Journal of Plankton Research - Advance Access

Vertical distribution and diel patterns of zooplankton abundance and biomass at Conch Reef, Florida Keys (USA)

Heidelberg, K. B., O'Neil, K. L., Bythell, J. C., Sebens, K. P. — Wed, 18 Nov 2009 21:00:30 PST

Zooplankton play an important role in the trophic dynamics of coral reef ecosystems. Detailed vertical and temporal distribution and biomass of zooplankton were evaluated at four heights off the bottom and at six times throughout the diel cycle over a coral reef in the Florida Keys (USA). Zooplankton abundance averaged 4396 ± 1949 SD individuals m^–3, but temporal and spatial distributions varied for individual zooplankton taxa by time of day and by height off the bottom. Copepods comprised 93–96% of the abundance in the samples. Taxon-based zooplankton CHN values paired with abundance data were used to estimate biomass. Average daily biomass ranged from 3.1 to 21.4 mg C m^–3 and differed by both height off the bottom and by time of day. While copepods were the numerically dominant organisms, their contribution to biomass was only 35% of the total zooplankton biomass. Our findings provide important support for the new emerging paradigm of how zooplankton are distributed over reefs.

Biovolume spectrum theories applied: spatial patterns of trophic levels within a mesozooplankton community at the polar front

Basedow, S. L., Tande, K. S., Zhou, M. — Fri, 13 Nov 2009 03:52:03 PST

Three-dimensional data on the mesoscale distribution of hydrography and mesozooplankton were collected at the Polar Front, northwestern Barents Sea, in spring 2008 (29 April–15 May) using a combination of multinet and towed instrument platform equipped with Laser Optical Plankton Counter, fluorometer and CTD. Trophic levels (TLs) within the zooplankton community (whole community and size-separated) were analysed for three consecutive periods using biovolume spectrum theory, which proved to be a powerful tool in the physically and biologically variable frontal system. Trophic structure was highly variable in time and across the Polar Front, but was mostly related to the phytoplankton bloom (as determined by fluorescence). High TLs of 5.5 within the zooplankton community were observed outside bloom situations (mostly in Atlantic Water) and were likely due to increased omnivory of Calanus spp., which dominated the large zooplankton size group that had a lower TL (2.2) during the bloom than outside blooms (max. TL 5.6). A strong input of herbivorous barnacle nauplii (Cirripedia) into the upper layer (35 000 ind. m^–3 in net samples) substantially decreased mean TL in the marginal ice zone. Differences in TL estimates based on biovolume spectrum theory and other methods (stable isotopes, lipid markers, dietary analyses) are discussed.

Reconsidering evidence for Mnemiopsis invasion in European waters: reply

Javidpour, J., Molinero, J. C., Sommer, U. — Tue, 10 Nov 2009 04:46:58 PST

Reconsidering evidence for Mnemiopsis invasion in European waters

Gorokhova, E., Lehtiniemi, M. — Tue, 10 Nov 2009 04:46:57 PST

Importance of the contribution of Limacina helicina faecal pellets to the carbon pump in Terra Nova Bay (Antarctica)

Manno, C., Tirelli, V., Accornero, A., Fonda Umani, S. — Mon, 09 Nov 2009 05:43:31 PST

The understanding of the role of the pteropods Limacina helicina in the ecosystem has become of greater interest as the debate on ocean acidification and its consequences for calcifying organisms has increased. Four incubation experiments were carried out in January and February 2006 in Terra Nova Bay Polynya (Ross Sea) to identify the faecal pellets (FPs) produced by L. helicina. Mean FP production rates were 6.1 ± 1.3 and 10.9 ± 2.1 pellets day^–1 individual^–1 in January and February, respectively. FPs produced by L. helicina had an oval shape with a more lengthened side. The identification of L. helicina faeces allowed us to quantify the amounts of L. helicina FPs in the material collected by sediment traps deployed in the same area from 1998 to 2001. We found that L. helicina FPs flux ranged from 71 x 10³ FP m^–2 year^–1 to 362 x 10³ FP m^–2 year^–1 and reach maximum values in March–April every year. The FPs flux of this organism contributed 19% of the particle organic carbon flux. The carbon pump may be modified if the L. helicina population declines as a consequence of the predicted acidification in polar and subpolar waters.

