Marine landscapes and faunal recruitment: a field test with seagrasses and copepods

Abstract

The influence of plant landscapes on recruitment of meiofaunal copepods was investigated in a New Zealand seagrass bed. Artificial plant mimics were placed into sediments at levels equivalent to natural blade densities (100 units per 0.5 X 0.25 m plot) in a variety of experimental treatments and retrieved 3 or 5 d later. To assess the effect of plant arrangement on faunal recruitment, plots were established within a seagrass bed in areas clipped of vegetation with (1) natural vegetation immediately surrounding the experimental plot; (2) natural vegetation clipped up to 0.5 m from plot edges; and (3) vegetation clipped up to 1 m from plot edges. Outside the natural seagrass bed plots were established in unvegetated sediments 0.5 m from the edge of the bed. Additionally, mimics were placed into plots 0.5 m from the edge of the bed which had sediment surfaces covered by plastic sheeting to determine whether recruitment onto plant mimics was from underlying sediments or from outside plots. Density of total copepods was highest on plant mimics with vegetation immediately adjacent to clipped areas inside the natural seagrass bed after 5 d. Densities of total copepods on mimics placed outside the bed were 5 x higher than those inside the bed and the covering of sediment significantly reduced recruitment. The dominant copepod species, Bulbarnphiascus sp., recruited to mimics irrespective of sediment border and probably invaded mimics from underlying sediments, although this was not true for other common species. While plant arrangement may influence recruitment of some copepod species, altering access to a source pool had a much greater effect on copepod densities on plant mimics.

Significance of copepod emergence to benthic, pelagic, and phytal linkages in a subtidal seagrass bed

“…Although sediment-emerging copepods appear to resettle rapidly, both water column dispersal (this study) and extended pelagic residence (Bell et al 1989) can delay benthic reentry. Dispersal of migrating phytal copepods also results in prolonged water column habitation by normally benthic taxa (Bell & Hicks 1991, Kurdziel & Bell 1992. The pelagic dispersal of benthic copepods will increase the probability of Interacting with both nektonic and planktonic assemblages.…”

“…Given the range in detectable density differences, it is possible that settlement of a small percentage of the sediment-emerging copepods onto blades would go unnoticed. Copepod migrations off blades were not measured directly, but previous studies indicate phytal copepods are highly moblle (Gunnill 1982, Bell & Hicks 1991, Kurdziel & Bell 1992). An accurate assessment of migration effects would require measurement of copepod turnover rates on individual blades.…”

“…In the present study we found that copepod emergence from benthic habitats resulted in (1) rapid (within hours) recolonization of benthic habitats by a significant portion of the Table 2. Summary of the linkages between benthic, pelagic, and phytal environments for subtidal , Kurdziel & Bell 1992, this study) and intertidal seagrass bed copepods (Bell & Hicks 1991). Resettlement was considered to occur if species' sediment or blade densities increased significantly during or just after periods of known emergence.…”

“…Macrophytes also are populated by unique copepod species (Rutledge & Fleeger 1994) and species that are capable of entering the water column (Hicks 1986, Palmer 1986, Kurdziel & Bell 1992. Phytal copepods in seagrass habitats can disperse through the water column and colonize blades > 2 0 m from a source bed (Bell & Hicks 1991, Kurdziel & Bell 1992. Although copepod morphology can identify potential habitat preferences and behavior in seagrass beds, many species that reside on blades also emerge from the sediment .…”

Can habitat loss be treated independently of habitat configuration? Implications for rare and common taxa in fragmented landscapes

“…The experiment was run for 2 mo, a much greater time than is required for large changes in such invertebrate assemblages, which can occur within days (e.g. Gunnill 1982, Bell & Hicks 1991.…”