)ORULGD6WDWH8QLYHUVLW\/LEUDULHV 2019 Caribbean sponge recruitment and growth on coral reef and mangrove sites in Belize Connor Daniel O'Halloran Follow this and additional works at DigiNole: FSU's Digital Repository. For more information, please contact [email protected] THE FLORIDA STATE UNIVERSITY COLLEGE OF ARTS & SCIENCES CARIBBEAN SPONGE RECRUITMENT AND GROWTH ON CORAL REEF AND MANGROVE SITES IN BELIZE By CONNOR O’HALLORAN A Thesis submitted to the Department of Biological Sciences in partial fulfillment of the requirements for graduation with Honors in the Major Degree Awarded: Spring 2019 2 The members of the Defense Committee approve the thesis of Connor O’Halloran defended on April 25, 2019. Dr. Janie Wulff Thesis Director Dr. Sven Kranz Outside Committee Member Dr. Andrew Rassweiler Committee Member 3 Abstract: Sponges play important roles in supporting coastal marine ecosystem health and have been shown to have particularly important ecological significance in both mangrove and reef ecosystems where they are found abundantly. This study aims to compare how recruitment differs between these habitats by observing recruitment rate, species composition, and community dynamics on recruitment surfaces placed in each location over 3 years. This study also aims to analyze the growth rates of individuals of 4 of the most common species of Caribbean reef sponges. This was done by measuring the same individuals of the 4 species at least annually over 5 years, while leaving them undisturbed in the field. This thesis was based on a dataset previously collected which included community composition data and size distribution data of sponges. Over 3 years, a total of 20 species and 13 species were identified on the recruitment substrata that were supplied in the reef site and the mangrove site respectively. The sponge fauna differed in all species between the two sites. Varying trends in the number of individuals recruited and total volume were also observed between sites such as a drop off in individuals in the reef site and a large increase in volume in the mangrove site over 3 years. Growth rates differed greatly among the 4 species of Caribbean reef sponges. Large differences in sponge volume and in sponge species composition, over all the years considered in this study, in comparisons both between and within the reef and mangrove sites suggest that sponge communities may be highly dynamic. 4 Introduction: Sponges (Phylum Porifera) are a group of ecologically and taxonomically diverse sessile organisms that are important to many coastal marine ecosystems. Sponges have simple but efficient body plans with specialized cells for life functions, particularly for immense filtration, but no organized tissues or organs. More interest has shifted into the study of coastal marine ecosystems because of the direct connection between ocean health and our own. This group has been shown to be much more complex and important than its deceivingly simple organization lets on. Sponges are highly efficient filter feeders and are able to displace large quantities of water relative to their size, which gives them the potential to significantly improve water quality in their environment (Perea-Blazquez et al. 2012). They also help facilitate the formation and restoration of important reef ecosystems by increasing coral survival by an order of magnitude (Wulff, 1979). Sponges can even function as bio-indicators for the health of their environment (Muricy, 1989). Still, there is relatively little known about sponges when compared to other organisms due to the difficulty of identifying and measuring these diverse organisms. Specifically, sponge growth and recruitment trends must be better understood for insight into such an impactful group. Sponge growth is quite a complex quality to study. Not only is there the logistical difficulty of performing a time series census in a marine setting, but sponges are also a diverse group. More than 20 orders of sponges are represented on coral reefs (Wulff 2017), and they can differ drastically in characteristics such as morphology and growth rate. Even within species of 5 sponge, there can be a decreased growth rate with an increase in size (Dayton 1979). While there have been some population or community level studies on Caribbean sponges (Wulff 2013), there have been fewer studies looking at the level of the individual. While community- level studies are integral to understanding a system, they have limits. Specifically, it does not differentiate between an individual sponge’s recovery rate from partial mortality, and their susceptibility to being wounded (Wulff 2006). Further, a better understanding of individual sponge growth rates may reveal trends in growth and survival that are unique to each species as well as variation within species. This part of my comparison aims to describe the long-term growth of four species of Caribbean reef sponge, focusing on the individual’s volume change. A sessile marine organism’s colonization process can be divided