Thermal responses of marine phytoplankton: Implications to their biogeography in the present and future oceans

Phytoplankton are ecologically significant as primary producers and as regulators of the biogeochemical cycle. However, some may form harmful algal blooms that are a global problem due to the production of toxins that pose a risk to public health, the environment, and our economy. Climate change poses a serious threat to phytoplankton communities. It is, therefore, crucial to advance our knowledge on how they respond to the changes in temperature that is projected to increase in the next decades. The main aim of this thesis is to investigate how temperature limits biogeography, growth, toxin production, and competition in marine phytoplankton. To achieve this aim, the thesis presents a series of chapters with independent objectives. In Chapter 2, I analysed a global dataset of species occurrence data to examine the global patterns in the realised thermal niche and geographic range of marine phytoplankton. In Chapter 3, I investigated the global patterns of thermal traits, thermal sensitivity, and exposure and vulnerability to warming in marine phytoplankton. In Chapter 4 and 5, I conducted laboratory experiments to examine the temperature dependence of growth and toxin production in marine dinoflagellates. In Chapter 6, I also conducted laboratory experiments to test the effect of increased temperature on growth and competition in marine phytoplankton using dinoflagellates as test organisms. The key results of this thesis are as follows: (1) the current distribution of marine phytoplankton is limited by temperature, (2) their thermal traits are contingent on their biogeography and phylogeny, (3) their growth and toxin production is affected by temperature, and (4) interspecific competition in dinoflagellates is altered by increasing temperature. The findings of this thesis advance our current predictive understanding of the ecological responses of marine phytoplankton to climate change

Bleaching threatens positive carbonate budgets on Bahraini reefs

Bleaching events impact coral reef functionality and carbonate budget dynamics, which is reflected in reduced reef framework accretion, hindering reef ability to keep pace with sea-level rise projections. Reefs in the Arabian Gulf exist in harsh environmental conditions with seasonal temperatures ranging between 16 and 36 °C. Despite the high thermal thresholds (~ 35 °C) of corals in this region, extensive bleaching and high coral mortality have been reported regionally in 2017. We quantify reef carbonate budgets at a near shore and an offshore reef site in Bahrain pre-bleaching in May 2017 and post-bleaching in May 2018 to assess the impacts of the 2017 severe bleaching event on the budgetary state. Results indicate an overall decrease in hard coral cover from 14.2 ± 5.5 to 8.5 ± 1.4% and a decline in the net carbonate budget state from 3.6 ± 2.2 to 0.3 ± 0.3 kg CaCO3 m−2 year−1 at the shallow nearshore Fasht Al Adhm reef indicating a shift from a positive budgetary state to net neutral, while the deeper offshore Reef Bul Thamah has increased positively from 3.7 ± 1.2 to 4.2 ± 0.6 kg CaCO3 m−2 year−1. We attribute the decline in the nearshore reef to the bleaching event which took place between July and October 2017, resulting in high coral mortality rates and subsequent reduced framework carbonate production. Predicted warming trends present a threat to the structural integrity of shallow Bahraini reefs, compromising their ability to keep pace with future sea-level rise projections.</jats:p

Embryotoxicity of Copper and Zinc in Tropical Sea Urchin Tripneustes gratilla

The study determined the individual toxicity of copper (Cu) and zinc (Zn) in sea urchin Tripneustes gratilla. Bioassay using inhibitions on fertilization, early cleavage, mid cleavage, late cleavage and blastulation as endpoints involved exposure of viable gametes to Cu and Zn for 0.5, 3, 6, 9 and 12 h, respectively. Inhibitions increased significantly with concentration of Cu and Zn. Probit analysis estimated EC50 values for Cu and Zn, respectively, at 32 and 67 μg·L-1 on fertilization; 31 and 93 μg·L-1 on early cleavage; 43 and 61 μg·L-1 on mid cleavage; 42 and 42 μg·L-1 on late cleavage; and 20 and 44 μg·L-1 on blastulation. Results showed that toxicity of Cu is significantly higher (p<0.05) than that of Zn in all developmental stages, except in late cleavage. Also, the inhibitions elicited by Cu showed sensitivity to life stages. This study provided evidence on heavy metal species-sensitive, concentration-dependent and stage-specif ic inhibitions on embryonic development in T. gratilla to Cu and Zn. Keywords: Embryotoxicity, sea urchin development, individual toxicity, heavy metal

