The Echinoid Parechinus Angulosus And Its Association With Other Invertebrates

ABSTRACT

Echinoids are recognized as important components of temperate kelp forests

because of the impact that they have by grazing. The provision of shelter by

some echinoid species for both juvenile conspecifics and for other species of

echinoids has been widely documented. The behaviour is thought to be

important in the survival of these species. The role of echinoids as protective

"nurseries" for several types of marine animals has also been suggested. Adult

echinoids are supported 1 - 2 cm above the substrate by the oral spines, this

leaves a gap under the echinoid where other organisms can shelter. This paper

examines firstly what types of organisms associate with the echinoid

Parechinus angulosus and the degree to which they display tight relationships

vs. chance associations. Secondly, it explores how much selectivity of the

echinoids was involved when compared to other physical shelters and open

substrate. This was done by comparing differences in the species associated

with level, flat rocks covered with crustose corallines; the holdfasts of Ecklonia

maxima; sand, and under echinoids. The study was done at four sites in False

Bay, Cape Peninsula, South Africa. Samples were collected on each habitat

type by placing a bottle over the substrate and scraping the sample into the

bottle. The organisms in each sample were identified under a microscope and

counted. The available habitat at each site was survey by divers swimming 6

am transects and noting the cover of a particular habitat falling under the tape

measure. The total number of species and organisms for each site were

compared using one-way and two-way ANOVA's on untransformed data. The

availability of different habitat types at each site was compared, using one-way

fixed-effects ANOVA. Results showed that there was no significant difference

between habitat availability at the different sites. Results of the two way

ANOVA's comparing site and habitat for individuals species showed that the

amphipod Paramoera capensis only occurred in significant numbers at one

echinoid site. The fact that 65 % of this species had a colour variation that

matched the echinoid, implied that the amphipod gains protection from

predators by being associated with subtidal echinoids. This relationship is not

obligate as this amphipod was found in other habitats. The echinoid Parechinus

angulosus appears to have a dual habitat preference with juveniles less than 1 O

mm in diameter sheltering beneath adult conspecifics and juveniles greater than

1 o mm in diameter sheltering in kelp holdfasts. The amphipod Hyale

grandicomis occurred in significant numbers associated with echinoids and had

a habitat preference for echinoids, suggesting that it has an important

relationship with subtidal echinoids. The amphipod is a known grazer of macroalgae

and thus it is possible that the amphipod gets access to a food resource

in the form of drift kelp, which is trapped by the echinoid. If this is the case then

the amphipod would also be gaining protection fr~ ators by being / S: ,,, "">-. 1

associated with the echinoid as the amount of time i(is exposec; hile foraging "'"'--" ~

is minimal. No relationship was found between ec~in~id~ a itosi midae this ,

was contrary to previous work and what was expec'et -d-a · elationship is

thought to be an obligate one. An important question that needs to be

answered by future research is whether the echinoid P. angu/osus is a drift

trapper or a grazer as it is has important impacts on commensal associations.