The Role of Connectivity in Structuring Community Composition and Diversity at Hydrothermal Vents Across the Northwest Pacific

Okinawa Institute of Science and Technology Graduate UniversityDoctor of PhilosophyConnectivity, or the movement of individuals among isolated habitat patches, promotes local and regional biodiversity, and its resilience to disturbances both natural and anthropogenic. Species associated with seafloor hydrothermal vent habitats are distinctly reliant on connectivity due to their spatial restriction to the point source of chemical energy from vent chimneys that fuels their chemosynthetic food web. Measuring connectivity among hydrothermal vents is particularly urgent in regions where mining of these ecosystems is imminent. Our understanding of connectivity is limited by the scarcity of observational data from these inaccessible deep-sea ecosystems. Modelling is a viable alternative to the study of connectivity, as the dispersal that facilitates connectivity is mostly dictated by predictable ocean currents, which can be reliably simulated. This thesis combines empirical observations of species’ distributions and environmental conditions at hydrothermal vents with simulations of dispersal, to model connectivity among vent sites in the Northwest Pacific. First, I curate a regional dataset of hydrothermal vent species distributions to infer connectivity in the form of a species assemblage network (Chapter 1). I then simulate how the planktonic larvae of vent species disperse among the vent sites in this region using Lagrangian particle tracking methods within an Ocean General Circulation Model (Chapter2). Finally, I combine the among-site dispersal estimates with observations of local environmental parameters to create a simulated species assemblage network using a metacommunity model (Chapter 3). This metacommunity model accurately recreated the empirical observations from chapter 1 and gives crucial insight into the interacting effects of dispersal barriers and environmental niche on driving diversity and community composition patterns at hydrothermal vents. Furthermore, I used the combination of observed and simulated connectivity results to quantitatively evaluate the relative role each individual hydrothermal vent plays in maintaining connectivity and biodiversity in the region. Such an evaluation has critical and timely implications for proposed mining and the spatial management of hydrothermal vents in this region. Lastly, we demonstrate that hydrothermal vents are natural laboratories for the advancement of metacommunity theory and conservation ecology due to their characteristic isolation and discrete nature.doctoral thesi

The Role of Connectivity in Structuring Community Composition and Diversity at Hydrothermal Vents Across the Northwest Pacific

Okinawa Institute of Science and Technology Graduate UniversityDoctor of PhilosophyConnectivity, or the movement of individuals among isolated habitat patches, promotes local and regional biodiversity, and its resilience to disturbances both natural and anthropogenic. Species associated with seafloor hydrothermal vent habitats are distinctly reliant on connectivity due to their spatial restriction to the point source of chemical energy from vent chimneys that fuels their chemosynthetic food web. Measuring connectivity among hydrothermal vents is particularly urgent in regions where mining of these ecosystems is imminent. Our understanding of connectivity is limited by the scarcity of observational data from these inaccessible deep-sea ecosystems. Modelling is a viable alternative to the study of connectivity as the dispersal that facilitates connectivity is mostly dictated by predictable ocean currents, which can be reliably simulated. This thesis combines empirical observations of species’ distributions and environmental conditions at hydrothermal vents with simulations of dispersal, to model connectivity among vent sites in the Northwest Pacific. First, I curate the most comprehensive regional dataset of hydrothermal vent species distributions to infer connectivity in the form of a species assemblage network (Chapter 1). I then simulate how the planktonic larvae of vent species disperse among the vent sites in this region using Lagrangian particle tracking methods within an Ocean General Circulation Model (Chapter 2). Finally, I combine the among-site dispersal estimates with observations of local environmental parameters to create a simulated species assemblage network using a metacommunity model (Chapter 3). This metacommunity model accurately recreated the empirical observations from chapter 1 and gives crucial insight into the interacting effects of dispersal barriers and environmental niche on driving diversity and community composition patterns at hydrothermal vents. Furthermore, I used the combination of observed and simulated connectivity results to quantitatively evaluate the relative role each individual hydrothermal vent plays in maintaining connectivity and biodiversity in the region. Such an evaluation has critical and timely implications for proposed mining and the spatial management of hydrothermal vents in this region. Lastly, we demonstrate that hydrothermal vents are natural laboratories for the advancement of metacommunity theory and conservation ecology due to their characteristic isolation and discrete nature.doctoral thesi

Paired high‐throughput, in situ imaging and high‐throughput sequencing illuminate acantharian abundance and vertical distribution

