New government survey shows long-spined sea urchin spreading devastation at alarming rate on Tasmania’s east coast. Urchin numbers are predicted to explode in the next three years – going from current levels of 15% to 32% – threatening large areas of the marine environment and iconic fisheries
The Institute of Marine and Antarctic Studies (IMAS) has just released a report of a survey of the distribution of the long-spined sea urchin (Centrostephanus rodgersii) on the east coast of Tasmania done in 2017-18 and comparing results with a survey in 2002. Both surveys extended from Cape Pillar in the southeast to Cape Portland in the north-east.
The IMAS survey confirms the TCT’s fears that we have lost 15% of the reef habitats on the east coast due to the long-spined sea urchin, up from 3.4%. The urchins have removed vital macroalgae, creating lifeless “urchin barrens” that replaces rich and productive rocky reefs.
This has caused a permanent loss to the marine environment and the recreational and commercial rock lobster and abalone industries.
Comparing the two surveys shows that places such as St Helens have already suffered enormous damage. Those areas that are less damaged in the south east are no reason for complacency, as research predicts urchin numbers are about to explode over the three years and beyond, and delaying action will result in an even bigger environmental catastrophe.
Modelling by scientists from IMAS shows that without direct intervention urchins barrens will destroy over 32 % of susceptible reef habitats on the east coast by 2021.
For at least the last ten years the TCT has been raising concerns regarding the spread of the long-spined sea urchin. The survey results and IMAS modelling demand urgent and decisive action. Most importantly, action must be taken to address the main cause, which is over fishing of large rock lobsters (which are the only natural predator of these urchins in Tasmanian waters). We cannot continue to fiddle around the edges of the problem by focusing on harvesting or culling, or blaming rising ocean temperatures that Tasmanians have little control over.
The former Minister for Primary Industries Sarah Courtney committed her department to bringing together all stakeholders to identify solutions to this problem. The Centrostephanus Forum 2018 will be held in Hobart on 14 December and the TCT has been invited to attend. While we commend the minister for this decision, the results of the survey and IMAS modelling demonstrate that this process must commence urgently and the state government has to be willing to take decisive action to stop the spread of this devastating sea urchin if it wants to manage the marine environment responsibly and if it wants to ensure the existence of productive and iconic commercial and recreational rock lobster fisheries on the east coast.
The long-spined Sea Urchin survey results show that:
– over the entire area of the east coast that was surveyed (between Cape Portland and Cape Pillar) the area of barren coverage has increased from 3.4% in 2002 to 15.2% in 2016-17
– the St Helens region is the worst affected, having the area of barrens in 0-15 metres increased from 10.7% in 25.1% 2016-17
– southern areas have seen a low level of barren development.
The total area and rate of change in the St Helens region is shocking and turning this around will be very difficult. This should be a warning of what will happen in the future in other regions if serious action is not taken.
The fact that some regions have negligible barren areas is not reason for comfort, these areas are heavily infested with long-spined sea urchins and only urgent action can stop them following the St Helens region.
IMAS modelling – what will happen in the next three years
We need decisive and urgent action because modelling shows that if that does not happen the urchin problem will get rapidly worse in just a few years time. This modelling, by IMAS, predicts urchin barrens will cover over 32% of susceptible rocky reef habitats on Tasmania’s east coast by 2021 if there are no significant changes to the management of the rock lobster fishery or introduction of other control measures.
While the results of this survey are alarming, the potential acceleration of urchin barren development that IMAS has modelled shows a catastrophe is coming and the state government must act urgently and decisively.
CENTROSTEPHANUS RODGERSII LONG-SPINED SEA URCHIN – BACKGROUND
The long-spined sea urchin has been proliferating in reef environments off Tasmania’s east coast for decades, consuming the critical reef macroalgae (seaweeds or kelps) and leaving largely lifeless “barrens”.
The long-spined sea urchin is a native species to Tasmania’s east coast but warming waters have allowed it to breed more successfully and increase in numbers over the last few decades. Scientific research shows that even where waters are warming and urchin numbers increase urchin barrens do not form if sufficient densities of large rock lobsters are retained.
These barrens are largely devoid of species other than micro algae, which continues to sustain the urchins.
Large rock lobsters are the primary natural predator of the long-spined sea urchin.
Scientific research shows that retaining high densities of large rock lobster is the critical method to prevent barrens developing or to stop barrens at an early stage (when infestations are just starting or incipient).
Once created, barrens are in all practical terms permanent without intensive, costly and ongoing human intervention and these may be limited to shallower waters. Logistical problems (e.g. divers being limited to shallow waters) and expense currently limit the effectiveness of culling, harvesting or other human intervention. Preventing the further spread of Centrostephanus urchin barrens must be the first priority of management.
Urchin barrens reduce abalone and rock lobster numbers to such an extent that both recreational and commercial abalone and rock lobster fisheries are excluded from damaged reef areas. Fin fish, such as important commercial species such as wrasse and banded morwong, are also excluded.
Non commercial species that are most effected include sea horses and weedy seadragons.
One the east coast, most recreational rock lobster fishing occurs in shallower waters of whereas most commercial rock lobster fishing occurs in deeper waters where commercial fishing if focused.
The east coast is relatively much more important to recreational fishers (where 80% of the take of the 19,000 licensed recreational fishers is taken).