Intertidal ecology topics

Country codes: HO (Honduras), IN (Indonesia), MA (Madagascar), ME (Mexico), PE (Peru), SA (South Africa)

IN31 Evaluating potential effects of rising environmental temperatures on thermal ecology of fiddler crabs

Often exhibiting high levels of biodiversity and endemism, mangrove forests demonstrate a remarkable interdependence between local flora and fauna such that a loss of diversity or density in one group has marked adverse effects on the other. Declines in burrowing crustacean populations, for example, have been shown to result in reduced organic turnover, decreased nutrient and energy cycling, and diminished primary productivity in mangrove species. Fiddler crabs, Uca species are one of several semi-terrestrial, burrowing, mangrove decapods making up a keystone group commonly referred to as engineers. Indonesia boasts the highest diversity of fiddler crab species of any country in the world with 14 total species, seven of which can be found within an area of 4-square meters within the Ambeua mangrove near Hoga Island. Previous research at the Hoga marine laboratory has shown that local fiddler crab populations are relatively tolerant of high temperatures; however, with environmental temperatures across the Malay Archipelago expected to increase by up to 4°C in coming decades, it is unclear how fiddler crab populations and ultimately mangrove ecosystems, may be affected. Potential dissertation projects could evaluate differences in thermal adaptations of Uca spp. occupying different intertidal regions, or may look at acclimation responses of a single Uca species. All studies would include a field observation component, though most of the empirical work would take place in the Hoga Island research laboratory. Students are strongly encouraged to contact their project field supervisor early in the proposal development process.

Extended Project Summary

IN34 Role of mangroves in marine ecosystems

The mangroves and associated seagrass beds around the island of Kaledupa and Hoga provide an excellent laboratory to study some of the effects of mangroves on the marine environment. Some of the mangroves suffer from harvesting and one project could look at the effects of this harvesting on the mangrove biota (both in fauna diversity – species that bore) and epiphytes in mangroves with different levels of exploitation. Another project could compare the effectiveness of mangroves that have been partially damaged from harvesting with more pristine areas in depositing sediment from the water column. Note this study could be extended to the adjacent seagrass areas and coral to assess their impact on sediment settlement. Another project could look at the processes which affect carbon release from mangroves. Different guilds of biodegrading organisms (e.g. bracket fungi, beetle larvae, termites and shipworms) process wood but their relative contribution to this process varies according to the length of time the woody detritus is submerged on a tidal cycle and the salinity levels. This could be examined by studying the biodegrading organisms on mangrove wood detritus at different distances form the strandline.

ME54 A comparison of pristine and degraded mangroves in Akumal and the impact of mangrove degradation on adjacent seagrasses and coral reefs

Mangrove forests are highly productive marine ecosystems that are essential for the health of adjacent ecosystems e.g. sea grass beds and coral reefs. Yet, as much as 1 – 2% of the global mangrove forests are lost per year. Mangroves draw down atmospheric CO2 sequester and trap fine sediments, facilitate vital biodiversity mechanisms (e.g. fish nurseries) and improve fishery productivity. Despite the obvious importance of mangroves, mangrove forests in the Yucatan Peninsula have been under considerable anthropogenic impact from harvesting, causing a reduction in important habitat and biodiversity, carbon sequestration, and the productivity of adjacent sea grass and coral reef ecosystems. If the ecosystem services that mangroves provide can be quantified, then there is scope to develop a mangrove equivalent of the REDD programme in which fishing communities could receive economic investment in exchange for continued protection of the mangroves. Projects could therefore focus on a comparison of the structure, function, and faunal diversity of pristine and degraded mangroves, or an investigation of wood degradation processes across mangroves of differing quality. In addition, projects could investigate health and diversity of seagrasses and coral reefs in relation to the level of degradation of adjacent mangroves. Belt transects and permanent plots will be used to record tree composition, basal areas and tree densities. Biodiversity assessments will be conducted by investigation of the available mangrove substrata. Snorkel and dive based transect and quadrat surveys may be used to assess diversity and coverage of seagrasses, hard corals and algae.

Extended Project Summary

ME55 Understanding the non-conventional cenote-mangrove forest system

The Yucatan Peninsula is formed of limestone karst substrate that was once coral reef. As limestone is porous, rainwater seeps through the rock surface to form an extensive network of underground rivers accessed from the surface by sink holes, known locally as cenotes. Mangrove forests associated with cenotes in coastal regions are not new, but research of them is. This novel project aims to investigate the driving forces behind the structure and function of these unusual mangrove ecosystems and to investigate differences of animal community structure in comparison with coastal mangrove forests. The majority of mangrove animals exploit the available hard substrata within mangrove ecosystems. Areas such as mangrove prop roots and in particular large wood detritus (LWD) are favourable for most mangrove fauna, but nothing is known about the organisms that process the fixed carbon in cenote mangrove forests. Projects may highlight new and unreported information from forest structure and function, to mangrove fauna diversity and niche separation. Continuous belt transects and plots will be used to establish the tree structure, composition and basal areas with the cenote mangrove forests. Biodiversity assessments of the fauna upon mangrove roots, substratum and LWD will be made, and animal observations will be employed. Degradation processes of LWD will be recorded in the forests and compared with those from conventional mangrove forests.

Extended Project Summary

ME56 How do mangrove trees reduce thermal stress and provide environmental buffering for fish in a Caribbean mangrove forest?

Mangrove forests are well known for their functional traits, particularly the nursery function enhanced by the complexity of Rhizophora prop roots. A less understood functional trait is how mangrove trees may benefit biodiversity mechanisms through environmental buffering and how such traits may influence fish behaviour. Rhizophora mangle trees will investigated for their biodiversity function of reducing thermal stress for the mosquitofish, Gambusia affinis. Diurnal distributions of fish populations between open channels and shaded tree areas will be investigated. During the morning, when temperatures are cooler, and in the afternoons when temperatures are at their most extreme, fish behaviour will be studied. This study will also investigate the critical point when fish populations switch from being exposed in the channels to moving in areas of more shade, which offer reduced thermal stresses to the fish. Environmental variables will be measured, temperature and salinity, and then correlated to patterns of fish movements within the mangroves. Size distributions of fish populations will also be made to determine if the fish are mature adults, immature or juveniles. If the fish are immature, then potentially, the thermal stresses caused by the excessive channel temperatures may impose serious developmental impacts that would be reduced by occupying the shaded tree areas. Thus, the mangrove tree may provide a little known refuge of environmental buffering for juvenile and adult fish, which would otherwise be exposed to lethal thermal stress.

Extended Project Summary