Biodiversity, ecosystem engineering, and trophic ecology of whale-bone and wood-fall habitats in the deep NE Pacific: A controlled experimental approach

Young, Emily Louise

Biodiversity, ecosystem engineering, and trophic ecology of whale-bone and wood-fall habitats in the deep NE Pacific: A controlled experimental approach

Files

Young_hawii_0085A_11652.pdf (4.37 MB)

Date

2023

Authors

Young, Emily Louise

Advisor

Smith, Craig R.

Department

Oceanography

Abstract

Organic-fall habitat islands are established when large organic-rich parcels, such as whale bones or wood, sink to the generally food-poor deep-sea floor. Organic-fall communities may pass through a succession of ecological stages, modulated by key ecosystem engineers that influence the availability of habitat and food resources in these ecosystems. Because biodiversity and ecosystem functions at organic falls are likely to vary with substrate type, size, and deployment times, comparisons between ocean regions and depths are problematic. In this study, a replicated experimental approach has been used to control the effects of substrate type, size, and deployment times. Three major aspects of organic-fall ecology were explored: patterns and drivers of biodiversity, the importance of a wood-boring ecosystem engineer to ecosystem structure and function, and variations in trophic structure between whale-bone and wood-fall assemblages. Four benthic landers containing replicate whale-bone, wood, and inorganic control substrates were concurrently deployed for 15 months on the Washington-Oregon margin; two each at depths of ~1600 and ~2800 m, separated by distances of > 200 km. Whale-bone, wood, and inorganic substrates supported assemblages with different community structures, even within landers. Community composition was significantly different between depths and between landers within a depth, indicating variability on bathymetric and regional scales. Wood blocks at ~1600 m were heavily degraded by wood-boring xylophagaid bivalves, which consumed up to ~90% of wood-block mass. Xylophagaid boring and defecation increased habitat availability and complexity as well as the range of nutritional niches; this led to a high abundance of macrofauna inhabiting the borings inside the wood. Xylophagaid colonization was absent to mild in deeper wood blocks at sites further offshore, which we hypothesize results partly from lower propagule supply at increased distances from terrestrial forests. Bulk stable isotope analyses revealed that co-located whale-bone and wood assemblages had different trophic structures. Whale-bone and wood were dominant basal food sources; however, the relative importance of background particulate organic matter (POM) to faunal diets varied among taxa, functional groups, and between whale-bone and wood substrates, with background POM less important on wood. We hypothesize that labile particulate organic material in xylophagaid feces provides an especially important food resource at wood falls. This dissertation provides deeper insight into drivers of variability and quantifies some important aspects of organic-fall ecology.

Keywords

Biological oceanography, biodiversity, deep sea, ecology, organic falls, whale bone, wood

URI

https://hdl.handle.net/10125/105101

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Ph.D. - Oceanography

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