Social behaviour of juvenile red sea urchins, Strongylocentrotus franciscanus (Agassiz)

Populahon recovery of D~a d e m a antrllarum following the Canbbean-wide mass mortality of the urchin in 1983 is documented In Barbados Recrultnlent (urchins 10 to 15 mm test diameter) occurred 3 to 4 mo after peak spawning Recruts settled near the front (offshore) of reefs and were aggregated \nth adults Populahons grew rapidly on all Barbados reefs the reef with fastest recovery retulning to 57 4 % of ~t s pre-mortality density by December 1985 Reefs \nth the hlghest density at the start of the study recovered most rapidly This may suggest that larvae settle preferentially on reefs wlth higher adult densltles, and/or, that luvenile mortality is lower on reefs wlth higher adult densities Populahons of D anMarum in Domlnica and St Lucia decreased dunng the study Moreover, recruitment strength to each island was posibvely correlated w~t h adult denslty on that Island This may suggest that Island populations are dlscrete breeding units Alternatively, the correlation of recruitment strength with island populahon denslty may reflect settlement preference by regionally dispersed larvae for areas of high adult density

Section: Discussionsupporting

confidence: 79%

Section: Discussionmentioning

confidence: 70%

Section: Discussionmentioning

confidence: 97%

See 1 more Smart Citation

Recruitment and population recovery of Diadema antillarum (Echinodermata; Echinoidea) in Barbados

Hunte¹,

Younglao²

1988

“…This is a social behavior which offers juvenile urchins protection from predation and a share of the adult's food (Tegner & Levin 1983, Breen et al 1985. Furthermore, red urchin populations with a wide size range of adults often show a significant increase in the number of juvenile urchins sheltered per adult with increasing adult size (Tegner 1989).…”

mentioning

confidence: 99%

Sea urchins, El Ninos, and the long term stability of Southern California kelp forest communities

Tegner¹,

Dayton²

1991

128

107

ABSTRACT. Southern California kelp forests experienced major losses during the El Nino of [1957][1958][1959]. The proximal reason for the decline was ascribed to sea urchin grazing, and the eventual recovery of some forests followed sea urchin control efforts, kelp restoration, and improvements In sewage disposal practices. The very strong El Nirio of 1982-84 allowed us to reexamine hypotheses regarding the interactions between kelps, sea urchins, and warm water, and to speculate about what happened during the earller El Nino Algal drift abundance, urchin recruitment rates, and changes in urchin density were followed at 5 sltes in the Point Loma kelp forest near San Diego from 1983 to 1987. Sea urchin recruitment rates were very low during 1982-84 and the apparent reasons for thls, namely decreased reproduction, depauperate planktonic conditions, and altered current patterns, probably prevailed during the earher El Nlrio as well. Algal drift did not become limiting during the recent event, but urchin grazing was triggered at one slte in 1987 after an amphipod infestation had reduced kelp biomass, and urchin recruitment and migration had increased grazing pressure. The Point Loma kelp forest showed significant recovery the year after the 1982-84 El Nirio, something that took over 5 yr in the 1960s. Decline in the density of red urchins Strongj~locentrotus franciscanus since the mid 1970s suggests that the fishery for this species, which became extensive in the late 1970s. was a n important contributor to the faster kelp recovery. In the absence of evidence for increased recruitment or temperature effects on grazing demand, it appears that the destructive grazing observed during and after the El NiAo of 1957-59 resulted from reductions in kelp standing stock and productivity below levels necessary to satisfy the existing grazing demand.

“…Sea urchins are interesting in this regard, as aggregation in many species is independent of size (Andrew & Choat 1985, Himmelman 1986, whereas aggregation in other species (i.e. red sea urchin Strongylocentrotus franciscanus) is a function of size, as small juveniles aggregate under much larger adult conspecifics (Low 1975, Tegner & Dayton 1977, Breen et al 1985, Sloan et al 1987. These associations may lead to intercohort competition, although examples of this type of interaction are rare (Fletcher 1988, Szabo 2002.…”

Section: Introductionmentioning

confidence: 99%

Juvenile-adult associations in sea urchins Strongylocentrotus franciscanus and S. droebachiensis: Is nutrition involved?

Nishizaki¹,

Ackerman²

2004

Juvenile-adult associations (i.e. juvenile sheltering) in sea urchins of the genus Strongylocentrotus provide an example of an important post-settlement behaviour in benthic invertebrates. It has been suggested that these associations provide a nutritional advantage to juveniles by facilitating access to kelp. We examined this hypothesis in a series of growth experiments involving 2 sea urchin species, Strongylocentrotus franciscanus and S. droebachiensis, which show high and low levels of juvenile sheltering, respectively. Juvenile sea urchins (7.73 ± 0.09 mm [mean ± SE] test diameter) of both species had lower growth rates in the presence versus absence of adults, regardless of food type, though the effect was more pronounced in S. franciscanus (0.2 ± 0.1 vs 1.2 ± 0.3 mm mo -1 ) than in S. droebachiensis (0.8 ± 0.5 vs 1.2 ± 0.7 mm mo -1 ). This relationship was not evident in the absence of food, which leads us to conclude that the reduction in growth is due to intercohort competition. Hence, other post-settlement factors (e.g. predation and hydrodynamic disturbance) are likely responsible for maintaining the juvenile-adult associations observed in S. franciscanus. Species-specific strategies in juvenile sheltering indicate that behavioural processes are important for the recruitment of benthic invertebrates with mobile juvenile stages.