Biochemical Variation in Caribbean Sponges of the Genus Aplysina

Sponges are among the simplest multicellular organisms, consisting of groupings of cells with similar functions rather than true tissues. Nonetheless, sponges are ecologically significant in many marine environments, including coral reefs. They are sedentary organisms that feed by filtration from the water column, which contributes to the numerous roles they play on coral reefs, including upkeep of the reef, production of usable energy, and recycling of nutrients. Like all multicellular organisms, sponges are made up of biologically significant macromolecules. These macromolecules provide the energy for the sponge, and their relative concentrations determine how sponges can store and access the energy necessary to perform required functions. These macromolecules include proteins, which are often structural, lipids, which function in long-term storage of energy, and carbohydrates, which allow easy access to energetically favorable breakdown pathways. Anything not contained in these categories is considered energetically inert, but may serve other purposes within the sponge, such as providing physical structure. This study evaluated the distribution of these biochemical components within three distinct morphotypes of Caribbean sponges: Aplysina fulva, Aplysina cauliformis thick morph, and Aplysina cauliformis thin morph. It was hypothesized that these morphotypes within the same genus would present differently in terms of biochemical components. The study also assessed the distribution of these biochemical components within the morphotypes at differentially impacted sites from St. Thomas, US Virgin Islands, and the Bahamas. It was again hypothesized that sponges would vary in their biochemical constituents due to variability in water quality among these sites. Results showed that the distribution of these biochemical components varied significantly, but not consistently, between both sites and morphotypes. Protein and carbohydrates were present at high concentrations at the most environmentally impacted site, while protein and lipid were present at high concentrations at the least impacted site, suggesting a relationship between assimilation of nutrients into macromolecules and water quality. Sites with an intermediate level of impact had an inverse relationship between percent carbohydrates and percent lipids in A. cauliformis and a proportional relationship in A. fulva, suggesting that these two components could be related in a site with limited resources