Oceanus.

v. 39, no. 1 (1996

Trehalose Is A Chemical Attractant In The Establishment Of Coral Symbiosis

Coral reefs have evolved with a crucial symbiosis between photosynthetic dinoflagellates (genus Symbiodinium) and their cnidarian hosts (Scleractinians). Most coral larvae take up Symbiodinium from their environment; however, the earliest steps in this process have been elusive. Here we demonstrate that the disaccharide trehalose may be an important signal from the symbiont to potential larval hosts. Symbiodinium freshly isolated from Fungia scutaria corals constantly released trehalose (but not sucrose, maltose or glucose) into seawater, and released glycerol only in the presence of coral tissue. Spawning Fungia adults increased symbiont number in their immediate area by excreting pellets of Symbiodinium, and when these naturally discharged Symbiodinium were cultured, they also released trehalose. In Y-maze experiments, coral larvae demonstrated chemoattractant and feeding behaviors only towards a chamber with trehalose or glycerol. Concomitantly, coral larvae and adult tissue, but not symbionts, had significant trehalase enzymatic activities, suggesting the capacity to utilize trehalose. Trehalase activity was developmentally regulated in F. scutaria larvae, rising as the time for symbiont uptake occurs. Consistent with the enzymatic assays, gene finding demonstrated the presence of a trehalase enzyme in the genome of a related coral, Acropora digitifera, and a likely trehalase in the transcriptome of F. scutaria. Taken together, these data suggest that adult F. scutaria seed the reef with Symbiodinium during spawning and the exuded Symbiodinium release trehalose into the environment, which acts as a chemoattractant for F. scutaria larvae and as an initiator of feeding behavior- the first stages toward establishing the coral-Symbiodinium relationship. Because trehalose is a fixed carbon compound, this cue would accurately demonstrate to the cnidarian larvae the photosynthetic ability of the potential symbiont in the ambient environment. To our knowledge, this is the first report of a chemical cue attracting the motile coral larvae to the symbiont

Harmful and toxic algae

The chapter provides basic facts about harmful and toxic algae. It also discusses the conditions that stimulate their occurrence, different types of harmful and toxic algal blooms and their effects to fish and marine environment. The different strategies in coping with the problem of harmful and toxic algal blooms are also discussed

Going ballistic in the plankton: anisotropic swimming behavior of marine protists

Diel vertical migrations (DVMs) of many plankton species, including single-celled protists, are well documented in the field and form a core component of many large-scale numerical models of plankton transport and ecology. However, the sparse quantitative data available describing motility behaviors of individual protists have frequently indicated that motility exhibits only short-term correlation on the order of a few seconds or hundreds of micrometers, resembling diffusive transport at larger scales—a result incompatible with DVM, which requires ballistic (straight-line) motion. We interrogated an extensive set of three-dimensional protistan movement trajectories in an effort to identify spatial and temporal correlation scales. Whereas the horizontal components of movement were diffusive, the vertical component remained highly correlated (i.e., nonrandom) for nearly all species for the duration of observation (up to 120 s and 6.1 mm) and in the absence of any environmental cues besides gravity. These persistent motility patterns may have been obscured in some previous studies due to the use of restrictive containers, dimensionally lumped, isotropic analyses, and/or an observation bias, inherent to observing free-swimming organisms with stationary cameras, which we accounted for in this study. Extrapolated over a 12-h period, conservative estimates of vertical travel ranges for the protists observed here would be 3–10 m, while diffusive horizontal motion would result in about 10 cm of travel at most. Hence, these extended observations of phylogenetically diverse swimming protists, coupled with a quantitative analysis that accounts for anisotropy in the data, illustrate the small-scale mechanistic underpinnings of DVM

Efectos a corto plazo de la RUV en la distribución vertical de Cyrtograpsus altimanus y Alexandrium tamarense de la Patagonia Atlántica

