1 research outputs found
Methodological bias in the estimations of important meroplanktonic components from near-shore bottoms
Este artÃculo contiene 9 páginas, 2 figuras, 1 tabla.In spite of the many direct observations on larval release, the presence of lecithotrophic
larvae of sponges and bryozoans has either been anecdotally or never reported in plankton studies.
We collected plankton over an artificial rocky reef and on adjacent sandy bottoms in the NW Mediterranean
and compared larval abundance and species richness of the major groups of invertebrates
found over each of such substrates. Observations in the laboratory showed that formalin (4% in seawater)
irreversibly damaged most sponge larvae. To elude the effects of preservation and make it
possible to culture larvae for later identification of juveniles, the samples were first identified in vivo
and successively fixed. We compared larval abundance and species richness of the major groups of
invertebrates found between samples observed in vivo and after preservation with formalin (a posteriori).
The majority of the sponge larvae (93%) were only visible in the samples observed in vivo
whereas abundance estimations of bryozoan and ascidian larvae were equally achieved with both
methods. Estimations of the species richness were biased after sample preservation for sponge and
bryozoan larvae. We found significant differences between the numbers of planktotrophic larvae
observed a posteriori and in vivo. Sponge larvae were the most abundant plankton collected over the
reef where the adults live (38% of the total larvae; maximum: 100 ind. m–3) and among the most
abundant over the sandy bottom (13%). Bryozoan and ascidian larvae were scarce over both substrates
(<1% of the total) even though they were more abundant near parental habitats than on the
sandy bottoms. Gastropod and mussel veligers and spionid larvae were the most abundant planktotrophic
larvae. Early and late developmental stages of long-lived larvae such as those of barnacles
and late stages of polychaetes and echinoderms were mostly collected over parental habitats (either
the reef or sandy bottoms). From this report it appears that the importance of lecithotrophic larvae of
sponges and bryozoans in near-shore meroplankton assemblages needs to be examined further.This research was supported by the
European Commission (Marie Curie Fellowship to S.M. and
INTAS 971-854 to M.J.U.) and the Spanish CICYT Agency
(REN2001-2312).Peer reviewe