Jellyfish of the Spanish Mediterranean coast: effects of environmental factors on their spatio-temporal dynamics and economic impacts

Abstract

During recent years, jellyfish blooms have become in a passionate issue among marine scientists with a series of studies and reviews. The main concern about this blooms are related with ecosystem and socio-economic impacts and lately with the possibility of a global increase in these blooms. Jellyfish populations are known to follow periodic fluctuations in occurrence, abundance (biomass), where some regions, like the Mediterranean Sea, appear to sustain a long-term increase. The Mediterranean Sea has been largely and historically affected with blooms of several jellyfish species. Among them Pelagia noctiluca is the most abundant and the most problematic jellyfish species in the Western Mediterranean. Nevertheless, little information about the environmental restriction on the spatio-temporal dynamics of jellyfish blooms is available. In order to address these needs, this thesis has been structured covering two geographical areas reflecting two different approaches to understanding jellyfish spatio-temporal dynamics, bloom formation, impacts and analytical procedures. The first part of the thesis (Papers 1-3) deals with the outbreaks of the cubozoan Carybdea marsupialis along the coast of Denia (Alicante), including innovative work to develop experimentally based tools and analyses to generate scientifically-based recommendations for stakeholders. The second part of this thesis was done on the northern Mediterranean Spanish coast (Catalan coast) (Papers 4-6). This work is mostly based on stranded jellyfish data collected by the MEDUSA project in association with the Catalan Water Agency (ACA). The general objective of the Thesis was to understand the spatio-temporal dynamics of the jellyfish along the Spanish Mediterranean coast and the economic impacts of their blooms. Along the coast of Denia (Alicante), the coastal box jellyfish Carybdea marsupialis has caused major concern due to its painful sting and high abundances since 2008.The effects of environmental variables on the local (~ tens of kilometres) abundance of the cubomedusae showed that sea surface temperature (SST) and salinity were the main environmental variables, followed by those related to primary and secondary production and local retention or transportation to the coast. This conclusion led to our management recommendation that, to reduce the blooms of C. marsupialis, crop fertilizers and sewage discharges should be reduced in highly populated or industrialized areas. Most importantly, high amounts of nutrients reaching the coast (by rivers or ground water discharges) should be prevented, especially in early spring. The mauve stinger Pelagia noctiluca is the most common jellyfish in the Mediterranean Sea. Along the Catalan Coast, stranded P. noctiluca medusae occurred throughout the sampling period, but with highest abundances in spring and spatially correlated with submarine canyons. Bayesian analysis of the importance of stochastic versus deterministic drivers of jellyfish outbreaks along the Catalan Coast showed that jellyfish outbreaks were more frequent in May and June, particularly in the years 2009 and 2010. Results indicated that deterministic processes were more important than the stochastic component of environmental variation, suggesting that extreme events, visualized as the compound effects of environmental variables, did not affect the probability of an outbreak along the Catalan Coast. From a stated-choice questionnaire we calculated that the well-being gains associated with a reduction of jellyfish outbreaks in this area would range between €312 and €322 million annually, corresponding approximately to 19% of the tourism expenditures of the Catalan population in 2012. Improvement in the beach water quality was, by far, the most valuable attribute for all types of respondents. Improvement in the beach infrastructure was ranked second and reduction in the risk of jellyfish outbreaks, third. This study confirms the urgency to provide daily information by use of the wide set of social media applications.

Los impactos de las proliferaciones masivas (blooms) de medusas sobre las actividades humanas, han aumentado en el último tiempo. Uno de los ecosistemas más afectados es el Mar Mediterráneo donde en las últimas décadas la frecuencia de los blooms, así como el número de especies involucradas han aumentado. Así, la necesidad de entender la dinámica espacio temporal de los blooms de medusas a lo largo de la costa Mediterránea española y sus impactos económicos, es de primera importancia. La primera parte de la tesis se desarrolló en la zona central (costa de Alicante), donde el bloom del cubozoo Carybdea marsupialis en 2008 afectó negativamente hasta 185 personas diarias, impactando negativamente al turismo local. La asociación positiva de esta especie con bajos niveles de salinidad y altos niveles de producción primaria permite sugerir que efectos sinérgicos de las descargas fluviales ricas en nutrientes por actividades agropecuarias, asociado a la transformación y alteración de hábitat, han favorecido a esta especie. La segunda parte se desarrolló en la zona norte (costa de Cataluña), donde un programa de monitoreo basado en ciencia ciudadana, reveló que siete especies de medusas son las más comunes en esta zona con diferentes dinámicas espacio – temporales. La especie más importante es el escifozoo Pelagia noctiluca, que mostró las máximas abundancias durante primavera. Altas abundancias de esta especie estuvieron espacialmente asociadas a la presencia de cañones submarinos, permitiendo establecer una nueva hipótesis acerca de la migración vertical estacional en esta especie. Los análisis bayesianos mostraron que las proliferaciones de medusas fueron más frecuentes en Mayo y Junio, particularmente en los años 2009 y 2010 en la costa Catalana. Los resultados mostraron también que los componentes determinísticos fueron más importantes que los componentes aleatorios de la variabilidad ambiental, sugiriendo que los eventos extremos no afectaron la probabilidad de una proliferación de medusas en estas costas. Basado en un cuestionario realizado a usuarios de la playa, se calculó que los bienes y servicios asociados a la reducción en proliferaciones masivas de medusas en la zona de la Costa Catalana estuvo entre €312 and €322 millones anuales, correspondiendo aproximadamente al 19% de los gastos en turismo en 2012. El mejoramiento en la calidad del agua fue el atributo más valorado, seguido por un mejoramiento en la infraestructura en las playas y la reducción en el riego de proliferaciones de medusas como el tercer atributo más valorado.