Uneven declines between corals and cryptobenthic fish symbionts from multiple disturbances

ABSTRACTWith the onset and increasing frequency of multiple disturbances, the recovery potential of critical ecosystem-building species and their mutual symbionts is threatened. Similar effects to both hosts and their symbionts following disturbances have been assumed. However, we report unequal declines between hosts and symbionts throughout multiple climate-driven disturbances in reef-building Acropora corals and cryptobenthic coral-dwelling Gobiodon gobies. Communities were surveyed before and after consecutive cyclones (2014, 2015) and heatwaves (2016, 2017). After cyclones, coral size and goby group size decreased similarly by 28-30%. After heatwave-induced bleaching, coral size decreased substantially (47%) and the few gobies recorded mostly inhabited corals singly. Despite several coral species still occurring after bleaching, all goby species declined, leaving 78% of corals uninhabited. These findings suggest that gobies, which are important mutual symbionts for corals, are unable to cope with consecutive disturbances. This disproportionate decline could lead to ecosystem-level disruptions through loss of key symbiotic services to corals.

In situ growth of deep-sea octocorals after the Deepwater Horizon oil spill

Although the role of deep-sea corals in supporting biodiversity is well accepted, their ability to recover from anthropogenic impacts is still poorly understood. An important component of recovery is the capacity of corals to grow back after damage. Here we used data collected as part of an image-based long-term monitoring program that started in the aftermath of the Deepwater Horizon oil spill to develop a non-destructive method to measure in situ growth rates of Paramuricea spp. corals and characterize the impact of the spill on growth. About 200 individual coral colonies were imaged every year between 2011 and 2017 at five sites (three that were impacted by the spill and two that were not). Images were then used to test different methods for measuring growth. The most effective method was employed to estimate baseline growth rates, characterize growth patterns, estimate the age of every colony, and determine the effects of impact and coral size on growth. Overall growth rates were variable but low, with average annual growth rates per site ranging from 0.14 to 2.5 cm/year/colony. Based on coral size and growth rates, some colonies are estimated to be over two thousand years old. While coral size did not have an influence on growth, the initial level of total impact in 2011 had a significant positive effect on the proportion of new growth after 2014. However, growth was not sufficient to compensate for branch loss at one of the impacted sites where corals are expected to take an average of 50 years to grow back to their original size. The non-destructive method we developed could be used to estimate the in situ growth rates on any planar octocoral, and would be particularly useful to follow the recovery of corals after impact or assess the effectiveness of Marine Protected Areas.

Paleoecology and biostratinomy of solitary rugose corals in the Stony Mountain Formation (Upper Ordovician), Stony Mountain, Manitoba

The four species of solitary Rugosa known from the Stony Mountain Formation at Stony Mountain in southern Manitoba belong to different genera, and differ from one another in external form. The distribution and abundance of taxa and their frequency with respect to one another were related to the degree of environmental restriction. The boundary between the Gunn Member and overlying Penitentiary Member corresponds to a marked increase in overall abundance and change in relative frequency. Helicelasma and Bighornia are dominant in the Gunn and lower Penitentiary, respectively. Deiracorallium and Lobocorallium decrease in frequency at the boundary.Larvae of these solitary Rugosa attached to the substrate with their cardinal side. Coralla of Helicelasma, Deiracorallium, and Lobocorallium were oriented in the sediment with the top of the convex cardinal side at or near the substrate surface and the upper part of the concave counter side exposed above it during life. Bighornia lay with the convex counter side in the sediment and the concave cardinal side at least partly exposed. Epizoic bryozoans generally became associated with live hosts, and were especially common on the exposed side of relatively large individuals. Microscopic boring algae infested the outer wall of most corals in the Gunn Member, usually while the hosts were alive. Responses of the polyp to stress and injury are indicated by redirection of the growth axis, constriction of the calice rim, and repair of broken calice rims. The attitudinal and directional orientations of solitary corals suggest that most and possibly all were transported after death. Differences in depositional orientation among the taxa are related to coral form. Currents were unidirectional from the present southeast during Gunn time, and either unidirectional from the southeast or northwest, or oscillating from both directions in early Penitentiary time. Abrasion of coral exteriors was primarily a post-mortem event associated with transportation. Trypanites borings were probably produced by one species of annelid after deposition of the corals. The degree of abrasion and frequency of annelid borings tended to increase with coral size and the duration of exposure before burial.