Article pubs.acs.org/est
Reconstruction of Pyrodinium Blooms in the Tropical East Pacific (Mexico): Are They Related to ENSO? Joan-Albert Sanchez-Cabeza,†,‡,* Ana Carolina Ruiz-Fernández,† Anne de Vernal,§ and Maria Luisa Machain-Castillo† †
Instituto de Ciencias del Mar y Limnología, Universidad Nacional Autónoma de México, 04510 Mexico City, Mexico Institut de Ciència i Tecnologia Ambientals, and Departament de Física, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain § GEOTOP, Université du Québec Montréal, Montréal H3C 3P8, Canada ‡
ABSTRACT: Some microplanktonic species, mostly dinoflagellates, causing Harmful Algal Blooms (HABs), produce toxins which may affect the environment and human health, thus causing important economic losses. The dinoflagellate Pyrodinium bahamense var. compressum is one of the main species causing harmful algal blooms along the tropical Pacific. Although it was first reported along the Mexican coast in the 1970s, here we report that a sedimentary record of Pyrodinium cysts from the Gulf of Tehuantepec in the tropical East Pacific (Mexico), which spans from the 1860s, showed the continuous occurrence of Pyrodinium cysts and that their presence has been declining in the last few decades. Although Pyrodinium HABs have been attributed to El Niñ o events in the tropical Indo-West Pacific, the record shows that most blooms in the tropical East Pacific appear in periods of low sea surface temperature and higher rainfall, as can be observed during rapid shifts from cold (La Niñ a) to warm (El Niñ o) conditions in that region. This mechanism offers new ways to better predict and facilitate early detection of Pyrodinium HABs worldwide.
■
■
INTRODUCTION Microplanktonic species causing Harmful Algal Blooms (HABs) produce toxins which may cause harm to public health and the environment, causing important economic losses.1−3 It has been suggested that the occurrence of HABs is increasing worldwide due to nutrient enrichment,4,5 shifts toward warmer global climate,6 or transport of algal species by ship ballast water.7 The dinoflagellate Pyrodinium bahamense var. compressum (henceforth named Pyrodinium) is the one of the main species causing HABs along the tropical Pacific.8 It was first reported along the Mexican coast in the 1970s 9 and it has been suggested that (i) the first detected Pyrodinium HAB in Guatemala (1987) may have been due to transport from the Western Pacific with ballast waters,1 and (ii) that Pyrodinium HABs are related to El Niño events.10 HABs are episodic phenomena and the lack of long-term data sets makes it difficult to assess the relative importance of the environmental factors which favor blooms and thus produce reliable predictions. Cysts in 210Pb dated sediment cores from Manila show that Pyrodinium was detected since the 1920s and exhibited increased occurrence since the 1980s.11,12 In this work, we describe a Pyrodinium cyst record in a 210Pb dated sediment core from the tropical East-Pacific and discuss the relation of Pyrodinium HABs with climatic conditions in the study area since the 1950s. © 2012 American Chemical Society
EXPERIMENTAL SECTION The Gulf of Tehuantepec (Figure 1) is very productive and sustains important commercial fisheries, including shrimp and tuna. Waters below 50 m are oxygen-depleted or even anoxic.13 Sampling details and 210Pb sediment radiochronology methods are described elsewhere.14,15 Palynological analysis was performed on sediment samples.16 Dinocysts concentrations ranged from 477 to 2300 cysts g−1. Of the 23 cyst taxa identified 17 three HAB-causing species were found: Operculodinium centrocarpum [= Cyst of Protoceratium reticulatum];18,19 Lingulodinium machaerophorum [= Cyst of Lingulodinium polyedrum (Stein)];20 and Polysphaeridium zoharyii [= Cyst of Pyrodinium bahamense21 var. compressum (Böhm 1931)].22 They are widely distributed species found in warm temperate and subtropical waters of coastal areas and produce toxins such as saxitoxin (STXs), associated to paralytic shellfish poisoning. In all samples, Pyrodinium cysts were the most abundant (32−830 cyst g−1) and their fluxes (cysts cm−2 yr−1) calculated as the product of the cyst concentrations and the 210Pb derived mass accumulation rates (MAR). Received: Revised: Accepted: Published: 6830
December 13, 2011 April 30, 2012 May 11, 2012 May 11, 2012 dx.doi.org/10.1021/es204376e | Environ. Sci. Technol. 2012, 46, 6830−6834
Environmental Science & Technology
Article
Figure 1. Sampling area. Core Tehua II was collected at 15°59.987′N and 94°48.469′W, at 66.7 m depth.
