We believe that this occurred in the early 2000s although it could have started after 1989 when we last visited the structures. We lack information on the most obvious and interesting observations: the mode of reproduction, the settlement biology, and the growth of this interesting sponge. The obvious questions relate to the explanation of the event. We have no knowledge of the actual propagules or the settlement, only recruitment to a size that can be seen and identified. There are no published descriptions of dispersal propagules of A. joubini, their settlement preferences, or their growth rates. We have seen very small buds that we assume are asexually produced by another hexactinellid, R. antarctica, and we have collected them in the water column in strong currents. Thus, we know that asexually produced buds can move through the water column where they could in principle be entrained and lifted by strong tidal currents; however, we have not seen R. antarctica or any other hexactinellid beside A. joubini on any of our settling surfaces. To our knowledge, there is no evidence of any Antarctic hexactinellid sponge demonstrating sexual reproduction, although it has been seen elsewhere. In our cases A. joubini propagules must have been abundant, at least around the gangplank on Ross Island and at Explorers Cove where there was massive recruitment high in the water column. Given the heavy recruitment observed on artificial surfaces well above the seafloor, we suggest that swimming larvae are released episodically. Why is the A. joubini recruitment predominantly on artificial surfaces? We have no data to address this interesting question, equipment for growing weed but we hypothesize that there are more predators on natural substrata and that these predators serve as a strong filter on the survivorship of the propagules as discussed by Thorson.
Oliver and Slattery offer strong evidence of the efficiency of a microcanopy of carnivorous invertebrates near the gangplank, and Suhr et al. demonstrated that three of the most common foraminifera, especially Astrammina rara, consume metazoa including planktonic invertebrates in Explorers Cove. Out of this, it is reasonable to speculate that benthic predation filters settling larvae as discussed by Thorson. Another obvious question relates to the fact that we saw no measurable growth of many naturally occurring A. joubini between 1967 and 1989, yet beginning sometime between then and 2004 they exhibited tremendous growth. With the exception of two small sponges, none of the structures had any A. joubini in 1989. However, in 2004 these structures were photographed with very large sponges that presumably had settled after 1998, but certainly no earlier than 1990 , and by 2010 sponges had obtained diameters ranging from 7 to 72 cm . Further, the estimated mass of a sponge observed on an artificial substrate at Cape Armitage in 2010 increased about 30% when it was re-photographed in 2012. Clearly, rapid growth rates are possible by A. joubini. What environmental factors were responsible for this sudden growth? The most likely correlate with the growth if not the settlement was a probable shift in plankton composition. Typically the transport of abundant primary production from the north results in a seasonal plankton bloom composed of relatively large phytoplankton . However, in the 2000s a series of large icebergs were grounded, blocking this transport and preventing the annual ice from breaking up and going out until 2011. The icebergs and thick sea-ice probably interfered with the advection and growth of the large phytoplankters that usually dominate in the water column. Thrush and Cummings and Conlan et al. summarized many populations that were negatively impacted by the lack of advected primary production over this decade.
The dynamics of A. joubini were also correlated with this phenomenon, and we suggest that changes in the plankton may have resulted in a shift from large phytoplankters to tiny dinoflagellates and bacteria. Margalef postulated such a relationship in water columns to result from reduced resources. Sea ice thickness and transparency affects benthic productivity and ecosystem function. Montes-Hugo et al. , described such regional changes in the Western Antarctic Peninsula suggesting a strong relationship between ice cover and the size of the phytoplankton. Orejas et al. and Thurber 2007 discuss the strong relationship between microplankton and Antarctic sponges. Reiswig and Yahel et al. , working on other hexactinellid sponges, demonstrated that they retain only very small particles of bacteria and protists. As hexactinellids in general seem restricted to feeding on tiny particles, the shift in plankters may have offered a strong pulse of appropriate food for A. joubini, triggering rapid growth that was previously not observed in this species. Moreover, our observations of relatively fast growth following a shift in the food is supported by Kahn et al. who report relatively fast temporal changes in the density of two deepwater hexactinellid sponge species in 4,000 m depth off Monterey, California, USA. These density shifts occur with a lag of 1–2 years following shifts in the food supply of the micro-particles they consume. Although A. joubini growing on the gangplank had a broader weight distribution than the same species growing on the floaters in Explorers Cove , we are hesitant to attribute these differences to the site location. It is very likely that the individual sponges that fell off the racks and floaters in Explorers Cove were larger than the sponges that remained on these substrata. Therefore, the measurements from these two substrata at Explorers Cove could be skewed to smaller-sized individuals. We also have preliminary but convincing evidence of A. joubini mortality.
