Table Of ContentRemote sensing, in situ monitoring and planktonic toxin
vectors of harmful algal events in the optically complex
waters of the Galician rias (NW Spain)
Memoria presentada por Evangelos Spyrakos:
Licenciado en Ciencias del Mar (University of Aegean, Greece, 2005)
MSc en Integrated Coastal Zone Management (University of Aegean, Greece, 2007)
MSc en Física Aplicada (Universidad de Vigo, España, 2009)
para optar al grado de Doctor por la Universidad de Vigo
Dirigida por:
Dr. Jesús M. Torres Palenzuela:
Laboratorio de Teledetección y SIG
Física Aplicada
Universidad de Vigo
Dra. África González Fernández:
Área de Inmunologia
Universidad de Vigo
Dr. Cástor Guisande:
Departamento de Ecologia y Biologia animal
Universidad de Vigo & FAO Roma
Vigo, October 2011
El Dr. Jesús M. Torres Palenzuela, profesor titular del departamento de Física Aplicada de la
Faultad de Ciencias de la Universidad de Vigo, la Dra África González Fernández, Directora
del Centro de Investigaciones Biomédicas y Catedrática de Inmunología de la Universidad
de Vigo y el Dr. Cástor Guisande González, Catedrático de Ecología de la Universidad de
Vigo,
INFORMAN:
Que la presente memoria, titulada ¨Remote sensing, in situ monitoring and planktonic toxin
vectors of harmful algal events in the optically complex waters of the Galician rias (NW
Spain)¨, presentada por D. Evangelos Spyrakos para optar al grado de Doctor por la
Universidad de Vigo, ha sido realizada bajo su dirección y reúne los requisitos necesarios
para ser defendida ante el tribunal calificador. Por tanto, autorizan su presentación ante el
Consejo de Departamento y la Comisión de Doctorado.
Y para que conste a los efectos oportunos, firman en la presente certificación
En Vigo a 25 de Octubre 2011
Dr. Jesús M. Torres Palenzuela Dra. África González Fernández Dr. Cástor Guisande González
This PhD project was supported by European Commission's Marie Curie Actions
through a grant within the project 20501 ECOsystem approach to Sustainable Management
of the Marine Environment and its living Resources (ECOSUMMER). MERIS data were
obtained through EUROPEAN SPACE AGENCY/ENVISAT project AO-623. A part of the
chlorophyll data base was provided by the Technological Institute for the Control of the
Marine Environment of Galicia.
Content
Summary ............................................................................................................................... iii
Summary in spanish .............................................................................................................. vi
Graphical abstract ................................................................................................................ ix
List of tables ........................................................................................................................... xi
List of figures ....................................................................................................................... xiii
List of abbreviations ............................................................................................................ xv
Acknowledgments .............................................................................................................. xvii
Dissemination of and development from work performed for this thesis ...................... xix
Thesis outline .......................................................................................................................... 1
CHAPTER I ▐
5 Overall introduction
9 1.1 Satellite remote sensing of coastal
optically complex waters
12 1.2 ELISA for DA detection
14 1.3 Harmful algae interactions with marine
planktonic grazers
15 1.4 Study area: Galician rias
17 1.5 Motivations and thesis objectives
21 1.6 References
CHAPTER II ▐
Development of regionally specific
chlorophyll a algorithms of optically complex 29
waters for MERIS full resolution data
Abstract 31
2.1 Introduction 32
2.2 Material and methods 34
2.3 Results 44
2.4 Discussion 52
2.5 References 57
CHAPTER III ▐
Application of a regionally specific
63 chlorophyll a algorithm for MERIS full
resolution data during an upwelling cycle
65 Abstract
66 3.1 Introduction
68 3.2 Material and methods
74 3.3 Results & Discussion
88 3.4 References
CHAPTER IV ▐
Remote sensing, in situ monitoring and
environmental perspectives of toxic Pseudo-
95
nitzschia events in the surface waters of two
Galician rias
Abstract 97
4.1 Introduction 98
i
4.2 Material and methods 100
4.3 Results 106
4.4 Discussion 116
4.5 References 122
CHAPTER V ▐
Ingestion rates of the heterotrophic
dinoflagellate Noctiluca scintillans fed on the
129
toxic dinoflagellate Alexandrium minutum
(Halim)
131 Abstract
132 5.1 Introduction
133 5.2 Material and methods
137 5.3 Results
141 5.4 Discussion
144 5.5 References
CHAPTER VI ▐
Modelling PST transfer and accumulation in 149
two planktonic grazers
Abstract 151
6.1 Introduction 152
6.2 Methods 154
6.3 Results 163
6.4 Discussion 171
6.5 References 174
CHAPTER VII
181 General discussion & further considerations
183 7.1 Development of regional specific chla
algorithms from MERIS FR data for optically
complex waters
184 7.2 Remote sensing chla mapping during an
upwelling cycle
186 7.3 Harmful Pseudo-nitzschia spp. events in
the surface waters of two Galician rias
187 7.4 Planktonic grazing on a PST-producer
dinoflagellate
188 7.5 General discussion to all chapters
189 7.6 References
Conclusions ........................................................................................................................ 191
Annex I ............................................................................................................................... 195
Annex II............................................................................................................................... 211
ii
Summary
Transient increases of phytoplankton abundance, referred to as blooms, are a
common and recurrent phenomenon in many coastal areas around the world including the
upwelling estuarine systems of the Galician rias (embayments in North-West Spain). Harmful
algal events due to toxic phytoplankton species and/or high-biomass blooms pose an
increasing threat to aquaculture and fishing industries, ecosystem health and diversity and
have possible implications to human health and activities. A multidisciplinary approach was
followed in this PhD thesis in order to detect and study harmful algal events and their
driving forces in the waters of the Galician rias and explore the possible toxin planktonic
vectors and the fate of the toxins in the marine system.
