(^) It is not necessary for all purposes to collect animals. A great deal can be learned from
photo- and videographs of the seafloor. Deep-sea cameras and lighting arrangements
became available in the 1960s and provided clear looks at the appearance of the
seafloor (Plate 13.1). Cameras can be left in place, taking time-series of photos. This
has indicated that benthic environments are moderately dynamic, with episodic
stirring of sediment by passing sea cucumbers and urchins, with mining and mound
building by burrowing deposit feeders. There are intense depositional events when
phytodetritus arrives at the end of the spring bloom, or when a large fish or mammal
carcass (a deadfall) sinks to the bottom. In regard to food deposition, important results
have been obtained by deploying cameras to take time-lapse photos of simply the
sediment surface or of baits, a tuna body for example, moored at or just above the
bottom. Declining blooms rather suddenly create turbid near-bottom phytodetritus
layers. Photo sequences of baits (Fig. 13.1) show an arrival sequence of mobile
animals.
Fig. 13.1 Macrourid fish attracted to a bait anchored just above the seafloor at 5850 m
in the northwest Pacific.
(^) (From the John Isaacs Papers, Scripps Institute of Oceanography Archives, University of California, San Diego.)
(^) Early collections of animals from the benthos were made with dredges. A simple
dredge is a flat, steel box open at two of the longer sides. One open side is attached to
a towing bail, the other to a collecting bag. The bag can be a mesh of chain or string.
The dredge is hauled over and partly through the sediment, sieving it and retaining
larger animals. Sufficiently rugged designs can be used to collect or scrape over rock.
Details of design vary, including epibenthic sleds that slide along, scraping up and
sieving the top decimeter or so of sediment. Megafauna can be collected by trawls
whose footrope drags along or through the sediment surface. Beam trawls (Fig. 13.2),
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