Category Archives: coral reefs

coral, coral reefs, dredging

Marine Pollution Bulletin: Environmental impacts of dredging and other sediment disturbances on corals: a review by PL Erftemeijer, B Riegl, BW oeksema and PA Todd

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http://www.ncbi.nlm.nih.gov/pubmed/22682583

Mar Pollut Bull. 2012 Sep;64(9):1737-65. doi: 10.1016/j.marpolbul.2012.05.008. Epub 2012 Jun 7.

This is another study available only for a price, but the abstract is instructive to the issue of how dredging harms corals. DV

Sinclair Knight Merz (SKM), P.O. Box H615, Perth, WA 6001, Australia. perftemeijer@globalskm.com
Abstract

A review of published literature on the sensitivity of corals to turbidity and sedimentation is presented, with an emphasis on the effects of dredging. The risks and severity of impact from dredging (and other sediment disturbances) on corals are primarily related to the intensity, duration and frequency of exposure to increased turbidity and sedimentation. The sensitivity of a coral reef to dredging impacts and its ability to recover depend on the antecedent ecological conditions of the reef, its resilience and the ambient conditions normally experienced. Effects of sediment stress have so far been investigated in 89 coral species (~10% of all known reef-building corals). Results of these investigations have provided a generic understanding of tolerance levels, response mechanisms, adaptations and threshold levels of corals to the effects of natural and anthropogenic sediment disturbances. Coral polyps undergo stress from high suspended-sediment concentrations and the subsequent effects on light attenuation which affect their algal symbionts. Minimum light requirements of corals range from <1% to as much as 60% of surface irradiance. Reported tolerance limits of coral reef systems for chronic suspended-sediment concentrations range from <10 mg L(-1) in pristine offshore reef areas to >100 mg L(-1) in marginal nearshore reefs. Some individual coral species can tolerate short-term exposure (days) to suspended-sediment concentrations as high as 1000 mg L(-1) while others show mortality after exposure (weeks) to concentrations as low as 30 mg L(-1). The duration that corals can survive high turbidities ranges from several days (sensitive species) to at least 5-6 weeks (tolerant species). Increased sedimentation can cause smothering and burial of coral polyps, shading, tissue necrosis and population explosions of bacteria in coral mucus. Fine sediments tend to have greater effects on corals than coarse sediments. Turbidity and sedimentation also reduce the recruitment, survival and settlement of coral larvae. Maximum sedimentation rates that can be tolerated by different corals range from <10 mg cm(-2) d(-1) to >400 mg cm(-2) d(-1). The durations that corals can survive high sedimentation rates range from <24 h for sensitive species to a few weeks (>4 weeks of high sedimentation or >14 days complete burial) for very tolerant species. Hypotheses to explain substantial differences in sensitivity between different coral species include the growth form of coral colonies and the size of the coral polyp or calyx. The validity of these hypotheses was tested on the basis of 77 published studies on the effects of turbidity and sedimentation on 89 coral species. The results of this analysis reveal a significant relationship of coral sensitivity to turbidity and sedimentation with growth form, but not with calyx size. Some of the variation in sensitivities reported in the literature may have been caused by differences in the type and particle size of sediments applied in experiments. The ability of many corals (in varying degrees) to actively reject sediment through polyp inflation, mucus production, ciliary and tentacular action (at considerable energetic cost), as well as intraspecific morphological variation and the mobility of free-living mushroom corals, further contribute to the observed differences. Given the wide range of sensitivity levels among coral species and in baseline water quality conditions among reefs, meaningful criteria to limit the extent and turbidity of dredging plumes and their effects on corals will always require site-specific evaluations, taking into account the species assemblage present at the site and the natural variability of local background turbidity and sedimentation.

coral, coral reefs, dredging, reef health

Marine Pollution Bulletin Report: Lethal and sublethal effects of dredging on reef corals by Rolf P.M. Bak

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Marine Pollution Bulletin, Volume 9, Issue 1, January 1978, Pages 14–16
Caribbean Marine Biological Institute (Carmabi), Piscaderabaai, Curaçao, Netherlands Antilles Netherlands

http://dx.doi.org/10.1016/0025-326X(78)90275-8,

The full article is only available by paying $39.95, but the extract ends with one very strong statement for those who think that the sediment from storms compares to the avoidable impacts of dredging on corals. DV

Purchase $39.95

Abstract

Effects of dredging on a coral reef are described. Under water light values at a depth of 12–13 m were reduced from about 30% to less than 1% surface illumination. Colonies of coral species which are inefficient sediment rejectors (Porites astreoides) lost their zooxanthellae and died. Calcification rates in Madracis mirabilis and Agaricia agaricites were observed to decrease by 33%. The period of suppressed calcification exceeds that of environmental disturbance.

coral, coral reefs, dredging, reef health

Science Network: Offshore dredging severely impacts coral reefs

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http://www.sciencewa.net.au/topics/fisheries-a-water/item/1684-offshore-dredging-severely-impacts-coral-reefs.html
Thursday, 13 September 2012 06:00

Murky coral
The study found that sediment accumulation on coral tissue was a “strong and consistent cause of tissue mortality” and resulted in the death of whole coral fragments over prolonged periods.

Murky_coral

Image: Dan Derret RESEARCH by the Australian Institute of Marine Science has discovered that proposed dredging works along the WA coast could severely impact certain coral species found in local waters.

Scientists from the Institute along with the Australian Research Centre of Excellence conducted laboratory tests to develop lethal and sub-lethal benchmarks for coral exposed to dredging-generated sediments related to offshore developments.