A set of neural network-based chlorophyll a (chla) algorithms for Medium
Resolution Imaging Spectrometer (MERIS) full resolution (FR) data using in situ data sets
and fuzzy clustering techniques was developed specifically for the optically complex waters
(defined as Case 2 waters) of the Galician rias. Three clusters were determined, which
represent the different structures found in the data base. Three different neural networks
(NNs) were developed: one including the whole data set, and two others using only data
points belonging to one of the clusters. The fitting results were fairly good and proved the
capability of the tools to predict chla concentrations in the study area. The best prediction
was given by the NN trained with high-quality data using the most abundant cluster data
set. The NNs developed in this study detected accurately the peaks of chla, in both training
and validation sets, outperforming the algorithms that are routinely used for MERIS data in
Case 2 waters. As a continuation, this thesis takes advantage of these regionally specific
algorithms and the characteristics of MERIS in order to deliver more accurate and detailed
chla maps of optically complex coastal waters during an upwelling cycle and harmful algal
events. The main changes in chla concentration and distribution were clearly captured in
the images. There was a significant variation in the timing and the extent of the maximum
chla areas. The maps confirmed that the spatial structure of the phytoplankton distribution
in the rias Baixas is complex and it is affected by the surface currents and winds on the
adjacent continental shelf. Relatively high biomass “patches” were mapped in detail inside
the rias.
During the sampling campaigns (2007-2009) that were carried out in the study area,
toxigenic events due to Pseudo-nitzshia spp. and high abundances of the harmful
dinoflagellate red Noctiluca scintillans were recorded.
iii
A combined analysis of satellite imagery data, measurements of biotic and abiotic
parameters and mixed effects modelling was used to study Pseudo-nitzschia blooms in the
surface waters of two of the rias. Domoic acid (DA) concentrations from natural Pseudo-
nitzshia populations in the Galician rias were for the first time, to our knowledge, measured
in the study area (below detection limits-2.5 μg L-1). Two DA outbreaks were recorded in the
area. P. australis was the dominant Pseudo-nitzschia species during the blooms. The
application of a regional algorithm in combination with the characteristics of MERIS FR
allowed for accurate mapping of chla and the detection of small, high in chla and Pseudo-
nitzschia spp. “patches” in the rias. The optimal model for the Pseudo-nitzschia spp.
abundance and DA concentration suggested the significant effect of some macronutrients
as well as other abiotic and biotic parameters, approximating in that way the potential
environmental causes and effects of the harmful Pseudo-nitzschia spp. blooms in the area.
In the case of N. scintillans, speciments of this species were collected from the rias
and were established in laboratory cultures. This species was fed with the toxic (Paralytic
Shellfish Poisoning or PSP) dinoflagellate Alexandrium minutum in order to evaluate its
ingestion and clearance rates and test for toxin accumulated in the individuals. N. scintillans
actively fed on A. minutum showing no satiated feeding. No detectable amounts of toxins in
the individuals revealed from the High Performance Liquid Chromatography (HPLC) toxin
analysis. In order to calculate detoxification rates of N. scintillans a new experiment this
time performed using a different strain and species of Alexandrium, A. catenatum which
was characterised by higher levels of toxin content. N. scintillans showed relatively high
detoxification rates (-0.17 pg toxin ind-1 h-1). Using the results of these two experiments in
combination to previously published data, dynamic models were developed in order to
study the PST transfer and accumulation in two planktonic organisms, namely the copepod
Acartia clausi and and the heterotrophic dinoflagellate N. scintillans.
This thesis shows the capability of NN models to predict chlorophyll concentrations
on the Galician coast from MERIS images following the widespread understanding of the
need for regionally specific models. According to the recorded in situ data, the model
presented here is an improvement on other previously used techniques, and made it
possible to obtain reliable chlorophyll maps using almost every image. These maps were
used to study the evolution of local oceanographic processes, which in turn were related to
the development of algal blooms in the area. The present study allows more detailed
examination of the chla distribution and detection of high biomass areas in the Galician rias
and the adjacent area and should be an integral part of the monitoring programs.
Moreover, the results of this study deduce that toxic events due to DA should be an
iv
Description:followed in this PhD thesis in order to detect and study harmful algal events and their driving forces in the waters of the Galician rias and explore the possible toxin planktonic vectors and the fate of the toxins in the marine system. A set of neural network-based chlorophyll a (chla) algorithms