Many marine species spend part of their development in upper layers of the water column, where they may be exposed to solar ultraviolet radiation (UVR). For many of these species, light is one of the key environmental clues which triggers behaviorally-mediated adjustments in vertical distribution. We incubated planktonic larvae of the crab Cyrtograpsus altimanus in column-like aquaria to study their responses with/without UVR (under a solar simulator) and with/without a potential prey (the dinoflagellate Alexandrium tamarense). Their vertical distribution was recorded and used to evaluate the combined effects of UVR and the presence of the dinoflagellate on larval behavior. When UVR was absent, most larvae showed a tendency to swim upwards and to aggregate near the surface, regardless of the dinoflagellate presence. However, UVR inhibited this tendency and induced a repellent effect, which resulted in a more homogeneous vertical distribution of larvae. A. tamarense did not affect the vertical distribution of larvae. These results suggest that UVR-triggered, quick adjustments in vertical distribution might be an important strategy for C. altimanus larvae to cope with high solar radiation, which typically occur during the hatching season.Muchas especies marinas pasan parte de su ciclo vital en las capas superficiales de la columna de agua, donde pueden estar expuestas a radiación ultravioleta (RUV). En muchos casos la luz constituye el factor ambiental que provoca ajustes del comportamiento en la distribución vertical. Se incubaron larvas planctónicas del cangrejo Cyrtograpsus altimanus en acuarios verticales para estudiar sus respuestas con/sin RUV y con/sin una potencial presa (el dinoflagelado Alexandrium tamarense). La distribución vertical de los plancteres fue registrada y se usó para evaluar el efecto combinado de la RUV y la presencia del dinoflagelado en el comportamiento larval. Cuando la RUV estaba ausente, las larvas de C. altimanus tendieron a nadar hacia arriba y agregarse cerca de la superficie, independientemente de la presencia del dinoflagelado. Sin embargo, la RUV inhibió esta tendencia e indujo un efecto repelente que llevó a una distribución vertical de larvas mucho más homogénea. Las larvas no parecieron ser afectadas en ningún caso por la presencia de A. tamarense. Los resultados sugieren que C. altimanus podría ajustar rápidamente su distribución vertical en respuesta a RUV, lo cual sería una estrategia importante para hacer frente a los altos niveles de radiación solar que típicamente ocurren durante sus primeros estadios de desarrollo.Fil: Gonçalves, Rodrigo Javier. Fundación Playa Unión. Estación de Fotobiología Playa Unión; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; ArgentinaFil: Hernández Moresino, Rodrigo Daniel. Fundación Playa Unión. Estación de Fotobiología Playa Unión; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; ArgentinaFil: Spinelli, Mariela Lorena. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Instituto de Biodiversidad y Biologia Experimental y Aplicada; Argentin

Measuring the translational and rotational velocity of particles in helical motion using structured light

We measure the rotational and translational velocity components of particles moving in helical motion using the frequency shift they induced to the structured light beam illuminating them. Under Laguerre-Gaussian mode illumination, a particle with a helical motion reflects light that acquires an additional frequency shift proportional to the angular velocity of rotation in the transverse plane, on top of the usual frequency shift due to the longitudinal motion. We determined both the translational and rotational velocities of the particles by switching between two modes: by illuminating with a Gaussian beam, we can isolate the longitudinal frequency shift; and by using a Laguerre-Gaussian mode, the frequency shift due to the rotation can be determined. Our technique can be used to characterize the motility of microorganisms with a full three-dimensional movement.Comment: 5 pages,5 figure

Soundings: the Newsletter of the Monterey Bay Chapter of the American Cetacean Society. 2004

(PDF contains 92 pages.

Vertical migration maintains phytoplankton position in a tidal channel with residual flow

A tidal channel can retain phytoplankton, despite a residual flow, if the phytoplankton migrate vertically with a daily rhythm. Tidal currents are slowed down by bed friction and so plankton experience faster flow when higher in the water column. The lateral movement of the plankton depends on the nature of the vertical migration, particularly the time spent near the surface and the phase of the tide. A model of this process accorded with observations of chlorophyll derived from in situ fluorescence at a mooring in a tidal channel. Peaks in chlorophyll at the end of the flood tide indicated the presence of a phytoplankton bloom downstream of the mooring. Peaks in chlorophyll at the ends of the morning flood tides were 3 to 4 times larger than at the ends of the evening floods, over several days. In contrast, well-mixed particulates were removed from the channel by the residual flow in just 2 d. Both the day-night asymmetry and the sustained presence of chlorophyll were explained by allowing for vertical migration of the phytoplankton and constraining the period during which they were near the surface. Tidal channels retaining phytoplankton that migrate vertically can be ecologically more diverse and yield higher commercial output of farmed bivalves. The natural timings of some phytoplankton blooms in tidal channels are controlled by the nature of the migration. Although a by-product of vertical migration, longer residence in the tidal channel affords the phytoplankton more nutrients than phytoplankton that advect offshore

