Community ecology
  black dot
Research study 1
  photograph of a sea-pen bed in Puget Sound courtesy Russ Wyeth & Owen Woodward
Sea pens Ptilosarcus gurneyi live in beds in sometimes high density. Whether these aggregations function in reproduction, defense, or something else, is not known. Photograph courtesy Russ Wyeth & Owen Woodward.
  black dot
photograph of a sea-pen bed Ptilosarcus gurneyi taken from a video

CLICK HERE to see a video of a sea-pen bed in Puget Sound, Washington.

NOTE the video replays automatically

  black dot
Research study 2

graph showing abundances of sea pansies Renilla amethystina around La Jolla, California
A 6-yr study on shallow (5-10m depth) sand-bottom communities in La Jolla, California reveals that populations of sea pansies Renilla amethystina (koellikeri) are remarkably stable.  Yet, it is evident that individual colonies move about a good deal.  The author describes them crawling on the sand surface of laboratory containers at rates of 2mm . min-1. The propulsive force for this comes from contraction waves passing along the colony edges, with the peduncle being dragged behind.  Movement is not random, for the colonies are significantly aggregated.  Fager 1968 Limnol Oceanogr 13: 448.

NOTE settlement, described by the author as “heavy”, occurs Aug-early Nov



  black dot
Research study 3

photographs of sea pansies Renilla amythestina in calm and turbulent water conditions courtesy Kastendiek 1976 Biol Bull 151: 518.Sea pansies Renilla amethystina (koellikeri) are morphologically adapted to live in conditions of turbulent water flow.  Their horizonatally expanded raches offer less resistance to water flow than do the vertically expanded ones of most other pennatulaceans.  Additionally, the anchoring peduncles are largest relative to rachis height among all Pennatulacea. In calm water conditions the rachis is expanded. In graph of degree of rachis inflation in relation to current velocity for sea pansies Renilla amythystinaturbulent water the rachis is flat.  If buried by shifting sediments Renilla can squirm its way out and re-anchor.  Studies at Zuma Beach, near Los Angeles, California show that anchoring strength decreases as the size of each colony increases (graph on Right).  Thus, small colonies with their relatively greater anchoring ability, are permitted to live at the nearshore (more turbulent) limits of the species distribution.  Kastendiek 1976 Biol Bull 151: 518.

NOTE the rachis (lit. “spine/backbone” G.) is the flat fleshy part of the colony, bearing the feeding polyps (autozooids) and the respiratory polyps (siphonozooids).  The author describes a third type of polyp that is large, bears highly toxic nematocysts, extends further out into the water column, and is used in defense, but other authors do not

NOTE peduncles scale allometrically with rachis size. Thus, small-diameter colonies (15mm) have peduncles almost 3 times longer than colony diameter, while ones of 95mm diameter have peduncles about 95mm in length. photograph showing top and bottom views of sea pansies Renilla amythystina

The 2 specimens shown here have peduncles
about 1.5 times the colony diameter

  black dot
Research study 4
  Data on distributions of sea pansies at Zuma Beach, near Los Angeles, California suggest that Renilla amethystina competes for living space with sand dollars Dendraster excentricus.  The graphed data shown here on numbers of each species . m-2 indicate a significant inverse relationship, but doesn’t tell us which species is dominant.  However, observations by the author on seasonal movements of sand-dollar beds show that Renilla is displaced as the beds shift in their direction, and Renilla is observed to colonise space recently vacated by the sand dollars.  Kastendiek 1982 Oecologia 52: 340.
  black dot