Algal vs. Macrophyte Inputs to Food Webs of Inland Saline Wetlands

Abstract

Abstract. Invertebrate food webs in wetlands were traditionally thought to be fueled mainly by decaying macrophytes, but recently it has been recognized that microalgae may be more important. In particular, the paradigm that shredders of vascular plant litter dominate food web processes may not apply to many wetlands where shredders are rare and microalgae more abundant. This issue is complicated by potential consumption of flocs of dissolved organic matter (DOM) released from living plants, and of exopolymer secretions (EPS) from both autotrophic and heterotrophic microbes. In Wyoming, we used gut contents and stable isotopes to investigate organic matter sources for the dominant invertebrates in oligosaline (0.5-5 g/L total dissolved solids) and mesosaline (5-18 g/L) wetlands. We examined the trophic importance of microalgae vs. macrophytes in wetlands with and without emergent vegetation (Scirpus acutus), with different growth forms and species of submersed plants (Chara spp. vs. Potamogeton pectinatus), with dominance by different microalgal types (phytoplankton, epiphyton, epipelon), and with different primary consumers (mainly amphipods vs. chironomid larvae). In all wetlands studied, guts of the major primary consumers contained little or no macrophyte tissue, but rather mostly amorphous detritus (organic particles with no recognizable cellular structure). Values of ␦ 13 C indicated that organic matter entering foodwebs was not from submersed macrophytes, but that emergent plants might be a source of DOM or EPS in amorphous detritus. However, in some wetlands, amphipods eating mainly amorphous detritus had the same ␦ 13 C values as chironomids eating a much higher fraction of diatoms, indicating that amorphous detritus was derived mainly from diatoms. Patterns of temporal change of ␦ 13 C in consumers, seston, and emergent plants supported this interpretation. We conclude that microalgae rather than macrophytes provided most organic matter for these food webs via amorphous detritus. Amorphous detritus is often thought to have poor nutrient quality and low assimilation efficiency, but this idea may not be true if amorphous detritus is largely flocs of labile DOM/EPS. Our results suggest that characterizing the origin and nature of amorphous detritus is key to understanding variations in macroinvertebrate production among saline wetlands and a broad range of wetland types.

Depth‐specific and spatiotemporal variation of δ13C and δ15N in Charophytes of Lake Constance: implications for food web studies

“…In benthic filamentous algae, considerable temporal ranges of variation in δ 13 C (up to 19.7‰) have been detected [41] and a tendency of δ 13 C to increase during summer was found in submerged aquatic vegetation. [42] We observed only a minor variation of δ 13 C over time in Chara spp. These results suggest that temporal changes in δ…”

Organic matter pathways to zooplankton and benthos under pack ice in late winter and open water in late summer in the north-central Bering Sea

“…Our stable isotope data provide only indirect evidence, but indicate important directions for future research. In particular, studies combining different assays (gut contents, stable isotopes, fatty acids, triacylglycerols) are needed to determine the seasonal importance of direct consumption of sedimented algae versus bacterial products by pelagic and benthic macroinvertebrates (Kharlamenko et al 2001, Scott et al 2002, Bachok et al 2003, Hart & Lovvorn 2003, Howell et al 2003.…”

A global perspective on wetland salinization: ecological consequences of a growing threat to freshwater wetlands

“…Algae and vascular vegetation.-There is increasing recognition of the importance of microalgae in wetland food webs (Bunn andBoon 1993, Hart andLovvorn 2003). There are few studies of the tolerance of freshwater algae to salinity, but it tends to be low (Nielsen et al 2003 and references therein).…”