Subtropical Coastal Environments Research Articles

Bridging archaeology and marine conservation in the Neotropics.

Anthropogenic impacts on tropical and subtropical coastal environments are increasing at an alarming rate, compromising ecosystem functions, structures and services. Understanding the scale of marine population decline and diversity loss requires a long-term perspective that incorporates information from a range of sources. The Southern Atlantic Ocean represents a major gap in our understanding of pre-industrial marine species composition. Here we begin to fill this gap by performing an extensive review of the published data on Middle and Late Holocene marine fish remains along the southern coast of Brazil. This region preserves archaeological sites that are unique archives of past socio-ecological systems and pre-European biological diversity. We assessed snapshots of species compositions and relative abundances spanning the last 9500 years, and modelled differences in species' functional traits between archaeological and modern fisheries. We found evidence for both generalist and specialist fishing practices in pre-European times, with large body size and body mass caught regularly over hundreds of years. Comparison with modern catches revealed a significant decline in these functional traits, possibly associated with overfishing and escalating human impacts in recent times.

Research on Mass Concrete Additives in Tropical Coastal Areas

The tropical coastal region of Malaysia has a hot climate, high average annual temperature, and varying quality of local raw materials, making it challenging and difficult to carry out large volume concrete projects in this region. In this paper, we developed a special admixture for bulk concrete in subtropical coastal environment by modifying the basis of acrylic acid-based polycarboxylic acid admixture. The concrete prepared with this admixture has good ease, no water secretion, excellent mechanical properties and greatly improved exothermic characteristics. The C50 mass concrete prepared with this admixture has an initial slump/extension of 220/585mm, a 2h slump/extension of 210/570mm, and a crack resistance class I.

Temporal and spatial distribution of epibenthic dinoflagellates in the Kattegat-Skagerrak, NE Atlantic–Focus on Prorocentrum lima and Coolia monotis

Epibenthic dinoflagellates occur globally and include many toxin-producing species of concern to human health and benthic ecosystem function. Such benthic harmful algal blooms (BHABs) have been well described from tropical and sub-tropical coastal environments, but assessments from north temperate waters, e.g., northern Europe, and polar regions are scarce. The present study addressed the biodiversity and distribution of potentially toxic epibenthic dinoflagellate populations along the west coast of Sweden (Kattegat-Skagerrak) by morphological and molecular criteria. Morphological analysis conducted by light- and electron-microscopy was then linked by DNA barcoding of the V4 region of 18S rRNA gene sequences to interpret taxonomic and phylogenetic relationships. The presence of two potentially toxigenic epibenthic dinoflagellates, Prorocentrum lima (Ehrenberg) F.Stein and Coolia monotis Meunier was confirmed, along with a description of their spatial and temporal distribution. For P. lima, one third of the cell abundance values exceeded official alarm thresholds for potentially toxic BHAB events (>1000 cells gr–1 of macroalgae fresh weight). The same species were recorded consecutively for two summers, but without significant temporal variation in cell densities. SEM analyses confirmed the presence of other benthic Prorocentrum species: P. fukuyoi complex, P. cf. foraminosum and P. cf. hoffmannianum. Analyses of the V4 region of the 18S rRNA gene also indicated the presence P. compressum, P. hoffmannianum, P. foraminosum, P. fukuyoi, and P. nanum. These findings provide the first biogeographical evidence of toxigenic benthic dinoflagellates along the west coast of Sweden, in the absence of ongoing monitoring to include epibenthic dinoflagellates. Harmful events due to the presence of Coolia at shellfish aquaculture sites along the Kattegat-Skagerrak are likely to be rather marginal because C. monotis is not known to be toxigenic. In any case, as a preliminary assessment, the results highlight the risk of diarrhetic shellfish poisoning (DSP) events caused by P. lima, which may affect the development and sustainability of shellfish aquaculture in the region.

Analysis of engineering application requirements of nano coating materials

Coatings are the primary means to control the corrosion of marine engineering structures. It is the frontier and hot spot of nano coating materials research to use nano materials to modify anti-corrosion coatings, realize the complementary advantages between different materials, and prepare high-performance, environmental protection, energy saving and functional anti-corrosion coatings. However, with the application of nano coating materials in the atmospheric subtropical coastal environment, there are many problems of poor weatherability. Based on the environmental corrosion characteristics of the subtropical coastal zone, this paper evaluates the environmental adaptability of several nano coating materials in the coastal atmospheric environment, analyzes the engineering application requirements of nano coating materials, and puts forward the measures and suggestions for the development of nano coating materials in marine engineering in view of the main problems existing in the engineering application of nano coating materials in China.