On the ecology of cold-water phytoplankton in the Baltic Sea

Increased anthropogenic loading of nitrogen (N) and phosphorus (P) has led to an eutrophication problem in the Baltic Sea, and the spring bloom is a key component in the biological uptake of increased nutrient concentrations. The spring bloom in the Baltic Sea is dominated by both diatoms and dinoflagellates. However, the sedimentation of these groups is different: diatoms tend to sink to the sea floor at the end of the bloom, while dinoflagellates to a large degree are been remineralized in the euphotic zone. Understanding phytoplankton competition and species specific ecological strategies is thus of importance for assessing indirect effects of phytoplankton community composition on eutrophication problems. The main objective of this thesis was to describe some basic physiological and ecological characteristics of the main cold-water diatoms and dinoflagellates in the Baltic Sea. This was achieved by specific studies of: (1) seasonal vertical positioning, (2) dinoflagellate life cycle, (3) mixotrophy, (4) primary production, respiration and growth and (5) diatom silicate uptake, using cultures of common cold-water diatoms: Chaetoceros wighamii, C. gracilis, Pauliella taeniata, Thalassiosira baltica, T. levanderi, Melosira arctica, Diatoma tenuis, Nitzschia frigida, and dinoflagellates: Peridiniella catenata, Woloszynskia halophila and Scrippsiella hangoei. The diatoms had higher primary production capacity and lower respiration rate compared with the dinoflagellates. This difference was reflected in the maximum growth rate, which for the examined diatoms range from 0.6 to 1.2 divisions d-1, compared with 0.2 to 0.3 divisions d-1 for the dinoflagellates. Among diatoms there were species specific differences in light utilization and uptake of silicate, and C. wighamii had the highest carbon assimilation capacity and maximum silicate uptake. The physiological properties of diatoms and dinoflagellates were used in a model of the onset of the spring bloom: for the diatoms the model could predict the initiation of the spring bloom; S. hangoei, on the other hand, could not compete successfully and did not obtain positive growth in the model. The other dinoflagellates did not have higher growth rates or carbon assimilation rates and would thus probably not perform better than S. hangoei in the model. The dinoflagellates do, however, have competitive advantages that were not included in the model: motility and mixotrophy. Previous investigations has revealed that the chain-forming P. catenata performs diurnal vertical migration (DVM), and the results presented here suggest that active positioning in the water column, in addition to DVM, is a key element in this species' life strategy. There was indication of mixotrophy in S. hangoei, as it produced and excreted the enzyme leucine aminopeptidase (LAP). Moreover, there was indirect evidence that W. halophila obtains carbon from other sources than photosynthesis when comparing increase in cell numbers with in situ carbon assimilation rates. The results indicate that mixotrophy is a part of the strategy of vernal dinoflagellates in the Baltic Sea. There were also indications that the seeding of the spring bloom is very important for the dinoflagellates to succeed. In mesocosm experiments dinoflagellates could not compete with diatoms when their initial numbers were low. In conclusion, this thesis has provided new information about the basic physiological and ecological properties of the main cold-water phytoplankton in the Baltic Sea. The main phytoplankton groups, diatoms and dinoflagellates, have different physiological properties, which clearly separate their life strategies. The information presented here could serve as further steps towards better prognostic models of the effects of eutrophication in the Baltic Sea.Övergödningen av Östersjön är ett välkänt problem som förorsakas av mänskligt utsläpp av kväve och fosfor. Många av dessa näringsämnen blir tagna upp av algerna under våren när ljusets ökade intensitet sätter igång en vårblomning hos algerna. Därför är kunskap om algernas växt under denna period viktig för förståelsen av eutrofieringsprocesser i Östersjön. Målsättningen av denna avhandling var att beskriva grundläggande fysiologiska och ekologiska egenskaper hos alger som är vanliga under vårblomningen i Östersjön. Detta mål uppnåddes genom specifika studier av (1) långskiktig vertikal placering (2) dinoflagellateers livscykler (3) mixotrofi (4) primärproduktion, respiration och tillväxt och (5) kiselalgers silikatupptag. Arbetet blev utfört i havet utanför Hangö och med laboratoriekulturer av kiselalgerna: Chaetoceros wighamii, C. gracilis, Pauliella taeniata, Thalassiosira baltica, T. levanderi, Melosira arctica, Diatoma tenuis, Nitzschia frigida, och dinoflagellaterna: Peridiniella catenata, Woloszynskia halophila and Scrippsiella hangoei. Kiselalgerna hade högre primär produktion och lägre respiration än dinoflagellaterna. Denna skillnad reflekterades också i den maximala tillväxthastigheten som för kiselalgerna var 0.6-1.2 delningar per dag och för dinoflagellaterna 0.2-0.3 delningar per dag. Bland kiselalgerna var det också arts specifika skillnader i användandet av ljus och upptagandet av silikat. C. wighamii hade den högsta primärproduktionen, silikatupptag och maximal tillväxthastighet. De fysiologiska egenskaperna hos kiselalgerna och dinoflagellaterna blev använda i en modell av tidpunkten för vårblomningen. För kiselalgerna kunde modellen förutspå vårblomingens början men dinoflagellaterna fick inte positiv växt i modellen. Dessa arter finns i Östersjön under våren och måste därför ha andra konkurrensegenskaper som inte var med i modellen så som mobilitet och mixotrofi (förmågan till att uppta näring i organisk form). Den kolonibildande dinoflagellaten P. catenata är en god simmare, och resultaten indikerar att aktiv positionering i vattenpelaren är viktigt för denna arts ekologiska strategi. Det var bevis för mixotrfi i S. hangoei eftersom arten producerar enzymet leucine aminopeptidase (LAP). Det var också resultat som indirekt pekade mot mixtotrofi hos W. halophila eftersom tillväxten var mycket högre än fixeringsraten av karbon indikerade. Det ursprungliga antal dinoflagellater verkar också vara mycket viktig för den biomassa som byggs upp under vårblomningen. Denna avhandling har beskrivit ny information om fysiologiska och ekologiska egenskaper hos algerna som är vanliga under vårblomningen i Östersjön. Detta är information som inte tidigare har funnits på artnivå