How important can the presence/absence of macrophytes be in determining phytoplankton strategies in two tropical shallow reservoirs with different trophic status?

Fonseca, B. M., Bicudo, C. E. D. M. — Fri, 06 Nov 2009 05:05:26 PST

This study aimed at comparing phytoplankton taxonomic classes and morpho-functional attributes in two shallow tropical reservoirs with different nutrient levels and representing extremes of the alternative stable states theory. The reservoirs, locally called Ninféias Pond (23°38'18.95''S; 46°37'16.3''W) and Garças Pond (23°38'40.6''S; 46°37'28.0''W), are located in the city of São Paulo, southeastern Brazil. Ninféias Pond is oligo-mesotrophic and has abundant submerged macrophytes; Garças Pond is eutrophic without submerged macrophytes, with cyclic cyanobacterial blooms. Sampling was carried out monthly from January to December 1997. Phytoplankton species were classified according to taxonomic classes and the following criteria: life form, size, biovolume, life strategy (C–S–R) and functional group. Statistical differences in taxa contribution were reported for both lakes considering all criteria tested, especially life forms. Taxonomic classes dominating Ninféias Pond were Prymnesiophyceae and Dinophyceae, which strongly influenced a community characterized by nanoplanktonic unicellular flagellated C/S-strategists, and the main functional groups were X2, L_O and W1. Garças Pond phytoplankton community was dominated by species belonging to Cyanobacteria and colonial non-flagellated nano/micro-planktonic S-strategists, and the main functional groups were M, S_N and L_M. Differences in trophic status are probably the main factor triggering such differences. However, the presence of macrophytes in Ninféias Pond also seems to qualitatively influence its phytoplankton community, favoring flagellated species.

Plankton: A Guide to their Ecology and Monitoring for Water Quality

Castellani, C. — Fri, 06 Nov 2009 05:05:24 PST

A review of phytoplankton ecology in estuarine and coastal waters around Ireland

O'Boyle, S., Silke, J. — Tue, 03 Nov 2009 06:00:12 PST

A review of the distribution of phytoplankton in coastal, shelf and estuarine waters around Ireland was undertaken to consolidate our understanding of the ecology of these organisms in the region. In broad terms, the review has highlighted the relative importance of vertical water column stability and horizontal transport processes in influencing the abundance and composition of phytoplankton. In coastal waters, the seasonal stabilization and de-stabilization of the water column accounts for most of the natural variation in both phytoplankton species composition and biomass. Much of the remaining natural variability can be explained by the interaction of phytoplankton with a number of oceanographic features and processes such as the presence of tidal and thermohaline fronts, wind and topographically associated coastal upwelling, advection landward of offshore water masses and the flow of coastal and oceanic currents. In estuarine waters, the scenario is somewhat reversed, and although seasonality is important in broad terms, the structure of phytoplankton populations is determined more by local factors operating over much smaller time-scales in the order of days and weeks. The interplay of these factors, such as the periodic rise and fall of the tide and episodic changes in river flow, creates a broad range of conditions that result in greater variation in phytoplankton biomass, while at the same time selecting for a reduced number of species that are adapted to survive in this highly changeable environment.

Ontogenetic differences in isotopic signatures and crop contents of Chaoborus

Persaud, A. D., Dillon, P. J. — Mon, 02 Nov 2009 02:41:37 PST

Intra-specific changes in trophic interactions due to ontogenetic transformations in macro-invertebrates can add to complexity of freshwater food webs. The objectives of this study are therefore to examine isotopic signatures and crop contents of different Chaoborus species and life stages, and to determine whether ontogenetic changes in diet are reflected in their isotopic signatures. Different Chaoborus species and life stages were collected from 15 Precambrian Shield lakes for stable isotope and crop contents analyses. In general, early instar Chaoborus ¹³C and ¹³C_LC (lipid corrected ¹³C) signatures were enriched in ¹³C, while their ¹⁵N_DC (Daphnia corrected ¹⁵N) signatures were lower compared to those of late instars and pupae. Larval Chaoborus size was significantly related to their ¹³C, ¹³C_LC&DC (lipid and Daphnia corrected ¹³C), and ¹⁵N_DC isotopic signatures. Chaoborus crop contents varied among species and larval instars. Generally, rotifers were numerically predominant in crops, with declining abundance in late instars. Larger quantities of copepods, nauplii and cladocerans were found in crops of late instars compared with early instars. Overall, early instars consumed more rotifers and phytoplankton and had lower ¹⁵N_DC, whereas late instars consumed comparatively larger quantities of copepods, nauplii, cladocerans and early instars, and had higher ¹⁵N_DC. Together, our results show that there are differences among larval Chaoborus life stages. Hence, different instars of these important aquatic predators cannot be grouped together, but should be separated by species and life stage when examining trophic interactions in freshwater food webs.

