Role of oxygen in shaping invertebrates sessile communities
thesisposted on 24.09.2019 by Lagos Orostica, Marcelo Eduardo
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Resources, and their use by organisms shape populations and communities. Oxygen is a key resource that may play an important role in marine communities. When low oxygen conditions are a risk, mobile organisms can always avoid the physiological stress through movement. Sessile organisms, however, must either actively avoid low oxygen environments during the mobile larval stage, or forever tolerate it at as adult. In the first two chapters, I use the marine invertebrate Bugula neritina as a model species to determine whether larvae can detect and avoid low oxygen conditions during habitat selection. Then I investigate whether larvae are capable of integrating information about oxygen levels in the water and biofilm characteristics to select settlement habitats with optimal oxygen levels. The results indicate that larvae respond to both cues in a hierarchical way. First they choose habitats according to the oxygen levels in the water, and then by oxygenation history of the biofilm. Next, I explore the role of artificial structures in altering local oxygen levels. Artificial structures create perfect niche opportunities that select invasive species and jeopardize natives by disrupting natural flows, and decreasing local oxygen levels. In the third and fourth chapter I measured oxygen availability and water flow at the micro-scale level (millimeters) in marinas and piers in Port Phillip Bay, Australia. I also collected individuals of 14 species to determine their metabolic rates and their tolerance to hypoxia. Species were classified according to their body shape (erect or flat) and invasive status (native or invasive). I found that invasive species and flat species are able to resist lower oxygen conditions more than natives and erect shaped organisms. Small invasive species have higher metabolic rates than natives with the same size, but both groups have similar metabolic rates at bigger body masses. Flat species have lower metabolic rates than erect species in every measured size. I found that oxygen availability was correlated with flow rates in marinas and piers. Low flow environments create more hypoxic and anoxic microenvironments that are likely to be physiologically stressful to native species in particular. Highly modified marinas with low flow conditions may therefore generate conditions that are conducive to the proliferation of invasive species.