Flexural behavior and modelling of FRP-bar reinforced seawater sea sand concrete beams exposed to subtropical coastal environment

This paper presents long-term flexural behavior of FRP-bar reinforced concrete beams exposed to subtropical coastal environment. Four-point bending tests were conducted and the effects of exposure duration, concrete type, and FRP-bar type were investigated. The load-deflection response of such beams features a nonlinear hardening following the linear ascending. Generally, their ultimate load-carrying capacity was reduced with the increasing exposure duration and further reduced when the seawater and sea sands were used, the BFRP-bar reinforced beams produced higher capacity than the GFRP-bar reinforced ones. For a design-oriented purpose, current American and Chinese codes were modified to determine their load-carrying and deformation capacities at both ultimate and serviceability limit states; for an analysis-oriented purpose, the finite element model has been established and justified to capture their failure modes and stress-strain response.

Phytoplankton composition in the subtropical coastal shelf environment of Cape Canaveral, Florida

The abundance and composition of the phytoplankton community off the coast of Cape Canaveral, Florida was examined from Fall 2013 to Summer 2015. The region is a shallow shelf environment. Water samples were collected quarterly at 24 sites from the surface and bottom of the water column; temperature and nutrient concentrations were determined. Photoautotrophic picoplanktonic prokaryotes (PPP) were consistently important in terms of numerical abundance and biomass throughout the study. Among the cyanobacteria, a surface bloom of the nitrogen-fixing filamentous species Trichodesmium was observed in Fall 2013. Dinoflagellates and diatoms were also major contributors to phytoplankton biomass. Many of the dominant dinoflagellates were mixotrophic or heterotrophic species. Nanoplanktonic eukaryotic algae were also periodically an important group in terms of biomass, such as prasinophytes (Chlorophyta). No consistent and reoccurring spatial patterns were observed, likely due to the dynamic water circulation in the open Cape Canaveral shelf environment. Depth-related differences in biomass were observed for dinoflagellates and diatoms. Dinoflagellate biomass was on average higher in surface samples, related to their motility. Conversely, diatom biomass was on average higher in bottom waters, reflecting the negative buoyancy of most species and the potential for re-suspension of cells from the sediment surface. The strong increase in the importance of PPP biomass observed in year 2 of the study may reflect the influence of high rainfall resulting from El Niño conditions on nutrient loads from regional land masses, as indicated by increases in phosphorus concentrations.

Carbon Flow for Plankton Metabolism of Saco do Mamanguá Ría, Bay of Ilha Grande, a Subtropical Coastal Environment in the South Brazil Bight

The autotrophic plankton assemblage along the subtropical coastal embayments of the South Brazil Bight is dominated by the cyanobacteria Synechococcus. This investigation evaluated the contribution of photosynthetic carbon fixation to the total Carbon metabolism within the planktonic system of Mamangua Ria, a sub-system of the Bay of Ilha Grande, southeast Brazilian coast. Our results reveal the Carbon budget inside the Ria is not balanced by autotrophic production. Net community production is generally negative throughout the year, with a deficit ranging from 0.5 to 1.5 mg m-2 d-1 below what is necessary to sustain the local plankton ecosystem. We argue that the offset between daily primary production and heterotrophic Carbon consumption may be balanced by grazing of nano-heterotrophs on heterotrophic bacteria. Our conclusions apply to the majority of the Brazilian inner shelf waters outside of estuarine plumes and upwelling systems, thus with meso-oligotrophic conditions

Environmental Variability and Cyanobacterial Blooms in a Subtropical Coastal Lagoon: Searching for a Sign of Climate Change Effects.

Cyanobacterial blooms in marine and freshwater environments may be favored by shifts in physical water column parameters due to warming under climate change. The Patos Lagoon (PL), a subtropical coastal environment in southern Brazil, is known for recurrent blooms of Microcystis aeruginosa complex (MAC). Here, we analyze the variability of these blooms and their relation to changes in wind direction and speed, rainfall and freshwater run-off from 2000 to 2017. Also, we discuss both longer time-series of air temperature and rainfall and a review of local studies with microcystins produced by these noxious species. Since the 1980s, MAC blooms were associated to negative anomalies in annual precipitation that occur during La Niña periods and, in the last years (2001–2014), accompanied by a trend in low river discharge. MAC blooms were conspicuous from December to March, i.e., austral summer, with massive patches seen in satellite images as for 2017. We suggest that low rainfall and run-off years under NE wind-driven hydrodynamics might accumulate MAC biomass in the west margin of the PL system. In contrast, a positive, long-term trend in precipitation (from 1950 to 2016; slope = 3.9868 mm/yr, p < 0.05) should imply in high river discharge and, consequently, advection of this biomass to the adjacent coastal region. Due to the proximity to urban areas, the blooms can represent recreational and economic hazards to the region.

