PHYCOTOXIN LOADS IN BOTTLENOSE DOLPHINS (TURSIOPS TRUNCATUS) FROM THE INDIAN RIVER LAGOON ESTUARY SYSTEM AND COASTAL ATLANTIC WATERS, FLORIDA: 2002 – 2011

Abstract

Harmful algal blooms (HABs) are dramatic increases of algae that produce phycotoxins, and these toxins lead to subsequent neurological dysfunction with symptomatic illness leading, in extreme cases, to mass mortalities of marine mammals. This presents a conservation challenge since the frequency and severity of HABs are increasing on a global scale. Two HAB species that impact marine mammals residing in and utilizing an eastern Florida estuary and surrounding coastal Atlantic waters are Karenia brevis (K. brevis) and Pyrodinium bahamense (Pyrodinium); these HAB species produce the neurotoxins brevetoxin (PbTx) and saxitoxin (STX), respectively. These toxins are present at times in high concentrations during a HAB and in almost all trophic levels in the food web of bottlenose dolphins (Tursiops truncatus), a sentinel marine mammal species in the Florida’s Indian River Lagoon estuary system (IRL) and coastal Atlantic waters. Ecological impacts of present HAB toxins in this region are not well understood. In 2007 a rare and toxic K. brevis HAB event in the coastal Atlantic waters bordering Mosquito Lagoon (a water basin bordering the northern Indian River Lagoon) resulted in the detection of PbTx (liver; 11 – 89 ng·g-1) in most of the dead-stranded dolphins analyzed in this region. However, lack of baseline concentrations for HAB toxins in dolphins from this region prevented a full understanding of the impact of phycotoxins in this event on a regional scale. The IRL is also an emerging area of concern for STX contamination of other marine organisms. In this study, we used an enzyme-linked immunosorbent assay (ELISA) method to analyze PbTx and STX in liver tissue from bottlenose dolphins recovered from the IRL from 2002–2011 (n = 119). This tissue aided in completing our primary objective establishing preliminary baseline concentration values and concentrations for HAB toxin exposure in these animals. For dolphins recovered during baseline conditions, toxin concentrations ranged between 0.27 – 1.2 ng·g-1 and 0.41 – 1.9 ng·g-1 for PbTx and STX, respectively. For liver samples from dolphins recovered during exposed conditions detected maximum concentrations of 12.1 ng·g-1 and 9.9 ng·g-1 for PbTx and STX. This research also involved attempting to model the probability of detecting HAB toxins in dolphins at a given cell abundance; which is a key component when determining a dolphins chance of receiving a toxin if its distribution overlaps with a ‘hot-spot’ for HABs within a period of time. The detection probability may be useful in predicting future HAB impacts on dolphins in this region. Although HABs in eastern Florida are infrequent, cell concentrations approach densities large enough to pose significant health risks for both dolphins and human inhabiting this region. Continued biomonitoring of HAB toxins is therefore warranted and can aid resource managers in assessing future impacts and risks to bottlenose dolphins, a sentinel species which inhabits both the IRL estuary and adjacent coastal Atlantic waters.