Dynamics of temperature and chlorophyll structures above a seamount: An oceanic experiment

Three hydrographic surveys comprised of densely spaced XBT and CTD stations were conducted over Minami-kasuga Seamount, in the northwest Pacific (21°36′N, 143°38′E). A cold dome, similar to a Taylor column, was observed above the seamount top during the first survey. Uplifted isotherms penetrated to the lower euphotic zone and were associated with higher chlorophyll concentrations. Vertical displacement of uplifted isotherms decayed with elevation above the seamount, so that both temperature and chlorophyll anomalies were undetectable at depths less than 80 m. Relatively high chlorophyll concentrations in a layer from 80 m to 100m depth formed a distinctive deep chlorophyll maximum (DCM) which was less well defined away from the seamount. Calculations based on the observed chlorophyll increase and on estimated phytoplankton growth rate suggested a minimal residence time of the cold dome on the order of several days. Zooplankton densities were also higher over the seamount top, both within and above the cold dome. No cold dome, chlorophyll increase, or high zooplankton biomass were detected above the seamount on the second and third surveys, carried out 2 and 17 days later, respectively. Mixing and deflections of isotherms occurred within a boundary zone around the seamount slope during the first and third surveys.Our observations suggest that seamounts are a source of both biological and physical patchiness in the surrounding ocean as features developed above them are swept away. The importance of the seamount-generated experiment is discussed in relation to field studies of the DCM. Specifically, our observations suggest that a sharp chlorophyll maximum can be formed by enhanced in situ growth following a sub-surface upwelling event

Abstracts of Papers Presented at the 7th ANNUAL CONFERENCE ON ETHNIC AND MINORITY STUDIES

This paper reviews some of the most salient aspects of E. M. Rogg\u27s (1974) seminal work, The Assimilation of Cuban Exiles; The Role of Community and Class--a sociological study of the Cuban community in the town of West New York in northeastern New Jersey. Although taking issue with some of the author\u27s theses, this paper elaborates on other findings of the book in question by means of more recent participant-observation field research in the same neighborhood. For example, the new data confirms Rogg\u27s proposition that the organized ethnic minority helps to direct the process of acculturation, though slowly

Effects of prey density and flow speed on plankton feeding by garden eels: a flume study

Feeding by zooplanktivorous fish depends on their foraging movements and the flux of prey to which they are exposed. While prey flux is a linear function of zooplankton density and flow speed, those two factors are expected to contribute differently to fish movements. Our objective was to determine the effects of these factors for garden eels, stationary fish that feed while anchored to the sandy bottom by keeping the posterior parts of their bodies inside a burrow. Using a custom-made flume with a sandy bottom, we quantified the effects of prey density and flow speed on feeding rates by spotted garden eels (Heteroconger hassi). Feeding rates increased linearly with prey density. However, feeding rates did not show a linear relationship with flow speed and decreased at 0.25 m s⁻¹. Using label-free tracking of body points and 3D movement analysis, we found that the reduction in feeding rates was related to modulation of the eel\u27s movements, whereby the expected increase in energy expenditure was avoided by reducing exposure and drag. No effects of flow speed on strike speed, reactive distance or vectorial dynamic body acceleration (VeDBA) were found. A foraging model based on the body length extended from the burrow showed correspondence with observations. These findings suggest that as a result of their unique foraging mode, garden eels can occupy self-made burrows in exposed shelter-free sandy bottoms where they can effectively feed on drifting zooplankton

Zooplanktivory in garden eels: benefits and shortcomings of being “anchored” compared with other coral-reef fish

Garden eels are elongated zooplanktivorous fish that live in colonies on sandy bottoms, often adjacent to coral reefs. Each eel digs its own burrow, from which it partially emerges to forage on drifting zooplankton while being “anchored” with its tail inside the burrow. Feeding rates and foraging movements were examined in the garden eel Gorgasia sillneri and compared with corresponding measurements carried out as part of this study and by (Genin et al.)1 with 3 species of “free”, site-attached coral-reef fish. Feeding rates by the garden eels were substantially lower than those of the free fish. In the eels, those rates monotonically increased with increasing current speed up to ~20 cm/s, whereas in the free fish maximum rates were observed under moderate flows. A nearly linear increase in feeding rate as function of prey density was observed in both the garden eels and the free fish. However, the slope of that increase in the eels was over an order of magnitude more gradual than that reported for the free fish. The different functional responses of the two fish groups appear to be related to their morphology and maneuverability capabilities. Being elongated, anchored in a burrow and able to modulate body posture according to the flow speed allow the eels high feeding rates under strong currents. The tradeoff, compared with free fish, include limited maneuverability, slower swimming, and smaller foraging volume, rendering the eels’ functional response less efficient to increasing prey density. This cost appears to be compensated by the eels’ ability to occupy sandy, shelter-less bottoms, which in some locations are immensely more abundant than coral-covered rocks, where most planktivorous free fish live

Food selectivity and diet switch can explain the slow feeding of herbivorous coral-reef fishes during the morning.

