Abundance and Size Distribution Dynamics of Abyssal Epibenthic Megafauna in the Northeast Pacific

Abstract

The importance of interannual variation in deep-sea abundances is now becoming recognized. There is, however, relatively little known about what processes dominate the observed fluctuations. The abundance and size distribution of the megabenthos have been examined here using a towed camera system at a deep-sea station in the northeast Pacific (Station M) from 1989 to 2004. This 16-year study included 52 roughly seasonal transects averaging 1.2 km in length with over 35600 photographic frames analyzed. Mobile epibenthic megafauna at 4100 m depth have exhibited interannual scale changes in abundance from one to three orders of magnitude. Increases in abundance have now been significantly linked to decreases in mean body size, suggesting that accruals in abundance probably result from the recruitment of young individuals. Examinations of size-frequency histograms indicate several possible recruitment events. Shifts in size-frequency distributions were also used to make basic estimations of individual growth rates from 1 to 6 mm/month, depending on the taxon. Regional intensification in reproduction followed by recruitment within the study area could explain the majority of observed accruals in abundance. Although some adult migration is certainly probable in accounting for local variation in abundances, the slow movements of benthic life stages restrict regional migrations for most taxa. Negative competitive interactions and survivorship may explain the precipitous declines of some taxa. This and other studies have shown that abundances from protozoans to large benthic invertebrates and fishes all have undergone significant fluctuations in abundance at Station M over periods of weeks to years.

The reproductive ecology of deep-sea ophiuroids around the Crozet plateau, Southern Indian ocean, under contrasting productivity regimes

“…Increases in POM flux were followed 17 to 22 months later by increases in smaller size classes of O. bathybia. Unlike holothurians, which feed directly on labile phytodetritus (Wigham et al 2003) and which may change suddenly in abundance (Billett et al 2001Ruhl, 2007;Smith et al 2009), O. bathybia had a longer reaction time. This may reflect the less responsive characteristics of the reproductive biology of the ophiuroids, or may be related to time-lagged responses of their food, principally macrofauna, to POM flux.…”

Inter-annual species-level variations in an abyssal polychaete assemblage (Sta. M, NE Pacific, 4000 m)

“…rostrata), suggesting differential responses to food supply, as previously noted among holothurians at Sta. M (Ruhl, 2007).…”

Carbon flows in the benthic food web of the Porcupine Abyssal Plain: The (un)importance of labile detritus in supporting microbial and faunal carbon demands

“…This finding initiated several large-scale programs at this station and the study site has now been established as PAPSustained Observatory with particular emphasis on export of particulate organic matter from the water column to the seafloor and responses by the benthic community, most notably holothurians (Lampitt et al 2010a). An important feature at PAP is its seasonal and multi-annual dynamics with respect to phytodetritus deposition, which is strongly linked to the spring phytoplankton bloom in surface waters (Billett et al 1983) and the response of the benthic community to seasonal and interannual supply of organic matter Ruhl et al 2008). It is not clear how important these phytodetritus pulses are in the total carbon budget of the PAP because data on carbon fluxes and benthic biomass have not been integrated at the food web level.…”