Date of Degree

9-2018

Document Type

Dissertation

Degree Name

Ph.D.

Program

Earth & Environmental Sciences

Advisor

Brett Branco

Committee Members

Juergen Polle

Charles Yarish

Chester Zarnoch

Subject Categories

Environmental Monitoring | Marine Biology

Keywords

eutrophication, Ulva, Jamaica Bay, water quality, macroalgae, nitrogen

Abstract

In this dissertation, I present three studies that further our understanding of macroalgae identity, growth, and proliferation. Eutrophication is prevalent in shallow coastal ecosystems world-wide. One of the ecosystem consequences is the development of a bloom forming green marine macroalgae, Ulva spp. Ulva can have negative effects such as Zostera spp. degradation, fish, and shellfish declines. I performed assessments of (1) identity of the bloom-forming Ulva and other macroalgae assemblage, (2) physical, chemical, and biological drivers of Ulva bloom growth and proliferation, and (3) optimal irradiance and temperature requirements for early growth stages in Ulva linza.

The first study is a comprehensive survey of the bloom-forming Ulva and other macroalgae. I performed in situ observations in a shallow coastal estuary, Jamaica Bay, New York. Jamaica Bay is a eutrophic estuary that receives excessive (>11,500 kg N day-1) nitrogen loads. This study utilized nuclear ribosomal DNA, Internal Transcribed Spacer Region (ITS), and chloroplast elongation factor, tufA DNA Barcoding techniques. The dominant blade forming species of Ulva were U. compressa, U. lactuca, and U. laetevirens. Other observed Ulva were U. cf. clathratioides, U. prolifera, and U. stipitata. Some of the other macroalgae observed were Gracilaria vermiculophylla, Fucus vericulosus, and Porphyra spp. The findings of this study can aid in the control of Ulva blooms. Knowing the species is the first step in determining the growth requirements and can build upon other studies world-wide.

In the second study of this work I analyzed the in situ standing biomass of Ulva spp., Gracilaria vermiculophylla, and determined the drivers of bloom-forming Ulva. I also compared 1995/1996 Ulva spp. standing biomass in Jamaica Bay to my field analysis and aimed at understanding the reasons for differences between two decades of time. Ulva spp. biomass was collected at two locations over the field season of 2015 in Jamaica Bay. Tissue nitrogen was measured during the season in Ulva spp. to determine if Ulva was nutrient limited. Water column nutrients, salinity, and temperature were measured to understand the drivers of Ulva spp. blooms. The Ulva spp. biomass at Norton Basin and Marine Park began to increase in May and lasted through September at Norton Basin with the average peak standing biomass at 232 g dry weight m-2. At Marine Park the bloom lasted through October with an average peak standing biomass at 139 g dry weight m-2. At Marine Park Gracilaria vermiculophylla biomass was larger than Norton Basin throughout the season with a peak standing biomass in July at 15.53 g dry weight m-2. The average nitrogen tissue contents of Ulva spp. ranged between 2 to 4.5 percent. The lowest tissue nitrogen content was during the Ulva spp. bloom months, June and July. Ulva spp. was not nutrient limited any time during the season. Water column ammonium was the most abundant nutrient and it appears that Ulva is growing on for most of the season. Nitrate was low during the bloom months at almost 0 mg N L-1. The occurrence of high ammonium in the water column is most likely from wastewater treatment discharge and remineralization in the sediments.

The third study of this work I performed a controlled laboratory experiment to determine the optimal growth at different irradiance and temperatures in the developmental stages of Ulva linza. The optimal growth at an irradiance of 200-µmol photons m-2 s-1 was at 25°C and at 100-µmol photons m-2 s-1 was 21°C.Previous studies have identified similar growth results in other species of Ulva including the closely related U. prolifera.

Overall this work has management implications because we know the abundance and nitrogen storage potential of Ulva spp. from this major bay in metropolitan New York City coastal waters. Modelling the storage of nitrogen in Ulva spp. could be useful for optimal harvesting purposes to manage Ulva blooms. These harvests can remove nitrogen from eutrophic estuarine systems. Since nitrogen can only be removed by denitrification harvesting allows managers to purposefully remove nitrogen.

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