into four main stages; dispersal of larvae, habitat choice, settlement, and recruitment (Keough & Downs 1982). Many biotic and abiotic factors can affect colonization success. When sponges sexually reproduce, the offspring possess a planktonic larval stage (Muricy, 1989). Even with sponges being a vital part of benthic communities, there are few studies on the recruitment of these larvae. In Caribbean species, sponges are not only important to reef ecosystems but mangrove prop root ecosystems as well. They are one of the most abundant groups found in mangrove prop roots when it comes to diversity of species as well as the amount of biomass present. (Rutzler & Feller 1996). Interestingly, they tend to overlap very little in terms of species composition between coral reef and mangrove habitats (Rutzler et al 2000), even when in relatively close proximity. This phenomenon may be explained by spongivorous fish preventing sponges typically found on mangrove roots from colonizing reefs through predation, or reef species getting outcompeted on mangrove roots by local species (Wulff 2004). There is also evidence that larvae disperse over relatively short distances and may not consistently reach the other area (Zea 1993). For this 6 study, sponge recruitment abundance and species composition were determined over three years for typical mangrove and coral reef habitats. Those being Hidden Creek and the Blue Ground Range, Belize respectively. These experiments aim to perform comparisons in sponge recruitment rate, volume change, and species composition between these habitats. Materials and Methods: Long Term Growth Analysis Near the Carrie Bow Cay field station of the Smithsonian, a 400 m2 census plot was established on a shallow reef in June 2006. Within the Blue Ground Range, a series of cays, seven areas of reef were selected as a representative of the reef. Maps of the underwater landscape were created and every sponge, coral, and gorgonian in the census plot was drawn within. Each sponge was then identified by its respective species. Linear measurements were taken of each sponge without distressing them and the volume of each was estimated by the conglomeration of geometric solids. The census was done about yearly since 2006, and all census data was collected by Dr. J. Wulff. This project will be looking at data collected from 2013 to 2018 and focusing on four sponge species; Iotrochota birotulata, Ircinia strobilina, Ircinia sp. A, and Verongula rigida. To analyze this data, the detailed maps of the census area will be used for analysis. Taking pictures of the sponges would not be the most accurate way of measurement because sponges are intricate 3-dimensional organisms, and taking a picture only gives you an unsatisfactory 2-dimensional view of them. (Wulff 1991). Each individual sponge will then be given a unique designation on the map. When using the word “individual”, this applies to all living material within a constant surface, since sponges can take on an innumerable amount of unique forms. For sponges with asexual fragmentation life history strategies, the term “individual” can also mean all pieces of the individual that have broken off and settled 7 somewhere within the census area. (Wulff 1991). The volume of each designated individual will be calculated and recorded for that year. Since sponges are sessile invertebrates, they should be in the same location for the subsequent years. This enables identification of the same individuals by matching their placement on the reef of new census maps to previous ones. The compiled and analyzed data are in the form of volumetric changes of individuals recorded yearly from 2013 to 2018 with all individuals overlaid on a graph. Recruitment To study reef recruitment, dead coral rubble was collected, then rinsed in the rain and dried in the sun for at least a week. The pieces were then combined into piles which were stabilized by 1mm cable ties and anchored onto the reef using 18-gauge stainless steel wire. 16 piles in total were placed onto eight patch reef locations within the Blue Ground Range. These recruitment piles were then surveyed annually for sessile recruits by gently pulling apart the piles and photographing the recruits. These individuals were measured by volume and identified for species. Small (2x2x3 mm) samples were taken for identification from those where the species was uncertain. To study mangrove recruitment, 17 PVC pipes with 2.2 cm outside diameter and 25 cm in length were suspended among mangrove roots in Hidden Creek, Twin Cays, Belize. At least yearly, every sessile individual found on each pipe was measured by volume and recorded. Each individual sponge species was identified, and small samples of individuals not able to be confidently identified were taken for identification to the lab. All data in this project was collected by Dr. J. Wulff. 8 Results: Community Development and Recruitment After three years, the 17 recruitment pipes in Hidden Creek were covered in a variety of sessile marine organisms.