Effects of the toxic dinoflagellate Alexandrium fundyense on the copepod Acartia hudsonica: a test of the mechanisms that reduce ingestion rates

Abstract

Reduced grazing on harmful algal bloom species has been attributed to both the feeding deterrence and toxicity of the algae. Both toxic and deterrent effects of dinoflagellates of the genus Alexandrium, which contain toxins that cause paralytic shellfish poisoning, have been reported on different copepod species. We examined how toxin-containing Alexandrium fundyense affected ingestion rates of 2 geographically distinct Acartia hudsonica (Copepoda: Calanoida) populations over short timescales. The copepod population from Great Bay, New Jersey, has never been exposed to blooms of toxic A. fundyense, whereas the population from Casco Bay, Maine, has experienced regular blooms of the highly toxic dinoflagellate for decades. Our goals were to examine the mechanisms by which toxin-containing Alexandrium reduced the ingestion rates of copepods and determine whether the mechanisms were related to the exposure history of copepod populations. Copepods were fed, for 48 h durations, sole diets of toxin-containing A. fundyense, non-toxin containing Alexandrium tamarense and the green flagellate Tetraselmis sp. (not known to have toxic effects) and different mixtures of each (70% Alexandrium/30% Tetraselmis sp., 40/60, 20/80). Changes in ingestion rates over time were determined by measuring ingestion at different time intervals (3, 6, 12, 24, 48 h) over the 48 h period using 3 h incubations. The naïve copepods from New Jersey initially ingested toxin-containing A. fundyense, in both sole and mixed diets, at high rates followed by decreases in ingestion over time. By 24 h, their total ingestion rates were near zero. The decreases in ingestion rates, which were not due to prey selection, were also accompanied by reduced respiration rates. In contrast, none of these effects were observed when the New Jersey copepods fed on non-toxic A. tamarense. Additionally, feeding rates of historically exposed copepods from Maine were not affected by the toxin-containing A. fundyense diets. These observations are consistent with the hypothesis that toxic A. fundyense physiologically incapacitated the copepods from New Jersey but not those from Maine. Such toxic effects, as opposed to deterrence effects, can have profound implications on the grazers' ability to control harmful algal blooms.

Copepods induce paralytic shellfish toxin production in marine dinoflagellates

“…tonsa was shown to be able to discriminate between different species of Alexandrium with different toxin content, with a significant preference for the least toxic species (Teegarden 1999; but see also Colin & Dam 2003). As far as we know, the present study is the first investigation using a single phytoplankton clone with variable PST content in order to investigate the feeding preference of grazing copepods.…”

“…for 3 days to cover both fast (e.g. behavioural rejection and physical incapacitation ;Colin & Dam 2003) and slow (e.g. associative learning) mechanisms that may result in discriminate feeding of the copepods.…”

“…Studies on the effects of PST-containing prey on consumers have shown variable results (Turner & Tester 1997) ranging from non-detectable in some copepods (Colin & Dam 2003) to decreased feeding (Teegarden 1999), decreased fecundity (Guisande et al 2002a), delayed development (Frangopulos et al 2000) and direct mortality in others (Colin & Dam 2003). Furthermore, the copepods Calanus finmarchicus (Turriff et al 1995), Eurytemora herdmanii and Acartia tonsa, as well as the barnacle Semibalanus balanoides (Teegarden 1999;Teegarden et al 2001) have been shown to avoid feeding on PST-containing prey when offered together with a nontoxic food option.…”

Effects of brown tide (Aureococcus anophagefferens) on hard clam Mercenaria mercenaria larvae and implications for benthic recruitment

“…Values below reference line indicate that A. anophagefferens is toxic and/or elicits avoidance rather than being of poor nutritional value relative to the control diet, based on the scheme proposed by Jónasdóttir et al (1998) to discriminate between toxicity and nutritional inadequacy 1987) or behavioral avoidance/deterrence from cues detected prior to ingestion. Colin & Dam (2003) have associated only the former mechanism to toxicity, in the context of algal species that contain endogenous toxins, such as the PSP-producer Alexandrium fundyense. However, these mechanisms may not be mutually exclusive, as behavioral deterrence may be elicited by a detectable toxic compound on the algal cell surface.…”

Testing for resistance of pelagic marine copepods to a toxic dinoflagellate

“…Colin and Dam (2003) found that toxic A. fundyense physiologically incapacitated non-resistant adult Acartia hudsonica, reducing their ability to feed effectively: diets containing only 20% toxic A. fundyense (by carbon, $50 lg CL )1 ) reduced the total ingestion rate of NJ Acartia hudsonica to near zero within 12 h of exposure. In our experiment, the treatment diet consisted of 25% A. fundyense and was provided at a higher concentration.…”