D. A. Fisk

Bio: D. A. Fisk is an academic researcher from University of Queensland. The author has contributed to research in topics: Coral & Catalaphyllia. The author has an hindex of 1, co-authored 1 publications receiving 39 citations.

Free-living corals: distributions according to plant cover, sediments, hydrodynamics, depth and biological factors

Abstract: in 1974, 8 free-living coral species were found to inhabit the sandy sea floor adjacent to Lizard Island, Great Barrier Reef (14°40′S; 145°78′E). They fall into two groups which colonize two dissimilar sediment types. Plant cover increases with depth and, because of its effect on sediment characteristics, is thought to be a significant factor affecting coral distributions. The shallower coarse to medium grain sediments (0.5 to 0.125 mm) are mainly colonized by Heteropsammia cochlea, Heterocyathus aequicostatus, Diaseris distorta, and to a lesser extent by Cycloseris cyclolites. The deeper sediments are made up of a biogenically derived coarse fraction (larger than 0.5 mm) combined with an equally high proportion of fine-grade material. Corals typically found on these sediments are: Trachyphyllia geoffroyi, Catalaphyllia jardinei, Cynarina lacrymalis, and Cycloseris patelliformis. The content of non-carbonate material in the sediments reflects the hydrodynamics of the area and hence the degree of sedimentation, i.e., traction, saltation, or suspension loads, the corals have to cope with. Depth of occurrence was found to predict local coral distributions but was not applicable to other regions. Other factors which are discussed in relation to coral distributions include: coral mobility, coral shape, the effect of an obligate sipunculan associate, Aspidosiphon jukesii, in Heteropsammia cochlea and Heterocyathus aequicostatus, and settlement requirements.

Diet of Worms Emended: An Update of Polychaete Feeding Guilds

Abstract: Polychaetes are common in most marine habitats and dominate many infaunal communities. Functional guild classification based on taxonomic identity and morphology has linked community structure to ecological function. The functional guilds now include osmotrophic siboglinids as well as sipunculans, echiurans, and myzostomes, which molecular genetic analyses have placed within Annelida. Advances in understanding of encounter mechanisms explicitly relate motility to feeding mode. New analyses of burrowing mechanics explain the prevalence of bilateral symmetry and blur the boundary between surface and subsurface feeding. The dichotomy between microphagous deposit and suspension feeders and macrophagous carnivores, herbivores, and omnivores is further supported by divergent digestive strategies. Deposit feeding appears to be limited largely to worms longer than 1 cm, with juveniles and small worms in general restricted to ingesting highly digestible organic material and larger, rich food items, blurring the macrophage-microphage dichotomy that applies well to larger worms.

Coarse-scale horizontal patchiness and vertical migration of zooplankton in Gulf Stream warm-core ring 82-H

Abstract: A 1-m 2 MOCNESS with 20 nets was used to make a series of tows in Gulf Stream meander/ring 82-H (September/October 1982) including two 0–100 m undulating “towyos”. One towyo, made at dusk in the core of 82-H (of Sargasso Sea/Gulf Stream origin) permitted study of the effect of diel migration on the spatial variability of copepod and euphausiid species abundance, and species composition in a region of low physical variability. The other towyo taken across a front on the outer edge of 82-H (a mixture of Gulf Stream, Shelf and Slope Water), allowed comparison of spatial variability of the same biological properties in a region of strong physical variability. A sharp transition in euphausiid species composition occurred in the ring core after sunset as dielly migrating euphausiids moved into the surface waters. A similar, but less extreme change took place in copepod species composition because a smaller proportion of these migrated. All copepod migrants also entered surface waters after sunset with species living deeper in the water column during the day arriving in the surface waters later than those living shallower. Enright 's (1977, Limnology and Oceanography , 22 , 856–872) hypothesis for the metabolic advantages available through diel vertical migration does not account for the observed behavior of the migrating copepods and euphausiids at this time and place. Estimated swimming speeds (typically 50–200 m h −1 ) of migrating copepods and euphausiids were similar in spite of large differences in body size between the two groups. Variations in species composition were substantially larger at the edge of the ring where species proportions changed radically in concert with changes in water-mass properties. There were also large differences in species composition between the samples from the ring core and the front which equaled those which occurred across the front. Hydrographic differences were stronger than diel changes due to migration for copepods but not for euphausiids. Streamers of surface water which originated within the frontal region and spiraled into the ring core could provide colonizers of many species not present at the time of ring formation.