Short-term decompositional state does not influence use of wood by macroinvertebrates in subtropical, coastal plain streams

Abstract

Woody debris is an important habitat component, particularly in streams that lack other hard substrates. Research suggests a general relationship between increasing invertebrate density, diversity, and taxa richness with increasing wood decay in lotic systems, with some authors observing invertebrate taxonomic succession as decay proceeds. We designed a field experiment using colonization of known-aged woody debris in two streams to examine patterns in invertebrate colonization, density, diversity, richness, and succession. After aging woody debris 0-6 weeks in laboratory tanks and then placing the debris in the two subtropical, coastal plain streams for five additional weeks, we did not detect any statistical relationship between invertebrate density, diversity, evenness, richness, or life-history pattern with increasing woody debris decay, nor did we detect any relationships between the colonization or abundance of individual taxa and the decompositional state of the wood. In this paper, we propose two non-exclusive explanations for these trends based on opportunistic colonization and evolutionary filtering. Despite the apparent unimportance of decompositional state, woody debris still supported many taxa and remains an important habitat component. Our research further supports the importance of flooding and maintenance of intact riparian and floodplain forests to the woody debris dynamics and macroinvertebrates in coastal plain lotic systems.

Wood distribution along streams draining old-growth floodplain forests in Congaree National Park, South Carolina, USA

“…Despite forming b20% of the area colonizable by macroinvertebrates in Congaree's Cedar Creek, instream wood has N90% of the standing crop at a given time, as well as the highest species richness and density of available substrates (Smock and Gilinsky, 1982). Studies of other bottomland hardwood wetlands and blackwater rivers also indicate that instream and floodplain wood is a hot spot for invertebrate richness and arthropod biomass (Benke, 2001;Braccia and Batzer, 2001), although macroinvertebrate abundance and diversity are also influenced by the location of the wood (swamp versus tributary and outflow stream sites; Thorp et al, 1985) and potentially by the degree to which the wood is decayed (Kaller and Kelso, 2006). Submerged wood is especially important in sand-bed streams, where it provides stable attachment points for filter-feeding macroinvertebrates (Benke, 1998).…”

Polychaetes associated with decaying wood in Térraba mangrove, South Pacific, Costa Rica

“…In this way, decaying wood is a perfect habitat to opportunist worms as capitellids and oligochaetes (Rizzo & Amaral, 2001;Dean, 2001b). Kaller and Kelso (2006) found that insects and molluscs are the main components in decaying woods, of coastal freshwater streams, in South-Western Louisiana. The adaptations of these groups to wood boring may have allowed them to dominate the decaying wood in low salinity regimes.…”

Effects of burn status and conditioning on colonization of wood by stream macroinvertebrates

“…For instance, invertebrate richness may increase with decay (Braccia andBatzer 2001, Ballinger et al 2010), and density may vary (Collier and Halliday 2000) or be unrelated to decay (Braccia and Batzer 2001). Based on some of these studies and on their own findings, Kaller and Kelso (2006) stressed the difficulty of making generalizations about the effect of decay on macroinvertebrates. We think that part of the difficulty arises from limited tracking of crucial features in the decay of sampled wood, such as decay time, age, size, species, and waterlogging period.…”

“…In contrast, Pitt and Batzer (2011) found that conditioning had minimal influence on how wood was used by macroinvertebrates in streams in the southeastern USA. Kaller and Kelso (2006) suggested that stream invertebrates readily used all incoming wood regardless of its condition, and they invoked opportunistic colonization as the primary mechanism explaining similar assemblages on wood with various conditioning. In disentangling this contradiction between our results and those reported by others, we first note that our systems differ markedly from those where most other related work has been conducted.…”

“…Others have addressed the structural effects of wood, e.g., effects on flow patterns and retention (Entrekin et al 2009, Testa et al 2011) on macroinvertebrate communities in streams (Wallace et al 1995, Hilderbrand et al 1997, Lemly and Hilderbrand 2000, Warren and Kraft 2006. Last, some researchers have specifically examined the colonization of submerged wood by macroinvertebrates (Magoulick 1998, Collier and Halliday 2000, Collier and Smith 2003, Kaller and Kelso 2007, Lyon et al 2009, Ballinger et al 2010), but results have been inconsistent making generalizations difficult (Kaller and Kelso 2006).…”