A test of stoichiometry across six Irish lakes of low-moderate nutrient status and contrasting hardness

McCarthy, V., Irvine, K. — Fri, 30 Oct 2009 04:02:54 PDT

The importance of stoichiometric food quality constraints in influencing zooplankton community structure and distribution in six lakes with categorical variations in alkalinity were investigated by assessing the relationship between seston nutrient content, bulk zooplankton nutrient content and the abundance of individual zooplankton taxa. Stoichiometric processes were viewed in the context of the overall biotic and abiotic environment. Distinct differences in the distribution of certain zooplankton taxa between high- and low-alkalinity lakes were observed and size-distribution analyses suggested that the size-selective foraging behaviour of fish may have been responsible for determining seasonal variation in community structure. Nevertheless, a positive correlation was observed between bulk zooplankton C:P content and bulk seston C:P content, and a negative relationship between Daphnia abundance and the seston C:P and N:P ratios, which suggests that with declining food P content, high-P taxa are replaced by low-P taxa. This would suggest that stoichiometric food quality constraints are in part involved in structuring the zooplankton community of the six lakes of this study. Although classic models of lake trophic structure based on carbon input (bottom-up) and predation (top-down) may provide explanations for broad community patterns, stoichiometry may provide an alternative or additional mechanism for understanding the details of zooplankton species composition and dynamics.

General patterns in the size scaling of phytoplankton abundance in coastal waters during a 10-year time series

Huete-Ortega, M., Maranon, E., Varela, M., Bode, A. — Wed, 28 Oct 2009 08:49:57 PDT

To ascertain the general patterns in phytoplankton size structure of a temperate, coastal ecosystem, we determined the scaling relationship between total abundance and cell size (size spectrum) for nano- and micro-phytoplankton in a shelf station off NW Iberian Peninsula on a monthly basis during the period 1993–2002. The inverse linear relationship between log abundance and log cell size was persistent throughout the water column and across seasonal and inter-annual time scales. In addition, and despite the high productivity and marked temporal variability in water column structure at our study site, departures from linearity in the size spectra were rare. The slope (–0.96) of the overall size spectrum for the entire time series indicated that roughly equal amounts of biomass were present over different logarithmic size classes in the size range considered. The phytoplankton size spectra had similar average slopes during winter mixing, early upwelling, summer stratification and autumn downwelling, suggesting that, under these oceanographic conditions, both nano- and micro-phytoplankton respond similarly to environmental variability. In contrast, significantly less negative slopes were observed during upwelling relaxation, indicating an increased importance of larger cells. Our results illustrate the utility of individual size distributions to provide a synthetic description of phytoplankton community structure in dynamic, non steady-state marine ecosystems.

Gut evacuation of larval Mnemiopsis leidyi A. Agassiz (Ctenophora, Lobata)

Sullivan, L. J. — Wed, 28 Oct 2009 08:49:55 PDT

Despite their potential importance as predators, the early life-history stages of ctenophores are relatively understudied. Measurements of digestion times for larvae are especially limited compared with adults, even though these measurements are required to calculate feeding rates using gut content analysis. This study reports digestion times for larval Mnemiopsis leidyi for a wide range of prey. Larval M. leidyi consumed the copepodite and naupliar stages of copepods, polychaete larvae, bivalve larvae, rotifers, rotifer eggs, ciliates and flagellates. Digestion times varied significantly among prey taxa and ranged from ~1 min for aloricate ciliates to 2 h for copepodites. Although ciliates and flagellates are frequently observed in ctenophore guts, feeding on protistan microplankton cannot be quantified adequately using gut content analysis because these prey items are often digested too rapidly to be identified in ctenophore guts.

