The use of a Canadian (perspective) grid in deep-sea photography

Abyssal deposit-feeding rates consistent with the metabolic theory of ecology

The Metabolic Theory of Ecology (MTE) posits that metabolic rate controls ecological processes, such as the rate of resource uptake, from the individual‐ to the ecosystem‐scale. Metabolic rate has been found empirically to be an exponential function of whole organism body mass. We test a fundamental assumption of MTE, whether resource uptake scales to metabolism, by examining detritivores accessing a single common resource pool, an ideal study case. We used an existing empirical model of ingestion for aquatic deposit feeders adjusted for temperature to test whether ingestion by abyssal deposit feeders conforms to MTE‐predicted feeding rates. We estimated the sediment deposit‐feeding rates of large invertebrates from two abyssal study sites using time‐lapse photography, and related those rates to body mass, environmental temperature, and sediment organic matter content using this framework. Ingestion was significantly related to individual wet mass, with a mass‐scaling coefficient of 0.81, with 95% confidence intervals that encompass the MTE‐predicted value of 0.75, and the same pattern determined in other aquatic systems. Our results also provide insight into the potential mechanism through which this fundamental assumption operates. After temperature correction, both deep‐ and shallow‐water taxa might be summarized into a single mass‐scaled ingestion rate.

Area Estimation of Deep-Sea Surfaces from Oblique Still Images

Estimating the area of seabed surfaces from pictures or videos is an important problem in seafloor surveys. This task is complex to achieve with moving platforms such as submersibles, towed or remotely operated vehicles (ROV), where the recording camera is typically not static and provides an oblique view of the seafloor. A new method for obtaining seabed surface area estimates is presented here, using the classical set up of two laser devices fixed to the ROV frame projecting two parallel lines over the seabed. By combining lengths measured directly from the image containing the laser lines, the area of seabed surfaces is estimated, as well as the camera’s distance to the seabed, pan and tilt angles. The only parameters required are the distance between the parallel laser lines and the camera’s horizontal and vertical angles of view. The method was validated with a controlled in situ experiment using a deep-sea ROV, yielding an area estimate error of 1.5%. Further applications and generalizations of the method are discussed, with emphasis on deep-sea applications.

Spatial and temporal variation in sponge spicule patches at Station M, northeast Pacific

Changes in habitat-forming organisms can have complex consequences for associated species. Sessile epibenthic glass "plate" sponges (Porifera: Hexactinellida) are conspicuous inhabitants of soft-sediment abyssal areas and their siliceous spicules create persistent spicule patches on the seafloor. Sponge spicule patch density, spatial dispersion, and percent cover were examined over a seven-year period (2006-2013) using remotely operated vehicle videos from Station M in the abyssal northeast Pacific (50˚00N, 123˚00W, ~4,000 m depth). There was an apparent large increase in newly dead plate sponges in February 2007 compared with December 2006, with this trend continuing through June 2007 (mean 0.03 % cover increasing to 0.33 %). A second increase in mean percent cover of dead plate sponges occurred from May 2011 (0.24 %) through June 2012 (0.60 %). Among the 28 megafaunal taxa occurring in association with the patches, the distributions of three taxa [two sponge taxa (Porifera) and brittle stars (Ophiuroidea)] suggested selectivity for the sponge spicule patches. The community structure of visible megafauna within sponge spicule patches was different when compared with that outside the patches suggesting that the sponges, after death, provide preferred habitat patches for certain benthic megafauna. These findings indicate that sponge spicule patches contribute to habitat heterogeneity in space and time.

Seasonal dynamics of megafauna on the deep West Antarctic Peninsula shelf in response to variable phytodetrital influx

The deep West Antarctic Peninsula (WAP) shelf is characterized by intense deposition of phytodetritus during spring/summer months, while very little food material reaches the seafloor during winter. The response of the shelf benthic megafauna to this highly variable food supply is still poorly understood. In order to characterize the deposition of phytodetritus and the megabenthic community response, we deployed a seafloor time-lapse camera at approximately 590 m depth on the mid WAP shelf west of Anvers Island for 15 months. Seafloor photographs were taken at intervals of 12 or 24 h nearly continuously from 9 December 1999 (austral winter) to 20 March 2001 (summer) and analysed for phytodetritus deposition and megafaunal dynamics. Seafloor images indicated a marked seasonal arrival of greenish phytodetritus, with large interannual and seasonal variability in the coverage of depositing phytodetrital particles. The surface-deposit-feeding elasipod holothurians Protelpidia murrayi and Peniagone vignoni dominated the epibenthic megafauna throughout the year, frequently constituting more than 80% of the megafaunal abundance, attaining total densities of up to 2.4 individuals m(-2). Elasipod abundances were significantly higher in summer than winter. During summer periods of high phytodetrital flux, Pr. murrayi produced faecal casts at higher rates, indicating intensified population-level feeding activity. In March-June 2000, faecal casts lasted longest, suggesting lower horizontal bioturbation activity during autumn-winter. Our data indicate that the Pr. murrayi population increases its feeding rates in response to increasing amounts and/or lability of organic matter on the sediment surface. Assuming that this species feeds on the top millimetre of the sediment, we estimate that, during periods of high phytodetrital flux, the Pr. murrayi population reworks one square metre of sediment surface in approximately 287 days. We suggest that Pr. murrayi is an important species for organic-carbon recycling on the deep WAP shelf, controlling the availability of deposited labile phytodetritus to the broader shelf benthic community.

Community change in the variable resource habitat of the abyssal northeast Pacific

Research capable of differentiating resource-related community-level change from random ecological drift in natural systems has been limited. Evidence for nonrandom, resource-driven change is presented here for an epibenthic megafauna community in the abyssal northeast Pacific Ocean from 1989 to 2004. The sinking particulate organic carbon food supply is linked not only to species-specific abundances, but also to species composition and equitability. Shifts in rank abundance distributions (RADs) and evenness, from more to less equitable, correlated to increased food supply during La Niña phases of the El Niño Southern Oscillation. The results suggest that each taxon exhibited a differential response to a sufficiently low dimension resource, which led to changes in community composition and equitability. Thus the shifts were not likely due to random ecological drift. Although the community can undergo population-level variations of one or more orders of magnitude, and the shape of the RADs was variable, the organization retained a significant consistency, providing evidence of limits for such changes. The growing evidence for limited resource-driven changes in RADs and evenness further emphasizes the potential importance of temporally variable disequilibria in understanding why communities have certain basic attributes.

ABUNDANCE AND SIZE DISTRIBUTION DYNAMICS OF ABYSSAL EPIBENTHIC MEGAFAUNA IN THE NORTHEAST PACIFIC

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.