Comparison of a sediment trap and plankton pump for time‐series sampling of larvae near deep‐sea hydrothermal vents

Abstract

Studies of larval dispersal and supply are critical to understanding benthic population and community dynamics. A major limitation to these studies in the deep sea has been the restriction of larval sampling to infrequent research cruises. In this study, we investigated the utility of a sediment trap for autonomous, time‐series sampling of larvae near deep‐sea hydrothermal vents. We conducted simultaneous deployments of a time‐series sediment trap and a large‐volume plankton pump in close proximity on the East Pacific Rise (2510‐m depth). Grouped and species‐specific downward fluxes of larvae into the sediment trap were not correlated to larval abundances in pump samples, mean horizontal flow speeds, or mean horizontal larval fluxes. The sediment trap collected a higher ratio of gastropod to polychaete larvae, a lower diversity of gastropod species, and over‐ or undercollected some gastropod species relative to frequencies in pump sampling. These differences between the two sampling methods indicate that larval concentrations in the plankton are not well predicted by fluxes of larvae into the sediment trap. Future studies of deep‐sea larvae should choose a sampling device based on specific research goals. Limited by battery power, a plankton pump in combination with a current meter is useful for estimating horizontal advective fluxes in short‐term (days to weeks) studies of larval dispersal. A sediment trap, selecting for larvae with downward trajectories, is more appropriate for studies of larval supply to the benthos. For some species, a time‐series sediment trap can collect sequential larval samples for long‐term studies (months to years) for correlation to larval settlement and recruitment patterns.

Larvae from afar colonize deep-sea hydrothermal vents after a catastrophic eruption

“…Supply of Cyathermia naticoides, Lepetodrilus spp., Gorgoleptis spiralis, and Bathymargarites symplector declined significantly after the eruption, despite the continued presence of potential source populations within 6 km to the south at V-vent. In contrast, Ctenopelta porifera, which had been virtually absent before the eruption [only a single individual in the 2004-2005 trap samples and one in a 2004 pump sample (25)] was supplied in significantly higher numbers afterward. During a few intervals of the larval sampling series, the change in supply of some species over several weeks was as high, or higher, than the difference in mean supply between pre-and posteruption.…”

“…On recovery, samples from the traps were maintained at approximately 4°C until the larvae (molluscs, polychaetes, and crustaceans) were sorted and identified morphologically (47) under a dissecting microscope to the lowest taxonomic level possible (e.g., species level for most gastropods). The traps collect larvae that are swimming or sinking downward, and flux into the trap is considered an indicator of larval supply to the benthos (25,48).…”

A biologist’s guide to assessing ocean currents: a review

“…For example, almost 30 yr ago, it was inferred that the anticyclonic (clockwise) flow of the North Atlantic gyre would carry hatching turtles from nesting beaches in Florida across the Atlantic to distant sites such as the Azores (Carr 1987). More recently, the easy access to direct measurements of currents has led biologists to examine some of the subtleties of current flows (Beaulieu et al 2009, Landry et al 2009, Lobel 2011. In some cases, biologists are also interested in knowing the currents at specific locations and at specific times where direct measurements are not always available.…”

Causes of decoupling between larval supply and settlement and consequences for understanding recruitment and population connectivity

“…Recently, "larval supply" 4 has been used broadly to describe abundance of available propagules. Operationally, researchers 5 have measured larval supply as the number of planktonic larvae available near settlement sites 6 (e.g., Minchinton and Scheibling, 1991;Bertness et al, 1992;Miron et al, 1995;Sponaugle and 7 Cowen, 1996;Noda et al, 1998;Jeffery and Underwood, 2000;Doherty et al, 2004;Jonsson et 8 al., 2004;Todd et al, 2006;Beaulieu et al, 2009), and we use this definition here. Researchers 9 have used other terminology to refer to these available larvae (e.g., Porri et al, 2006).…”