Phytoplankton in a changing world: cell size and elemental stoichiometry

Wed, 28 Oct 2009 08:49:54 PDT

Global increases in atmospheric CO₂ and temperature are associated with changes in ocean chemistry and circulation, altering light and nutrient regimes. Resulting changes in phytoplankton community structure are expected to have a cascading effect on primary and export production, food web dynamics and the structure of the marine food web as well the biogeochemical cycling of carbon and bio-limiting elements in the sea. A review of current literature indicates cell size and elemental stoichiometry often respond predictably to abiotic conditions and follow biophysical rules that link environmental conditions to growth rates, and growth rates to food web interactions, and consequently to the biogeochemical cycling of elements. This suggests that cell size and elemental stoichiometry are promising ecophysiological traits for modelling and tracking changes in phytoplankton community structure in response to climate change. In turn, these changes are expected to have further impacts on phytoplankton community structure through as yet poorly understood secondary processes associated with trophic dynamics.

Fish kairomones alter life cycle and growth of a calanoid copepod

Gutierrez, M. F., Paggi, J. C., Gagneten, A. M. — Thu, 22 Oct 2009 07:06:02 PDT

In this study, we evaluate the effects of chemical information present in exudates of the zooplanktivorous fish Cnesterodon decemmaculatus (Poeciliidae) on the life cycle and growth of the planktonic copepod Notodiaptomus conifer. Semi-static assays were carried out using five concentrations of fish water (FW; 0.41–3.3 fish L^–1), and a control (without fish). Copepods responded to FW by faster development and earlier maturation at smaller body size which resulted in a decline in the number of eggs in the first clutch. The proportional duration of each larval stage was not modified in the presence of fish chemical information, indicating that N. conifer maintained an equiproportional development according to the growth model proposed for copepods. Some parameters of the copepod life history changed depending on FW concentration, while other responses were induced merely by the presence of fish exudates, regardless of concentration. This study shows that calanoid copepods display as clear individual life history responses to kairomones as those that have been known for cladocerans, since 1980s. The observed responses are consistent with physiological mechanisms acting directly on development and constitute an example of the importance of predator–prey interactions as a selective force in aquatic environments.

Temperature-driven phenological changes within a marine larval fish assemblage

Wed, 09 Sep 2009 03:26:03 PDT

Most marine teleosts have a pelagic phase during their early life history, but few studies have investigated how the timing of events within the planktonic larval fish assemblage is related to environmental variability. We examined this issue using a data series of 534 larval fish samples collected between 1975 and 1987 in the Western English Channel, near Plymouth, UK. Two sets of species were identified: spring spawning (April to July) and summer spawning (July to September). The timing of appearance of the spring-spawning group in the plankton was significantly dependent on sea temperatures the previous November and December, with earlier appearance during cooler years. We suggest that this could be due to colder years triggering earlier winter migration of adults from cool inshore habitat to warmer offshore overwintering grounds, which in turn results in earlier gonad maturation and spawning. In contrast, the timing of appearance of the summer-spawning group was significantly dependent on sea temperatures the preceding March, with earlier spawning during warmer years. This may be due exclusively to more rapid gonad maturation in offshore waters. These data emphasize that marine fish populations do not always respond uniformly to temperature change. Moreover, since appropriate timing of larval fish appearance in the plankton may be critical for the match or mismatch with essential trophic resources, the thermally induced phenological changes identified have potential to influence annual recruitment success.

Sardine (Sardina pilchardus) egg abundance at station L4, western English Channel, 1988-2008

Coombs, S. H., Halliday, N. C., Conway, D. V. P., Smyth, T. J. — Thu, 13 Aug 2009 01:17:50 PDT

Results from sampling for sardine (Sardina pilchardus) eggs at station L4 in the coastal western English Channel over the period 1988–2008 are presented and discussed in relation to environmental conditions. As previously observed in this area, there is a summer spawning season (mid-March to early July) and one in the autumn (early September to mid-November). The historical trend for increasing autumn spawning has continued. The mean spawning temperatures were 12.6 and 14.5°C for the summer and autumn seasons, respectively. Temperature was negatively correlated with summer egg abundance and positively with autumn egg abundance. A negative correlation between egg abundance and the North Atlantic Oscillation index suggested a link between egg numbers and plankton production.