Date of Award

Spring 4-30-2016

Degree Type

Thesis

Degree Name

Bachelor of Science

Department

Biology

Abstract

The Laurencia complex encompasses multiple species of red macroalgae commonly present on coral reefs. While some species are usually chemically defended and abundant, others are palatable, cryptic and could constitute part of the diet of herbivorous fish. However, field and laboratory species identification of the Laurencia complex is difficult because of their morphological similarities, which limit ecological and morphological studies at the species level. This research identifies and describes the morphology and the ecological pressures of the common species, Laurencia cervicornis. To evaluate seasonality of L. cervicornis in the absence of herbivory, limestone tiles (n=32) were placed in herbivores exclosure treatments at Pickles reef during Aug. 2011- Mar. 2012 to recruit L. cervicornis. Seasonal abundance was recorded and samples were collected for morphological and genetic studies. In November 2015, feeding assays were conducted at Conch Reef to evaluate the herbivory impact on algal species including L. cervicornis. A marked seasonality of algal abundance within the exclosures was reported, with a low abundance (~6%) of L. cervicornis in spring and almost completely disappearing in winter (0%). The abundance of L. cervicornis dropped in the first four hours of exposure of the tiles to herbivores, suggesting the effectiveness of grazers controlling this species. The specimens recruited on the tiles display diagnostic characteristics typical of the genera Chondrophycus and Palisada. Reproductive structures were reported for the first time and were consistent with this view. The phylogenetic position of this species was inferred by an analysis of chloroplast-encoded rbcL gene sequences of 53 taxa, using two members of the Rhodomelaceae and two of the Ceramiaceae as outgroups. The samples of L. cervicornis showed 0.2-0.9% genetic divergence indicating that all represent the same species. In all analyses, Laurencia cervicornis was phylogenetically distant from the genus Laurencia, and joined with Palisada with high support. On the basis of both molecular and morphological data, L. cervicornis should be transferred to the genus Palisada, but in order to rename and transfer L. cervicornis to Palisada, morphological characteristics will require revision.

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