Although we were not able to relocate all transects in 2010 and therefore may have missed some surviving sponges, at least 67 large A. joubini died in the 40 years of this program with no known survivors. We have no reason to question earlier observations that some mortality results from predation by A. conspicuous and the amphipod S. antarctica. Additionally, Cerrano et al., report patches of diatoms inside A. joubini, but speculate that the diatoms had invaded and are detrimental to the sponges. We agree and have seen the amphipod, S. antarctica, eating patches of the sponge that subsequently are colonized by diatoms. In 2012 we photographed considerable evidence of incipient amphipod infestation on A. joubini at the gangplank; however, the actual mortality sources within this study are not known and some may reflect ice formation on the sponge that kills the tissue in a patchy manner, later becoming infected with S. antarctica. We emphasize that many of these large A. joubini surely do live longer, and we are only considering sponges in our localized study sites, but this is still a very high mortality rate for a species of sponge thought to be long-lived. Summarizing the A. joubini observations of massive recruitment and growth and rapid mortality, we suggest that this sponge has much more dynamic life history than previously suspected. What of the other Hexactinellida in our study sites? We know that R. antarctica grows relatively fast as this was studied in the 1970s. We observed surprisingly fast growth and asexual reproduction of mature individuals and we also observed some 40 very small R. antarctica buds to increase their volume as much as two orders of magnitude . This species is by far the dominant sponge in the 25–50 m depth range at McMurdo Station, but it is so inconspicuous that it is extremely difficult to evaluate the population patterns. Obviously it has the potential to multiply relatively quickly, yet we have no evidence of sufficient mortality to balance the reproduction and growth rates observed. The other common Antarctic hexactinellid is R. nuda/racovitzae. This knobby, volcano-shaped sponge is smaller than A. joubini and remains an enigma with regard to its population dynamics and growth rate. Prior to the removal of the cages in 1977, seven R. racovitzae survived inside cages , while 2 died inside their cages. Those survivors did not show significant growth during that time period. The mortalities may have resulted from sea star predation or infestation of S. antarctica. Our extensive surveys in 2010 may have come across a few young R. nuda/racovitzae although they were not collected and we are not sure of their identification. It is interesting to note that Fallon et al., report a relatively-small, 15 cm diameter specimen from the Ross Sea was approximately 440 years old. Many of the R. racovitzae in our area were at least a meter tall, so this species might obtain great age. Rossella fibulata is a rare sponge in the McMurdo Sound area; however, two individuals settled on a rack at Explorers Cove and on a cage at Cape Armitage. It appears to grow rapidly but otherwise little is known of its biology. In any case, the four hexactinellid species in this shallow habitat certainly have different life history patterns, with the fast turn-over of A. joubini being the most surprising. Our observations complement those of Teixido´ et al. who report high frequencies of asexual reproductive strategies in three deep-water Hexactinellida in which 35% of the observed R. nuda were actively budding. In addition, grow tables 4×8 many R. racovitzae exhibited reproduction by fragmentation while R. vanhoeffeni reproduced with bipartition. Thus, it appears that each of the Antarctic Hexactinellida species exhibits different life history biology.
In summary, these observations allow us to test and reject the prevailing notion of slow rate processes for both recruitment and growth of A. joubini. The population dynamics imply that A. joubini are fast to respond to an environmental shift, but the population increase may be relatively short and we need to re-evaluate ideas of slow processes and stability over century time scales. These surprising results are set in a time of climate- and fishing-related environmental changes. Certainly these results demonstrate the great importance of comprehensive, long-term data sets designed to better understand such processes. Voucher specimens collected in the 1960s were sent to the Smithsonian Oceanographic Sorting Center and the specimens seem to be lost; however, a collection of specimens is available at the Scripps Invertebrate Collections.Adolescence is a critical period of development marked by the formation of self-concept and identity, independence from parental guidance, and growth in cognitive and socioemotional skills such as empathy, resilience, and creativity. However, some adolescents also begin to engage in risky behaviors, such as use of tobacco, cannabis, alcohol and other substances. These behaviors are significant, as they can negatively influence this important developmental period and contribute to a vicious cycle whereby risky behaviors interfere with school engagement and academic performance and vice versa. This negative feedback loop is suggested by Richard Jessor’s Theory of Problem Behavior, which proposes that school climate, including the social environment of peers, contributes to adverse adolescent behaviors and outcomes including school disengagement, risky behaviors, and academic failure. These adolescent behaviors in turn influence the school climate, as when groups of students normalize delinquent behaviors, undermining academic engagement more broadly. This vicious cycle in adolescence can have significant downstream effects in adulthood, potentially affecting educational and socioeconomic opportunities as well as overall health outcomes. While Jessor’s theory suggests reciprocal effects between a negative school climate and adolescent risky behaviors, it may also suggest that a positive school climate could create a virtuous cycle of improved academic success, greater school engagement, academically and prosocially supportive peers, and better academic and behavioral outcomes among teens. This is supported by prior literature which has shown that positive school climate is linked to better academic performance, student well being, and school engagement, and lower rates of problem behaviors such as disruptive, antisocial, violent, bullying, or delinquent behavior. Although there is no standardized measure of school climate, there are several domains which have been used to characterize school climate and show predictive potential, among them: the institutional environment, student-teacher relationships , and disciplinary styles. However, prior studies have primarily only examined a limited set of school climate variables and adolescent risky behaviors and most have been limited to cross-sectional designs. As a result, it is still unknown which aspects of school climate might be targeted to improve specific academic or health outcomes. The present study sought to identify and compare associations between school climate measures across multiple domains and multiple downstream health and academic outcomes longitudinally.