Eutrophication results from the supply of excessive plant nutrient substances to an aquatic ecosystem leading to enhanced plant growth or to a change in the composition of plant and other species.
Green turtles that reside in coastal areas of the Hawaiian Archipelago have been documented by the author feeding on 56 species of algae, one marine angiosperm, and nine types of invertebrates. However, 9 species of algae out of approximately 400 species present in the Hawaiian Archipelago account for the major food sources utilized. Codium and ulva are major dietary components of juveniles, subadults, and adults in both segments of the Hawaiian Archipelago, joined by Pterocladia and Amansia in the main islands, and Caulerpa, Turbinaria, and Spyridia in the [Northwest Hawaiian Islands].
Feeding grounds may attract a high density of susceptible turtles that would facilitate the transmission of pathogens in a density-dependent fashion, as has been shown for horizontally transmitted damselfish neurofibromatosis and the herpes virus of Lucke's renal adenocarcinoma.
[Return to the essay]For example, papilloma viruses (papovaviridae) cause papillomas, fibromas, and fibropapilloma in many vertebrate species (Sundberg 1987) and have been observed in hyperplastic skin lesions of Bolivian side-necked turtles (Jacobson, et al. 1982).
The experimental evidence of Herbst et al. provides the clearest indication that an infectious subcellular agent, most probably a virus, is the etiology of GTFP. The agent responsible for positive experimental transmission has not yet been identified.
[The] virus is shed from epidermal cells when these are sloughed off and is transmitted by direct contact (esp. genital warts) and indirect contact.
The fact that the turtles have fibropapilloma certainly means that mechanical transmission of tumor cells is possible. Cattle suffer from ocular papillomas and one theory is that these can be transmitted by flies etc if the flies actually pick up tumor cells and then carry these to another animal. The papilloma viruses aren't excreted (or at least not in large quantities) so cells are more efficient.
Bovine papillomas are often transmitted during minor surgical procedures eg taking blood samples, skin biopsies etc.
We estimate that five to 10 turtles "resident" at a cleaning station are required as a stable food source for a single specialized cleaner.
Cleaners might even serve as a carrier or vector for the agent that causes the fibropapilloma.
Skin diving conducted out to the breakers on the same morning revealed dense growths of algae, especially Codium spp., Gelidium sp., Acanthophora, and Pterocladia with entangled Ulva reticulata often growing on it. The depth in most of this area was only 1.0 to 1.5 m, with many calcareous outcroppings covered with Pterocladia exposed at low tide. The abundance of known food sources that exists at this site is undoubtedly correlated to the presence of turtles previously seen by Heacock.
The wrasses have probably learned to recognize the barnacles as a food supply and how to remove this food in a manner that promotes cooperation and apparent solicitation by the turtles.
Also:
The opportunistic nature of T. duperry and the plasticity of its feeding habits argue for the likelihood of its learning to specialize on this food supply.
The epizootiologic patterns observed among free-ranging green turtle populations including the sudden appearance of GTFP at new geographic sites, variation in prevalence over relatively short distances, and temporal variation within a locality are compatible with an infectious etiology.
There are insufficient data to reconstruct the temporal and spatial pattern of disease spread among regions. The early reports from Florida and Malaysia suggest that the disease may have always had a worldwide albeit sporadic distribution.
Disease transmission would be enhanced by high population densities of vectors or intermediate host species, sediment types favoring pathogen survival outside the host, and low flushing rates. Some marine sites may attract a high density of susceptible turtles, which would facilitate the transmission of pathogens in a density-dependent fashion, as has been shown for horizontally transmitted damselfish neurofibromatosis and the herpes virus of Lucke's renal adenocarcinoma.
Table 5-8 presents average values of water quality parameters from a study of Fellsmere Farms, Sebastian River, and Indian River Farms Water Control Districts (Harper and Marshall, 1993). This table shows that TKN, TN, and TP concentrations are consistently high compared to the Lagoon open water values shown in Table 5-5.
[Ehrhart] netted in various other spots in the early days, including much work in Mosquito Lagoon (during 70s) to the north, but found more turtles in the area we work today, so he concentrated on that area (since around 81 or 82).
Large differences in prevalence among demographically matched populations may be found over very short distances, (<1 km) as seen, for example, by comparing the prevalence of GTFP in the Indian River (about 50%) with that from the nearshore Sabellariid worm reef on the ocean side of the barrier island at Wabasso Beach (0%).
Coastal eutrophication is recognised as a worldwide and growing problem in areas affected by agricultural and urban run-off (GESAMP 1990; Nixon 1990; Smayda 1990; Rosenberg 1985). Some of the problems in Australian fresh and marine waters have been summarised in recent publications (e.g. Brodie et al. 1990; AEC 1987; Cullen 1986). The principal nutrients associated with eutrophication are nitrogen (N) and phosphorus (P) but others such as organic carbon, silicon, iron, molybdenum and manganese may play a supplementary role. On a global scale, it is now estimated that the input of nutrients to the oceans from human sources via rivers is equal to, or greater than, the natural input (Windom 1992).