Benthic Herbivores are not Deterred by Brevetoxins Produced by the Red Tide Dinoflagellate Karenia Brevis

Abstract

Gulf of Mexico blooms of the dinoflagellate Karenia brevis produce neurotoxic cyclic polyethers called brevetoxins. During and after a red tide bloom in southwestern Florida, K. brevis cells lyse and release brevetoxins, which then sink to the benthos and coat the surfaces of seagrasses and their epiphytes. We tested the possibility that these brevetoxin-laden foods alter the feeding behavior and fitness of a common benthic herbivore within Floridean seagrass beds, the amphipod Ampithoe longimana. We demonstrated that coating foods with K. brevis extracts that contain brevetoxins at post-bloom concentrations (1 microg g(-1) drymass) does not alter the feeding rates of Florida nor North Carolina populations of A. longimana, although a slight deterrent effect was found at eight and ten-fold greater concentrations. During a series of feeding choice assays, A. longimana tended not to be deterred by foods coated with K. brevis extracts nor with the purified brevetoxins PbTx-2 and PbTx-3. Florida juveniles isolated with either extract-coated or control foods for 10 days did not differ in survivorship nor growth. A similar lack of feeding response to brevetoxin-laden foods also was exhibited by two other generalist herbivores of the southeastern United States, the amphipod A. valida and the urchin Arbacia punctulata. Given that benthic mesograzers constitute a significant portion of the diet for the juvenile stage of many nearshore fishes, we hypothesize that the ability of some mesograzers to feed on and retain brevetoxins in their bodies indicates that mesograzers may represent an important route of vertical transmission of brevetoxins through higher trophic levels within Gulf of Mexico estuaries.

Pelagic microalgae as suitable diets for the benthic harpacticoid copepod Tigriopus japonicus

“…Although there is more research recently on the effects of toxins produced by pelagic microalgae on the invertebrate microbenthos, this remains a relatively poorly researched area. Sotka et al (2009) reported that, after a red tide bloom, the brevetoxin-producing red tide dinoflagellate Karenia brevis [(Davis) G.…”

“…It is generally believed that dinoflagellates are a nutritional food source for marine copepods and conducive to their growth and development. In the case of the dinoflagellate P. Micans, the toxins secreted by could potentially cause a problem (Koski et al, 2008;Sotka et al, 2009;Zheng, 2011). Additionally, among the five microalgae species, I. galbana, N. closterium f. minutissima, and P. micans are suspended in the water column as single cells, while the two diatoms, C. muelleri and S. costatum, normally form chains of multiple cells.…”

Trophic transfer of brevetoxins to the benthic macrofaunal community during a bloom of the harmful dinoflagellate Karenia brevis in Sarasota Bay, Florida

“…This indicates natural settlement of K. brevis cells, coating/adsorption of benthic food sources by brevetoxins released by lysed K. brevis cells, and/or possible deposition of zooplankton (e.g., copepod) fecal pellets containing undigested dinoflagellates (Maneiro et al, 2000). The crustacean amphipods, Ampithoe longimana and A. valida, common herbivores in Florida seagrass beds and an important food source for juvenile fish, readily ingested and accumulated brevetoxins from their own food (freeze-dried seaweed) experimentally coated with K. brevis extracts or purified brevetoxins (Sotka et al, 2009). Benthic crustaceans (the barnacle, Balanus eburneus and mud crab Eurypanopeus depressus) were found to be relatively resistant to the effects of brevetoxins even when exposed to lysed K. brevis cells (Sievers, 1969).…”

Brevetoxin persistence in sediments and seagrass epiphytes of east Florida coastal waters

“…Motile invertebrate mesograzers such as copepods, isopods, and amphipods live several months and are primary grazers of seagrass epiphytes (Jernakoff et al, 1996). Amphipods are relatively resistant to brevetoxin toxicity (Sotka et al, 2009) and could likely serve as a vector transferring toxins in seagrass communities. In addition, some mobile filter feeders like the wing oyster Pinctada imbricata , can detach from senescing seagrass blades and reattach to living blades in the canopy (J. Fourqurean, personal observations), providing another potential vector.…”