Bleaching threatens positive carbonate budgets on Bahraini reefs

Carbonate budget data sets for Bahrai

Comparison of thermal traits between non-toxic and potentially toxic marine phytoplankton: Implications to their responses to ocean warming

Understanding the effect of temperature on growth in marine phytoplankton is crucial in predicting the biogeography and phenology of algal blooms in the warming ocean. Here, we investigated the temperature dependence of the growth of non-toxic and potentially toxic marine phytoplankton. Using non-toxic strains (Prorocentrum sp. NRR 188, Prorocentrum micans CCAP 1136/15, and Alexandrium tamutum PARALEX 242) and potentially toxic strains (Prorocentrum minimum Poulet, Prorocentrum lima CCAP 1136/11, and Alexandrium minutum PARALEX 246) of dinoflagellates as test organisms, we measured their growth rates along a wide temperature gradient and estimated their maximum growth rates, thermal traits (e.g. thermal optima (Topt), critical thermal minima (CTmin), critical thermal maximum (CTmax), fundamental thermal niche (FTN), and skewness), thermal sensitivity, and warming vulnerability. To allow a comparison of these traits with an adequate number of observations, we independently analyzed datasets compiled from published laboratory experiments. Our experiments revealed that the temperature traits were independent of the toxicity of phytoplankton, except for Topt and CTmax. Also, the results of the analysis of the published datasets showed that maximum growth rates and thermal traits were comparable between non-toxic and potentially toxic phytoplankton. Our findings suggest that non-toxic and potentially toxic phytoplankton have generally comparable temperature traits that they can use to respond to climate change. However, depending on the climate scenario, non-toxic phytoplankton may be more vulnerable to warming than potentially toxic phytoplankton. Further studies are needed to improve our understanding of the response of marine phytoplankton to temperature, which can advance our ability to predict algal blooms in response to ongoing climate change

A benchmark survey of plankton, fish and benthic composition in Poblacion and Kadurong Reefs in Liloan, Cebu, Philippines

Coral reefs offer valuable ecosystem goods and services, such as coastal protection, erosion regulation, fishery, biodiversity, habitat and nursery grounds. However, they face threats from anthropogenic activities, including poor water quality, global warming, coastal development and unsustainable fisheries. Marine Protected Areas (MPAs) provide a structured and holistic approach in addressing these threats. Regular monitoring and assessment of these MPAs are crucial components in evaluating the MPAs design and effectiveness. Two coral reefs (i.e. Poblacion and Kadurong Reefs) were established as MPAs in Liloan, Cebu, Philippines to protect crucial habitat and biodiversity with the hope of improving fisheries by avoiding fish stock disintegration. These coral reefs provide shelter to many commercially-significant fish species, supporting subsistence and livelihood in the community. These MPAs are not only biologically rich, but they also support socio-economic stability. Hence, management and protection of the coral reefs in the MPAs of Liloan, Cebu is of paramount importance. To formulate conservation and applicable management measures, research and monitoring should be in place. This paper presents the data collected from the short term monitoring in the Poblaction and Kadurong Reefs. The paper describes an important set of data that can be used by the stakeholders to benchmark biophysical assessments for management of marine-protected areas in Liloan.This data paper provides baseline information on the health of the coral reefs of the MPAs in Liloan, Cebu. Datasets covering physico-chemical and biological parameters inclusive of water quality, coral reef cover, fish and plankton occurrence and abundance were determined using the standard protocols for surveying tropical marine resources. The results will serve as a benchmark in formulating guidelines and implementing relevant policies for the effective management and protection of the MPAs in Liloan, Cebu, Philippines