Underwater observations of gelatinous zooplankton: Sampling problems, feeding biology, and behavior1

Abstract

Observations by SCUBA divers on the distribution and biology of gelatinous zooplankton have stimulated speculations about the structure of tropical oceanic ecosystems. The gelatinous group represents one of four apparent strategies for survival in pelagic animals. Conventional plankton collection probably does not sample these organisms accurately due to their patchy distribution, fragility, and escape responses. Many gelatinous plankters filter feed using mucous structures; these mechanisms are important because of their efficiency in collecting particulate material, and because mucus is a source of organic aggregates in the sea. Such aggregates are often large, irregularly distributed, and of complex composition; these properties are rarely discerned by conventional sampling gear. The aggregates contribute considerable spatial heterogeneity to a seemingly homogeneous environment. An entire category of pelagic animals lives in association with these floating substrates. The diversity and trophic complexity of epipelagic plankton communities have been underestimated by previous investigators.

The Arctic sea butterfly Limacina helicina: lipids and life strategy

“…L. helicina has a thin and fragile shell that is often damaged and broken during sampling, and the thin parapodia are easily torn or ripped off when collected in nets (Hamner et al 1975;Gilmer 1990). In addition, single undamaged adults were collected from the surface with a sieve (20 cm diameter) on a rod or with 1-l plastic jars from a Zodiac.…”

The chemical composition of macroscopic aggregates in two neretic seas1

“…It has been suggested that macroscopic aggregates are rich food sources (Alldredge 1972(Alldredge , 1976Hamner et al 1975;Silver ct al. 1978;Trent et al 1978).…”

“…Particles >l mm have been consistently overlooked in determinations of particle size distributions in the ocean, primarily because most collecting and sizing techniques destroy them (Hamner et al 1975;Trent et al 1978). However, direct observations from submersibles (Suzuki and Kato 1953) and by SCUBA indicate that fragile, amorphous macroscopic aggregates, ranging from 1 mm to several meters in diameter, are abundant and significant components of pelagic communities.…”

“…Macroscopic aggregates serve as enrichment sites for organic carbon, pheopigments, and chlorophyll (Alldredge 1976;Trent et al 1978), as microhabitats (Alldredge 1972;, and as sources of microscale heterogeneity (Hamner et al 1975). Suspended sediment traps collect many apparently large, heavy, and dense particles (Bishop et al 1977).…”

The role of particulate matter in the productivity of surface waters

“…Some zooplankton, such as appendicularians and pteropods, discard gelatinous materials in the surface waters as part of their normal activities (Gilmer, 1972;Hamner, et al, 1975;Alldredge, 1976). These materials can account for extremely high local POC values in the surface waters.…”