A Century of Copepods: The U.S. Fisheries Steamer Albatross

The marine invertebrates of North America received little attention before the arrival of Louis Agassiz in 1846. Agassiz and his students, particularly Addison E. Verrill and Richard Rathbun, and Agassiz's colleague Spencer F. Baird, provided the concept and stimulus for expanded investigations. Baird's U.S. Commission of Fish and Fisheries (1871) provided a principal means, especially through the U.S. Fisheries Steamer Albatross (1882). Rathbun participated in the first and third Albatrossscientific cruises in 1883-84 and published the fist accounts of Albatross parasitic copepods. The first report of Albatross planktonic copepods was published in 1895 by Wilhelm Giesbrecht of the Naples Zoological Station. Other collections were sent to the Norwegian Georg Ossian Sars. The American Charles Branch Wilson eventually added planktonic copepods to his extensive published works on the parasitic copepods from the Albatross. The Albatross copepods from San Francisco Bay were reported upon by Calvin Olin Esterly in 1924. Henry Bryant Bigelow accompanied the last scientific cruise of the Albatross in 1920. Bigelow incorporated the 1920 copepods into his definitive study of the plankton of the Gulf of Maine. The late Otohiko Tanaka, in 1969, published two reviews of Albatross copepods. Albatross copepods will long be worked and reworked. This great ship and her shipmates were mutually inspiring, and they inspire us still

Latitudinal Differentiation in the Effects of the Toxic Dinoflagellate Alexandrium spp. on the Feeding and Reproduction of Populations of the Copepod Acartia Hudsonica

Blooms of the dinoflagellate Alexandrium spp. increase in their frequency, toxicity and historical presence with increasing latitude from New Jersey (USA) to the Gaspé peninsula (Canada). Biogeographic variation in these blooms results in differential exposure of geographically separate copepod populations to toxic Alexandrium. We hypothesize that the ability of copepods to feed and reproduce on toxic Alexandrium should be higher in copepods from regions that are frequently exposed to toxic Alexandrium blooms. We tested this hypothesis with factorial common environment experiments in which female adults of the copepod Acartia hudsonica from five separate populations ranging from New Jersey to New Brunswick were fed toxic and non-toxic strains of Alexandrium, and the non-toxic flagellate Tetraselmis sp. Consistent with the hypothesis, when fed toxic Alexandrium we observed significantly higher ingestion and egg production rates in the copepods historically exposed to toxic Alexandrium blooms relative to copepods from regions in which Alexandrium is rare or absent. Such differences among copepod populations were not observed when copepods were fed non-toxic Alexandrium or Tetraselmis sp. These results were also supported by assays in which copepods from populations both historically exposed and naı̈ve to toxic Alexandrium blooms were fed mixtures of toxic Alexandrium and Tetraselmis sp. Two-week long experiments demonstrated that when copepods from populations naı̈ve to toxic Alexandrium were fed a toxic strain of Alexandrium they failed to acclimate, such that their ingestion rates remained low throughout the entire two-week period. The differences observed among populations suggest that local adaptation of populations of A. hudsonica from Massachusetts (USA) to New Brunswick (Canada) has occurred, such that some populations are resistant to toxic Alexandrium

A Lagrangian model of copepod dynamics: Clustering by escape jumps in turbulence

Planktonic copepods are small crustaceans that have the ability to swim by quick powerful jumps. Such an aptness is used to escape from high shear regions, which may be caused either by flow per- turbations, produced by a large predator (i.e., fish larvae), or by the inherent highly turbulent dynamics of the ocean. Through a combined experimental and numerical study, we investigate the impact of jumping behaviour on the small-scale patchiness of copepods in a turbulent environment. Recorded velocity tracks of copepods displaying escape response jumps in still water are here used to define and tune a Lagrangian Copepod (LC) model. The model is further employed to simulate the behaviour of thousands of copepods in a fully developed hydrodynamic turbulent flow obtained by direct numerical simulation of the Navier-Stokes equations. First, we show that the LC velocity statistics is in qualitative agreement with available experimental observations of copepods in tur- bulence. Second, we quantify the clustering of LC, via the fractal dimension $D_2$. We show that $D_2$ can be as low as ~ 2.3 and that it critically depends on the shear-rate sensitivity of the proposed LC model, in particular it exhibits a minimum in a narrow range of shear-rate values. We further investigate the effect of jump intensity, jump orientation and geometrical aspect ratio of the copepods on the small-scale spatial distribution. At last, possible ecological implications of the observed clustering on encounter rates and mating success are discussedComment: 13 pages, 9 figure

