Effects of Karenia brevis harmful algal blooms on nearshore fish communities in southwest Florida

Abstract

Blooms of the toxic alga Karenia brevis, commonly referred to as 'Florida red tides,' occur along Florida's west coast on a near-annual basis, causing massive fish kills. However, few quantitative data on the ecological effects of red tides on fish communities exist. We surveyed fish communities in 5 habitats within Sarasota Bay and the adjacent Gulf of Mexico during the summers of 2004 to 2007 using a purse seine. We collected contemporaneous data on fish densities, fish species composition, K. brevis cell densities, water temperature, salinity, dissolved oxygen, and turbidity. Fish density (catch per unit effort [CPUE]) and species richness were significantly lower in all habitats during red tides. Shannon-Wiener diversity indices were significantly lower in 4 of 5 habitats during red tides. Classification and regression tree analysis showed significant negative relationships between K. brevis density and non-clupeid CPUE, and between K. brevis density and species richness. Fish community structure differed significantly between red tide and non-red tide conditions. Canonical correspondence analysis showed that of all the environmental factors investigated, K. brevis density had the greatest influence on community structure. Most trophic guilds were negatively associated with K. brevis density, whereas the guild that included clupeids was positively associated with K. brevis density. Florida's fish kill database showed that 96% of local fish kills during 2003 to 2007 occurred during red tides. We concluded that red tides caused the observed changes in fish abundance and community structure. Harmful algal blooms occur throughout the world and may play an important, yet little understood, role in regulating fish communities.

Reference ranges for body condition in wild bottlenose dolphins Tursiops truncatus

“…Selecting the most recent measurement for an individual also helped to build the sample size for larger animals, providing a more even distribution across length classes. Also, dolphins measured during 2005 and 2006 were excluded due to a red tide harmful algal bloom that significantly reduced prey availability and impacted the nutritional status of Sarasota Bay dolphins (Gannon et al 2009, Powell & Wells 2011.…”

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

“…Ichthyotoxic concentrations are considered to be 100 000 cells l −1 (Quick & Henderson 1974, Landsberg & Steidinger 1998, Gannon et al 2009), although toxicity may vary due to the concentration of brevetoxin in the water and is not necessarily a reflection of cell concentration. Cell concentrations can be much lower than 100 000 cells l −1…”

“…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). Inshore fish communities in a southern neighboring estuary (Sarasota Bay) also experienced decreased abundance and diversity with changes in community structure during red tide months (Gannon et al 2009).…”

Monthly Variability of Chlorophyll-α Concentration in Persian Gulf using Remote Sensing Techniques

“…However, the fact that nearly every species in all habitats showed the same pattern of changes in abundance (with the exception of clupeids) suggests a large-scale environmental perturbation was the underlying cause. Red tide phenomena corresponded with massive fish kills, decreases in fish abundance and diversity, and changes in community structure (Gannon et al 2009). In the present study, distinct differences were found between red tide and non-red tide periods regarding the structures of the fish communities (Figures 9 and 10).…”