Large-scale climatic effects on traditional Hawaiian fishpond aquaculture.

Aquaculture accounts for almost one-half of global fish consumption. Understanding the regional impact of climate fluctuations on aquaculture production thus is critical for the sustainability of this crucial food resource. The objective of this work was to understand the role of climate fluctuations and climate change in subtropical coastal estuarine environments within the context of aquaculture practices in Heʻeia Fishpond, Oʻahu Island, Hawaiʻi. To the best of our knowledge, this was the first study of climate effects on traditional aquaculture systems in the Hawaiian Islands. Data from adjacent weather stations were analyzed together with in situ water quality instrument deployments spanning a 12-year period (November 2004 –November 2016). We found correlations between two periods with extremely high fish mortality at Heʻeia Fishpond (May and October 2009) and slackening trade winds in the week preceding each mortality event, as well as surface water temperatures elevated 2–3°C higher than the background periods (March-December 2009). We posit that the lack of trade wind-driven surface water mixing enhanced surface heating and stratification of the water column, leading to hypoxic conditions and stress on fish populations, which had limited ability to move within net pen enclosures. Elevated water temperature and interruption of trade winds previously have been linked to the onset of El Niño in Hawaiʻi. Our results provide empirical evidence regarding El Niño effects on the coastal ocean, which can inform resource management efforts about potential impact of climate variation on aquaculture production. Finally, we provide recommendations for reducing the impact of warming events on fishponds, as these events are predicted to increase in magnitude and frequency as a consequence of global warming.

Performance of Denitrifying Bioreactors at Reducing Agricultural Nitrogen Pollution in a Humid Subtropical Coastal Plain Climate

Denitrifying bioreactors are an agricultural best management practice developed in the midwestern United States to treat agricultural drainage water enriched with nitrate‐nitrogen (NO3N). The practice is spreading rapidly to agricultural regions with poor water quality due to nutrient enrichment. This makes it imperative to track bioreactor NO3‐N reduction efficiency as this practice gets deployed to new regions. This study evaluated the application and performance of denitrifying bioreactors in the humid subtropical coastal plain environment of the Chesapeake Bay catchment to provide data about regionally specific NO3‐N reduction efficiencies. NO3‐N samples were taken before and after treatment at three denitrifying bioreactors, in addition to other nutrients (orthophosphate‐phosphorus, PO4‐P; ammonium‐nitrogen, NH4‐N; total nitrogen, TN; total phosphorus, TP) and water quality parameters (dissolved oxygen, DO; oxidation reduction potential, ORP; pH; specific conductance, SPC). Total removal ranged drastically between bioreactors from 10 to 133 kg N, with removal efficiencies of 9.0% to 62% and N removal rates of 0.21 to 5.36 g N removed per m3 of bioreactor per day. As the first bioreactor study in the humid subtropical coastal plain, this data provides positive proof of concept that denitrifying bioreactor is another tool for reducing N loads in agricultural tile drainage in this region.

Does fire alter soil water repellency in subtropical coastal sandy environments?

AbstractIrregular wetting, water repellency, and preferential flow are well‐documented properties of coastal sandy podzols, though little is known about the effect of fire on unsaturated zone processes in this environment. This study investigates water repellency at and below the soil surface in two coastal sandy podzols following bushfire. Water drop penetration time tests were applied to burned and unburned soils at a high dune field site in South East Queensland, Australia. It was found that the mean water drop penetration time of the burned soil was four times that of the unburned soil, but both soils were largely non‐repellent. Post‐fire repellency peaked below the surface in a patchy layer, in contrast to the laterally extensive layer reported in other studies, and high organic matter content in the soil did not appear to significantly influence repellency post‐burn. Non‐parametric statistics were used to quantify the high spatial variability in water repellency, which was ultimately insufficiently captured by atypically large (n = 1000 drop) datasets. This study confirms the presence of naturally occurring repellency and patchy infiltration in sandy soils while demonstrating that conclusively describing the influence of fire is challenging in a soil with heterogeneous infiltration characteristics. With respect to this uncertainty, it appears that fire does not increase soil water repellency such that infiltration and runoff processes due to fire‐induced water repellency would differ post‐burn.

