태안해안국립공원 인근의 허베이스피리트 사고를 포함한 유류유출 해역의 식물플랑크톤 생태계 1. 하계 식물플랑크톤 군집의 연변동

Phytoplankton Ecosystems at Oil Spill Coasts Including the Hebei Spirit Oil Spill Site Near Taeanhaean National Park, Korea 1. Interannual Variability of Phytoplankton Community in Summer

Abstract

Right after the 2007 Hebei Spirit Oil Spill phytoplankton ecosystems were investigated for 11 years based on the seasonal monitoring of the composition and abundance of phytoplankton species. Comparable time-series data from the 1989 Exxon Valdez or the 2010 Deepwater Horizon Oil Spill sites were not available. It was suggested that the ecological healthiness of phytoplankton ecosystems at EVOS sites had recovered after 10 years following the oil spill based on chlorophyll concentrations even though these concentrations only represented phytoplankton communities in most cases. Chlorophyll concentrations can only reflect limited aspects of highly complex phytoplankton ecosystems. During the last 11 years following the 2017 HSOS, extreme variabilities were met in the seasonally averaged ratios of diatoms to phototrophic flagellates including dinoflagellates based on the microscopic cell countings. Summer phytoplankton communities exhibited some cyclic interannual changes in dominant groups every 2-4 years. During the early years (2008-2010) cryptophytes or raphidophytes (Chattonella spp.) dominated alternately each year, which was repeated again in 2014, 2015 and 2017. Two thecate dinoflagellates, Tripos fusus and Tripos furca, together accounted for 52.5% and 50.0% of all organisms in the summers of 2011 and 2012, respectively, which was repeated again in 2018. Summer occurrence and dominance by the phototrophic flagellates including HABs (Harmful Algal Blooms) species as well as their interannual variabilities in the oil spill sites could be utilized as markers for the stable and long-term management of healthy ecosystems. For this type of scientific ecosystem management monitoring of chlorophyll concentrations may sometimes be insufficient to gain a proper and comprehensive understanding of phytoplankton communities located in areas where oil spills have occurred and harmed the ecosystem.

Fig. 1. Location of the 15 sampling stations in the coastal waters of the Taeanhaean National Park

Fig. 2. Interannual variations in the accumulated annual frequency points (3 points for the first dominant species, 2 point for the second, and 1 point for the third in a season) for the three groups such as diatoms, dinoflagellates and others at the coastal waters of the Taeanhaean National Park for the first 10 years following the 2007 HSOS (Hebei Spirit Oil Spill)

Fig. 3. Abundance based percent dominance of top 3−6 dominant phytoplankton species in each seasonal cruise covering 15 stations at the coastal waters of the Taeanhaean National Park in 2015

Fig. 4. Relative composition of diatom groups (blue bar) and phototrophic flagellate groups (green bar) in terms of summer-averaged cell abundances from microscopic cell counts at the coastal waters of the Taeanhaean National Park for the first 11 years following the 2007 HSOS (Hebei Spirit Oil Spill). Pink arrows indicate the years with cryptophyte and raphidophytes as the top dominants while green arrows indicate the years with two thecate dinoflagellates species, Tripos fusus and Tripos furca as top dominant flagellates

Fig. 5. Relative composition of diatom groups (blue bar) and dinoflagellate groups (brown bar) in terms of summer-averaged cell abundances from microscopic cell counts at the coastal waters of the Taeanhaean National Park for the first 11 years following the 2007 HSOS (Hebei Spirit Oil Spill). Pink triangle in the left side (for the year 2008−2010) represent the portion occupied by the sum of cryptophyte and raphidophytes. Yellow arrow emphasizes the “second” predominance by the two thecate dinoflagellates species, Tripos fusus and Tripos furca. following the same “first peak” in 2012

Table 1. Sample-averaged total phytoplankton abundance in 30 samples from each cruise covering 15 stations at the coastal waters of the Taeanhaean National Park for the first 10 years following the 2007 HSOS (Hebei Spirit Oil Spill)

Table 2. Top three dominant phytoplankton species based on sample-averaged total abundance in each cruise covering 15 stations at the coastal waters of the Taeanhaean National Park for the first 11 years following the 2007 HSOS (Hebei Spirit Oil Spill)