Factors influencing the abundance, composition and diversity of deep-water benthic megafaunal communities

Abstract

This thesis examines the role of the physical environment in influencing the abundance, composition and diversity of epibenthic megafaunal communities – i.e. organisms > 2-3 cm living on the seafloor – in deep waters on continental margins (>100 m). In particular, I examine the role of fine-scale substrate features (e.g. presence of cobbles, boulders), the shape of the seafloor at local scales (100 m – kilometers), and oceanographic properties (temperature, currents, water column structure) at broader spatial scales (1 – 100s km). Factors were assessed at varying spatial scales (< 1 m to 100s of km), and in various deep-water habitats on continental shelves (~75 – 530 m depth), in a submarine canyon (~650 – 850 m depth), and at the base of the continental slope (~1000 – 3000 m depth). Sampling tools for biological communities included a 4-year field experiment, optical imagery from high-definition video and photographic cameras, and epibenthic trawling surveys. At fine spatial scales (< 1 m), recruitment of 2 species of deep-water corals in a submarine canyon was influenced by substrate type, with a preference for hard substrate (Chapter 2). I suggested that recruitment is also dependent on reproductive mode in corals, which differed between species, and local hydrodynamics. To further examine the role of substrate at fine spatial scales, I developed an approach using optical imagery to estimate substrate complexity based on principles of computer vision (Chapter 3). At local scales (10 m – 1 km), using the approach I developed in Chapter 3, I determined the influence of variability in substrate types on epibenthic megafaunal community composition and diversity (Chapters 4 and 5). In contrast, megafaunal abundance was correlated with variability in geomorphometry and oceanographic properties (Chapter 5). At mesoscales (10 – 100s km), on a dynamic continental shelf influenced by a strong oceanographic front, community composition was best explained by oceanographic properties, especially spatial patterns in temperature (Chapter 6). This thesis provided new approaches (Chapters 3 and 6) to study deep benthic ecosystems, and described scale-specific species-environment relationships (Chapters 2, 4, 5 and 6) necessary to design sampling surveys in unexplored environments and establish conservation strategies.