Molecular Phylogeny and Biogeography of the Amphidromous Fish Genus Dormitator Gill 1861 (Teleostei: Eleotridae).

Species of the genus Dormitator, also known as sleepers, are representatives of the amphidromous freshwater fish fauna that inhabit the tropical and subtropical coastal environments of the Americas and Western Africa. Because of the distribution of this genus, it could be hypothesized that the evolutionary patterns in this genus, including a pair of geminate species across the Central American Isthmus, could be explained by vicariance following the break-up of Gondwana. However, the evolutionary history of this group has not been evaluated. We constructed a time-scaled molecular phylogeny of Dormitator using mitochondrial (Cytochrome b) and nuclear (Rhodopsin and β-actin) DNA sequence data to infer and date the cladogenetic events that drove the diversification of the genus and to relate them to the biogeographical history of Central America. Two divergent lineages of Dormitator were recovered: one that included all of the Pacific samples and another that included all of the eastern and western Atlantic samples. In contrast to the Pacific lineage, which showed no phylogeographic structure, the Atlantic lineage was geographically structured into four clades: Cameroon, Gulf of Mexico, West Cuba and Caribbean, showing evidence of potential cryptic species. The separation of the Pacific and Atlantic lineages was estimated to have occurred ~1 million years ago (Mya), whereas the four Atlantic clades showed mean times of divergence between 0.2 and 0.4 Mya. The splitting times of Dormitator between ocean basins are similar to those estimated for other geminate species pairs with shoreline estuarine preferences, which may indicate that the common evolutionary histories of the different clades are the result of isolation events associated with the closure of the Central American Isthmus and the subsequent climatic and oceanographic changes.

Using mercury isotopes to understand the bioaccumulation of Hg in the subtropical Pearl River Estuary, South China

Coastal and estuarine regions are important areas of mercury pollution. Therefore, it is important to properly characterize the sources and bioaccumulation processes of mercury in these regions. Here, we present mercury stable isotopic compositions in 18 species of wild marine fish collected from the Pearl River Estuary (PRE), south China. Our results showed variations in mass-independent fractionation (Δ199Hg: +0.05 ± 0.10‰ to +0.59 ± 0.30‰) with a Δ199Hg/Δ201Hg of ∼1.26, suggesting that aqueous MeHg underwent photo-degradation prior to incorporation into the food chain. For the results, we discovered small but significant differences of Δ199Hg values among herbivorous, demersal, and carnivorous fish, indicating that different feeding guilds of fish may have incorporated MeHg with various degrees of photo-demethylation. The consistent mercury isotope compositions between fish feeding habitat and mercury sources in the estuary provide potentially important findings on the transformation and bioaccumulation of this toxic metal in subtropical coastal environments.

Reproductive Ecology of Mangrove Flora: Conservation and Management

ABSTRACT Mangroves are dynamic and unique inter-tidal ecosystems, common in tropical and subtropical coastal environments. They are among the world’s most productive ecosystems and are important in protecting coasts from erosion by fierce tides, in promoting the diversity of marine organisms and fisheries by contributing a quantity of food and providing favourable habitats for animals. These economic uses of mangroves indicate that they play an important role in the lives and economies in the coastal regions of different countries. Mangrove forests are under immense threat worldwide due to their multiple economic uses and alterations of freshwater inflows by various upstream activities in catchment areas. Mangrove plants with unique adaptations play a crucial role in sustaining life in mangrove forests. Their reproductive biology is central to understanding the structural and functional components of mangrove forests. The success of sexual reproduction and subsequent population expansion in mangrove plants is linked to flowering timings, pollinators and tidal currents. Viviparous and cryptoviviparous plants are true mangroves while non-viviparous ones are mangrove associates. The dispersal propagule is seedling in viviparous and non-viviparous plants while it is seed in nonviviparous plants. In this study, viviparous and crypto-viviparous species were included for study. These species are self-compatible, self-pollinating and also cross-pollinating; such a breeding system is a requirement for the success of sexual reproduction and subsequent build up and expansion of population. They are entomophilous in the study region. The viviparous plants include Ceriops tagal, C. decandra, Rhizophora apiculata, R. mucronata, Bruguiera gymnorrhiza and B. cylindrica. The non-viviparous plants include Avicennia alba, A. marina, A. officinalis, Aegiceras corniculatum and Aegialitis rotundifolia. Sexual reproduction and regeneration events are annual in these plants and are dependent on local insects, tidal currents and nutrient content in estuarine environment. In recent times, erratic and insufficient rainfall together with industrial pollutants released into rivers is causing negative effects on the growth, development and regeneration of mangrove flora. In effect, there is a gradual decrease in mangrove cover. Added to this is continuous exploitation of mangrove plants for fuel wood, creation of shelters for cattle and changes for industrial establishments and aquaculture development in estuarine regions. As a consequence, the existing mangrove cover is struggling to survive and also not in a position to support local needs and provide livelihood opportunities through fishery resources. Further, reduced mangrove cover is showing catastrophic effects on fishing communities who live along the shore line during the period of cyclonic surges and tsunami events.

