Century-scale changes in phytoplankton phenology in the Gulf of Maine.

Nicholas R Record,William M Balch,Karen Stamieszkin

doi:10.7717/peerj.6735

Abstract

The phenology of major seasonal events is an important indicator of climate. We analyzed multiple datasets of in situ chlorophyll measurements from the Gulf of Maine dating back to the early 20th century in order to detect climate-scale changes in phenology. The seasonal cycle was consistently characterized by a two-bloom pattern, with spring and autumn blooms. The timing of both spring and autumn blooms has shifted later in the year at rates ranging from ∼1 to 9 days per decade since 1960, depending on the phenology metric, and trends only emerged at time scales of >40 years. Bloom phenology had only weak correlations with major climate indices. There were stronger associations between bloom timing and physical and chemical variables. Autumn bloom initiation correlated strongly with surface temperature and salinity, and spring bloom with nutrients. A later spring bloom also correlated with an increased cohort of Calanus finmarchicus, suggesting broader ecosystem implications of phytoplankton phenology.

Highlights

One of the earliest studied and most striking oceanographic phenomena is the spring phytoplankton bloom
The second most common was a two-bloom cycle where the spring and autumn blooms were of closer magnitude to each other, again peaking in April and October
The shift toward later autumn blooms is consistent with this expectation, but the shift toward later spring blooms is unexpected in this context

Summary

Introduction

One of the earliest studied and most striking oceanographic phenomena is the spring phytoplankton bloom. Efforts to predict the timing of the spring bloom in the Gulf of Maine helped to coalesce the interdisciplinary and quantitative approaches that underlie modern oceanography (Riley, 1949). Phytoplankton blooms are spectacular events, and their timing is important to marine ecosystems in strongly seasonal climes. Because they constitute the primary source of carbon fixation for the pelagic food web, animals across trophic levels have life history strategies tuned to the seasonal cycle of production.

Results

Discussion

Conclusion