Most herbivorous coral-reef fishes feed slower in the morning than in the afternoon. Given the typical scarcity of algae in coral reefs, this behavior seems maladaptive. Here we suggest that the fishes' slow feeding during the morning is an outcome of highly selective feeding on scarcely found green algae. The rarity of the food requires longer search time and extended swimming tracks, resulting in lower bite rates. According to our findings by noon the fish seem to stop their search and switch to indiscriminative consumption of benthic algae, resulting in apparent higher feeding rates. The abundance of the rare preferable algae gradually declines from morning to noon and seems to reach its lowest levels around the switch time. Using in situ experiments we found that the feeding pattern is flexible, with the fish exhibiting fast feeding rates when presented with ample supply of preferable algae, regardless of the time of day. Analyses of the fish's esophagus content corroborated our conclusion that their feeding was highly selective in the morning and non-selective in the afternoon. Modeling of the fishes' behavior predicted that the fish should perform a diel diet shift when the preferred food is relatively rare, a situation common in most coral reefs found in a warm, oligotrophic ocean

Abundance and distribution of nocturnal fishes over a coral reef during the night

Coral reefs are characterized by high abundance of fishes, which often have marked effects on the recruitment, nutrition, and reproduction of coral reef inhabitants. Despite the fact that fish are active over the coral reef at night, very little is known of their whereabouts or about their contribution to those processes. In the present study, the abundance and distribution of nocturnal fishes were studied over a coral reef near Eilat, Red Sea. Sampling was conducted between the surface and 15 m depth, using a stereoscopic camera system that surveyed 3.5 m(3) of water every 2 min. The density of zooplanktivorous species ranged from 0.7 to 7.4 fish 100 M-3, accounting for > 60 % of the total nocturnal fishes recorded. Fish abundance decreased with increasing distance from shore and with increasing height above bottom. Larger fish foraged at greater heights above bottom. While the appearance of zooplanktivorous fishes after sunset and their disappearance before sunrise corresponded to that of demersal zooplankton, inter-night variation in fish abundance was unrelated to variation in zooplankton abundance. Furthermore, neither current speed nor moon illumination accounted for inter-night variations in fish abundance, perhaps indicating some degree of site fidelity. The abundance of zooplanktivorous fishes was similar to 30-fold lower during the night than day. However, since nocturnal fishes feed on larger zooplankters, the biomass of zooplankton preyed upon by nocturnal fishes was similar to that of diurnal species. This study suggests that the paradigm of negligible predation by nocturnal fishes should be reconsidered

Abundance and distribution of nocturnal fishes over a coral reef during the night

Coral reefs are characterized by high abundance of fishes, which often have marked effects on the recruitment, nutrition, and reproduction of coral reef inhabitants. Despite the fact that fish are active over the coral reef at night, very little is known of their whereabouts or about their contribution to those processes. In the present study, the abundance and distribution of nocturnal fishes were studied over a coral reef near Eilat, Red Sea. Sampling was conducted between the surface and 15 m depth, using a stereoscopic camera system that surveyed 3.5 m(3) of water every 2 min. The density of zooplanktivorous species ranged from 0.7 to 7.4 fish 100 M-3, accounting for > 60 % of the total nocturnal fishes recorded. Fish abundance decreased with increasing distance from shore and with increasing height above bottom. Larger fish foraged at greater heights above bottom. While the appearance of zooplanktivorous fishes after sunset and their disappearance before sunrise corresponded to that of demersal zooplankton, inter-night variation in fish abundance was unrelated to variation in zooplankton abundance. Furthermore, neither current speed nor moon illumination accounted for inter-night variations in fish abundance, perhaps indicating some degree of site fidelity. The abundance of zooplanktivorous fishes was similar to 30-fold lower during the night than day. However, since nocturnal fishes feed on larger zooplankters, the biomass of zooplankton preyed upon by nocturnal fishes was similar to that of diurnal species. This study suggests that the paradigm of negligible predation by nocturnal fishes should be reconsidered