Acantharians (supergroup Rhizaria) can be important contributors to surface primary production and to carbon flux to the deep sea, but are often underestimated because their delicate structures are destroyed by plankton nets or dissolved by chemical fixatives. As they are also uncultured, relatively little is known about acantharian biology, especially regarding their life cycles. Here, we take a paired approach, bringing together high-throughput, in situ imaging and metabarcode sequencing, to investigate acantharian abundance, vertical distribution, and life history in the western North Pacific. Concentrations of imaged acantharian cells correlated well with relative abundances of 18S rRNA gene sequences from acantharians with known, recognizable morphologies, but not to sequences corresponding to acantharians with unknown morphology. These results suggest that morphologically undescribed clades may lack the characteristic star-shaped acantharian skeleton or are much smaller than described acantharians. The smaller size of acantharians imaged at depth supports current hypotheses regarding nonsymbiotic acantharian life cycles: cysts or vegetative cells release reproductive swarmer cells in deep water and juvenile cells grow as they ascend toward the surface. Moreover, sequencing data present the possibility that some photosymbiotic acantharians may also reproduce at depth, like their nonsymbiotic, encysting relatives, which is counter to previous hypotheses. Finally, in situ imaging captured a new acantharian behavior that may be a previously undescribed predation strateg

Species assemblage networks identify regional connectivity pathways among hydrothermal vents in the Northwest Pacific

The distribution of species among spatially isolated habitat patches supports regional biodiversity and stability, so understanding the underlying processes and structure is a key target of conservation. Although multivariate statistics can infer the connectivity processes driving species distribution, such as dispersal and habitat suitability, they rarely explore the structure. Methods from graph theory, applied to distribution data, give insights into both connectivity pathways and processes by intuitively formatting the data as a network of habitat patches. We apply these methods to empirical data from the hydrothermal vent habitats of the Northwest Pacific. Hydrothermal vents are “oases” of biological productivity and endemicity on the seafloor that are imminently threatened by anthropogenic disturbances with unknown consequences to biodiversity. Here, we describe the structure of species assemblage networks at hydrothermal vents, how local and regional parameters affect their structure, and the implications for conservation. Two complementary networks were formed from an extensive species assemblage dataset: a similarity network of vent site nodes linked by weighted edges based on their pairwise assemblage similarity and a bipartite network of species nodes linked to vent site nodes at which they are present. Using these networks, we assessed the role of individual vent sites in maintaining network connectivity and identified biogeographic sub-regions. The three sub-regions and two outlying sites are separated by their spatial arrangement and local environmental filters. Both networks detected vent sites that play a disproportionately important role in regional pathways, while the bipartite network also identified key vent sites maintaining the distinct species assemblages of their sub-regions. These regional connectivity pathways provide insights into historical colonization routes, while sub-regional connectivity pathways are of value when selecting sites for conservation and/or estimating the multivent impacts from proposed deep-sea mining

Hydrothermal vent fauna of the western Pacific Ocean: Distribution patterns and biogeographic networks

Aim: Deep-sea hydrothermal vent habitats support a low-diversity fauna in which most species are unique to the ecosystem. To inform conservation planning around this vulnerable marine ecosystem, we examine species distributions over a wide area to assess the underlying beta-diversity components and to examine biogeographic patterns. We assess the concept of a highly connected fauna that would repopulate areas of local extinction from distal locations. Location: Western Pacific Ocean from Japan to New Zealand. Methods: We assemble a database of 295 confirmed species records for 11 western Pacific vent systems. The SET beta-diversity framework supports query of the distribution of pairwise pattern components in comparisons among vent systems. We build a network based in graph theory to examine connectivity among vent systems based on shared species similarity. A bipartite network revealed the relative role of each species in linkages among vent system nodes. We assess the importance of sampling bias and distance between systems. Results: Overall, two-thirds of the taxa are restricted to a single basin or arc. The Mariana Trough system has the highest corrected weighted endemism for vent-specific species, followed by that of the Okinawa Trough. Species replacement is the dominant feature of beta-diversity. Eleven vent systems form seven network modules with stronger connectivity in the Southwest than Northwest Pacific. The Manus Basin vent system emerges as a network ‘hub’ reflecting its central geographic near the equator. Main Conclusion: Two western Pacific biogeographic provinces arise, north and south of the equator that few species transcend. Local and regional conservation plans should consider the low network connectivity and high system endemism in management of hydrothermal vent ecosystems in the event of seabed mining. Species recruitment is unlikely to transcend vent system boundaries. We identify Okinawa Trough, Mariana Trough, Manus Basin, Feni-Tabar Arc and Kermadec Arc for development of conservation plans that initiate or expand protection