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.

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 strategy.

Acantharians are important contributors to surface primary production and to carbon flux 10 to the deep sea, but are often underestimated because their delicate structures are destroyed by plankton nets or dissolved by preservatives. As a result, 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 high-throughput sequencing, to investigate acantharian abundance, vertical distribution, and life-history 15 in the western North Pacific. Observed concentrations of acantharian cells correlated well with sequence abundances from acantharians with known, recognizable morphologies, but not to sequences from those without known morphology (basal environmental clades). These results suggest basal clades may lack characteristic starshaped skeletons or are much smaller than known acantharians. The decreased size-20 range of acantharians imaged at depth supports current hypotheses regarding asymbiotic acantharian life cycles: cysts or vegetative cells release reproductive swarmer cells at depth and juvenile cells grow as they ascend towards the surface. Moreover, sequencing data present the possibility that photosymbiotic acantharians also reproduce at depth, like their asymbiotic, encysting relatives, which is counter to 25 previous hypotheses. Finally, in-situ imaging captured a new acantharian behavior that may be a previously undescribed predation strategy.

Connectivity among isolated habitat patches via planktonic larval dispersal is crucial for maintaining the regional diversity of hydrothermal vents. Despite, increasing sophistication of techniques for simulating dispersal, limited information on biological and behavioural traits of vent-associated species has unknown affects on the applicability of these methods for conservation. Here we focus on the role of periodic reproduction on dispersal among hydrothermal vents, as periodic spawning has increasingly been observed in a variety of taxa. For generalizeability, we simulate the dispersal of larvae under treatments of periodic and aperiodic release timing at various depths, with a consistant but variable planktonic larval duration. Our results show a highly variable effect of periodicity on the characteristics and distribution of dispersal, which are heavily modified by the dispersal depth and source location. The capacity for reproductive periodicity to impact the among-site dispersal warrents further investigation into its prevelance and timing among vent-associated fauna.

No abstract

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 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 hydrothermal vent species assemblage networks, how local and regional parameters affect their structure, and the implications this has for conservation. Two complementary networks were formed from an extensive species assemblage dataset: a bipartite network of species nodes linked to vent site nodes at which they are present, and a similarity network of vent site nodes linked by weighted edges based on their pairwise assemblage similarity. Using these networks, we assessed the role of individual vent sites in linking their network 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 colonisation routes, while sub-regional connectivity pathways are of value when selecting sites for conservation and/or estimating the multi-vent impacts from proposed deep-sea mining.