estuarine and freshwater fish to access elevated primary and secondary floodplain production (Pettit et al 2011;Adame et al 2017). However, floodplain inundation across much of northern Australia is often short and does not necessarily occur every year (Jardine et al 2012a(Jardine et al , 2012b; these characteristics may therefore constrain the extent to which fish do indeed make use of floodplain habitats, particularly as spawning areas.…”

Relationships between algal primary productivity and environmental variables in tropical floodplain wetlands

“…The floodplain includes 3 wetland types: riverine (rivers, streams); lacustrine (large waterbodies with permanent water such as lakes and lagoons); and palustrine (wetlands that have fluctuating water residency, such as swamps; Shine and Klemm 1999). These wetlands support several types of aquatic macrophytes (Ward et al 2013) known to provide structural habitat for algal growth and aquatic consumers (Adame et al 2017).…”

“…We measured primary productivity as carbon (C) uptake from incubations with 13 C-bicarbonate (Burford et al 2012, Adame et al 2017. For the epiphyton experiment, we carefully collected macrophytes from each habitat so as not to disturb the attached epiphyton and placed them in aerated buckets of water from the site until the experiments were conducted (<48 h from collection).…”