■
Pyrodinium cyst fluxes were compared with several climate data from the region. The monthly values of the Multivariate ENSO Index (MEI) 23 were obtained from NOAA (http:// www.esrl.noaa.gov/psd/enso/mei/table.html), which are only available since 1950. From the database, monthly extremes were calculated. The time derivative was computed as the MEI variation over the time interval (1 month). The monthly Sea Surface Temperature (SST) at the Gulf of Tehuantepec was extracted from the Extended Reconstructed Sea Surface Temperature 24 (ERSST.v3b, resolution 2 × 2°) from NOAA (http://www.ncdc.noaa.gov/oa/climate/research/sst/ersstv3. php). Monthly rainfall data for the Mexican South Pacific basin were provided by the Servicio Meteoroló g ico Nacional, Méx ico, on 28/06/2007. Paleoecological data, spanning several years per section, were compared with extreme climatic values during the period covered by each section. For the time period of each dated layer, Pyrodinium flux, MAR, minimum MEI, maximum MEI derivative, and maximum rainfall were compared by using a nonrotated Principal Components Analysis (PCA) using the SPSS software.
RESULTS AND DISCUSSION
HABS were unknown in Mexico before the mid-70s 25 but 561 poisoning episodes have been reported during 1970−2004,26 mostly due to Gymnodinium catenatum and Pyrodinium bahamense, and attributed to coastal pollution and ENSO events.10 It is widely considered that one of the limiting factors to explain the appearance of HABs, and thus their prediction, is the lack of sufficient long-term observations. Therefore, environmental records become a plausible, and maybe the only, option. The examination of Pyrodinium cysts in a 210Pb dated sediment core from the Gulf of Tehuantepec 14 revealed an intriguing distribution (Figure 2). Although it has been proposed that the first detected Pyrodinium HAB in Guatemala (1987) may have been due to transport with ballast waters,1 the examination of Pyrodinium cysts in the Gulf of Tehuantepec revealed that Pyrodinium cysts are present in the whole sequence, spanning from the 1860s to present. Hence, no recent transport from the Indo-Pacific region needs to be invoked to explain Pyrodinium occurrence in the tropical East Pacific. A secondary conclusion is that the cysts appear to be well preserved even after 150 years burial at this site. 6831
dx.doi.org/10.1021/es204376e | Environ. Sci. Technol. 2012, 46, 6830−6834
Environmental Science & Technology
Article
Figure 2. (a) Flux of Pyrodinium cysts (PBC) in the Tehua II sediment core from Tehuantepec, (b) reconstructed SST in the Gulf of Tehuantepec (threshold: 25.5 °C), (c) monthly rainfall in the Mexican South Pacific basin (threshold 400 mm month−1), (d) derivative of the MEI index (threshold 7 yr−1), and (e) MEI index. Vertical lines indicate the presence of maximum (red) and some minimum (blue) Pyrodinium cyst fluxes.
The observed Pyrodinium cyst flux (Figure 2) ranged from 10 cyst cm−2 yr−1 in 2002−2004 to 159 cyst cm−2 yr−1 in 1951−1953. Excluding the two large maxima observed in the 1950s and the 1960s, the overall trend is weak but significantly negative (r = 0.33, p = 0.01), and markedly negative since 1990 (r = 0.77, p < 0.05), when minimum sea surface temperature (SST) was higher. This shows that Pyrodinium blooms have decreased during the last few decades. HABs occurrence depends on a large number of factors, including salinity, temperature, nutrient availability and water residence time,3,4 all of them sensitive to climate change and events, notably ENSO in the Pacific. Pyrodinium blooms in the Indo-West Pacific are correlated with El Niño conditions,1,9 when SST regionally decrease. Since 1950, enhanced Pyrodinium fluxes in the Gulf of Tehuantepec were observed during 10 of the 15 La Niña episodes, also characterized by low SST (Table 1), whereas the recent strong El Niño events (1982 and 1998, red vertical lines in Figure 2) correspond to minimum Pyrodinium cyst fluxes. Although a causal analysis of the Pyrodinium cyst fluxes is difficult because of the limited resolution of this sedimentary
record and the rarity of local instrumental data, some patterns are clear (Table 1). In 81% of the cases, periods of enhanced Pyrodinium fluxes are coincident with strong rainfall months (>400 mm), resulting in high nutrient delivery. The lowest SST episodes (
