Did algal toxins cause monk seal mortality?

Abstract

colony have so far been found dead. Five pups present at the onset of the event were clinically healthy and still alive at the time of writing, even though four of their mothers had died. This mortality pattern is inconsistent with other recent morbillivirus outbreaks in aquatic mammals, in which juveniles were more severely affected than adults 2,3 .Most of the seals died at sea, and 14 of the fresher carcasses were analysed. Our observations of these carcasses, together with behavioural observations of terminally ill animals, showed that the seals were in a good nutritional state, with no pulmonary emphysema or gross lesions in evidence.The seals' lungs were congested and their lungs and airways were filled with fluid. The terminally ill animals also exhibited clinical signs of lethargy, motor incoordination and paralysis in the water: animals floated horizontally, apparently paralysed and incapable of effective voluntary movement, although still breathing and not undergoing convulsions or respiratory distress. The period between the onset of clinical signs and the death of the seals was short. These conditions are consistent with drowning caused by paralysis due to poisoning.Osterhaus et al., who isolated the morbillivirus in affected seals 1 , presented no histopathological data. However, we carried out histopathological examination of lung and other tissues (S. Kennedy, personal communication) from the 14 fresh carcasses, and found no indication of typical morbillivirus lesions. In particular, there was no evidence of primary viral damage or secondary opportunistic infections in lung tissue, which are hallmarks of morbillivirus infections in other aquatic mammal species 4 .We analysed eight water samples collected from near the colony during the mortality event, and identified three species of toxic dinoflagellates (Alexandrium minutum, Gymnodinium catenatum and Dinophysis acuta). A. minutum was by far the most abundant dinoflagellate (2,000 to 16,500 cells per litre). We successfully isolated and cultured it at the Vigo laboratories. We did not succeed in obtaining cultures from G. catenatum and D. acuta.We analysed tissues from eight dead seals, 18 fish collected in the feeding grounds and ten composite bivalve samples, using mouse bioassays and high-performance liquid chromatography (HPLC) to search for paralytic toxins. (Our complete procedures, and results from phycological and toxicological studies, will be published elsewhere.) Mouse bioassays performed by the AOAC 5 method yielded results below and close to the detection limit (30-40 µg saxitoxin (STX) equivalents per 100 g of tissue) in six seal samples and positive results in two fish (Diplodus sargus and Dicentrarchus punctatus). The symptoms observed in the mice were consistent with the effects of paralytic toxins, but all the bivalve samples were negative by mouse bioassay.Using reverse-phase HPLC with postcolumn reaction and fluorometric detection 6 (detection limit from 0.25 µg for decarbamoyl saxitoxin (dcSTX) to 5.0 µg for neosaxitoxin (NeoS...

Status of the Mediterranean monk seal Monachus monachusin the western Sahara and the implications of a mass mortality event

“…While research on the role of the morbillivirus in the die-off has been inconclus~ve (Harwood et al 1998), there are no indications that this agent, if it occurred before the event, was a significant cause of mortality for the seal population. Intoxication by PSP saxitoxins produced by dinoflagellates has been identified as another likely cause of mass mortality (Hernandez et al 1998), and it is likely that events of this type sporadically afflict the region, causing massive marine mammal mortalities (Maigret 1979). However, during the last 2 decades, when monitoring of the colony has been most comprehen-sive and population numbers are likely to have remained stable, no mass mortalities were detected until 1997.…”

“…Zone 4 likely causes were the intoxication through the consumption of fish contaminated with paralytic shellfish poison (PSP) saxitoxins (Hernandez et al 1998), and a morbilivirus outbreak (Osterhaus et al 1997). Consequently, concerns for the viability and con-…”

Host-Virus Specificity of the Morbillivirus Receptor, SLAM, in Marine Mammals: Risk Assessment of Infection Based on Three-Dimensional Models

“…Hence, it remains unclear whether morbillivirus was the agent responsible for the dramatic deaths. The involvement of an algal bloom was also suggested as the primary cause [41]. In any case, when populations of many marine mammal species are decreasing, morbillivirus infection may cause a fatal blow.…”

Water quality and antibiotic resistance at beaches of the Galápagos Islands

“…The release of human, animal, and industrial sewage is the number one contributor of waste into the oceans and is a major source of nutrient input, leading to environmental damage and eutrophication (Nixon, 1995;Prüss, 1998;Shahidul Islam and Tanaka, 2004). Sewage release can also increase mortality of marine organisms (Hernández et al, 1998) and infect these animals with pathogens (Bossart et al, 1990). The quality of recreational waters is not only critical to environmental health, but is also closely tied to human health (Fleming et al, 2006).…”