W. Shen

Bio: W. Shen is an academic researcher. The author has contributed to research in topics: Upwelling & Zooplankton. The author has an hindex of 1, co-authored 1 publications receiving 7 citations.

Predictability of patches of neritic salps and doliolids (Tunicata, Thaliacea)

Abstract: The occurrence of large patches of gelatinous zooplankton has for decades been considered to be unpredictable. An evaluation of our own data and published results on abundances of doliolids and salps from ocean margins reveals that a considerable degree of prediction is possible, based upon meteorological and boundary current intrusion dynamics.

Distribution and abundance of thaliaceans and copepods off the southeastern U.S.A. during winter

Abstract: The abundance and distribution of planktonic copepods and tunicates were studied in relation to physical and biological variables from late January to early February 1990 on the middle and outer shelf off South Carolina, U.S.A. The inner and part of the middle shelf were vertically mixed throughout the study period, the middle and outer shelf only after passage of a storm on 4 and 5 February. Subtidal currents at the 40 m isobath were highly correlated with local alongshore winds, whereas at the 75 m isobath the currents showed a mixed response to wind and Gulf Stream events. Chlorophyll concentrations in the study area usually surpassed 0.5 and reached levels of 3 μg l−1. Zooplankton was characterized by high abundances of doliolids (Tunicata, Thaliacea) and relatively low concentrations of calanoid and cyclopoid copepods. When doliolids were very abundant the vertical distribution of doliolids was inversely related to those of the calanoids. We hypothesized that this inverse relationship could be the result of (a) doliolids removing food particles, thus reducing food particle concentrations, and through that calanoid reproduction rates; (b) doliolids ingesting calanoid eggs and nauplii, thereby reducing copepod recruitment; (c) active avoidance of doliolids by downward migration of copepods; and (d) vertical shear between the upper and lower part of the stratified water column. At stations on the middle shelf the abundance of photo- and heterotrophic nanoplankton was inversely related to the abundance of doliolids. The frequency of occurrence of thaliacea in neritic regions is evaluated in relation to hydrographic regimes and the availability of seed populations. From previous and present observations we assume that thaliacea due to their high rates of feeding, individual and population growth could impact zooplankton communities two-fold: indirectly, by reducing phytoplankton concentrations rapidly thus affecting reproduction of certain calanoid taxa, and directly, by consuming copepod eggs.

Digestion of diatoms by planktonic copepods and doliolids

Abstract: The goal of our studies was to quantify the digestive performance of a calanoid copepod in comparison to a commonly occurring pelagic tunicate. A comparison of the carbon and nitrogen content of quantitatively recovered fecal pellets with ingested amounts revealed that the large calanoid Eucalanus hyalinus digested the diatoms Thalassiosira weissflogii and Rhizosolenia alata significantly better than the doliolid Dolioletta gegenbauri did. This was attributed to the copepods' ability to crush the diatom cells after ingestion, while the doliolids caused minimal physical damage to the diatom cells. As for D. gegenbauri, it digested the large diatom R. alata far better than the small diatom T. weissflogii. The pellets from the latter contained nearly 50% of the ingested carbon and nitrogen. These findings are supported by visual observations. The results imply that doliolids are not able to utilize diatoms as efficiently as calanoid copepods, and will most likely rely more on soft- walled food particles such as flagellates. These findings also imply that a considerable percentage of particulate organic matter ingested by doliolids, in water masses dominated by diatoms, could become available to the benthic communities of continental shelves since the doliolid pellets sink quite rapidly.

SHORT COMMUNICATION Determination of generation time and asexual fecundity of doliolids (Tunicata, Thaliacea)

Abstract: The goal of this study was to provide temporal information on the generation time of Dolio- letta gegenbauri and some of the life cycle's components. At 20°C and ~90 µg C l-1 of ingestible phyto- plankton, D.gegenbauri's life cycle is completed in 20.5 days. Phorozooids ♢ 5 mm produce on average 11.0 gonozooids day-1 over a period of 8-18 days. Utilizing field data on the abundance and size distri- bution of an assemblage of phorozooids and nurses, in conjunction with experimentally obtained rates, indicates that asexual production per cubic meter by phorozooids with that of nurses should result in rapid colonization of a wide shelf by doliolids, as observed during July and August 1981 on the southeastern continental shelf of the USA.