The researchers tested two species of coral found in offshore locations to six levels of total suspended solids for 16 weeks, including a four week recovery period.

They tested the horizontal foliaceous species Montipora Aequituberculata and the upright branching species Acropora Millepora, both of which are found along WA’s coast.

Montipora Aequituberculata proved to be more susceptible as after 12 weeks all coral tissue under the sediment had died, exposing white coral skeleton.

Australian Institute of Marine Science senior principal research scientist Ross Jones says the sediment can affect coral by impacting their ability to feed as well as settling on the coral’s surface, causing it to expend energy cleaning itself.

“It can also attenuate light—light attenuation is a key thing because a lot of these habitats are primary producer habitats so the corals and sea life need light to photosynthesise and light is attenuated by the sediments,” Dr Jones says.

“It is like having permanently cloudy weather all the time, so it has the potential to have an effect on the marine environment.”

The study found that sediment accumulation on coral tissue was a “strong and consistent cause of tissue mortality” and resulted in the death of whole coral fragments over prolonged periods.

“What the study showed was that one species which was generally a flat plate-like coral was affected more so that the branching Acropora species because the sediment began to pile up on the coral,” Dr Jones says.

“That happened to an extent and rate at which it couldn’t clear itself, so it gradually became buried because the sedimentation rate was faster than its ability to clear itself.”

Woodside Energy funded the study and was cited as the operator of the proposed $30 billion Browse liquefied natural gas development at James Price Point, north of Broome.

Dr Jones says Woodside commissioned the study because it was investigating the effects of dredging at Browse.

“This study was initially commissioned by Woodside to try and come up with some numbers to build an environmental assessment of the project,” Dr Jones says.

He says this report is only a small amount of the research that will be conducted in the next few years into what sediment does to corals and other marine life in response to the proposed dredging.

coral, coral reefs, cruise ships, dredging, Florida Keys National Marine Sanctuary, Florida Keys reefs, reef health

Key West Harbor Reconnaissance Report by US Army Corp of Engineers

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key_west_harbor_excerpt

Perhaps most importantly, this brief 7-page report ends with the following: DV

Under the Endangered Species Act (ESA) of 1973; the threatened coral Acropora cervicornis (staghorn coral) and Acropora palmata (elkhorn coral) could be located adjacent to the channel in the areas proposed for expansion (Figure 2) as this area is designated as critical habitat for these species. While it is possible to relocate the actual colonies of coral, the critical habitat would be permanently removed. It is highly likely that the removal of several acres of occupied designated critical habitat (habitat where the species has been shown to be able to flourish under baseline conditions) could be considered an adverse modification of critical habitat under Section 7 of the ESA. This would be Jacksonville District’s first adverse modification of critical habitat determination in the last 15 years. It is also unknown what reasonable and prudent alternatives and measures National Marine Fisheries Service (NMFS) would include in a biological opinion to avoid the project adversely modifying designated critical habitat, as required under Section 7 of the Act. It is expected that resource agencies would oppose any channel modifications outside the existing footprint.

coral, coral reefs, dredging, Florida Keys National Marine Sanctuary, Florida Keys reefs, reef health

Academia.Edu: Dredging and shipping impacts on southeast Florida coral reefs by Brian K. Walker, et. al.

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http://academia.edu/1258184/Dredging_and_shipping_impacts_on_southeast_Florida_coral_reefs
Proceedings of the 12th International Coral Reef Symposium, Cairns, Australia, 9-13 July 201219A Human impacts on coral reefs: general session

Authors: Brian K. Walker 1, David S. Gilliam 1, Richard E. Dodge 1, Joanna Walczak²
1 National Coral Reef Institute, Nova Southeastern University, Dania Beach, FL, USA
² Florida Department of Environmental Protection, Miami, FL, USA
Corresponding author: walkerb@nova.edu

Abstract.
Many coastal regions have experienced extensive population growth during the last century. Commonly, this growth has led to port development and expansion as well as increased vessel activity which can have detrimental effects on coral reef ecosystems. In southeast Florida, three major ports built in the late 1920’s along 112 km of coastline occur in close proximity to a shallow coral reef ecosystem. Recent habitat mapping data were analyzed in GIS to quantify the type and area of coral reef habitats impacted by port and shipping activities. Impact areas were adjusted by impact severity: 100% of dredge and burial areas, 75% of grounding and anchoring areas, and 15% of areas in present anchorage. Estimates of recent local stony coral density and cover data were used to quantify affected corals and live cover. After adjusting for impact severity,312.5 hectares (ha) of impacted coral reef habitats were identified. Burial by dredge material accounted for 175.8 ha. Dredging of port inlet channels accounted for 84.5 ha of reef removal. And 47.6 ha were impacted from a large ship anchorage. Although the full extent of all ship groundings and anchor drags associated with the ports is unknown, the measured extents of these events totaled 6 ha. Based on the adjusted impact areas,over 8.1 million corals covering over 11.7 ha of live cover were impacted. Burial impacts were the greatest. The planned expansion of two of the ports would remove an additional approximate 9.95 ha of coral reef habitat.Ongoing marine spatial planning efforts are evaluating the placement of large ship anchorages in an effort reduce future impacts from ship anchoring. However, increasing populations and shipping needs will likely continue to be prioritized over protection of these valuable natural resources.

Full text and tables at:
Walker_et_al_ICRS2012_Proceedings_SEFL_Shipping_Impacts_Revision