Phytoplankton blooms in estuarine and coastal waters: Seasonal patterns and key species

Abstract

Phytoplankton blooms are dynamic phenomena of great importance to the functioning of estuarine and coastal ecosystems. We analysed a unique (large) collection of phytoplankton monitoring data covering 86 coastal sites distributed over eight regions in North America and Europe, with the aim of investigating common patterns in the seasonal timing and species composition of the blooms. The spring bloom was the most common seasonal pattern across all regions, typically occurring early (February-March) at lower latitudes and later (April-May) at higher latitudes. Bloom frequency, defined as the probability of unusually high biomass, ranged from 5 to 35% between sites and followed no consistent patterns across gradients of latitude, temperature, salinity, water depth, stratification, tidal amplitude or nutrient concentrations. Blooms were mostly dominated by a single species, typically diatoms (58% of the blooms) and dinoflagellates (19%). Diatom-dominated spring blooms were a common feature in most systems, although dinoflagellate spring blooms were also observed in the Baltic Sea. Blooms dominated by chlorophytes and cyanobacteria were only common in low salinity waters and occurred mostly at higher temperatures. Key bloom species across the eight regions included the diatoms Cerataulina pelagica and Dactyliosolen fragilissimus and dinoflagellates Heterocapsa triquetra and Prorocentrum cordatum. Other frequent bloom-forming taxa were diatom genera Chaetoceros, Coscinodiscus, Skeletonema, and Thalassiosira. Our meta-analysis shows that these 86 estuarinecoastal sites function as diatom-producing systems, the timing of that production varies widely, and that bloom frequency is not associated with environmental factors measured in monitoring programs. We end with a perspective on the limitations of conclusions derived from metaanalyses of phytoplankton time series, and the grand challenges remaining to understand the wide range of bloom patterns and processes that select species as bloom dominants in coastal waters.

Spatial variability in an estuarine phytoplankton and suspended microphytobenthos community

“…6). Carstensen et al (2015) reported that PPL blooms were mainly composed of diatoms and dinoflagellates throughout the salinity gradient (0-33) in eight estuaries located north of 30°N in North America and Europe, as also found during the present study. They also reported the spatial distributions of Skeletonema costatum (Grev.)…”

“…dominated at the same salinity levels as those described above. Because of their species-specific salinity tolerances (Kirst 1989), PPL taxa appeared at different salinity levels in Lake Furen, as has been observed in many other estuaries (Brand 1984, Rijstenbil 1988, Marshall & Alden 1990, Mallin 1994, Litaker et al 2002, Shikata et al 2008, Carstensen et al 2015.…”

“…Salinity has served as a convenient natural tracer in studies of estuarine water quality (Smith 1994). It has been particularly useful as an indicator of the spatial distributions of various elements, such as flushing times (Hall et al 2013), nutrients (Boynton & Kemp 2008), and phytoplankton communities (Carstensen et al 2015).…”

“…The spatial distribution of microalgae in the water column has primarily been evaluated by dividing the species composition into classes and/or species, rather than by functional groups such as PPL and/or SMPB (Potapova 2011, Carstensen et al 2015). The spatial distributions of PPL and SMPB need to be clarified to determine estuarine material circulation.…”

Bridging the Gap between Policy and Science in Assessing the Health Status of Marine Ecosystems

“…For example, we developed four new indicators for microbes (bacteria and cyanobacteria), but their poor score on pressure responsiveness and the potential to set targets indicated a need for further development and validation . Some phytoplankton biomass indicators, such as chlorophyll-a concentration from satellite measurements, provide valuable assessments of pressures leading to eutrophication, but linking changes in diverse and rapidly fluctuating phytoplankton composition with impacts of nutrient loading has proved challenging Carstensen et al, 2015).…”