A model of chlorophyll a destruction by Calanus spp. and implications for the estimation of ingestion rates using the gut fluorescence method

Chlorophyll a (chl a) destruction by groups of Calanus spp. with different long-term in situ feeding histories was compared. For copepods that had fed during both pre- and early-bloom conditions, degrees of chl a destruction were relatively constant at high ingestion rates and increased as ingestion rates decreased. Assuming that 2 pools of chlorophyll bleaching enzymes (CBEs) were involved in the destruction of chl a (one derived from the copepods and one from the ingested algae), a new model was developed to describe the kinetics of chl a destruction. In this model, the CBE activity of each pool was described using a Michaelis-Menten expression and the total CBE activity was given by the sum of the 2 expressions. Parameter estimates of V(c)(max), the maximum activity of the copepod CBE, were higher for the early-bloom copepods than for the pre-bloom copepods, suggesting that the former had a higher destructive capacity. Estimates of R(p)(max), the phytoplankton 'CBE activity coefficient' which is analogous to V(max), were similar between the 2 groups of experiments. This is reasonable since most of the food fed to the copepods was healthy, actively growing diatoms. The model could also describe the kinetics of chl a destruction for Calanus spp. that had fed during late-bloom conditions. For the late-bloom data, V(c)(max) and R(p)(max) values were higher than for the pre- and early-bloom copepods and phytoplankton. This suggests that the late-bloom copepods and the in situ phytoplankton that they ate had higher destructive capacities, perhaps because the spring-bloom was more advanced. Expressions were derived from the new model to describe the relationship between real ingestion rate (I(r)) and apparent ingestion rate (I(a)), over a range of I(a) values, where the latter are values which would have been determined using gut fluorescence methodology. Correction factors (I(r)/I(a)) varied by a factor of less than 2 (for I(a) values ranging from 0.1 to 100 ng chi a ind.-1 h-1) between different groups of copepods (pre-, early- and late-bloom) and sources of algae (actively growing and senescent). In future it will be important to validate this model under controlled conditions (e.g. using single species of copepods and phytoplankton food) and to assess whether correction factors derived from our model are generally applicable, if results of studies using gut fluorescence methods are to be interpreted properly

Ocean odours

The ocean's distinctive smell is caused by a single chemical released by plankton and other marine life, dimethyl sulphide (DMS). A study by a group of investigators from the University of Groningen used a technique called laser-sheet particle image velocimetry to monitor the water flows produced by aquatic animals. The investigators looked closely at how DMS affects copepods. Their tests showed that when DMS hit a copepod, the test animal reacted with a search behaviour. This demonstrates that copepods can smell the DMS and suggests that this and possibly other compounds released by phytoplankton and microzooplankton may help copepods in finding their prey

Copepods encounter rates from a model of escape jump behaviour in turbulence

A key ecological parameter for planktonic copepods studies is their interspecies encounter rate which is driven by their behaviour and is strongly influenced by turbulence of the surrounding environment. A distinctive feature of copepods motility is their ability to perform quick displacements, often dubbed jumps, by means of powerful swimming strokes. Such a reaction has been associated to an escape behaviour from flow disturbances due to predators or other external dangers. In the present study, the encounter rate of copepods in a developed turbulent flow with intensity comparable to the one found in copepods' habitat is numerically investigated. This is done by means of a Lagrangian copepod (LC) model that mimics the jump escape reaction behaviour from localised high-shear rate fluctuations in the turbulent flows. Our analysis shows that the encounter rate for copepods of typical perception radius of ~ {\eta}, where {\eta} is the dissipative scale of turbulence, can be increased by a factor up to ~ 100 compared to the one experienced by passively transported fluid tracers. Furthermore, we address the effect of introducing in the LC model a minimal waiting time between consecutive jumps. It is shown that any encounter-rate enhancement is lost if such time goes beyond the dissipative time-scale of turbulence, {\tau}_{\eta}. Because typically in the ocean {\eta} ~ 0.001m and {\tau}_{\eta} ~ 1s, this provides stringent constraints on the turbulent-driven enhancement of encounter-rate due to a purely mechanical induced escape reaction.Comment: 11 pages, 10 figure

Temperature affects the use of storage fatty acids as energy source in a benthic copepod (Platychelipus littoralis, Harpacticoida)

