Plankton tethering to assess spatial patterns of predation risk over a coral reef and seagrass bed

Abstract

Difficulties associated with manipulating plankton in situ have limited the ability of investigators to assess among-habitat variation in predation risk for plankton. We used plankton tethering units (PTUs) to tether zooplankton in a variety of reef and seagrass habitats, and used field and laboratory assays to test PTUs for tethering artifacts. Tethering did not affect the survivorship of 5 species of plankton (sizes <1 to 6 mm), indicating that the method works with a range of planktonic organisms. We then used the reef mysid Mysidium columbiae in additional assays and found that: (1) mysids remained on PTUs unless they were attacked by predators; (2) PTUs did not prevent planktivorous fishes from consuming tethered mysids; (3) untethered mysids commonly evaded predators, while mysids on PTUs did not; (4) the same types of predators consumed untethered and tethered mysids in the field; and (5) fishes were neither attracted to nor repelled from PTUs. We used PTUs and mysids to assess predation risk for plankton over various coral reef or seagrass habitats. Risk of attack varied among habitats and was correlated with abundance of planktivorous fishes. On the reef, attack rates were most intense over a topographically complex reef ledge, less intense over the less structurally complex center of the reef, and least intense over a structurally simple sand plain. Within the seagrass bed, attack rates were highest at the edge of the bed and less intense to the center of the seagrass bed and over an adjacent sand plain. Thus, attack rates at these sites varied tremendously over small spatial scales (meters). KEY WORDS: Invertebrate larvae · Mysids · Mysidium columbiae · Planktivory · Tethering · ZooplanktonResale or republication not permitted without written consent of the publisher Mar Ecol Prog Ser 225: 17-28, 2002 rates or potential predation pressure (Aronson & Heck 1995, and references within). Although investigators have tethered some plankton (Paffenhöffer & Lewis 1989, Thetmeyer & Kils 1995, Acosta & Butler 1999, this approach has been uncommon due to the difficulties of manipulating tethered plankton in the field (but see Acosta & Butler 1999). Tethering small plankton (i.e. most plankton) has been especially difficult and rare.To work with tethered plankton, logistical problems associated with transporting tethered plankton to the field must be overcome. Tethered plankton must stay continuously submerged during transport, the tethers cannot become entangled, and the tethered plankton must be able to be deployed quickly without damage in the field. Additionally, tethering can produce biases that confound results (e.g. Peterson & Black 1994). For example, tethering can make organisms more or less susceptible to predators by affecting their behavior, apparency, or mortality. In addition, complex interactions can occur between tethers and treatments if tethers differentially affect the susceptibility of tethered organisms in different habitats (Peterson & Black 1994). Such interactions will often ...

Variation in fish density, assemblage composition and relative rates of predation among mangrove, seagrass and coral reef habitats

“…Specifically, the nursery function of mangroves/seagrass habitats was unclear since mortality of young individuals varied significantly between sites and time of day. Similarly, Bullard & Hay (2002) observed highly variable mortality in tethered zooplankton within and between coral reef and seagrass habitats, and as a result both their study and ours urge that generalizations regarding the nursery potential of certain habitats be reconsidered. This conclusion also identifies the need of similar studies to be conducted that substantially replicate habitats and thus better assess nursery function.…”

Resource distribution influences positive edge effects in a seagrass fish

“…Because seagrass plant structure influences edge permeability, it has the potential to intercept any planktonic crustaceans along seagrass edges (Hendriks et al 2008), so it may be advantageous for pipefish to concentrate along edges. At edges, pipefish can have first access to planktonic crustaceans before they are potentially consumed by other fish and invertebrate predators within the seagrass (Bullard and Hay 2002). Furthermore, seagrass disrupts the formation of swarming crustaceans and this improves capture success by ambush predators (Flynn and Ritz 1999).…”

Influence of habitat configuration on connectivity between fish assemblages of Caribbean seagrass beds, mangroves and coral reefs

“…Both recruitment into these habitats and ontogenetic migrations towards the reef may be easier in open systems than in semi-enclosed systems (Gratwicke & Speight 2005). However, open systems are also more accessible for migrating predators, resulting in a higher predation pressure in these habitats than in habitats in semi-enclosed bays away from the coral reef (Bullard & Hay 2002, Belmaker et al 2005. Habitat configuration should therefore be taken into account when assessing the value and contribution of seagrass-mangrove habitats to the fish assemblage on the coral reef, and vice versa (Eggleston et al 2004, Chitaro et al 2005.…”