Response of bacterioplankton to a glucose gradient in the absence of lysis and grazing

Bacterial utilization of dissolved organic matter plays an important role in marine carbon cycling. In this study, the response of bacterioplankton to a gradient of carbon (glucose) addition was investigated experimentally in a subtropical coastal environment in the absence of top-down control by viruses and flagellates. Bacterial abundance and production were stimulated by glucose addition corresponding to a gradient of glucose. Differences in the extent of stimulation suggested different bacterial life strategies under different nutrient conditions. Bacterial community diversity as revealed by denaturing gradient gel electrophoresis (DGGE) showed a unimodal productivity-diversity (number of DGGE bands) relationship after 3-day incubation. DNA fingerprinting profiling and cluster analysis showed clear and gradual changes in bacterial community structure along the gradient of glucose concentrations, reflecting the competition for carbon supply among bacterial groups. Sequencing analysis of the DGGE bands disclosed the relative abundance of seven bacterial genotypes in the Alteromonadaceae and Roseovarius that gradually decreased with the glucose enrichment while two Vibrio genotypes showed the reverse increasing trend. This suggested that Vibrio was a more successful opportunist at high carbon availability.

Mercury in tropical and subtropical coastal environments

Anthropogenic activities influence the biogeochemical cycles of mercury, both qualitatively and quantitatively, on a global scale from sources to sinks. Anthropogenic processes that alter the temporal and spatial patterns of sources and cycling processes are changing the impacts of mercury contamination on aquatic biota and humans. Human exposure to mercury is dominated by the consumption of fish and products from aquaculture operations. The risk to society and to ecosystems from mercury contamination is growing, and it is important to monitor these expanding risks. However, the extent and manner to which anthropogenic activities will alter mercury sources and biogeochemical cycling in tropical and sub-tropical coastal environments is poorly understood. Factors as (1) lack of reliable local/regional data; (2) rapidly changing environmental conditions; (3) governmental priorities and; (4) technical actions from supra-national institutions, are some of the obstacles to overcome in mercury cycling research and policy formulation. In the tropics and sub-tropics, research on mercury in the environment is moving from an exploratory “inventory” phase towards more process-oriented studies. Addressing biodiversity conservation and human health issues related to mercury contamination of river basins and tropical coastal environments are an integral part of paragraph 221 of the United Nations document “The Future We Want” issued in Rio de Janeiro in June 2012.

Characterization and expression of calmodulin gene during larval settlement and metamorphosis of the polychaete Hydroides elegans

The polychaete Hydroides elegans (Serpulidae, Lophotrochozoa) is a problematic marine fouling organism in most tropical and subtropical coastal environment. Competent larvae of H. elegans undergo the transition from the swimming larval stage to the sessile juvenile stage with substantial morphological, physiological, and behavior changes. This transition is often referred to as larval settlement and metamorphosis. In this study, we examined the possible involvement of calmodulin (CaM) - a multifunctional calcium metabolism regulator, in the larval settlement and metamorphosis of H. elegans. A full-length CaM cDNA was successfully cloned from H. elegans (He-CaM) and it contained an open reading frame of 450 bp, encoding 149 amino acid residues. It was highly expressed in 12h post-metamorphic juveniles, and remained high in adults. In situ hybridization conducted in competent larvae and juveniles revealed that He-CaM gene was continuously expressed in the putative growth zones, branchial rudiments, and collar region, suggesting that He-CaM might be involved in tissue differentiation and development. Our subsequent bioassay revealed that the CaM inhibitor W7 could effectively inhibit larval settlement and metamorphosis, and cause some morphological defects of unsettled larvae. In conclusion, our results revealed that CaM has important functions in the larval settlement and metamorphosis of H. elegans.

