ABSTRACT. Coral reef sponges are considered to b e important space competitors. Competitive interactions between sponges and corals often result in overgrowth of the coral. It is assumed that sponges are even more successful in environments sub-optimal for corals. In order to test the hypothesis that coral overgrowth by reef sponges increases when corals are under stress, the frequency of sponge/ coral interactions was quantified along a gradient of physical stress. At 15 stations, encompassing 5 localities and 3 depths (5, 10 and 20 m) dlong the coast of Santa Marta (NE Colombia), the number and categories of interactions were scored in belt transrcts (10 X 1 m'). Four categories of interactions were distinguished. Physical factors such as sedimentation and visibility were measured. 21 coral species and 95 sponge species were encountered In a total of 3866 spongc/coral interactions. Only 2.5";* (96 ~n t e r a c t~o n s ) consisted of ovcrgrowth of corals by sponges. The frequency of such overgrowth depended on the presence of pdrticular sponge specles, which appeared to be more aggressive towards corals In locahtlcs wlth hlgh coral cover, relatively low sedimentation and high visibility. Thus, we reject the hypothesis that coral overgro~vth by sponges occurs more frequently in localities under physical stress. Overgrowth was related to the presence of aggressive sponge specles, rather than to characteristics of the corals. It is concluded that reef sponges differ notably in their competitive abilities. By influencing the sponge cornrnunlty coinposition on the reef, the physlcal environment may indirectly determine the extent of overgrowth of corals by sponges.

Acoustic disturbance is a growing conservation concern for wildlife populations because it can elicit physiological and behavioral responses that can have cascading impacts on population dynamics. State‐dependent behavioral and life history models implemented via Stochastic Dynamic Programming (SDP) provide a natural framework for quantifying biologically meaningful population changes resulting from disturbance by linking environment, physiology, and metrics of fitness. We developed an SDP model using the endangered western gray whale (Eschrichtius robustus) as a case study because they experience acoustic disturbance on their summer foraging grounds. We modeled the behavior and physiological dynamics of pregnant females as they arrived on the feeding grounds and predicted the probability of female and offspring survival, with and without acoustic disturbance and in the presence/absence of high prey availability. Upon arrival in mid‐May, pregnant females initially exhibited relatively random behavior before they transitioned to intensive feeding that resulted in continual fat mass gain until departure. This shift in behavior co‐occurred with a change in spatial distribution; early in the season, whales were more equally distributed among foraging areas with moderate to high energy availability, whereas by mid‐July whales transitioned to predominate use of the location that had the highest energy availability. Exclusion from energy‐rich offshore areas led to reproductive failure and in extreme cases, mortality of adult females that had lasting impacts on population dynamics. Simulated disturbances in nearshore foraging areas had little to no impact on female survival or reproductive success at the population level. At the individual level, the impact of disturbance was unequally distributed across females of different lengths, both with respect to the number of times an individual was disturbed and the impact of disturbance on vital rates. Our results highlight the susceptibility of large capital breeders to reductions in prey availability, and indicate that who, where, and when individuals are disturbed are likely to be important considerations when assessing the impacts of acoustic activities. This model provides a framework to inform planned acoustic disturbances and assess the effectiveness of mitigation strategies for large capital breeders.

Coral overgrowth by sponge species was studied on Caribbean reefs to determine whether it depends on coral cover and species composition. Overgrowth was quantified in belt transects at 4 localities on the reefs of Curaqao (Netherlands Antilles) and compared to 5 localities sampled on Colombian reefs. Coral perimeter, coral cover, sponge cover, sponge abundance and species richness were measured at each locality. The species nchness of aggressive sponges was not influenced by coral cover, whereas the species richness of non aggressive sponges decreased with increasing coral cover. At coral covers of >25Sb, the sponge community was characterised by more aggressive species. This is a clear example of the importance of spatial competition, indicating that only aggressive sponge species are able to survive on reefs wlth high coral cover. Below 25 % coral cover, the increasing presence of aggressive sponge species resulted in an increasing number of overgrowth interactions. At higher coral cover this relation is distorted. The average coral cover was significantly higher on the reefs of Curalao than on the Colombian reefs. As a consequence, more sponge species were involved in overgrowth interactions on Curaqao than on Colombian reefs. The Importance of this overgrowth capacity is emphasised by the impact of sponge species composition. The occurrence of coral overgrowth was dependent on the sponge species composition rather than on the abundance of sponge species. The coral species composition did not influence the frequency of sponge/coral overgrowth interactions. I conclude that competition for space between sponges and corals is important on reefs with high coral cover as more aggressive sponge species and hence more overgrowth lnteractions occur. Successful overgrowth of corals by sponges depends on coral cover (irrespective of coral species) and sponge species composition

Abstract. Benthic organisms compete for space, and standoff interactions, i. e. interactions with no clearly observable outcome such as win or loss, are very common in marine hard substratum communities. Standoffs were more common than overgrowths among all sponge‐coral interactions observed in a coral reef community off Santa Marta, NE Colombia. The dynamics of these standoffs and the role played by each of the interacting organisms were examined in a series of standard observations of sponge‐coral interactions involving the sponge species Niphates erecta, Rhaphidophlus venosus, Scopalina ruetzleri and the coral Montastraea cavernosa. Most sponge‐coral standoffs in this study displayed rapid changes in number of polyps along the coral border, sponge area and sponge‐coral distance. The outcome of sponge‐coral standoffs depended on the ecological stategy (e.g., growth) of the sponge species. Scopalina ruetz­leri and N. erecta did not show any signs of direct competition with Montastraea cavernosa. R. venosus, however, was often observed to take over vacant space formed by dead coral polyps (54 % of interactions). The impact of coral damage (lesions) on the interaction process between R. venosus and M. cavernosa was shown by a significant increase in coral polyp death in damaged compared with undamaged M. cavernosa colonies (22.7 % versus 6.9 %). This study demonstrates that (1) sponge‐coral standoffs are actually quite dynamic because of the continually changing distance between the organisms, (2) the dynamic nature of sponge‐coral standoffs depends on growth‐related strategies (growth form, growth rate) of the competing sponge species, (3) the actual frequency of coral overgrowth by (thinly encrusting) sponge species can only be determined by means of intermittent observations; space gained at the cost of coral tissue cannot be seen by single observations, (4) coral damage (lesions) on reefs may enhance deterioration of corals by increasing their susceptibility to sponge overgrowth.

2013. Subarctic cetaceans in the southern Chukchi Sea: Evidence of recovery or response to a changing ecosystem. Oceanography 26(4):136-149, http://dx.