Macroinvertebrate community assembly on deep‐sea wood falls in Monterey Bay is strongly influenced by wood type

Abstract

Environmental filtering, including the influence of environmental constraints and biological interactions on species' survival, is known to significantly affect patterns of community assembly in terrestrial ecosystems. However, its role in regulating patterns and processes of community assembly in deep-sea environments is poorly studied. Here we investigated the role of wood characteristics in the assembly of deep-sea wood fall communities. Ten different wood species (substrata) that varied in structural complexity were sunk to a depth of 3,100 m near Monterey Bay, CA. In total, 28 wood parcels were deployed on the deep-sea bed. After 2 yr, the wood parcels were recovered with over 7,000 attached or colonizing macroinvertebrates. All macroinvertebrates were identified to the lowest taxonomic level possible, and included several undescribed species. Diversity indices and multivariate analyses of variance detected significant variation in the colonizing community assemblages among different wood substrata. Structural complexity seemed to be the primary factor altering community composition between wood substrata. For example, wood-boring clams were most abundant on solid logs, while small arthropods and limpets were more abundant on bundles of branches that provided more surface area and small, protected spaces to occupy. Other factors such as chemical defenses, the presence of bark, and wood hardness likely also played a role. Our finding that characteristics of woody debris entering the marine realm can have significant effects on community assembly supports the notion of ecological and perhaps evolutionarily significant links between land and sea.

Stable Isotopic Evidence of Mixotrophy in Xylophagaids, Deep-Sea Wood-Boring Bivalves

“…The δ 13 C values of the 40 specimens of Xylophaga s.l. zierenbergi removed from different types of wood by Judge and Barry (2016) and likely preserved in the same batch of 95% ethanol exceeded the isotopic δ 13 C range of the other 32 specimens considered, regardless of different chemicals used to preserve the latter (Figure 1). The specimens analyzed that were preserved by different chemical treatments (Table 1) did not significantly differ in either δ 13 C or δ 15 N isotopic values from specimens reported in the literature that had been frozen (noted in Table 3) prior to isotopic analyses (for δ 13 C isotopic values W = 0.514; p > 0.05; for δ 15 N isotopic values W = 0.543; p > 0.05).…”

“…Specimens of Xylophaga zierenbergi removed from bark-covered pine and oak logs have distinctly depleted δ 13 C values compared to conspecifics from the wood of spice bush, island ironwood, and Douglas fir. Those from logs of P. pinea, identified by Judge and Barry (2016), also have relatively enriched δ 15 N values. Why these seemingly anomalous values are present remains open to conjecture and may offer an attractive area for future research.…”

“…zierenbergi from six deployments. wood bundles (WB) except aqua diamonds: from Douglas fir on Endeavour Segment, Juan de Fuca Ridge at 2211 m depth (Voight, 2007); all others are from deployments near Monterey Canyon at 3100 m depth (Judge and Barry, 2016): blue crosses bark-covered pine log (WB17); green circles bark-covered oak log (WB23); orange triangles gingko logs (WB26); pink stars spicebush sticks (WB19); purple squares island ironwood (WB32).…”

“…Although filter feeding may be opportunistic and not necessarily occur in every habitat or in every taxon, assuming that wood is the sole source of energy available to wood-fall communities may be fallacious. The amount of unknown variation in the composition of wood-fall communities (McClain and Barry, 2014;Judge and Barry, 2016) argues that assumptions should be re-examined.…”

Habitat structure as an alternative explanation for body‐size patterns in the deep sea

“…It is possible that this heterogeneity modifies the relationship. The importance of heterogeneity also plays a role in wood falls; for example, when there is heterogeneity in species of wood and what part of the tree is present, different communities are assembled on the food resource (Judge and Barry ). While the isolation of wood falls makes for excellent study systems, most other systems are not so isolated, and understanding the interplay between this lack of isolation and body‐size relationships will be important in explaining patterns across systems.…”