Higher diversity of deposit‐feeding macrofauna enhances phytodetritus processing

Abstract

The link between biodiversity and ecosystem functioning is an important question that remains unresolved, particularly in marine systems, in which cycling of organic matter by benthic organisms is of global significance. Direct observations of specific resource use by each species in single- and multispecies communities, as quantified by stable isotopes, facilitates a mechanistic understanding of the importance of each species for ecosystem functioning. We tested the effects of altered biodiversity (species richness) of deposit-feeding macrofauna on incorporation and burial of phytodetritus in combinations of three species representing natural communities found in the sediments of the species-poor Baltic Sea. The three species, two amphipods and a bivalve, had different rates of incorporation and burial and different needs for carbon (C) and nitrogen (N). The amphipods exhibited clear resource partitioning in sympatry, as a result of vertical separation in the sediment and consequent differential use of food. Communities of several species incorporated more C and N than expected from the respective single-species treatments, due to higher incorporation by surface feeders in multispecies treatments. Community incorporation of N in the most diverse treatment even exceeded N incorporation by a single-species treatment of the best-performing species, showing transgressive over-yielding. This over-yielding was primarily due to positive complementarity in all treatments. Diverse soft bottoms are also likely to be more productive in the long run, as species-specific traits (subsurface feeding) preserve fresh phytodetritus by burying it to depths in the sediment at which the mineralization rate is low. The more diverse sediment communities showed more efficient trophic transfer of phytodetritus, a finding of general significance for understanding biological processes driving the transformation of nutrients and energy in benthic ecosystems.

Living on the edge: single-species dominance at the Pakistan oxygen minimum zone boundary

“…Increased total resource use by a dominant species has been demonstrated previously for a wide range of environments (Cardinale et al 2006) and specifically for coastal echinoderms (Godbold et al 2009a). The results of Woulds et al (2007) contradict those of Karlson et al (2010), who found that higher metazoan macrofaunal species diversity (maximum number of species = 3, minimum number of species = 1) led to enhanced processing of phytodetritus. However, the results shown here from the PM are representative of larger multi-species communities (maximum number of species = 53, minimum number of species = 2) and demonstrate that dominant species in OMZs can have a significant impact on carbon processing.…”

“…More recently, Karlson et al (2010) were able to mimic field conditions in the species-poor Baltic Sea in order to understand the effect of biodiversity on OM processing, using pulse-chase experiments. Those authors concluded that ecosystems with higher species diversity (maximum number of species = 3) incorporated more carbon and nitrogen, displayed more efficient trophic transfer of phytodetritus and were more productive than monocultures.…”

Marine biodiversity and ecosystem function relationships: The potential for practical monitoring applications

“…Bioturbation can enhance nutrient cycling by as much as 35% (Gutiérrez, 2011), and nutrients derived in this way can contribute up to 80% of those required by pelagic primary producers (Dale and Prego, 2002). With the exception of one study (Bolam et al, 2002), Karlson et al (2010) concluded that the positive, over-yielding relationship between benthic macrofaunal deposit feeders and phytodetrial processing observed was mainly explained by niche partitioning and/or facilitation (complementarity) rather than identity effects.…”

Burial and decomposition of plant pigments in surface sediments of the Baltic Sea: role of oxygen and benthic fauna

“…This effect is likely a combination of bioturbation and deposit feeding, but since the material was relatively fresh, bioturbation was probably the main factor. In addition, Macoma is less efficient in assimilating phytodetritus compared with, for example, Monoporeia (Karlson et al 2010).…”