The utilization of storage lipids and their associated fatty acids (FA) is an important means for organisms to cope with periods of food shortage, however, little is known about the dynamics and FA mobilization in benthic copepods (order Harpacticoida). Furthermore, lipid depletion and FA mobilization may depend on the ambient temperature. Therefore, we subjected the temperate copepod Platychelipus littoralis to several intervals (3, 6 and 14 days) of food deprivation, under two temperatures in the range of the normal habitat temperature (4, 15 degrees C) and under an elevated temperature (24 degrees C), and studied the changes in FA composition of storage and membrane lipids. Although bulk depletion of storage FA occurred after a few days of food deprivation under 4 degrees C and 15 degrees C, copepod survival remained high during the experiment, suggesting the catabolization of other energy sources. Ambient temperature affected both the degree of FA depletion and the FA mobilization. In particular, storage FA were more exhausted and FA mobilization was more selective under 15 degrees C compared with 4 degrees C. In contrast, depletion of storage FA was limited under an elevated temperature, potentially due to a switch to partial anaerobiosis. Food deprivation induced selective DHA retention in the copepod's membrane, under all temperatures. However, prolonged exposure to heat and nutritional stress eventually depleted DHA in the membranes, and potentially induced high copepod mortality. Storage lipids clearly played an important role in the short-term response of the copepod P. littoralis to food deprivation. However, under elevated temperature, the use of storage FA as an energy source is compromised

Testing for Resistance of Pelagic Marine Copepods to a Toxic Dinoflagellate

With few exceptions, the evolutionary consequences of harmful algae to grazers in aquatic systems remain unexplored. To examine both the ecological and evolutionary consequences of harmful algae on marine zooplankton, we used a two-fold approach. In the first approach, we examined the life history responses of two geographically separate Acartia hudsonica (Copepoda Calanoida) populations reared on diets containing the toxic dinoflagellate Alexandrium fundyense . One copepod population was from a region, Casco Bay, Maine, USA, that has experienced recurrent blooms of highly toxic Alexandrium spp. for decades; whereas the other population from Great Bay, New Jersey, USA, has never been exposed to toxic Alexandrium blooms. The life history experiment demonstrated that when the copepod population from New Jersey was reared on a diet containing toxic A. fundyense it exhibited lower somatic growth, size at maturity, egg production and survival than the same population reared on a diet without toxic A. fundyense . In contrast, toxic A. fundyense did not affect the life-history traits of the Maine population. Fitness, finite population growth rate (λ), was significantly reduced in the New Jersey population, but not in the Maine population. These results are consistent with the hypothesis of local adaptation (resistance) of the historically exposed copepod population to the toxic dinoflagellate. In the second approach, we further tested the resistance hypothesis with a laboratory genetic selection experiment with the naïve New Jersey copepod population exposed to a diet containing toxic A. fundyense. This experiment demonstrated that the ingestion and egg production of adult females of naïve copepods fed A. fundyense improved after three generations of being reared on a diet containing the toxic dinoflagellate. The results of the present study have important implications for understanding how grazer populations may respond to the introduction of toxic algae to their environment, and suggest that grazer resistance may be a feedback mechanism that may lead to bloom control

Effect of Grazing-Mediated Dimethyl Sulfide (DMS) Production on the Swimming Behavior of the Copepod Calanus helgolandicus

Chemical interactions play a fundamental role in the ecology of marine foodwebs. Dimethyl sulfide (DMS) is a ubiquitous marine trace gas that acts as a bioactive compound by eliciting foraging behavior in a range of marine taxa including the copepod Temora longicornis. Production of DMS can rapidly increase following microzooplankton grazing on phytoplankton. Here, we investigated whether grazing-induced DMS elicits an increase in foraging behavior in the copepod Calanus helgolandicus. We developed a semi-Automated method to quantify the effect of grazing-mediated DMS on the proportion of the time budget tethered females allocate towards slow swimming, typically associated with feeding. The pooled data showed no differences in the proportion of the 25 min time budget allocated towards slow swimming between high (23.6 ± 9.74%) and low (29.1 ± 18.33%) DMS treatments. However, there was a high degree of variability between behavioral responses of individual copepods. We discuss the need for more detailed species-specific studies of individual level responses of copepods to chemical signals at different spatial scales to improve our understanding of chemical interactions between copepods and their prey. © 1996-2013 MDPI AG