Chapter three - The Role of Sponges in the Mesoamerican Barrier-Reef Ecosystem, Belize

Abstract

Over the past four decades, sponge research has advanced by leaps and bounds through endeavours such as the Caribbean Coral Reef Ecosystems (CCRE) programme at the U.S. National Museum of Natural History in Washington, D.C. Since its founding in the early 1970s, the programme has been dedicated to a detailed multidisciplinary study of a section of the Mesoamerican Barrier Reef, the Atlantic's largest reef complex, and has generated data far beyond the capability of lone investigators and brief expeditions. This reef complex extends 250 km southward from Yucatan, Mexico, into the Gulf of Honduras, most of it lying 20-40 km off the coast of Belize. A relatively unspoiled ecosystem, it features a great variety of habitats in close proximity, ranging from mangrove islands, seagrass meadows, and patch reefs in its lagoon to the barrier reef along the margin of the continental shelf. Among its varied macrobenthos, sponges stand out for their ubiquity, range of colours, rich species and biomass, and ecological importance; they populate rocky substrates, some sandy bottoms, and the subtidal stilt roots and peat banks of mangroves. Working from a field station established in 1972 on Carrie Bow Cay, a sand islet atop the reef off southern Belize, experts in numerous disciplines from both the Museum and academic institutions throughout the world have explored the area's biodiversity in the broadest sense and community development over time. At last count, 113 researchers (88 working on site) have focused on the biological and geological role of Porifera in Carrie Bow's reef communities, with the results reported in 125 scientific papers to date. The majority of these sponge studies have centred on systematics and faunistics, including quantitative distribution among the various habitats. Taxonomic approaches have ranged from basic morphology to fine structure, DNA barcoding, and ecological manipulations and culminated in a mini-workshop involving several experts on Caribbean Porifera. Ecological work has covered a broad spectrum as well: bioerosion, silica and nutrient cycling, symbiosis, mutualism, space competition, predation, disease, and the effects on sponge individuals and populations of environmental factors such as light, temperature, salinity, desiccation, substrate, and sedimentation. Many projects were enhanced by scientific illustration, laboratory studies of larvae settlement preferences and development, and investigations of microbial and invertebrate sponge associates, notably symbiotic cyanobacteria, parazoanthid epizoans, and crustacean and ophiuroid endobionts. Of the striking discoveries, the work on alpheid shrimps colonizing sponges off Carrie Bow Cay has yielded the first report of eusociality in marine organisms.