The importance of plant life form on spatial associations along a subtropical coastal dune gradient

AbstractQuestionsDoes the spatial association between isolated adult trees and understorey plants change along a gradient of sand dunes? Does this association depend on the life form of the understorey plant?LocationCoastal sand dunes, southeast Brazil.MethodsWe recorded the occurrence of understorey plant species in 100 paired 0.25 m2 plots under adult trees and in adjacent treeless sites along an environmental gradient from beach to inland. Occurrence probabilities were modelled as a function of the fixed variables of the presence of a neighbour, distance from the seashore and life form, and a random variable, the block (i.e. the pair of plots). Generalized linear mixed models (GLMM) were fitted in a backward step‐wise procedure using Akaike's information criterion (AIC) for model selection.ResultsThe occurrence of understorey plants was affected by the presence of an adult tree neighbour, but the effect varied with the life form of the understorey species. Positive spatial association was found between isolated adult neighbour and young trees, whereas a negative association was found for shrubs. Moreover, a neutral association was found for lianas, whereas for herbs the effect of the presence of an adult neighbour ranged from neutral to negative, depended on the subgroup considered. The strength of the negative association with forbs increased with distance from the seashore. However, for the other life forms, the associational pattern with adult trees did not change along the gradient.ConclusionsFor most of the understorey life forms there is no evidence that the spatial association between isolated adult trees and understorey plants changes with the distance from the seashore, as predicted by the stress gradient hypothesis, a common hypothesis in the literature about facilitation in plant communities. Furthermore, the positive spatial association between isolated adult trees and young trees identified along the entire gradient studied indicates a positive feedback that explains the transition from open vegetation to forest in subtropical coastal dune environments.

Diel Aquatic CO2 System Dynamics of a Bermudian Mangrove Environment

Mangrove ecosystems play an important, but understudied, role in the cycling of carbon in tropical and subtropical coastal ocean environments. In the present study, we examined the diel dynamics of seawater carbon dioxide (CO2) and dissolved oxygen (DO) for a mangrove-dominated marine ecosystem (Mangrove Bay) and an adjacent intracoastal waterway (Ferry Reach) on the island of Bermuda. Spatial and temporal trends in seawater carbonate chemistry and associated variables were assessed from direct measurements of dissolved inorganic carbon, total alkalinity, dissolved oxygen (DO), temperature, and salinity. Diel pCO2 variability was interpolated across hourly wind speed measurements to determine variability in daily CO2 fluxes for the month of October 2007 in Bermuda. From these observations, we estimated rates of net sea to air CO2 exchange for these two coastal ecosystems at 59.8 ± 17.3 in Mangrove Bay and 5.5 ± 1.3 mmol m?2 d?1 in Ferry Reach. These results highlight the potential for large differences in carbonate system functioning and sea-air CO2 flux in adjacent coastal environments. In addition, observation of large diel variability in CO2 system parameters (e.g., mean pCO2: 390–2,841 ?atm; mean pHT: 8.05–7.34) underscores the need for careful consideration of diel cycles in long-term sampling regimes and flux estimates.

Temporal stability of marine phytoplankton in a subtropical coastal environment

We investigated the temporal stability of phytoplankton at a subtropical coastal site for 9 months by conducting chlorophyll and flow cytometric measurements at relatively high frequency (roughly at 2–5 day interval). Phytoplankton cells were grouped based on their sizes obtained from flow cytometric signals. We also conducted dilution experiments to estimate the growth and grazing mortality rates of different phytoplankton groups to assess whether the temporal stability of phytoplankton abundances was related with phytoplankton growth/grazing rates. Based on size-fractionated chlorophyll measurements, there was some indication that smaller phytoplankton cells were more stable than larger ones. However, by cytometric counting, there was no evidence for greater stability in small cells. Synechococcus, which had the lowest stability and dominated the <1 μm size class, showed a strong seasonal cycle that was highly dependent on temperature whereas eukaryotes did not have evident seasonal cycles. In general, biomass of a phytoplankton group consisting of several size classes was more stable than that of its sub component, consistent with the hypothesis that higher diversity leads to higher stability, probably related with the effect of statistical averaging (portfolio effect). Stability of heterotrophic bacteria was much higher than that of phytoplankton, leading to the speculation that bacteria were more diverse than phytoplankton. Phytoplankton stability was not related with their growth or grazing mortality rates. Our study suggests that species diversity should be taken into account when considering the temporal stability of phytoplankton.