Effects of a Persistent Red Tide (Karenia brevis) Bloom on Community Structure and Species-Specific Relative Abundance of Nekton in a Gulf of Mexico Estuary

Abstract

An unusually persistent red tide event caused by the ichthyotoxic dinoflagellate Karenia brevis occurred along the southwest Florida coast in 2005. Extensive fish kills led to concerns regarding the effect of red tide on fish populations and their subsequent recruitment. Community structure differences were analyzed for all small-and largebodied nekton species collected by fisheries-independent monitoring from 1996 through 2006. Indices of abundance of five economically important fish species were also calculated from this time period. A significant change in small-and large-bodied nekton community structure was apparent from summer 2005 through spring 2006. Declines in the annual recruitment of juvenile spotted seatrout (Cynoscion nebulosus), sand seatrout (Cynoscion arenarius), and red drum (Sciaenops ocellatus) were evident in 2005 and 2006. Species-specific subadult and adult abundances, however, were consistent with those of previous years. These community shifts and speciesspecific declines appear to be associated with the red tide event.

Effects of Karenia brevis red tide on the spatial distribution of spawning aggregations of sand seatrout Cynoscion arenarius in Tampa Bay, Florida

“…Although ichthyotoxic levels of K. brevis were continuously detected in Zones 2 and 3 throughout the summer, these levels never extended into Zone 1. Similarly, K. brevis data collected by the Environmental Protection Commission of Hillsborough Bay (EPC) during 2005 in Zone 1 and Hillsborough Bay did not contain bloom level concentrations of K. brevis (Flaherty & Landsberg 2011).…”

“…data). Community shifts in small-and largebodied nekton, as well as declines in recruitment for 3 economically important fish species, including sand seatrout, were noted in Tampa Bay during and following the 2005 red tide (Flaherty & Landsberg 2011). The 2005 red tide was also responsible for radical shifts in the structure of the artificial reef epibenthic macroinvertebrate and fish communities located 19 to 25 km west of Tampa Bay, with fish species richness declining by > 50% and significant reductions in the abundances of most species (Dupont et al 2010).…”

“…Initiated off the west-central Florida coast in early January 2005, the red tide bloom affected coastal waters through January 2006, causing extensive mortalities of fish, turtles, birds, marine mammals, and benthos (Landsberg et al 2009, Dupont et al 2010, Flaherty & Landsberg 2011 unpubl. data).…”

“…data) because salinity limitations are usually at the lowest tolerance level of ~24 (Steidinger & Ingle 1972, Landsberg & Steidinger 1998, Brown et al 2006, Magaña & Villareal 2006, Steidinger 2009). This relatively high optimal salinity requirement of K. brevis along with the hydrology of Tampa Bay usually prevents its occurrence in lower salinity areas of the bay, typically those of the upper bay (Flaherty & Landsberg 2011). However, in summer 2005, fish kill reports attributed to K. brevis for the Tampa Bay area reached record high numbers (FWC unpubl.…”

Diversity in young shark habitats provides the potential for portfolio effects

“…Accordingly, the conservation of a geographically diverse range of juvenile habitats has been identified as an important factor in the recovery of the endangered smalltooth sawfish Pristis pectinata in the USA by minimising the risk of stochastic local-scale disasters including hurricanes and fish kills (NMFS 2009). Indeed, toxic dinoflagellate algae blooms (red tides) have caused mass fish mortality within inshore embayments within P. pectinata's range (Flaherty & Landsberg 2011), and the population-level impacts of these events will be partially mitigated by production of juveniles in other less-affected areas. In the absence of such extreme events, portfolio effects across multiple areas may also stabilise the population-level production of juvenile P. pectinata.…”